CN113373326B - Method for preparing pure rare earth sulfate solution - Google Patents
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Abstract
The invention relates to a method for preparing a pure rare earth sulfate solution from sulfated roasted rare earth ore. By utilizing the dynamic characteristics and the rule of influence of temperature on the solubility of rare earth sulfate in the leaching process of rare earth sulfate roasted ore, more than 50% of rare earth is separated out in a sulfuric acid rare earth recrystallization phase with higher purity through low liquid-solid ratio rapid leaching and then heating for recrystallization, so as to realize the primary separation of rare earth and impurities. The residual rare earth is separated from impurities again in a neutralization impurity removal mode: (1) The magnesium bicarbonate solution can be used for replacing the magnesium oxide one-step impurity removal in the traditional process, so that the total consumption of the solid magnesium oxide is reduced by 90%, the recycling of magnesium is realized, and the impurities introduced by the magnesium oxide and the slag produced by incomplete reaction are also reduced; (2) The total consumption of solid magnesium oxide is reduced by about 10% compared with the traditional process by adopting two steps of magnesium oxide for impurity removal. The preparation method of the invention improves the total recovery rate of the rare earth by 1-3%.
Description
Technical Field
The invention relates to the field of rare earth hydrometallurgy extraction and separation, in particular to a method for preparing a pure rare earth sulfate solution from sulfated roasted rare earth ore.
Background
The rare earth elements mean 17 kinds of metal elements including 15 kinds of lanthanoid elements and yttrium and scandium. Since the rare earth resource plays an important role in developing clean energy economy and high and new technology industries, the rare earth resource is a strategic resource of the nation. Typical rare earth mineral resources in China include inner Mongolia baotite mixed rare earth ore (hereinafter referred to as baotite), bastnaesite in Sichuan and Shandong and ion adsorption rare earth ore in seven provinces in south China, wherein the baotite rare earth ore has the highest storage capacity and is the most important light rare earth resource in China at present.
Currently, about 90% of baotite in China's industry is smelted and separated by a ' third acid method ': concentrated sulfuric acid high-temperature reinforced roasting, water leaching, magnesium oxide neutralization and impurity removal are carried out to obtain a relatively pure sulfuric acid rare earth solution (shown in figure 1), and then the subsequent transformation separation and other processes are carried out to obtain different rare earth products. The rare earth sulfate leachate obtained in the water leaching process is 30-40 g/L calculated by rare earth oxide, when solid magnesium oxide is used for one-time neutralization and impurity removal, as the solid magnesium oxide contains a large amount of impurities and the solid-liquid reaction efficiency is relatively low, a large amount of phosphorus iron slag with high water content is generated, the entrainment and adsorption loss of rare earth are relatively high, the neutralized slag needs to be further washed by acid, and the consumption of acid and alkali is increased. Therefore, in the process of extracting and separating the rare earth by hydrometallurgy, a new optimization process needs to be provided aiming at the process to further optimize the process so as to improve the yield of the rare earth and reduce the consumption of acid and alkali.
Disclosure of Invention
Aiming at the problem that liquid phase rare earth is entrained and lost along with slag when roasted ore obtained by roasting rare earth concentrate by sulfuric acid is subjected to water leaching and magnesium oxide neutralization impurity removal, the invention provides a method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore, which aims to further improve the recovery rate of rare earth and reduce the consumption of magnesium oxide and acid in the technical process, and comprises the following steps:
(1) Leaching sulfated roasted rare earth ore for the first time to obtain supersaturated rare earth sulfate solution and first leaching slag;
(2) Heating and crystallizing the supersaturated rare earth sulfate solution obtained by primary leaching to obtain pure rare earth sulfate crystals and a crystallization mother solution;
(3) Carrying out secondary leaching and impurity removal on the crystallized mother liquor obtained by heating crystallization and the leaching residue obtained by primary leaching after water supplement or magnesium bicarbonate solution, so as to obtain secondary leaching liquid and secondary leaching residue;
(4) And (3) dissolving the pure rare earth sulfate crystal obtained in the step (2) by using the leachate obtained by the secondary leaching to obtain a rare earth sulfate solution.
Further, the method comprises the step (5) of deeply removing impurities from the rare earth sulfate solution to obtain a pure rare earth sulfate solution and neutralized slag.
Further, the sulfated and roasted rare earth ore is obtained by sulfating and roasting a mixed ore of bastnaesite, monazite and at least one of bastnaesite, monazite and xenotime.
Further, the primary leaching temperature in the step (1) is 10-50 ℃, preferably 30-45 ℃, and the solid-to-solid ratio of the leaching solution is 0.5: 1-4: 1mL/g or m 3 T, preferably 1.0: 1 to 2.5:1mL/g or m 3 The leaching time is 1-30 min, preferably 5-15 min.
Further, the crystallization mode in the step (2) comprises at least one of induced crystallization and temperature-rising crystallization, preferably temperature-rising crystallization, wherein the temperature of the temperature-rising crystallization is 50-90 ℃, preferably 55-70 ℃, and the crystallization time is 20-120 min, preferably 30-90 min.
Further, the secondary leaching of the crystallization mother liquor and the leaching residue obtained by the primary leaching in the step (3) comprises: and after secondary leaching for 10-60 min, adding a magnesium bicarbonate solution to remove impurities, and continuing leaching, wherein the total volume of the crystallization mother liquor and the magnesium bicarbonate solution is that the mass of the leaching residue of the primary leaching is =7: 1-15: 1mL/g, the leaching temperature is 20-60 ℃, preferably 30-40 ℃, the total leaching time is 30-180 min, preferably 60-120min, and the concentration of magnesium bicarbonate is 2-12 g/L, preferably 6-10 g/L, measured as MgO.
And further comprising a step (6) of mixing leaching slag obtained by the secondary leaching and the neutralized slag and then washing, wherein the obtained washing liquid is used as a leaching agent for preparing the supersaturated sulfuric acid rare earth solution in the step (1).
Further, the secondary leaching of the crystallization mother liquor and the leaching residue obtained by the primary leaching in the step (3) comprises: and (3) supplementing water into the crystallization mother liquor, mixing the crystallization mother liquor with the leaching residue obtained by the primary leaching, and performing secondary leaching, wherein the mass ratio of the crystallization mother liquor to the primary leaching residue after supplementing water is =7: 1-15: 1mL/g, the leaching temperature is 20-50 ℃, and the leaching time is 30-180 min, preferably 60-120min.
Further, the impurity removal in the step (3) comprises the steps of adding a magnesium-containing alkaline substance into the secondary leachate for neutralization until the pH value is 1.0-2.5, and then carrying out solid-liquid separation to obtain a primary neutralization solution and primary neutralization slag, wherein the neutralization temperature is 25-50 ℃, and the neutralization time is 30-180 min.
And further, the method also comprises a step (6), wherein the leaching residue obtained by secondary leaching in the step (3), the primary neutralization residue and the neutralization residue obtained by deep impurity removal in the step (5) are mixed and washed, and a washing liquid is used as a leaching agent for preparing the supersaturated sulfuric acid rare earth solution in the step (1).
Further, the solid-to-solid ratio of the leachate obtained by the secondary leaching in the dissolving in the step (4) to the pure rare earth sulfate crystal is 15: 1-30: 1mL/g, and the temperature is 25-45 ℃.
Further, a magnesium-containing alkaline substance is added during neutralization in the step (5), the neutralization temperature is 25-40 ℃, the neutralization time is 30-180 min, and the neutralization pH is = 3.0-4.0.
The invention also provides a pure rare earth sulfate solution prepared by the method for preparing the pure rare earth sulfate solution from the sulfated roasted rare earth ore, which is characterized in that the total concentration of rare earth oxides in the pure rare earth sulfate solution is 30-40 g/L, the content of iron oxides is less than 30mg/L, and the content of phosphorus oxides is less than 1mg/L.
The technical scheme of the invention has the following beneficial technical effects:
(1) The invention recovers the rare earth by steps of two phases, improves the recovery rate of the rare earth, reduces the consumption of magnesium oxide: by utilizing the dynamic characteristic of dissolving rare earth and iron (the rare earth can be quickly leached to exceed a saturated state) and the characteristic that the solubility of rare earth sulfate is reduced along with the rise of temperature in the leaching process of sulfuric acid roasted ore of the rare earth, the rare earth is quickly leached at a low liquid-solid ratio and then is heated for recrystallization, so that more than 50 percent of rare earth is separated out in a sulfuric acid rare earth recrystallization phase with higher purity to realize the primary separation of the rare earth and main impurity elements of iron and phosphorus. Leading main impurities of iron and phosphorus in a liquid phase to preferentially form iron phosphate and hydroxide precipitate through neutralization and impurity removal so as to realize separation from the rest of rare earth existing in the leaching solution, wherein the neutralization and impurity removal process comprises the following steps: (1) The magnesium bicarbonate solution can be used for replacing the magnesium oxide one-step impurity removal in the traditional process, so that the total consumption of the solid magnesium oxide is reduced by 90%, the recycling of magnesium is realized, and the impurities introduced by the magnesium oxide and the slag produced by incomplete reaction are also reduced; (2) Compared with the traditional one-step impurity removal process of magnesium oxide, the two-step neutralization impurity removal (coarse impurity removal under the condition of low pH and deep impurity removal under the condition of high pH) of magnesium oxide is adopted, so that the operation difficulty is greatly reduced, the reaction stability and the neutralization efficiency of magnesium oxide are improved, and the total consumption of solid magnesium oxide is reduced by about 10%. The two-phase stepwise recovery of rare earth reduces the concentration of liquid phase rare earth participating in the process of neutralization and impurity removal by about 50 percent compared with the traditional one step, thereby reducing the entrainment loss of rare earth in the discharged wet slag in the original process and the hydrolysis loss in the neutralization process and improving the total recovery rate of rare earth by 1 to 3 percent.
(2) And (3) reducing acid consumption: as the rare earth is recovered from solid phase and liquid phase step by step, the concentration of the rare earth in the leachate is greatly reduced in the process of neutralization and impurity removal, the entrainment loss of the rare earth in the discharged wet slag in the original process and the hydrolysis loss in the neutralization process are reduced, and the acid amount added for dissolving and recovering the rare earth lost by hydrolysis in the process of washing the slag in the original process is also reduced.
Drawings
FIG. 1 is a schematic diagram of a conventional process flow of one-step neutralization and impurity removal of magnesium oxide by leaching sulfated roasted rare earth ore with water.
FIG. 2 is a schematic view of the process of preparing pure rare earth sulfate solution by secondary leaching of magnesium bicarbonate according to the present invention.
FIG. 3 is a schematic flow chart of the present invention for preparing pure rare earth sulfate solution by non-magnesium bicarbonate secondary leaching.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
The invention provides a method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore, which is combined with a figure 2 and comprises the following steps:
step S100, preparing supersaturated sulfuric acid rare earth solution by leaching sulfated roasted rare earth ore for one time;
the invention takes rare earth sulfate roasted ore treated by a sulfuric acid reinforced roasting method as a raw material, quickly leaches the roasted ore obtained by the sulfuric acid reinforced roasting under the condition of low liquid-solid ratio by using water, and obtains primary leachate solution and primary leaching slag by solid-liquid separation. The weakly acidic slag washing liquid generated in the subsequent cleaning process replaces water to be quickly leached under the condition of low liquid-solid ratio, on one hand, the cyclic utilization of the washing liquid is realized, and on the other hand, the weakly acidic washing liquid contains rare earth and can further recover the rare earth.
The roasted ore of sulfuric acid may be at least one of bastnaesite, monazite, bastnaesite and xenotime after sulfating roasting. The leaching temperature is 10-50 ℃, preferably 30-45 ℃, and the liquid-solid ratio of water or washing liquor to the rare earth sulfate roasted ore is 0.5: 1-4: 1 (mL/g or m) 3 T), preferably 1.0: 1 to 2.5:1mL/g or m 3 The leaching time is 1-30 min, preferably 5-15 min.
The leaching time in the existing leaching process is about 2-3 hours, the liquid-solid ratio and the leaching time are obviously reduced, the dissolving speed of the rare earth is higher than that of iron, the dissolving amount of the iron is less within 1-30 min, the preliminary separation of the iron and the rare earth is realized, the iron content in the primary leaching solution is reduced, and the rare earth content is improved. The total rare earth oxide concentration of the obtained primary leachate is 70-130 g/L, the hydrogen ion concentration is 0.2-1.5mol/L, the iron oxide content is 5-50 g/L, and the phosphorus oxide content is 10-30 g/L.
Step S200, heating and crystallizing the primary leaching solution to prepare pure rare earth sulfate crystals;
and (5) heating the primary leaching solution obtained in the step (S100) for recrystallization and carrying out solid-liquid separation to obtain pure rare earth sulfate crystals and low-concentration rare earth sulfate crystallization mother liquor.
The recrystallization temperature is 50 to 90 ℃, preferably 55 to 70 ℃, the crystallization time is 20 to 120min, preferably 30 to 90min, and the stirring speed is 100 to 300rpm. The obtained sulfuric acid rare earth crystal contains rare earth oxide 30-45 wt%, iron oxide less than 1 wt%, phosphorus oxide less than 0.5 wt%, calcium oxide less than 1 wt%, water 10-30 wt% and sulfate radical for the rest. The rare earth sulfate crystal can be directly used as a product for subsequent use. It can be seen that the iron and phosphorus contents are both low and the purity of the product is high.
According to the invention, through the difference of crystallization kinetics of rare earth and impurity ions such as phosphorus, iron and the like, phosphorus, iron and other impurities are separated by adopting a crystallization method, the content of rare earth in rare earth mother liquor is reduced, rare earth sulfate crystals are obtained, and the rare earth loss in the subsequent impurity removal process is reduced.
Step S300, carrying out secondary leaching and impurity removal on the crystallization mother liquor obtained by heating crystallization and the leaching residue obtained by primary leaching to obtain a secondary leaching solution and a secondary leaching residue; the secondary leaching and impurity removal can be carried out by adopting the following two modes:
and S310, returning the crystallization mother liquor obtained in the step S200 to the leaching step S100 to obtain leaching residues, directly leaching for the second time, adding a magnesium bicarbonate solution to continue leaching while neutralizing and removing impurities after leaching for 10-60 min, and performing solid-liquid separation to obtain a secondary leaching solution and secondary leaching residues by combining with a figure 2. The addition of the magnesium bicarbonate solution in step S300 can reduce the amount of the magnesium-containing basic substance added in step S500, and can reduce the consumption of 90% of the magnesium-containing basic substance. Compared with the method that solid magnesium alkaline substances such as magnesium oxide and the like are added after water leaching for neutralization and impurity removal, the neutralization and impurity removal can be realized while leaching is carried out by adopting a magnesium bicarbonate solution. Magnesium bicarbonate is as weak alkaline aqueous solution, and liquid-liquid reaction efficiency is higher during the impurity removal of neutralization, not only can avoid local alkali lye concentration too high to cause the tombarthite to deposit and cause the rate of recovery to reduce, moreover, can neutralize the residual acid and make the basicity moderately avoid the tombarthite to deposit, and then make the tombarthite rate of recovery high, and the leaching of restraining impurity ion simultaneously to realized this application and gone on the technical scheme simultaneously with the neutralization process with the leaching process of calcination ore.
The crystal mother liquor can be directly added into the leaching residue of the primary leaching, the primary residue of the primary leaching is added with water for 10-60 min, and then magnesium bicarbonate solution is added to leach the primary residue together, wherein the concentration of the magnesium bicarbonate is 2-12 g/L calculated by magnesium oxide. The total volume of the crystallization mother liquor, the water and the magnesium bicarbonate solution is equal to the mass of the leaching residue leached in the first time in the step S100 =7: 1-15: 1 (ml/g or m) 3 T), adding the magnesium bicarbonate solution slowly after leaching for 10-60 min at 20-60 ℃ for 30-180 min, preferably 60-120min.
And S320, combining the crystal mother liquor obtained in the step S200 with the leaching residue obtained in the primary leaching in the step S100, performing secondary leaching, and performing solid-liquid separation to obtain a secondary leaching liquor and a secondary leaching residue. The mass of the total volume of the crystal mother liquor after water supplement to the primary leaching residue is =7: 1-14: 1mL/g, the leaching temperature is 20-50 ℃, and the leaching time is 30-180 min, preferably 60-120min.
And then removing impurities from the secondary leachate, adding a magnesium-containing alkaline substance such as magnesium oxide into the secondary leachate for neutralization until the pH is = 1.0-2.5, and then carrying out solid-liquid separation to obtain primary neutralization solution and primary neutralization slag, wherein the neutralization temperature is 25-50 ℃, the neutralization time is 30-180 min, and the stirring speed is 100-300 rpm. The concentration of total rare earth in the obtained primary neutralization solution is 10-18 g/L, the content of iron oxide is 1-2 g/L, and the content of phosphorus oxide is less than 100mg/L. It can be seen that the total rare earth concentration in the neutralization solution is greatly reduced. The addition of magnesium oxide for neutralization by this step reduced the total magnesium oxide usage by about 10%.
The secondary leachate obtained in the step S300 is low in rare earth, iron and phosphorus, the total rare earth concentration is 10-18 g/L, the iron oxide content is 1-15 g/L, the phosphorus oxide content is 0.5-8 g/L, and the pH value is 1.0-2.5.
Step S400, dissolving the pure rare earth sulfate crystal obtained in the step (2) by using a leachate obtained by secondary leaching to obtain a rare earth sulfate solution;
and (4) dissolving the leachate obtained by the secondary leaching in the step (S300) and the rare earth sulfate crystal obtained in the step (S200) to obtain a high-concentration rare earth sulfate solution. The high-concentration rare earth sulfate solution generates magnesium sulfate waste liquid in the subsequent use process, and the magnesium sulfate waste liquid can be adopted to prepare magnesium bicarbonate solution, and the magnesium bicarbonate solution is returned to the step S300 for utilization.
The solid-to-solid ratio of the leachate obtained by secondary leaching in the dissolving process to the rare earth sulfate crystal liquid is 15: 1-30: 1mL/g, the temperature is 25-45 ℃, the stirring speed is 100-300 rpm, and the dissolving time is 30-180 min. The total rare earth concentration of the obtained sulfuric acid rare earth solution is 30-40 g/L, the content of iron oxide is less than 1g/L, and the content of phosphorus oxide is less than 0.5g/L.
Further, the method can also comprise a step S500 of neutralizing and removing impurities from the sulfuric acid rare earth solution to obtain a neutralized liquid and neutralized slag;
one embodiment is that light-burned magnesia is added for neutralization and impurity removal, the neutralization temperature is 25-40 ℃, and the neutralization time is 30-180 min. The concentration of the total rare earth in the obtained neutralization solution is 30-40 g/L, the content of iron oxide is less than 30mg/L, and the content of phosphorus oxide is less than 1mg/L. The adding amount of the light calcined magnesia is controlled according to the pH value in the neutralization process, and the pH value is 3.0-4.0.
Because the consumption of magnesium oxide is reduced, the condition of local excessive alkali in a link is reduced, excessive acid is not required to be added in the subsequent steps to clean the rare earth, the consumption of acid in the acid washing process is reduced, and the loss of the rare earth is reduced
Further, the method can also comprise a step S600 of washing the secondary leaching slag and the neutralized slag;
the following two types of methods can be adopted:
s610, with reference to FIG. 2, for the case of removing impurities by using magnesium bicarbonate in step S300, mixing the secondary slag obtained in step S300 and the neutralized slag obtained in step S500, washing with weak acid water to obtain a washing solution and a final slag, and returning the washing solution to the step S100 for primary leaching to further recover rare earth.
And S620, with reference to FIG. 3, for the case of removing impurities by using magnesium oxide in the step S300, mixing the secondary slag, the primary neutralization slag and the secondary neutralization slag obtained in the step S300, washing with weak acid water to obtain a washing liquid and a final slag, and returning the washing liquid to be used for primary leaching in the step S100 to further recover rare earth.
The weak acid water for washing slag is dilute sulfuric acid with the pH = 2-4, and the liquid-solid ratio of the weak acid water for washing slag to the mixed slag is 5: 1-20: 1.
The invention also provides a pure rare earth sulfate solution obtained by the method, wherein the total concentration of rare earth oxides in the pure rare earth sulfate solution is 30-40 g/L, the content of iron oxides is less than 30mg/L, and the content of phosphorus oxides is less than 1mg/L.
The invention takes rare earth sulfate roasted ore treated by a sulfuric acid reinforced roasting method as a raw material, and supersaturated rare earth sulfate solution and iron-rich primary leaching slag are obtained after low-liquid-solid-ratio rapid water leaching and solid-liquid separation; heating the primary leaching solution for recrystallization and solid-liquid separation to obtain pure rare earth sulfate crystals and crystallization mother liquor; dissolving pure rare earth sulfate crystals in the crystallization mother liquor, neutralizing and removing impurities by magnesium oxide to obtain pure rare earth sulfate solution, and mixing the pure rare earth sulfate solution with the rare earth sulfate crystals to obtain high-concentration pure rare earth sulfate. Because the concentration of liquid-phase rare earth is reduced in the processes of neutralization impurity removal and secondary leaching, the rare earth entrained and lost in primary slag and neutralization slag is greatly reduced, the rare earth yield in the processes of leaching and neutralization is comprehensively improved, and the acid consumption of the neutralization slag in the process of washing by using dilute acid is also reduced.
The temperature range of the primary leaching in the preparation process of the invention is 10-50 ℃, preferably 30-45 ℃. The leaching rate of iron is greatly reduced when the temperature is too low, so that the primary slag quantity is large and the liquid content is high, rare earth of a sulfuric acid rare earth crystal phase obtained by next recrystallization is less, the rare earth yield is relatively reduced, and the magnesium oxide consumption is relatively increased; the temperature is too high to promote the crystallization and precipitation of supersaturated rare earth, the relative yield of rare earth is reduced, and the relative consumption of magnesium oxide is increased.
The time range of the primary leaching in the preparation process of the invention is 1-30 min, preferably 1-15 min. The rare earth starts to crystallize and separate out after the leaching equilibrium time of 40 ℃ is about 10min and 15min, so that the rare earth is less leached at one time when the leaching time is too short or too long, the amount of rare earth entering a crystal phase obtained by recrystallization is reduced, the relative yield of rare earth is reduced, and the relative consumption of magnesium oxide is increased.
In the preparation process, the liquid-solid ratio of primary leaching is 0.5: 1-4: 1mL/g, preferably 1.0: 1-2.5: 1mL/g. The solid-to-solid ratio of the primary leaching solution is too low, the solid content in the leaching process is high, so that the primary slag amount is large, the liquid content is high, the volume of the primary leaching solution obtained by separation is small, the rare earth of the rare earth sulfate crystal phase obtained by subsequent recrystallization is small, and the rare earth yield is reduced; if the liquid-solid ratio is too large, the supersaturation degree of the rare earth in the primary leaching liquid is reduced, the rare earth in the sulfuric acid rare earth crystal phase obtained by subsequent recrystallization is also reduced, the rare earth yield is reduced, and the relative consumption of magnesium oxide is increased.
The crystallization temperature in the preparation process of the invention is 50-90 ℃, preferably 55-70 ℃. The leaching temperature is too low, the yield of the rare earth in the crystallized part is reduced, when the temperature is higher than 60 ℃, the effect of increasing the temperature on the yield of the rare earth is not obvious, but the evaporation loss of water in the crystallization mother liquor is increased, the iron and phosphorus impurities in crystals are increased, the consumption of magnesium oxide in the deep impurity removal process is increased, and the energy consumption is increased.
The crystallization time in the preparation process of the invention is 20-120 min, preferably 30-90 min. When the recrystallization temperature is 60 ℃ and the stirring speed is 250rpm, the recrystallization equilibrium time is about 60min, and if the crystallization time is too short, the amount of the rare earth entering a crystal phase is small, and finally the relative yield of the rare earth is reduced. After the crystallization time exceeds 60min, the rare earth crystallization approaches to equilibrium.
The stirring speed in the crystallization process is 100-300 rpm. The low recrystallization stirring rate requires long crystallization time, the crystallization equilibrium time under the condition of 100rpm is about 90min, and the rare earth entering the rare earth sulfate crystal phase obtained by recrystallization is reduced when the crystallization equilibrium time is lower than the equilibrium time.
In the preparation process, the liquid-solid ratio of the secondary leaching is 7: 1-15: 1mL/g. The low solid ratio of the secondary leaching liquid means that the volume of the added magnesium bicarbonate is small, and the rare earth concentration of the obtained secondary leaching liquid is high, so the rare earth loss along with the secondary leaching residue is relatively increased.
The leaching time of the secondary leaching in the preparation process is 30-180 min, preferably 60-120min. The secondary leaching time is short, the iron leaching is insufficient, so that the concentration of iron in the secondary leaching solution is low, the iron-phosphorus ratio is low, and the loss of rare earth precipitation formed by rare earth after adding magnesium bicarbonate is increased.
The leaching temperature of the secondary leaching in the preparation process is 20-50 ℃. Because the concentration of the secondary leaching rare earth is greatly reduced, the secondary leaching temperature rise has little influence on the leaching effect, but the energy consumption is increased.
In the preparation process of the invention, a magnesium bicarbonate solution is added in the secondary leaching to remove impurities and continue leaching, wherein the concentration of magnesium bicarbonate is 2-12 g/L (MgO), and preferably 6-9 g/L. The effect of secondary leaching, acid reduction and impurity removal can be influenced by reducing the concentration of the magnesium bicarbonate to be too low, and the preparation cost is increased because the magnesium bicarbonate is unstable and easy to decompose when the concentration of the magnesium bicarbonate is too high.
In the re-dissolving process, the concentration of the dissolved rare earth can be improved by reducing the solid-to-solid ratio of the re-dissolving solution, but the concentration is not suitable to be too low, the rare earth sulfate can be saturated by too low, and the rare earth sulfate crystal cannot be completely dissolved. In the re-dissolving process, the temperature is raised to reduce the solubility of the rare earth, but in a proper temperature range, the temperature is raised to have little influence on the dissolution of the rare earth sulfate crystal.
In the non-magnesium bicarbonate route, the whole process is divided into two times of impurity removal, wherein the pH value is controlled to be 1.0-2.5 after the first time of secondary soaking, the second time of deep impurity removal is carried out on rare earth sulfate solution with lower impurity content obtained after rare earth sulfate crystal dissolution, and the pH value is controlled to be 3.0-4.0 in the process. The main reason for reducing the rare earth loss is that the rare earth hydrolysis loss in the solid magnesium oxide neutralization impurity removal process is greatly influenced by the solid content in the neutralization impurity removal process, and particularly in the high pH (more than 2.5) impurity removal stage, when the solid content is higher, a precipitate in the neutralization process can adsorb newly added solid magnesium oxide, so that the mass transfer of magnesium oxide is not facilitated, the possibility of local alkali passing is increased, and the rare earth hydrolysis loss and the consumption of magnesium oxide are increased. The rare earth loss in the deep impurity removal process can be greatly reduced by adopting two-step impurity removal.
In the process of deep impurity removal, a magnesium-containing alkaline substance is added, and the pH value is controlled to be 3.0-4.0. The pH value of the deep impurity removal is increased, the consumption of magnesium oxide and the hydrolysis loss of rare earth are increased, and the pH value of the deep impurity removal is too low to be beneficial to the deep removal of impurities such as iron and the like.
The present invention is described in further detail below with reference to specific examples, which are not to be construed as limiting the scope of the invention as claimed.
As a basis for comparison, mixed ore of bastnaesite and monazite is sulfated and roasted and then subjected to water leaching under conventional conditions, wherein the temperature is 40 ℃, the time is 180min, and the liquid-solid ratio is 7: 1mL/g; then magnesium oxide is adopted for neutralization and impurity removal, the temperature is 40 ℃, the time is 2.5 hours, and the pH value of the finally obtained solution is 3.5. The total rare earth concentration of the obtained sulfuric acid rare earth solution is calculated by oxide, REO is 31.42g/L, fe 2 O 3 The content of P is 28.37mg/L 2 O 5 The content of (B) is 0.32mg/L. The yield of rare earth is 91.52%; the consumption of magnesium oxide per kg of rare earth oxide extracted during the process was 391.25g.
The first to thirteenth sets of embodiments are embodiments employing a magnesium bicarbonate solution.
Referring to table 1 for a first set of examples, examples 1-3 used different leaching temperatures for one leach. Referring to table 1 for a second set of examples, examples 4-7 use different leaching times for one leach. Third group of examples referring to table 2, examples 8-10 use different leach liquor to solid ratios for one leach. Fourth group of examples referring to table 2, the primary leachate obtained in example 2 was used, and examples 11 to 13 used different crystallization temperatures. In a fifth set of examples, referring to table 3, the primary leach solution obtained in example 2 was used, and examples 14 to 16 used different crystallization times. In a sixth set of examples, see table 3, the first leachate obtained in example 2 was used, and example 17 was carried out using a different stirring speed for crystallization than in example 2. In the seventh to tenth groups of examples, referring to table 4, the primary leachate, the primary leaching residue, the crystallization mother liquor and the rare earth sulfate crystals obtained in example 2 were used, example 18 used a different liquid-solid ratio from the secondary leaching in example 2, example 19 used a different leaching time from the secondary leaching in example 2, example 20 used a different leaching temperature from the secondary leaching in example 2, and example 21 used a different magnesium bicarbonate concentration from the secondary leaching in example 2. In the eleventh to thirteenth groups of examples, referring to table 5, the secondary leachate and rare earth sulfate crystals obtained in example 2 are used, the solid ratio of the redissolution in example 22 is different from that in example 2, the redissolution temperature in example 23 is different from that in example 2, and the deep impurity removal pH in example 24 is different from that in example 2.
Fourteenth to fifteenth sets of examples, see table 6, are examples employing non-magnesium bicarbonate.
In examples 25 to 27, the primary leachate, the primary leaching residue, the mother solution for crystallization, and the rare earth sulfate crystal obtained in example 2 were used, and the secondary leaching impurity removal end points had different pH values. Examples 28 to 30 were carried out using the primary leachate, the primary leaching residue, the mother liquid for crystallization, and the rare earth sulfate crystal obtained in example 2, and the pH for deep impurity removal was different.
In conclusion, the invention provides a method for preparing pure rare earth sulfate solution, which utilizes the dynamic characteristic of rare earth dissolution in the leaching process of sulfuric acid roasted ore of rare earth and the characteristic that the solubility of rare earth sulfate is reduced along with the temperature rise, and adopts the low liquid-solid ratio rapid leaching and then the temperature rise recrystallization to separate out more than 50 percent of rare earth in sulfuric acid rare earth recrystallization phase with higher purity so as to realize the primary separation of rare earth and impurity elements. And the rare earth remained in the solution phase is separated from the impurities again by the way of neutralizing and removing impurities by using magnesium bicarbonate solution or magnesium oxide. The preparation method of the invention improves the total recovery rate of the rare earth by 1-3%. The preparation method reduces the total consumption of magnesium oxide by about 90 percent when the magnesium bicarbonate solution is adopted for secondary leaching and impurity removal, and reduces the consumption of magnesium oxide by about 10 percent when non-magnesium bicarbonate two-step neutralization impurity removal is adopted.
It should be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, equivalent replacement, improvement and the like made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the appended claims or the equivalents of such scope and boundaries.
Claims (15)
1. A method for producing a pure rare earth sulfate solution from sulfated calcined rare earth ore comprising:
(1) Carrying out primary leaching on roasted ore obtained by roasting rare earth concentrate by using sulfuric acid, so as to obtain supersaturated rare earth sulfate solution and primary leaching slag, wherein the primary leaching temperature is 10-50 ℃, and the solid-to-solid ratio of leaching solution is 0.5-4: 1mL/g or m 3 The leaching time is 1-30 min;
(2) Crystallizing the supersaturated rare earth sulfate solution obtained by the primary leaching to obtain pure rare earth sulfate crystals and a crystallization mother solution;
(3) Carrying out secondary leaching and impurity removal on the crystallized mother liquor obtained by crystallization and the leaching residue obtained by primary leaching after water supplement or magnesium bicarbonate solution, so as to obtain secondary leaching liquid and secondary leaching residue;
(4) Dissolving the pure rare earth sulfate crystal obtained in the step (2) by using the leachate obtained by the secondary leaching to obtain a rare earth sulfate solution;
(5) Deeply removing impurities from the rare earth sulfate solution to obtain a pure rare earth sulfate solution and neutralized slag.
2. The method of claim 1, wherein the sulfated roasted rare earth ore is a mixed ore of bastnaesite and at least one of monazite and xenotime, and is obtained by sulfating roasting.
3. The method for preparing the pure rare earth sulfate solution from the sulfated roasted rare earth ore according to claim 1, wherein the primary leaching temperature in the step (1) is 30-45 ℃, and the leaching solution-solid ratio is 1-2.5: 1mL/g or m 3 And t, leaching time is 5-15 min.
4. The method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore according to claim 1, wherein the crystallization mode in the step (2) comprises at least one of induced crystallization and temperature-rising crystallization.
5. The method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore according to claim 4, wherein the crystallization in the step (2) is a temperature-rising crystallization method, the crystallization temperature is 50-90 ℃, and the crystallization time is 20-120 min.
6. The method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore according to claim 5, wherein the temperature-rising crystallization method has a crystallization temperature of 55-70 ℃ and a crystallization time of 30-90 min.
7. The method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore according to claim 1, wherein the secondary leaching of the crystallization mother liquor and the leaching residue obtained from the primary leaching in the step (3) comprises: secondary leaching outAdding a magnesium bicarbonate solution for removing impurities and continuously leaching after 10-60 min, wherein the total volume of the crystallization mother liquor and the magnesium bicarbonate solution is as follows: the mass of the leaching slag of the primary leaching is =7 3 The leaching temperature is 20-60 ℃, the total leaching time is 30-180 min, and the concentration of magnesium bicarbonate is 2-12 g/L calculated by MgO.
8. The method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore according to claim 7, wherein the leaching temperature of the secondary leaching is 30-40 ℃, the total leaching time is 90-120 min, and the concentration of magnesium bicarbonate is 6-10 g/L calculated as MgO.
9. The method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore according to claim 7 or 8, further comprising a step (6) of mixing leaching residue obtained by the secondary leaching and the neutralized residue and then washing the mixture, wherein the washing liquid is used as a leaching agent for preparing supersaturated rare earth sulfate solution in the step (1).
10. The method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore according to claim 1, wherein the secondary leaching of the mother liquor from crystallization and the leaching residue from the primary leaching in the step (3) comprises: and (3) mixing the crystal mother liquor after water replenishing with leaching residues obtained by primary leaching for secondary leaching, wherein the total volume of the crystal mother liquor after water replenishing is as follows: the mass of the primary leaching residue =7 3 The leaching temperature is 20-50 ℃, and the leaching time is 30-180 min.
11. The method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore according to claim 10, wherein the leaching time of the secondary leaching is 60-120min.
12. The method for preparing the pure rare earth sulfate solution from the sulfated roasted rare earth ore according to claim 10 or 11, wherein the step (3) of removing impurities comprises the steps of adding magnesium-containing alkaline substances into secondary leachate for neutralization until the pH is = 1.0-2.5, and then carrying out solid-liquid separation to obtain primary neutralized liquid and primary neutralized slag, wherein the neutralization temperature is 25-50 ℃, and the neutralization time is 30-180 min.
13. The method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore according to claim 12, further comprising a step (6) of mixing leaching residue obtained by the secondary leaching in the step (3), primary neutralization residue and the neutralization residue obtained by deep impurity removal in the step (5) and then washing the mixture, wherein the washing solution is used as a leaching agent for preparing supersaturated rare earth sulfate solution in the step (1).
14. The method for preparing the pure rare earth sulfate solution from the sulfated roasted rare earth ore according to claim 1, wherein the solid-to-solid ratio of the leachate obtained by the secondary leaching in the step (4) to the pure rare earth sulfate crystal solution is 15-30 3 The temperature is 25-45 ℃.
15. The method for preparing pure rare earth sulfate solution from sulfated roasted rare earth ore according to claim 1, wherein magnesium-containing alkaline substance is added during the neutralization in the step (5), the neutralization temperature is 25-40 ℃, the neutralization time is 30-180 min, and the neutralization pH is = 3.0-4.0.
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