EP4240696A1 - Process for the production of lithium hydroxide - Google Patents

Process for the production of lithium hydroxide

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Publication number
EP4240696A1
EP4240696A1 EP21887939.3A EP21887939A EP4240696A1 EP 4240696 A1 EP4240696 A1 EP 4240696A1 EP 21887939 A EP21887939 A EP 21887939A EP 4240696 A1 EP4240696 A1 EP 4240696A1
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EP
European Patent Office
Prior art keywords
lithium
nitrate
mol
containing solution
sulfate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
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EP21887939.3A
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German (de)
French (fr)
Inventor
Wolfgang Voigt
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Rock Tech Lithium Inc
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Rock Tech Lithium Inc
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Publication date
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Publication of EP4240696A1 publication Critical patent/EP4240696A1/en
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D15/00—Lithium compounds
    • C01D15/02—Oxides; Hydroxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity

Definitions

  • the invention relates to a method for the production of lithium hydroxide through crystallization of lithium hydroxide monohydrate from a solution of lithium nitrate.
  • lithium hydroxide as monohydrate or anhydrous in highly pure form is recently in particular demand.
  • the reaction product is leachable with water and provides a solution of lithium sulfate with concentrations of 15 - 25 g/L (approx. 1.0 - 1.5 mol/L Li 2 SO 4 )
  • Lithium sulfate-containing solutions are also produced during the processing of sulfate-rich brines from salt lakes such as in the Salar de Uyuni or the Atacama (NPL1 ). Generally, lithium is recovered from these salt lakes as chloride, if sufficient calcium chloride-containing solutions are available for the separation of sulfate as gypsum. For brines with high sulfate contents, the isolation of pure lithium sulfate as an intermediate has also been considered (NPL1 ).
  • Lithium sulfate-containing solutions are also produced in recycling processes of lithium batteries when the materials are leached with sulfuric acid.
  • lithium hydroxide solution and insoluble calcium carbonate it is possible to precipitate lithium from solutions of easily soluble lithium salts such as sulfate or chloride as lithium carbonate and subsequently react the same with calcium hydroxide to form lithium hydroxide solution and insoluble calcium carbonate.
  • Outotec has recently presented a process for the production of lithium hydroxide which is based on a two-step alkaline leaching.
  • lithium is extracted from silicate minerals in a pressure leaching using sodium carbonate.
  • the reaction leads to the formation of soluble lithium carbonate and the mineral component analcime (NaA ⁇ Oe FW) as main components.
  • lithium carbonate is solubilized in a conversion reaction to form a lithium hydroxide solution and solid calcium carbonate; see NPL4 (Tiihonen, Marika; Haavanlammi, Liisa et al.: chiefOutotec Lithium Hydroxide Process - A novel direct leach process for the production of battery grade lithium hydroxide monohydrate from calcined spodumen", published in ..Hydrometallurgy Newsletter 1/2019“ on https://www.outotec.com/products-and-services/newsletters/hydrometallurgy-newsletter/)
  • Various easily soluble calcium salts can be used in order to precipitate and separate the sulfate in the form of a poorly soluble calcium sulfate (gypsum, hemihydrate, anhydrite) from lithium sulfate-containing solutions, e.g. with calcium nitrate solution according to reaction (2) as proposed in PTL3 (CN 102602967 A).
  • the filtrate then each contains lithium combined with the anion of the easily soluble calcium salt used for precipitation, in the case mentioned the nitrate ion. Formate, , acetate, citrate, bromide etc. can be used as further anions.
  • the resulting lithium salt solution is suitable for the further processing to lithium hydroxide.
  • no double salts should form with lithium.
  • the anions of the added calcium salt must not adversely affect other process stages of LiOH production.
  • reaction of sodium hydroxide with lithium nitrate is carried out at such a high lithium concentration of 150-180 g/L that not all lithium nitrate can be dissolved, i.e. the reaction (3) proceeds in a suspension of solid and solution from start to the finish. Reaction temperatures of 60 °C, 70 °C and 80 °C and crystallization times of 5 hours, 4 hours and 6 hours are taught.
  • NPL1 Garrett, D. E. Handbook of Lithium and Natural Calcium Chloride, Elsevier Ltd., Amsterdam, 2004.
  • NPL2 Tong, T.; Elimelech, M. Environ. Sol. Techno/., 2016, 50, 6846-6855.
  • NPL3 Grageda, M. et al. Energy 2015, 89, 667-677.
  • NPL4 Tiihonen, Marika; Haavanlammi, Liisa et al.: perennialOutotec Lithium Hydroxide Process - A novel direct leach process for the production of battery grade lithium hydroxide monohydrate from calcined spodumen", published in ..Hydrometallurgy Newsletter 1/2019 on https://www.outotec.com/products-and- services/newsletters/hydrometallurgy-newsletter/
  • Object of the invention is to provide an economical and efficient process for the production of lithium hydroxide in high yield and purity.
  • the present invention was made in view of the mentioned disadvantages of the prior art.
  • the present invention relates to
  • Process according to item 8 further comprising a step of, after the leaching, removing at least one impurity selected from heavy metals, aluminum, magnesium, sulfate and carbonate from the obtained lithium sulfate-containing solution by usual purification processes.
  • Process according to any one of items 6 to 10, comprising a further step wherein, after step i), unreacted calcium nitrate is reacted with lithium carbonate or sodium carbonate in order to form and precipitate calcium carbonate, and the same is separated from the remaining lithium nitrate-containing solution.
  • Process according to any one of items 2 to 11 further comprising a step of generating the sodium hydroxide hydrate melt in a separate reactor from NaOH in solid form (e.g. pellets) and water at temperatures above 60 °C, where the water content is preferably determined such that the concentration of nitrate mentioned in item 3 can be obtained.
  • Process according to any one of items 1 to 12, wherein the approximately stoichiometric amount of the sodium hydroxide in step b) is from 0.9 mol to 1.1 mol NaOH per mol lithium nitrate, preferably from 0.95 mol to 1.05 mol NaOH per mol lithium nitrate, more preferably 1.0 mol NaOH per mol lithium nitrate.
  • An advantage of the process of the invention is that the formation and crystallization of lithium hydroxide monohydrate proceeds within a relatively short period of time and yet a high lithium yield is obtained.
  • a further advantage of the invention lies in that lithium hydroxide monohydrate is obtained in high purity, without the need for a further purification step, e.g., recrystallization.
  • the process of the invention is distinguished from the known process for the production of lithium hydroxide in that energy-intensive cooling steps are not necessary. Further advantages result from the following detailed description.
  • a preferable and advantageous aspect of the process of the invention is that the lithium hydroxide monohydrate is crystallized from a lithium nitrate-containing solution (i.e.
  • Fig. 1 is a schematic depiction of a preferable embodiment of the process of the invention, wherein a powder from the “acid roast” process is used as starting material for the production of lithium hydroxide.
  • hydrate melt is generally understood to mean liquids that result from the melting of salt hydrates or metal hydroxide hydrates in their own crystal water, e.g. LiNO 3 3H 2 O, Ca(NO 3 ) 2 -4H 2 O, and NaOH H 2 O.
  • the water contents are generally between 1 - 6 mol H 2 O per mol salt or metal hydroxide, and do not have to correspond exactly to the contents of the crystalline hydrates.
  • Solutions of salts with water contents that do not form crystalline hydrates, such as NaNO 3 are also named or characterized as salt hydrate melts (also see H.-H. Emons, Th. Fanghanel, R. Naumann, W. Voigt, volunteerSalzhydratschmelzen“; Wegungsberichte der Akademie dermaschineen der DDR, 3N/1986, Akademie-Verlag Berlin).
  • a solution essentially consisting of lithium nitrate and unavoidable impurities is preferably used as lithium nitrate-containing solution.
  • the content of lithium nitrate, with respect to all dissolved solids, is preferably at least 95.0 wt.-%, more preferably at least 97.0 wt.-%, e.g. at least 99.0 wt.-%.
  • the content of metal salts that can be precipitated with hydroxide should preferably be less than 0.25 wt.-%, particularly less than 0.1 wt.-%.
  • Some of the impurities that may be present in larger amounts, since they are less likely to affect the purity of the lithium hydroxide product, are NaNO 3 or KNOs.
  • solution is understood as aqueous solution, unless otherwise stated.
  • the source of the lithium nitrate-containing solution is not particularly limited.
  • a suitable source are lithium nitrate-containing solutions, which were obtained by dissolving lithium battery wastes (with nitric acid) and, optionally, subsequent purification steps.
  • the lithium nitrate-containing solution can be generated by dissolving lithium carbonate with correspondingly concentrated nitric acid. This offers the possibility of recycling the lithium carbonate, which can be obtained at the end of the process by introducing CO 2 into the liquid obtained by washing the crystallizate, into the process.
  • the lithium nitrate-containing solution is preferably obtained by conversion of a lithium sulfate-containing solution.
  • the lithium sulfate-containing solution can be reacted with calcium nitrate according to reaction (2), in order to form lithium nitrate and calcium sulfate and precipitate the calcium sulfate.
  • step a) If one starts from a lithium sulfate-containing solution, it is preferred according to the invention to provide the lithium nitrate-containing solution used in step a) in a process comprising the followings steps: (i) generating a lithium nitrate-containing solution with a concentration of at least 3.5 mol/L lithium, preferably at least 4.0 mol/L lithium, e.g. within the range of 3.5 - 6.0 mol/L lithium, from a lithium sulfate-containing solution by reacting with calcium nitrate, preferably a calcium nitrate hydrate melt, at a temperature of 10 to 100 °C, preferably 50 - 70 °C,
  • sulfate is produced as calcium sulfate, which can be sold on and used for example as gypsum in the building materials industry. In contrast to known processes for the production of lithium hydroxide, less byproducts are formed that must be stored in landfills.
  • the calcium nitrate is used in at least the stoichiometrically required amount for the reaction of the lithium sulfate, preferably in a 1% to 10% excess with regard to the amount stoichiometrically required.
  • the calcium nitrate can be in solid or liquid form, preferably in liquid form as hydrate melt.
  • the added calcium nitrate hydrate melt usually has a temperature of 40 °C to 70 °C.
  • the calcium nitrate hydrate melt may contain water in an amount of 3 - 4 mol H 2 O per mol Ca(NO 3 )2.
  • the reaction can be carried out at a temperature of 10 - 100 °C, preferably 50 - 70 °C.
  • the reaction can also be carried out at a temperature of 20 - 40 °C.
  • the reaction mixture is preferably thoroughly mixed when the calcium nitrate is added (preferably as salt hydrate melt).
  • the advantage of adding a salt hydrate melt is that a good mixing is achieved, without having to add the calcium nitrate as solution, which would undesirably increase the water content of the resulting lithium nitrate-containing solution.
  • the source of the lithium sulfate-containing solution is not particularly limited, and the lithium sulfate-containing solution can originate from usual processes for producing lithium sulfate from lithium-containing minerals or salts or the recycling process of lithium ion batteries.
  • the lithium sulfate-containing solution is preferably obtained from the roast product of betaspodumene in the presence of sulfuric acid (“acid roast” process) and subsequent leaching (with water or dilute aqueous solutions, e.g. washing solution from downstream process stages).
  • the lithium sulfate solution can be subjected to usual purification processes after leaching, or these purification steps can be carried out only after the conversion into a LiNO 3 solution, i.e.
  • steps i), iii are, for example, a step-by-step pH increase by base addition to precipitate aluminum, iron, manganese etc., a fine purification by precipitation of sulfate as BaSO 4 and carbonate as BaCO 3 or the inclusion of ion exchange processes.
  • a base e.g. sodium hydroxide, calcium hydroxide
  • a fine purification of sulfate and carbonate can be carried out by precipitation as BaSO 4 and BaCO 3 , respectively, by adding Ba(OH) 2 or Ba(NO 3 ) 2 .
  • an ion-exchanger In order to remove remaining aluminum, magnesium, calcium, but also heavy metals, such as iron or manganese, an ion-exchanger can be also used.
  • the pH is preferably adjusted to 4 - 7, preferably 5 - 6.
  • the concentration of lithium sulfate in the lithium sulfate-containing solution used in step a) is preferably at least 1.5 mol/L, more preferably 2.0 mol/L, e.g. at least 2.4 mol/L.
  • This concentration gives a lithium nitrate-containing solution with preferably at least 3.0 mol/L, more preferably at least 4.0 mol/L lithium, e.g. at least 4.8 mol/L.
  • the concentration of the lithium sulfate in the lithium sulfate-containing solution is preferably well below the solubility of lithium sulfate and preferably no more than 3.0 mol/L.
  • U2SO4 concentrations are within the range of 1 - 1.5 mol/L. If the preferred minimum concentration of U2SO4, i.e. at least 1.5 mol/L, preferably 2.0 mol/L, is not achieved by the leaching process, U2SO4 from other sources can be added. Alternatively or additionally, the content of U2SO4 in the H2SO4 solution obtained by the leaching of the “acid roast” product can be also generated in situ by neutralization of excess H 2 SO 4 with Li 2 CO 3 . This process variant offers a further option for circulation. Lithium carbonate can be obtained at the end of the process from the crystallizate washing liquid by introducing CO 2 . Therefore, in a process variant, the formed lithium carbonate can be reacted with sulfuric acid to lithium sulfate and used in the above step i).
  • the calcium sulfate precipitated by the reaction (2) is separated from the lithium nitratecontaining solution (step ii).
  • the separation techniques used for the CaSO 4 separation e.g. filtration (vacuum, pressure), centrifugation, or thickener
  • temperature and solution concentration solid content in the suspension and additives for morphology control are parameters that can be optimized by using the generally known principles of precipitation and crystallization.
  • step iii After the precipitation and separation of the calcium sulfate (preferably as gypsum), optionally further purification steps can be used before the concentration increase in step iii).
  • unreacted calcium nitrate in the lithium nitrate-containing solution can be reacted with lithium carbonate or sodium carbonate, in order to form and precipitate calcium carbonate.
  • the calcium carbonate is then separated from the remaining lithium nitratecontaining solution.
  • the remaining heavy metals and magnesium can be separated by the usual methods by pH value increase using alkali hydroxide and/or alkali carbonate.
  • alkali carbonate sodium carbonate or lithium carbonate is preferably used.
  • carbonate and sulfate can be precipitated and filtered off with barium hydroxide. If necessary, trace of multivalent metal ions can be further removed through a cation exchanger.
  • the optionally purified LiNOs solution is preferably neutralized with HNO3.
  • the resulting pH value is preferably within the range of 6.0 - 8.0, more preferably 6.5 - 7.5.
  • step iii) the concentration of the lithium nitrate-containing solution is then brought to the desired concentration of lithium nitrate of 13.0 - 15.4 mol/kgw, preferably 13.5 to 15.4 mol/kgw, more preferably 14.0 to 15.0 mol/kgw. This takes place preferably by evaporation.
  • lithium nitrate from other sources could be added or Li 2 CO 3 could be reacted with HNO 3 in situ to LiNOs, which can be also used for circulation for the reasons explained.
  • step i) to Hi are preceded by the essential process steps a) to c
  • the entire process from step i) to step c) preferably does not require any cooling steps with cooling liquids or gases, which cool down to temperatures below 20 °C, in particular no deep-cooling step to temperatures below 5 °C.
  • cooling liquids or gases which cool down to temperatures below 20 °C, in particular no deep-cooling step to temperatures below 5 °C.
  • this also applies to the preferred variant, which starts from “acid roast powder” as the starting material.
  • Fig. 1 illustrates a possible embodiment of the present invention, wherein “acid roast powder” is used as starting material.
  • the lithium sulfate in “acid roast powder” is leached with water, and the remaining silicate is filtered off from the lithium sulfate-containing solution (filtrate FL1 ).
  • the silicate is washed with water once or multiple times, and the washing solution(s) (WF1 ) can be introduced again into the leaching step.
  • the washed silicate can be landfilled or processed.
  • the filtrate (FL1 ) is neutralized by addition of NaOH, soda or U2CO3, in order to form and precipitate iron- and aluminum hydroxide.
  • the precipitated iron and aluminum hydroxides are filtered off from the solution.
  • Calcium nitrate is added to the lithium sulfate- containing filtrate (FL2), in order to form lithium nitrate and calcium sulfate by the reaction (2), where calcium sulfate (gypsum) precipitates.
  • the calcium sulfate is for example filtered off and washed with water, and the washing solution(s) (WF2) can be combined with the washing solution(s) WF1 and introduced again into the leaching step.
  • the washed calcium sulfate can be landfilled. It is however preferably prepared and sold for processing, e.g. in the building materials industry.
  • the lithium nitrate-containing filtrate (FL3) in general contains still remaining calcium, sulfate and carbonate from the previous process.
  • the calcium in filtrate (FL3) is precipitated as calcium carbonate by addition of alkali hydroxide and/or alkali carbonate and removed from the solution (FL4). Carbonate and sulfate are then precipitated and filtered off in the next step by addition of barium hydroxide or addition of Ba(NO 3 )2.
  • the filtrate (FL5) is evaporated in order to achieve the preferred concentration of lithium of 14 - 15 mol/kgw.
  • the obtained lithium nitrate-containing solution can be used further for the crystallization and separation steps as described below.
  • Step b crystallization of lithium hydroxide monohydrate
  • lithium hydroxide is formed by reaction (3) and lithium hydroxide monohydrate is crystallized, while sodium nitrate remains fully dissolved.
  • the crystallization of lithium hydroxide monohydrate takes place by the addition of an approximate stoichiometric amount of sodium hydroxide, preferably in form of a hydrate melt, to this lithium nitrate-containing solution at a temperature within the range of 70 - 85 °C, preferably 75 - 85 °C.
  • the approximate stoichiometric amount of sodium hydroxide is preferably 0.9 mol to 1.1 mol NaOH per mol lithium nitrate, more preferably 0.95 mol NaOH to 1.05 mol per mol lithium nitrate, particularly 1.0 mol NaOH per mol lithium nitrate.
  • the reaction mixture is preferably supplied with an amount of water (in mol) which stoichiometrically corresponds to at least 50% of the amount of lithium ions (in mol) in the reaction mixture, preferably at least 70%, more preferably at least 80%.
  • the preferred upper limit is 100%, since a dilution by unnecessary addition of water would reduce the yield of LiOH H 2 O.
  • the amount and the type of the sodium hydroxide hydrate are controlled in view of the amount of water introduced into the reaction mixture.
  • the preferred ranges given above for the amount of water are considered to this end.
  • the nitrate concentration in the reaction mixture can also be adjusted.
  • the amount and the type of the sodium hydroxide hydrate is preferably selected, such that, after the addition of the sodium hydroxide hydrate, the nitrate concentration, i.e. the total concentration of lithium nitrate and sodium nitrate, is within the range of 13.0 - 15.4 mol/kgw, preferably 13.5 - 15.4 mol/kgw, more preferably 14.0 - 15.0 mol/kgw.
  • the nitrate concentration i.e. the total concentration of lithium nitrate and sodium nitrate
  • the nitrates remain dissolved before and after the reaction with NaOH, i.e. the lithium nitrate before the reaction and the sodium nitrate after the reaction. This contributes to the purity of the final product.
  • the sodium hydroxide hydrate melt can be generated in a separate reactor from NaOH in solid form (e.g. pellets) and water at temperatures above 60 °C.
  • the water content is preferably measured as described above.
  • the heat of hydration of the NaOH is sufficient, in order to achieve the required temperatures above 60 °C.
  • the formed lithium hydroxide monohydrate is separated from the sodium nitrate-containing solution by usual methods, such as centrifugation or filtration (e.g. pressure filtration) and optionally subsequently washed, preferably with little water.
  • the separation of the lithium hydroxide monohydrate is carried out at the same temperature as in the step of the crystallization of lithium hydroxide monohydrate, i.e. within the range of 70 - 85 °C, preferably 75 - 85 °C.
  • the steps b) and c) can be also denoted as “isothermal reaction”, since the temperature is kept after the start of the NaOH addition until the separation of the lithium hydroxide monohydrate within the range of 70 - 85 °C, preferably 75 - 85 °C. It is also preferred to keep temperature fluctuations as small as possible within this temperature range, preferably at ⁇ 5 0 C, in particular ⁇ 3 0 C.
  • the obtained, usually still wet lithium hydroxide monohydrate is optionally washed with water, e.g. one or multiple times and in portions with a total amount that preferably does not exceed 0.2 kg of water per kg lithium hydroxide monohydrate.
  • water instead of water, also a dilute LiOH solution could be used, preferably in the same amount.
  • the lithium hydroxide monohydrate obtained by the process according to the invention achieves a typical battery quality without a further purification step, e.g. recrystallization.
  • the content of LiOH in the obtained product is preferably at least 54 wt.-%, e.g. 54.8 - 56.5 wt.-%.
  • the amount of impurities in the product is preferably less than 0.5 wt.-%, more preferably less than 0.3 wt.- %, further preferably less than 0.25 wt.-%, for example less than 0.2 wt.-%, less than 0.1 wt.- %, or less than 0.05 wt.-% and lies e.g.
  • the content of CO 2 is preferably less than 0.5 wt.-%, particularly 0.035 - 0.35 wt.- %.
  • the solution for example the centrifugate or filtrate, which is obtained after the separation of the lithium hydroxide monohydrate, still contains lithium.
  • This solution which still has a temperature close to the temperature when leaving the LiOH reactor (approx. 70 - 85 °C, preferably 75 - 85 °C), can be directly reacted with carbon dioxide at this temperature, e.g. at a temperature of 65 to 80 °C, in order to form and precipitate lithium carbonate.
  • the lithium carbonate can be used e.g. in the above described purification step, wherein excess calcium nitrate in the lithium nitrate-containing solution is reacted in order to form and precipitate calcium carbonate.
  • the lithium from the lithium carbonate can, however, as described above, also be reintroduced (recycled) elsewhere into the process, for example as lithium nitrate after the reaction with nitric acid or after being sold.
  • the solution which is obtained after the separation of the lithium hydroxide monohydrate and the precipitation of the Li 2 CO 3 , contains sodium nitrate as main component.
  • the sodium nitrate can be crystallized by evaporation of the solution. Before the evaporation, the sodium nitrate-containing solution can be neutralized with nitric acid.
  • Fig. 1 describes an example for the processing of the byproducts obtained.
  • the solution (FL6) which is obtained after the separation of the lithium hydroxide monohydrate, is reacted with carbon dioxide in order to precipitate the remaining lithium as lithium carbonate.
  • the lithium carbonate is filtered off and partially used in the step of the calcium removal. A further part or the remainder can be either sold or reacted with nitric acid to lithium nitrate.
  • the washing solution (WF3) which is obtained by washing the lithium hydroxide monohydrate crystallizate, can be combined with the solution FL6 and then handled in the same way.
  • the filtrate (FL7) which is obtained by filtration of lithium carbonate, can be neutralized by the addition of nitric acid and further evaporated, in order to crystallize sodium nitrate.
  • the sodium nitrate is then filtered off.
  • Fig. 1 also shows by way of example that the lithium nitrate obtained by reacting lithium carbonate and nitric acid can be reintroduced into the process between the evaporator and the LiOH crystallizer, i.e. to increase the concentration of the LiNOs-containing solution.
  • the solution was subsequently made weakly acidic (pH value less than 7) by adding a small amount of nitric acid (HNOs) so that dissolved carbonate was expelled. If necessary, the solution can be passed through a cation exchange column, in order to remove traces of multivalent ions such as Ca 2+ or Mg 2+ . After the precipitation and separation of the calcium sulfate (gypsum) and the described purification steps, the Li concentration is at 4 mol/L.
  • the purified lithium nitrate-containing solution with 4 mol/L Li which was obtained in Reference Example 1 , was brought to a concentration of 14.5 mol/kgw LiNOs by evaporation. The amount of solution was then 2 kg.
  • the mixture was stirred at 80 °C and 600 rpm for further 60 minutes using a stirrer that is as tightly sealed as possible.
  • the lithium hydroxide monohydrate formed was centrifuged off in a heated centrifuge at the same temperature. addition until the complete formation of the crystallizate.
  • the crystallizate contained 81.4% of the lithium in the lithium nitrate solution used.
  • the crystallizate was washed in the centrifuge 3 times with 30 ml_ of hot water each.
  • the sodium content in the crystallizate fell below 0.1%.
  • the lithium loss by washing the crystallizate, based on the initial content of the lithium nitrate solution used, was 2.3% and was determined by measuring the lithium content in the washing solution (WF3).
  • suitable technical measures e.g. working under water vapour in the centrifuge chamber
  • suitable technical measures are to be taken to ensure that no water evaporates from the filter cake and no crystallization of sodium nitrate takes place.
  • the lithium carbonate formed was filtered off, the filtrate (FL7) was brought to a pH of 7 with concentrated HNO 3 and subsequently 80% of the water was evaporated and the remaining solution of the salt paste obtained was centrifuged off at 50 °C.
  • the solution remaining after the centrifugation contains, in addition to NaNO 3 , a very small amount of LiNO 3 .
  • the latter was formed by neutralization with HNO 3 .
  • the centrifugate can be combined with the filtrate FL7 and evaporated. This recylization can continue until an acceptable value of LiNO 3 concentration is exceeded.
  • Example 1 As in Example 1 , 797 g of hydrate melt of sodium hydroxide were produced in a separate container. The same was slowly poured into the concentrated lithium nitrate-containing solution and thereafter it was proceeded in the same manner as in Example 1 . The total yield of lithium hydroxide monohydrate after deducting the lithium loss by washing was 79%. The crystallization was complete after 60 minutes.
  • Comparative Example 1 In the purified lithium nitrate-containing solution with 4 mol/L Li, which was obtained in Reference Example 1 , the lithium nitrate concentration was increased to 10 mol LiNO 3 per kg of water by evaporation followed by adding under stirring the stoichiometric amount of NaOH in pelletized form, whereby the temperature at the end of the reaction was 60 °C.
  • the crystallizate was centrifuged off at 60 °C and washed directly in the centrifuge with a small amount of hot water to the required purity.
  • the washing loss of LiOH H 2 O was 20 g of LiOH H 2 O, corresponding to 10.5% of the crystallized product, whereby the total yield fell to 62.5%.
  • Example 1 was repeated, with the difference that the mixture obtained by addition of the NaOH hydrate melt was stirred at 70 °C and the lithium hydroxide monohydrate formed was centrifuged off in a heated centrifuge at the same temperature. The yield of the LiOH monohydrate decreased to less than 70%.

Abstract

The present invention relates to a process for the production of lithium hydroxide by crystallization of lithium hydroxide monohydrate from a solution of lithium nitrate, comprising the following steps: (a) providing a lithium nitrate-containing solution with a concentration of lithium nitrate of 13.0 – 15.4 mol/kgw, preferably 13.5 – 15.4 mol/kgw, more preferably 14.0 – 15.0 mol/kgw (kgw = kg H2O), (b) adding an approximately stoichiometric amount of sodium hydroxide to the lithium nitrate-containing solution at a temperature within the range of 70 – 85 °C, preferably 75 – 85 °C, in order to crystallize lithium hydroxide monohydrate, and (c) separating the formed lithium hydroxide monohydrate at a temperature within the range of 70 – 85 °C, preferably 75 – 85 °C, preferably by centrifugation and optionally washing of the separated lithium hydroxide monohydrate with water. The process is efficient and lead tohigh yield of lithium hydroxide monohydrate.

Description

Process for the Production of Lithium Hydroxide
Description
Technical Field
The invention relates to a method for the production of lithium hydroxide through crystallization of lithium hydroxide monohydrate from a solution of lithium nitrate.
Background of the Invention
For the production of lithium ion batteries, lithium hydroxide as monohydrate or anhydrous in highly pure form is recently in particular demand. A standard process for lithium recovery from spodumene ore or concentrate is a conversion of alpha-spodumene to beta-spodumene at approx. 1000 to 1100 °C, followed by subsequent roasting with concentrated sulfuric acid between 200 - 300 °C. The latter is usually referred to as “acid roast” process (NPL1 = Garrett, D. E. Handbook of Lithium and Natural Calcium Chloride, Elsevier Ltd., Amsterdam, 2004). The reaction product is leachable with water and provides a solution of lithium sulfate with concentrations of 15 - 25 g/L (approx. 1.0 - 1.5 mol/L Li2SO4)
Lithium sulfate-containing solutions are also produced during the processing of sulfate-rich brines from salt lakes such as in the Salar de Uyuni or the Atacama (NPL1 ). Generally, lithium is recovered from these salt lakes as chloride, if sufficient calcium chloride-containing solutions are available for the separation of sulfate as gypsum. For brines with high sulfate contents, the isolation of pure lithium sulfate as an intermediate has also been considered (NPL1 ).
Lithium sulfate-containing solutions are also produced in recycling processes of lithium batteries when the materials are leached with sulfuric acid.
To separate the lithium hydroxide, LiOH H2O, in pure form from the lithium sulfate-containing solutions, the sulfate portion must first be separated. This is currently done by reacting an Li2SO4 solution freed from interfering metal ions with sodium hydroxide according to reaction equation (1 ) and crystallizing and separating the sodium sulfate as Glauber's salt, Na2SO4-10H2O, by deep cooling (between -15 - +5 °C) (PTL1 = GN 1214981 C). The low temperatures are necessary because above 0 C the sodium sulfate combines with lithium sulfate to form a double salt and crystallizes out, which would lead to high lithium losses. Also, because of the double salt formation between alkali sulfate and lithium sulfate, it is not possible to crystallize pure lithium hydroxide from these solutions by simple evaporation. Cooling steps, however, are not desirable because they lead to high energy consumption.
Furthermore, the resulting sodium sulfate must be processed into a merchantable quality, since it is not directly landfillable. This leads to a more complicated process. In addition, the market for sodium sulfate is becoming increasingly saturated, as it is also produced in a series of other processes such as zero-liquid-discharge technologies (NPL2 = Tong, T.; Elimelech, M. Environ. Sci. Technol., 2016, 50, 6846-6855).
In base solubilization processes for lithium extraction from spodumene, no lithium sulfate is produced, but the basic media solubilize a large part of the aluminum and silicate, which causes a high consumption of basic additive (CaO, NaOH) and leads to problems in the separation of the silica and aluminum hydroxide in the subsequent steps. One process using soda reduces silicate and aluminate solubilization but operates under hydrothermal leaching conditions. The resulting poorly soluble lithium carbonate is extracted in a second step as hydrogen carbonate under increased CO2 pressure (PTL2 = US 09255012).
Generally, it is possible to precipitate lithium from solutions of easily soluble lithium salts such as sulfate or chloride as lithium carbonate and subsequently react the same with calcium hydroxide to form lithium hydroxide solution and insoluble calcium carbonate. This is historically the oldest process for the production of lithium hydroxide (NPL1 ) and is still in use today. Since the reactants calcium hydroxide and lithium carbonate are poorly soluble, the reaction proceeds slowly, results in dilute solutions and is technically complex (NPL3 = Grageda, M. et al. Energy 2015, 89, 667-677).
Furthermore, Outotec has recently presented a process for the production of lithium hydroxide which is based on a two-step alkaline leaching. First, lithium is extracted from silicate minerals in a pressure leaching using sodium carbonate. The reaction leads to the formation of soluble lithium carbonate and the mineral component analcime (NaA^Oe FW) as main components. In the second step, lithium carbonate is solubilized in a conversion reaction to form a lithium hydroxide solution and solid calcium carbonate; see NPL4 (Tiihonen, Marika; Haavanlammi, Liisa et al.: „Outotec Lithium Hydroxide Process - A novel direct leach process for the production of battery grade lithium hydroxide monohydrate from calcined spodumen", published in ..Hydrometallurgy Newsletter 1/2019“ on https://www.outotec.com/products-and-services/newsletters/hydrometallurgy-newsletter/) Various easily soluble calcium salts can be used in order to precipitate and separate the sulfate in the form of a poorly soluble calcium sulfate (gypsum, hemihydrate, anhydrite) from lithium sulfate-containing solutions, e.g. with calcium nitrate solution according to reaction (2) as proposed in PTL3 (CN 102602967 A).
U2SO4 + Ca(NO3)2 CaSO4 + 2 LiNOs (2)
After the CaSO4 separation, the filtrate then each contains lithium combined with the anion of the easily soluble calcium salt used for precipitation, in the case mentioned the nitrate ion. Formate, , acetate, citrate, bromide etc. can be used as further anions.
However, it is essential for the use of easily soluble calcium salts for the sulfate precipitation that the resulting lithium salt solution is suitable for the further processing to lithium hydroxide. In particular, no double salts should form with lithium. Furthermore, the anions of the added calcium salt must not adversely affect other process stages of LiOH production.
In PTL4 (CN 111470520 A), the processing of a lithium nitrate-containing solution to lithium hydroxide by reaction with anhydrous sodium hydroxide (NaOH flakes) according to reaction (3) is proposed, wherein the LiNOs solution was obtained from the recycling of lithium batteries by extraction with nitric acid.
In PTL4, the reaction of sodium hydroxide with lithium nitrate is carried out at such a high lithium concentration of 150-180 g/L that not all lithium nitrate can be dissolved, i.e. the reaction (3) proceeds in a suspension of solid and solution from start to the finish. Reaction temperatures of 60 °C, 70 °C and 80 °C and crystallization times of 5 hours, 4 hours and 6 hours are taught.
Non-Patent Literature
NPL1: Garrett, D. E. Handbook of Lithium and Natural Calcium Chloride, Elsevier Ltd., Amsterdam, 2004.
NPL2: Tong, T.; Elimelech, M. Environ. Sol. Techno/., 2016, 50, 6846-6855.
NPL3: Grageda, M. et al. Energy 2015, 89, 667-677.
NPL4: Tiihonen, Marika; Haavanlammi, Liisa et al.: „Outotec Lithium Hydroxide Process - A novel direct leach process for the production of battery grade lithium hydroxide monohydrate from calcined spodumen", published in ..Hydrometallurgy Newsletter 1/2019 on https://www.outotec.com/products-and- services/newsletters/hydrometallurgy-newsletter/
Patent Literature
PTL1 : CN 1214981 C
PTL2: US 09255012
PTL3: CN 102602967 A
PTL4: CN 111470520 A
Summary of the Invention
Object of the invention is to provide an economical and efficient process for the production of lithium hydroxide in high yield and purity.
The present invention was made in view of the mentioned disadvantages of the prior art. The present invention relates to
1. a process for the production of lithium hydroxide by crystallization of lithium hydroxide monohydrate from a solution of lithium nitrate, which comprises the following steps:
(a) providing a lithium nitrate solution with a concentration of lithium nitrate of 13.0 - 15.4 mol/kgw, preferably 13.5 to 15.4 mol/kgw, more preferably 14.0 to 15.0 mol/kgw (kgw = kg H2O),
(b) adding an approximately stoichiometric amount of sodium hydroxide to the lithium nitrate-containing solution at a temperature within the range of 70 - 85 °C, preferably 75 - 85 °C in order to crystallize lithium hydroxide monohydrate, and
(c) separating the formed lithium hydroxide monohydrate at a temperature within the range of 70 - 85 °C, preferably 75 - 85 °C, preferably by centrifugation and optionally washing with water.
The invention also extends to the following preferred embodiments of the process:
2. Process according to item 1 , wherein the sodium hydroxide is added in form of a hydrate melt to the lithium nitrate-containing solution.
3. Process according to item 2, where the amount and the type of the sodium hydroxide hydrate is selected such that, after the addition of the sodium hydroxide hydrate, the concentration of nitrate in the reaction mixture lies within the range of 13.0 - 15.4 mol/kgw, preferably 13.5 - 15.4 mol/kgw, more preferably 14.0 - 15.0 mol/kgw. 4. Process according to item 1 , 2 or 3, further comprising a step of generating the lithium nitrate-containing solution mentioned in a) from solutions of lower concentration by evaporation.
5. Process according to any one of items 1 to 4, further comprising a step of generating the lithium nitrate-containing solution mentioned in a) by dissolving lithium carbonate with correspondingly concentrated nitric acid.
6. Process according to any one of item 1 to 4, comprising the following steps:
(i) generating a lithium nitrate-containing solution with a concentration of at least 3.5 mol/L, preferably at least 4.0 mol/L lithium, by reacting a lithium sulfate- containing solution with calcium nitrate, preferably a calcium nitrate hydrate melt, at a temperature of 10 to 100 °C, preferably 50 - 70 °C,
(ii) separating the precipitated calcium sulfate from the remaining lithium nitratecontaining solution, and
(iii) increasing the concentration of the lithium nitrate-containing solution to a lithium nitrate concentration of 13.0 - 15.4 mol/kgw, preferably 13.5 - 15.4 mol/kgw, more preferably 14.0 - 15.0 mol/kgw, preferably by evaporation and/or addition of lithium nitrate.
7. Process according to item 6, wherein the calcium nitrate is used in a 1% to 10% excess with respect to the amount stoichiometrically required for the reaction of the lithium sulfate.
8. Process according to item 6 or 7, further comprising a step of obtaining the lithium sulfate-containing solution from spodumene by calcination in the presence of sulfuric acid (“acid roast” process) and subsequent leaching with water or aqueous solution.
9. Process according to item 8, further comprising a step of, after the leaching, removing at least one impurity selected from heavy metals, aluminum, magnesium, sulfate and carbonate from the obtained lithium sulfate-containing solution by usual purification processes.
10. Process according to item 6, 7 or 8, further comprising a step wherein, after generating the lithium nitrate-containing solution, preferably after separating the calcium sulfate in step ii), at least one impurity selected from heavy metals, aluminum, magnesium, calcium, sulfate and carbonate is removed from the obtained lithium nitrate-containing solution by usual purification processes.
11. Process according to any one of items 6 to 10, comprising a further step wherein, after step i), unreacted calcium nitrate is reacted with lithium carbonate or sodium carbonate in order to form and precipitate calcium carbonate, and the same is separated from the remaining lithium nitrate-containing solution.
12. Process according to any one of items 2 to 11 , further comprising a step of generating the sodium hydroxide hydrate melt in a separate reactor from NaOH in solid form (e.g. pellets) and water at temperatures above 60 °C, where the water content is preferably determined such that the concentration of nitrate mentioned in item 3 can be obtained.
13. Process according to any one of items 1 to 12, wherein the approximately stoichiometric amount of the sodium hydroxide in step b) is from 0.9 mol to 1.1 mol NaOH per mol lithium nitrate, preferably from 0.95 mol to 1.05 mol NaOH per mol lithium nitrate, more preferably 1.0 mol NaOH per mol lithium nitrate.
14. Process according to any one of items 1 to 13, wherein the solution obtained after separating the lithium hydroxide monohydrate is reacted with carbon dioxide in order to form lithium carbonate from the unreacted dissolved lithium and to precipitate the same.
15. Process according to item 14, wherein the lithium carbonate formed is reacted with nitric acid to form lithium nitrate, and the lithium nitrate is used to provide the lithium nitrate-containing solution mentioned in step a) of item 1.
16. Process according to item 14, wherein the lithium carbonate formed is reacted with sulfuric acid to form lithium sulfate, and the lithium sulfate is used in step i) of item 6.
An advantage of the process of the invention is that the formation and crystallization of lithium hydroxide monohydrate proceeds within a relatively short period of time and yet a high lithium yield is obtained. A further advantage of the invention lies in that lithium hydroxide monohydrate is obtained in high purity, without the need for a further purification step, e.g., recrystallization. Finally, the process of the invention is distinguished from the known process for the production of lithium hydroxide in that energy-intensive cooling steps are not necessary. Further advantages result from the following detailed description. A preferable and advantageous aspect of the process of the invention is that the lithium hydroxide monohydrate is crystallized from a lithium nitrate-containing solution (i.e. no dispersion containing solid materials / slurry) by adding an approximately stoichiometric amount of sodium hydroxide within a controlled temperature range, particularly by adding an (also homogeneous) NaOH solution or hydrate melt. Pure lithium hydroxide monohydrate crystals can be therefore obtained from the resulting reaction mixture.
Brief Description of the Drawing
Fig. 1 is a schematic depiction of a preferable embodiment of the process of the invention, wherein a powder from the “acid roast” process is used as starting material for the production of lithium hydroxide.
Detailed Description of the Invention
The invention and its embodiments are described in more detail below.
Insofar as this description relates to preferred embodiments, combinations of these preferred embodiments are also considered to be disclosed (regardless of the degree of preference), as long as this is technically sensible.
The expressions “comprise” or “contain” or “-containing” are to be understood as non- restrictive with regard to the listed components, elements, features, etc. In one embodiment of the invention, these expressions can be replaced by “consist of” insofar as this is technically sensible.
The term “hydrate melt” is generally understood to mean liquids that result from the melting of salt hydrates or metal hydroxide hydrates in their own crystal water, e.g. LiNO3 3H2O, Ca(NO3)2-4H2O, and NaOH H2O. The water contents are generally between 1 - 6 mol H2O per mol salt or metal hydroxide, and do not have to correspond exactly to the contents of the crystalline hydrates. Solutions of salts with water contents that do not form crystalline hydrates, such as NaNO3, are also named or characterized as salt hydrate melts (also see H.-H. Emons, Th. Fanghanel, R. Naumann, W. Voigt, „Salzhydratschmelzen“; Sitzungsberichte der Akademie der Wissenschaften der DDR, 3N/1986, Akademie-Verlag Berlin).
The expression “kgw” (kg water) in the present description of the invention relates to the water available as a solvent, and thus does not include water of crystals which has been removed from the system by precipitation as a hydrate. (Step a - providing a lithium nitrate-containing solution)
According to the process of the present invention, a lithium nitrate-containing solution with a concentration of lithium nitrate of 13.0 - 15.4 mol/kgw, preferably 13.5 to 15.4 mol/kgw, more preferably 14.0 to 15.0 mol/kgw (kgw = kg H2O) is provided. If necessary, the lithium nitratecontaining solution can be generated from a solution of lower concentration by evaporation.
A solution essentially consisting of lithium nitrate and unavoidable impurities is preferably used as lithium nitrate-containing solution. The content of lithium nitrate, with respect to all dissolved solids, is preferably at least 95.0 wt.-%, more preferably at least 97.0 wt.-%, e.g. at least 99.0 wt.-%. Furthermore, the content of metal salts that can be precipitated with hydroxide (particularly the total content of heavy metal salts, magnesium salts, aluminum salts and calcium salts) should preferably be less than 0.25 wt.-%, particularly less than 0.1 wt.-%. Some of the impurities that may be present in larger amounts, since they are less likely to affect the purity of the lithium hydroxide product, are NaNO3 or KNOs.
In the present invention, the term “solution” is understood as aqueous solution, unless otherwise stated.
The source of the lithium nitrate-containing solution is not particularly limited. A suitable source are lithium nitrate-containing solutions, which were obtained by dissolving lithium battery wastes (with nitric acid) and, optionally, subsequent purification steps. Alternatively, the lithium nitrate-containing solution can be generated by dissolving lithium carbonate with correspondingly concentrated nitric acid. This offers the possibility of recycling the lithium carbonate, which can be obtained at the end of the process by introducing CO2 into the liquid obtained by washing the crystallizate, into the process.
The lithium nitrate-containing solution is preferably obtained by conversion of a lithium sulfate-containing solution. The lithium sulfate-containing solution can be reacted with calcium nitrate according to reaction (2), in order to form lithium nitrate and calcium sulfate and precipitate the calcium sulfate.
U2SO4 + Ca(NO3)2 CaSO4 + 2 LiNO3 (2)
If one starts from a lithium sulfate-containing solution, it is preferred according to the invention to provide the lithium nitrate-containing solution used in step a) in a process comprising the followings steps: (i) generating a lithium nitrate-containing solution with a concentration of at least 3.5 mol/L lithium, preferably at least 4.0 mol/L lithium, e.g. within the range of 3.5 - 6.0 mol/L lithium, from a lithium sulfate-containing solution by reacting with calcium nitrate, preferably a calcium nitrate hydrate melt, at a temperature of 10 to 100 °C, preferably 50 - 70 °C,
(ii) separating the precipitated calcium sulfate from the remaining lithium nitrate-containing solution, and
(iii) increasing the concentration of the lithium nitrate-containing solution to a lithium nitrate concentration of 13.0 - 15.4 mol/kgw, preferably 13.5 - 15.4 mol/kgw, more preferably 14.0 - 15.0 mol/kgw, preferably by evaporation.
One advantage of this embodiment is that the sulfate is produced as calcium sulfate, which can be sold on and used for example as gypsum in the building materials industry. In contrast to known processes for the production of lithium hydroxide, less byproducts are formed that must be stored in landfills.
In step i), the calcium nitrate is used in at least the stoichiometrically required amount for the reaction of the lithium sulfate, preferably in a 1% to 10% excess with regard to the amount stoichiometrically required. The calcium nitrate can be in solid or liquid form, preferably in liquid form as hydrate melt. The added calcium nitrate hydrate melt usually has a temperature of 40 °C to 70 °C.
The calcium nitrate hydrate melt may contain water in an amount of 3 - 4 mol H2O per mol Ca(NO3)2. The reaction can be carried out at a temperature of 10 - 100 °C, preferably 50 - 70 °C. The reaction can also be carried out at a temperature of 20 - 40 °C. The reaction mixture is preferably thoroughly mixed when the calcium nitrate is added (preferably as salt hydrate melt).
The advantage of adding a salt hydrate melt is that a good mixing is achieved, without having to add the calcium nitrate as solution, which would undesirably increase the water content of the resulting lithium nitrate-containing solution.
The source of the lithium sulfate-containing solution is not particularly limited, and the lithium sulfate-containing solution can originate from usual processes for producing lithium sulfate from lithium-containing minerals or salts or the recycling process of lithium ion batteries. The lithium sulfate-containing solution is preferably obtained from the roast product of betaspodumene in the presence of sulfuric acid (“acid roast” process) and subsequent leaching (with water or dilute aqueous solutions, e.g. washing solution from downstream process stages). The lithium sulfate solution can be subjected to usual purification processes after leaching, or these purification steps can be carried out only after the conversion into a LiNO3 solution, i.e. after step i), but before the concentration increase in step iii). Such steps are, for example, a step-by-step pH increase by base addition to precipitate aluminum, iron, manganese etc., a fine purification by precipitation of sulfate as BaSO4 and carbonate as BaCO3 or the inclusion of ion exchange processes.
The selective removal of calcium before the conversion into a LiNO3 solution, i.e. before step i), is not necessary, since in step i), during the conversion into the LiNO3 solution, Ca(NO3)2 is added.
For the separation of the solubilized secondary components, which form poorly soluble hydroxides, e.g. aluminum, but also magnesium, manganese and iron, a base (e.g. sodium hydroxide, calcium hydroxide) can be added. A fine purification of sulfate and carbonate can be carried out by precipitation as BaSO4 and BaCO3, respectively, by adding Ba(OH)2 or Ba(NO3)2.
In order to remove remaining aluminum, magnesium, calcium, but also heavy metals, such as iron or manganese, an ion-exchanger can be also used.
The preferred sequence of these purification steps is as follows:
1 ) bringing the acidic solution to a pH of approx. 7 (e.g. pH 6-8), in order to precipitate in particular AI(OH)3 and a part of the Fe(OH)3, 2) filtering, then 3) further increasing the pH to approx. pH 10, and 4) precipitating the rest of the hydroxides.
The previously described purification steps can be used likewise for Li2SO4 as well as LiNO3 solutions. It makes essentially no difference, which solution is purified. The same purification steps can be used in both cases.
Before the purified lithium sulfate-containing solution is processed, the pH is preferably adjusted to 4 - 7, preferably 5 - 6.
In order to obtain a most concentrated possible lithium nitrate-containing solution, the concentration of lithium sulfate in the lithium sulfate-containing solution used in step a) is preferably at least 1.5 mol/L, more preferably 2.0 mol/L, e.g. at least 2.4 mol/L. This concentration gives a lithium nitrate-containing solution with preferably at least 3.0 mol/L, more preferably at least 4.0 mol/L lithium, e.g. at least 4.8 mol/L. The concentration of the lithium sulfate in the lithium sulfate-containing solution is preferably well below the solubility of lithium sulfate and preferably no more than 3.0 mol/L.
According to the current technical leaching processes, U2SO4 concentrations are within the range of 1 - 1.5 mol/L. If the preferred minimum concentration of U2SO4, i.e. at least 1.5 mol/L, preferably 2.0 mol/L, is not achieved by the leaching process, U2SO4 from other sources can be added. Alternatively or additionally, the content of U2SO4 in the H2SO4 solution obtained by the leaching of the “acid roast” product can be also generated in situ by neutralization of excess H2SO4 with Li2CO3. This process variant offers a further option for circulation. Lithium carbonate can be obtained at the end of the process from the crystallizate washing liquid by introducing CO2. Therefore, in a process variant, the formed lithium carbonate can be reacted with sulfuric acid to lithium sulfate and used in the above step i).
The calcium sulfate precipitated by the reaction (2) is separated from the lithium nitratecontaining solution (step ii). Depending on the separation techniques used for the CaSO4 separation (e.g. filtration (vacuum, pressure), centrifugation, or thickener), temperature and solution concentration, solid content in the suspension and additives for morphology control are parameters that can be optimized by using the generally known principles of precipitation and crystallization.
After the precipitation and separation of the calcium sulfate (preferably as gypsum), optionally further purification steps can be used before the concentration increase in step iii). For example, unreacted calcium nitrate in the lithium nitrate-containing solution can be reacted with lithium carbonate or sodium carbonate, in order to form and precipitate calcium carbonate. The calcium carbonate is then separated from the remaining lithium nitratecontaining solution. From the lithium nitrate-containing solution, the remaining heavy metals and magnesium can be separated by the usual methods by pH value increase using alkali hydroxide and/or alkali carbonate. As alkali carbonate, sodium carbonate or lithium carbonate is preferably used. In a further separation step, carbonate and sulfate can be precipitated and filtered off with barium hydroxide. If necessary, trace of multivalent metal ions can be further removed through a cation exchanger.
Before step iii), the optionally purified LiNOs solution is preferably neutralized with HNO3. The resulting pH value is preferably within the range of 6.0 - 8.0, more preferably 6.5 - 7.5.
In step iii), the concentration of the lithium nitrate-containing solution is then brought to the desired concentration of lithium nitrate of 13.0 - 15.4 mol/kgw, preferably 13.5 to 15.4 mol/kgw, more preferably 14.0 to 15.0 mol/kgw. This takes place preferably by evaporation. In principle, to achieve the highest possible L1NO3 concentration, lithium nitrate from other sources could be added or Li2CO3 could be reacted with HNO3 in situ to LiNOs, which can be also used for circulation for the reasons explained.
If the optional, but preferred process steps i) to Hi) are preceded by the essential process steps a) to c), the entire process from step i) to step c) preferably does not require any cooling steps with cooling liquids or gases, which cool down to temperatures below 20 °C, in particular no deep-cooling step to temperatures below 5 °C. Of course, this also applies to the preferred variant, which starts from “acid roast powder” as the starting material.
Fig. 1 illustrates a possible embodiment of the present invention, wherein “acid roast powder” is used as starting material. The lithium sulfate in “acid roast powder” is leached with water, and the remaining silicate is filtered off from the lithium sulfate-containing solution (filtrate FL1 ). The silicate is washed with water once or multiple times, and the washing solution(s) (WF1 ) can be introduced again into the leaching step. The washed silicate can be landfilled or processed. The filtrate (FL1 ) is neutralized by addition of NaOH, soda or U2CO3, in order to form and precipitate iron- and aluminum hydroxide. The precipitated iron and aluminum hydroxides are filtered off from the solution. Calcium nitrate is added to the lithium sulfate- containing filtrate (FL2), in order to form lithium nitrate and calcium sulfate by the reaction (2), where calcium sulfate (gypsum) precipitates. The calcium sulfate is for example filtered off and washed with water, and the washing solution(s) (WF2) can be combined with the washing solution(s) WF1 and introduced again into the leaching step. The washed calcium sulfate can be landfilled. It is however preferably prepared and sold for processing, e.g. in the building materials industry. The lithium nitrate-containing filtrate (FL3) in general contains still remaining calcium, sulfate and carbonate from the previous process. The calcium in filtrate (FL3) is precipitated as calcium carbonate by addition of alkali hydroxide and/or alkali carbonate and removed from the solution (FL4). Carbonate and sulfate are then precipitated and filtered off in the next step by addition of barium hydroxide or addition of Ba(NO3)2. The filtrate (FL5) is evaporated in order to achieve the preferred concentration of lithium of 14 - 15 mol/kgw. The obtained lithium nitrate-containing solution can be used further for the crystallization and separation steps as described below.
Each of the optional steps described above with reference to Fig. 1 can be used individually or in a combination of two or more steps for the further implementation of the process of the invention. In a preferred embodiment of the invention, several of these steps are combined or all steps are used for the implementation of the process of the invention, for example on an industrial scale.
(Step b - crystallization of lithium hydroxide monohydrate) In the next step, lithium hydroxide is formed by reaction (3) and lithium hydroxide monohydrate is crystallized, while sodium nitrate remains fully dissolved.
LiNO3 + NaOH -> LiOH + NaNO3 (3)
The crystallization of lithium hydroxide monohydrate takes place by the addition of an approximate stoichiometric amount of sodium hydroxide, preferably in form of a hydrate melt, to this lithium nitrate-containing solution at a temperature within the range of 70 - 85 °C, preferably 75 - 85 °C.
The approximate stoichiometric amount of sodium hydroxide is preferably 0.9 mol to 1.1 mol NaOH per mol lithium nitrate, more preferably 0.95 mol NaOH to 1.05 mol per mol lithium nitrate, particularly 1.0 mol NaOH per mol lithium nitrate.
It is preferred according to the invention to at least partially replace the water withdrawn from the reaction mixture by the crystal water of the LiOH H2O. To this end, the reaction mixture is preferably supplied with an amount of water (in mol) which stoichiometrically corresponds to at least 50% of the amount of lithium ions (in mol) in the reaction mixture, preferably at least 70%, more preferably at least 80%. The preferred upper limit is 100%, since a dilution by unnecessary addition of water would reduce the yield of LiOH H2O.
This reduces the probability of oversaturation of sodium nitrate, since the water removed from the reaction mixture due to the crystal water of LiOH H2O is at least partially replaced.
According to this embodiment, it is possible to add NaOH and water separately. According to the invention, however, it is preferred to add sodium hydroxide in form of a hydrate melt to the lithium nitrate-containing solution.
For the reasons explained above, the amount and the type of the sodium hydroxide hydrate are controlled in view of the amount of water introduced into the reaction mixture. In one embodiment of the invention, the preferred ranges given above for the amount of water are considered to this end.
Alternatively, to control the amount of water introduced into the system, the nitrate concentration in the reaction mixture can also be adjusted. Here, the amount and the type of the sodium hydroxide hydrate is preferably selected, such that, after the addition of the sodium hydroxide hydrate, the nitrate concentration, i.e. the total concentration of lithium nitrate and sodium nitrate, is within the range of 13.0 - 15.4 mol/kgw, preferably 13.5 - 15.4 mol/kgw, more preferably 14.0 - 15.0 mol/kgw. In this way, an oversaturation of sodium nitrate is also unlikely or completely avoided, since the water removed from the reaction mixture due to the crystal water of the UOH H2O is at least partially replaced. To simplify the calculation, it is hypothetically assumed with these concentration data that 80% of the dissolved lithium ions were removed from the system by precipitation as lithium hydroxide hydrate.
By carrying out the reaction in this way, the nitrates remain dissolved before and after the reaction with NaOH, i.e. the lithium nitrate before the reaction and the sodium nitrate after the reaction. This contributes to the purity of the final product.
The sodium hydroxide hydrate melt can be generated in a separate reactor from NaOH in solid form (e.g. pellets) and water at temperatures above 60 °C. The water content is preferably measured as described above. The heat of hydration of the NaOH is sufficient, in order to achieve the required temperatures above 60 °C.
(Step c - separation of lithium hydroxide monohydrate)
The formed lithium hydroxide monohydrate is separated from the sodium nitrate-containing solution by usual methods, such as centrifugation or filtration (e.g. pressure filtration) and optionally subsequently washed, preferably with little water. The separation of the lithium hydroxide monohydrate is carried out at the same temperature as in the step of the crystallization of lithium hydroxide monohydrate, i.e. within the range of 70 - 85 °C, preferably 75 - 85 °C.
The steps b) and c) can be also denoted as “isothermal reaction”, since the temperature is kept after the start of the NaOH addition until the separation of the lithium hydroxide monohydrate within the range of 70 - 85 °C, preferably 75 - 85 °C. It is also preferred to keep temperature fluctuations as small as possible within this temperature range, preferably at ± 5 0 C, in particular ± 3 0 C.
Furthermore, during the separation of the lithium hydroxide monohydrate, care should preferably be taken, for example by suitable process operation (e.g. supply of water vapour) and/or devices, that the evaporation of water from the still wet separated crystals is reduced or substantially suppressed. In this way the contamination by NaNOs can be reduced.
The obtained, usually still wet lithium hydroxide monohydrate is optionally washed with water, e.g. one or multiple times and in portions with a total amount that preferably does not exceed 0.2 kg of water per kg lithium hydroxide monohydrate. Instead of water, also a dilute LiOH solution could be used, preferably in the same amount.
It is also preferable that the lithium hydroxide monohydrate obtained by the process according to the invention achieves a typical battery quality without a further purification step, e.g. recrystallization. The content of LiOH in the obtained product (lithium hydroxide monohydrate) is preferably at least 54 wt.-%, e.g. 54.8 - 56.5 wt.-%. The amount of impurities in the product is preferably less than 0.5 wt.-%, more preferably less than 0.3 wt.- %, further preferably less than 0.25 wt.-%, for example less than 0.2 wt.-%, less than 0.1 wt.- %, or less than 0.05 wt.-% and lies e.g. within the range of 0.02 to 0.25 wt.-%. In this context, residual moisture and/or CO2 bound as carbonate in the product are not regarded as impurities. The content of CO2 is preferably less than 0.5 wt.-%, particularly 0.035 - 0.35 wt.- %.
For typical impurities of lithium hydroxide monohydrate, the following Table 1 indicates preferred ranges, which stand individually but also in combination for “battery quality” of the lithium hydroxide monohydrate. These values can be achieved with the process according to the invention without complex post-purification steps, such as recrystallization.
Table 1] The solution, for example the centrifugate or filtrate, which is obtained after the separation of the lithium hydroxide monohydrate, still contains lithium. This solution, which still has a temperature close to the temperature when leaving the LiOH reactor (approx. 70 - 85 °C, preferably 75 - 85 °C), can be directly reacted with carbon dioxide at this temperature, e.g. at a temperature of 65 to 80 °C, in order to form and precipitate lithium carbonate. The lithium carbonate can be used e.g. in the above described purification step, wherein excess calcium nitrate in the lithium nitrate-containing solution is reacted in order to form and precipitate calcium carbonate. The lithium from the lithium carbonate can, however, as described above, also be reintroduced (recycled) elsewhere into the process, for example as lithium nitrate after the reaction with nitric acid or after being sold.
The solution, which is obtained after the separation of the lithium hydroxide monohydrate and the precipitation of the Li2CO3, contains sodium nitrate as main component. The sodium nitrate can be crystallized by evaporation of the solution. Before the evaporation, the sodium nitrate-containing solution can be neutralized with nitric acid.
Further, Fig. 1 describes an example for the processing of the byproducts obtained. The solution (FL6), which is obtained after the separation of the lithium hydroxide monohydrate, is reacted with carbon dioxide in order to precipitate the remaining lithium as lithium carbonate. The lithium carbonate is filtered off and partially used in the step of the calcium removal. A further part or the remainder can be either sold or reacted with nitric acid to lithium nitrate. The washing solution (WF3), which is obtained by washing the lithium hydroxide monohydrate crystallizate, can be combined with the solution FL6 and then handled in the same way. The filtrate (FL7), which is obtained by filtration of lithium carbonate, can be neutralized by the addition of nitric acid and further evaporated, in order to crystallize sodium nitrate. The sodium nitrate is then filtered off. Fig. 1 also shows by way of example that the lithium nitrate obtained by reacting lithium carbonate and nitric acid can be reintroduced into the process between the evaporator and the LiOH crystallizer, i.e. to increase the concentration of the LiNOs-containing solution.
Examples
The following examples serve to illustrate the invention.
Reference Example 1 - Production of a lithium nitrate-containing solution
An aqueous solution (FL1 ) of lithium sulfate with a U2SO4 content of 2 mol/L, obtained from the “acid roast process” of spodumene, was adjusted to pH 5-6 by addition of NaOH solution (30%). The iron and aluminum hydroxides thus formed were removed by filtration. The filtrate (FL2) was reacted in portions according to reaction (2) with more than a stoichiometric amount of Ca(NO3)2 in form of its tetrahydrate with thorough mixing. The tetrahydrate was previously melted at temperatures above 45 °C and introduced in liquid form into the precipitation reactor, which was preheated to approx. 50 °C. In order to remove the sulfate as completely as possible, a 1% Ca(NO3)2 excess was used. The temperature of the gypsum precipitation in this example was 50 - 70 °C. After a minimum reaction time of 2 hours under stirring, the gypsum was filtered off (filtrate FL3) and suspended with the same amount of water and filtered again (wash filtrate WF2). The wash filtrate (WF2) is preferably reintroduced into the leaching process of the “acid roast process”. The washing of the gypsum can also require further washing stages in order not to exceed a required limit for the lithium content in the gypsum. This washing water is also preferably used again for leaching the “acid roast powder”.
The pH of filtrate (FL3) was adjusted in two steps by adding NaOH solution and soda (first to pH = 7-8, filtration and then to pH > 10) in order to precipitate the remaining aluminum and excess calcium as carbonate which were then filtered off (filtrate FL4). By addition barium hydroxide remaining carbonate and sulfate were then precipitated and filtered off (filtrate FL5). The solution was subsequently made weakly acidic (pH value less than 7) by adding a small amount of nitric acid (HNOs) so that dissolved carbonate was expelled. If necessary, the solution can be passed through a cation exchange column, in order to remove traces of multivalent ions such as Ca2+ or Mg2+. After the precipitation and separation of the calcium sulfate (gypsum) and the described purification steps, the Li concentration is at 4 mol/L.
Example 1 - Production and crystallization of LIOH monohydrate
The purified lithium nitrate-containing solution with 4 mol/L Li, which was obtained in Reference Example 1 , was brought to a concentration of 14.5 mol/kgw LiNOs by evaporation. The amount of solution was then 2 kg. In a separate container, 585 g of NaOH pellets (= 14.6 mol NaOH) were mixed with 212 g of water, sealed and shaken. The temperature rose to approx. 90 0 C and a homogeneous hydrate melt was formed. Within 15 minutes this hydrate melt was slowly and under stirring added to the concentrated lithium nitrate-containing solution. The concentration of nitrate in the solution was then approx. 14.6 mol/kgw.
The mixture was stirred at 80 °C and 600 rpm for further 60 minutes using a stirrer that is as tightly sealed as possible. The lithium hydroxide monohydrate formed was centrifuged off in a heated centrifuge at the same temperature. addition until the complete formation of the crystallizate. The crystallizate contained 81.4% of the lithium in the lithium nitrate solution used.
The crystallizate was washed in the centrifuge 3 times with 30 ml_ of hot water each. The sodium content in the crystallizate fell below 0.1%. The lithium loss by washing the crystallizate, based on the initial content of the lithium nitrate solution used, was 2.3% and was determined by measuring the lithium content in the washing solution (WF3).
During centrifugation and in situ washing in the centrifuge, suitable technical measures (e.g. working under water vapour in the centrifuge chamber) are to be taken to ensure that no water evaporates from the filter cake and no crystallization of sodium nitrate takes place.
The hot filtrate (FL6) obtained after the separation of lithium hydroxide was combined with the washing solution (WF3) and CO2 was passed through this solution until the pH value dropped to 8. The lithium carbonate formed was filtered off, the filtrate (FL7) was brought to a pH of 7 with concentrated HNO3 and subsequently 80% of the water was evaporated and the remaining solution of the salt paste obtained was centrifuged off at 50 °C. The solution remaining after the centrifugation contains, in addition to NaNO3, a very small amount of LiNO3. The latter was formed by neutralization with HNO3. The centrifugate can be combined with the filtrate FL7 and evaporated. This recylization can continue until an acceptable value of LiNO3 concentration is exceeded.
Example 2 - Production and crystallization of LIOH monohydrate
536 g of pure lithium carbonate were mixed with 1.4 kg of 65% HNO3 and 0.51 kg of water. The solution was heated to 80 °C under stirring and the CO2 formed was discharged, and in this manner a lithium nitrate-containing solution of the same concentration as in Example 1 was generated. It was taken care that the solution was fully homogeneous.
As in Example 1 , 797 g of hydrate melt of sodium hydroxide were produced in a separate container. The same was slowly poured into the concentrated lithium nitrate-containing solution and thereafter it was proceeded in the same manner as in Example 1 . The total yield of lithium hydroxide monohydrate after deducting the lithium loss by washing was 79%. The crystallization was complete after 60 minutes.
Comparative Example 1 In the purified lithium nitrate-containing solution with 4 mol/L Li, which was obtained in Reference Example 1 , the lithium nitrate concentration was increased to 10 mol LiNO3 per kg of water by evaporation followed by adding under stirring the stoichiometric amount of NaOH in pelletized form, whereby the temperature at the end of the reaction was 60 °C.
A crystallizate amount of 189.36 g (7.3 mol) LiOH H2O per kg water (= 73% yield) was obtained. The crystallizate was centrifuged off at 60 °C and washed directly in the centrifuge with a small amount of hot water to the required purity. The washing loss of LiOH H2O was 20 g of LiOH H2O, corresponding to 10.5% of the crystallized product, whereby the total yield fell to 62.5%.
Comparative Example 2
Example 1 was repeated, with the difference that the mixture obtained by addition of the NaOH hydrate melt was stirred at 70 °C and the lithium hydroxide monohydrate formed was centrifuged off in a heated centrifuge at the same temperature. The yield of the LiOH monohydrate decreased to less than 70%.

Claims

Claims A process for the production of lithium hydroxide by crystallization of lithium hydroxide monohydrate from a solution of lithium nitrate, comprising the following steps:
(a) providing a lithium nitrate-containing solution with a concentration of lithium nitrate of 13.0 - 15.4 mol/kgw, preferably 13.5 - 15.4 mol/kgw, more preferably 14.0 - 15.0 mol/kgw (kgw = kg H2O),
(b) adding an approximately stoichiometric amount of sodium hydroxide to the lithium nitrate-containing solution at a temperature within the range of 70 - 85 °C, preferably 75 - 85 °C, in order to crystallize lithium hydroxide monohydrate, and
(c) separating the formed lithium hydroxide monohydrate at a temperature within the range of 70 - 85 °C, preferably 75 - 85 °C, preferably by centrifugation and optionally washing of the separated lithium hydroxide monohydrate with water. Process according to claim 1 , wherein the sodium hydroxide is added in form of a hydrate melt to the lithium nitrate-containing solution. Process according to claim 2, wherein the amount and the type of the sodium hydroxide hydrate is selected such that, after the addition of the sodium hydroxide hydrate, the concentration of nitrate in the reaction mixture lies within the range of 13.0 - 15.4 mol/kgw, preferably 13.5 - 15.4 mol/kgw, more preferably 14.0 - 15.0 mol/kgw. Process according to claim 1 , 2 or 3, further comprising a step of generating the lithium nitrate-containing solution mentioned in a) from solutions of lower concentration by evaporation. Process according to any one of claims 1 to 4, further comprising a step of generating the lithium nitrate-containing solution mentioned in a) by dissolving lithium carbonate with correspondingly concentrated nitric acid. Process according to any one of claims 1 to 4, comprising the following steps:
(i) generating a lithium nitrate-containing solution with a concentration of at least 3.5 mol/L, preferably at least 4.0 mol/L lithium, by reacting a lithium sulfate- containing solution with calcium nitrate, preferably a calcium nitrate hydrate melt, at a temperature of 10 to 100 °C, preferably 50 - 70 °C,
(ii) separating the precipitated calcium sulfate from the remaining lithium nitratecontaining solution, and (in) increasing the concentration of the lithium nitrate-containing solution to a lithium nitrate concentration of 13.0 - 15.4 mol/kgw, preferably 13.5 - 15.4 mol/kgw, more preferably 14.0 - 15.0 mol/kgw, preferably by evaporation and/or addition of lithium nitrate.
7. Process according to claim 6, wherein the calcium nitrate is used in a 1% to 10% excess with respect to the amount stoichiometrically required for the reaction of the lithium sulfate.
8. Process according to claim 6 or 7, further comprising a step of obtaining the lithium sulfate-containing solution from spodumene by calcination in the presence of sulfuric acid (“acid roast” process) and subsequent leaching with water or aqueous solution.
9. Process according to claim 8, further comprising a step of, after the leaching, removing at least one impurity selected from heavy metals, aluminum, magnesium, sulfate and carbonate from the obtained lithium sulfate-containing solution by usual purification processes.
10. Process according to claim 6, 7 or 8, further comprising a step wherein, after generating the LiNOs-containing solution, preferably after separating the calcium sulfate in step ii), at least one impurity selected from heavy metals, aluminum, magnesium, calcium, sulfate and carbonate is removed from the obtained lithium nitrate-containing solution by usual purification processes.
11 . Process according to any one of claims 6 to 10, comprising a further step wherein, after step i), unreacted calcium nitrate is reacted with lithium carbonate or sodium carbonate in order to form and precipitate calcium carbonate, and the same is separated from the remaining lithium nitrate-containing solution.
12. Process according to any one of claims 2 to 11 , further comprising a step of generating the sodium hydroxide hydrate melt in a separate reactor from NaOH in solid form (e.g. pellets) and water at temperatures above 60 °C, wherein the water content is preferably determined such that the concentration of nitrate mentioned in claim 3 can be obtained.
13. Process according to any one of claims 1 to 12, wherein the approximately stoichiometric amount of the sodium hydroxide in step b) is from 0.9 mol to 1.1 mol NaOH per mol lithium nitrate, preferably from 0.95 mol to 1.05 mol NaOH per mol lithium nitrate, more preferably 1.0 mol NaOH per mol lithium nitrate. Process according to any one of claims 1 to 13, wherein the solution obtained after the separation of the lithium hydroxide monohydrate is reacted with carbon dioxide in order to form lithium carbonate from the unreacted, dissolved lithium and to precipitate the same. Process according to claim 14, wherein the lithium carbonate formed is reacted with HNO3 to form lithium nitrate, and the lithium nitrate is used to provide the lithium nitratecontaining solution mentioned in step a) of claim 1 . Process according to claim 14, wherein the lithium carbonate formed is reacted with sulfuric acid to form lithium sulfate, and the lithium sulfate is used in step i) of claim 6.
EP21887939.3A 2020-11-03 2021-10-29 Process for the production of lithium hydroxide Pending EP4240696A1 (en)

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