WO2014027348A1 - Procédé de fabrication d'acide phosphorique à teneur en cadmium réduite - Google Patents

Procédé de fabrication d'acide phosphorique à teneur en cadmium réduite Download PDF

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Publication number
WO2014027348A1
WO2014027348A1 PCT/IL2013/050686 IL2013050686W WO2014027348A1 WO 2014027348 A1 WO2014027348 A1 WO 2014027348A1 IL 2013050686 W IL2013050686 W IL 2013050686W WO 2014027348 A1 WO2014027348 A1 WO 2014027348A1
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WO
WIPO (PCT)
Prior art keywords
phosphoric acid
cadmium
concentration
low
mixture
Prior art date
Application number
PCT/IL2013/050686
Other languages
English (en)
Inventor
Malka NIR
Uri Sasson COHEN
Shimon ISRALOVITZ
Original Assignee
Rotem Amfert Negev Ltd.
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Rotem Amfert Negev Ltd. filed Critical Rotem Amfert Negev Ltd.
Publication of WO2014027348A1 publication Critical patent/WO2014027348A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/18—Phosphoric acid
    • C01B25/234—Purification; Stabilisation; Concentration
    • C01B25/237—Selective elimination of impurities
    • C01B25/238—Cationic impurities, e.g. arsenic compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/18—Phosphoric acid
    • C01B25/22—Preparation by reacting phosphate-containing material with an acid, e.g. wet process
    • C01B25/222—Preparation by reacting phosphate-containing material with an acid, e.g. wet process with sulfuric acid, a mixture of acids mainly consisting of sulfuric acid or a mixture of compounds forming it in situ, e.g. a mixture of sulfur dioxide, water and oxygen
    • C01B25/232—Preparation by reacting phosphate containing material with concentrated sulfuric acid and subsequently lixiviating the obtained mass, e.g. clinker process
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/18—Phosphoric acid
    • C01B25/234—Purification; Stabilisation; Concentration
    • C01B25/237—Selective elimination of impurities
    • C01B25/2372—Anionic impurities, e.g. silica or boron compounds
    • C01B25/2377—Sulfate
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/46—Sulfates

Definitions

  • the present invention relates to a process of purifying phosphoric acid and providing a product with lowered levels of cadmium.
  • Phosphoric acid is consumed in huge amounts in chemical industry, mainly in manufacturing fertilizers, detergents, and food products.
  • the world production is about 30 million tons per year (as P2O5), most of which employs so called wet process, in which sulfuric acid reacts with naturally occurring phosphate rocks.
  • the main reaction of the wet process is the formation of the desired product and calcium sulfate.
  • the side product, calcium sulfate may be found in three polymorphs differing in the amount of crystal water, as dihydrate, hemihydrate, and anhydride; the amount of water bound in calcium sulfate is important for the course and balance of the wet process.
  • Said dihydrate is called gypsum, but the term is often used for all calcium sulfate forms, and the same simplification is used throughout the present text.
  • the phosphate rocks comprise calcium phosphate, less of fluorides and silicates, and many other admixtures.
  • Said admixtures comprise cadmium, of which level in the marketed products is regulated still more strictly, especially when the product could contaminate the environment, but particularly strictly when the product is used in food industry. It is therefore an object of the invention to provide a process for manufacturing phosphoric acid with lower content of cadmium.
  • the present invention provides a process for manufacturing low-cadmium phosphoric acid comprising the steps of i) providing a mass of raw phosphoric acid having a concentration of between 45 and 55 % P2O5, and containing up to 50 ppm cadmium; ii) admixing to said phosphoric acid of step i) concentrated sulfuric acid to reach a concentration of between 4 and 12% SO4" 2 in the mixture; iii) admixing to said phosphoric acid of step i) a naturally occurring phosphate rock in an amount corresponding to between 5 and 15% of said mass; iv) reacting said rock with said sulfuric acid at a temperature of between 80 and 90°C to obtain a mixture comprising phosphoric acid and suspended particles of calcium sulfate; and v) filtering the suspension of step iv) at a temperature of at least 80°C; thereby obtaining a filtration cake of calcium sulfate with bound cadmium ions, and a product of low-cadmium
  • the present invention provides a process for manufacturing a low-cadmium and low-sulfate phosphoric acid product.
  • concentrations in the present text the term “percent” or symbol "%" means weight percent.
  • water can be added to adjust the concentrations to desired values. Water may be removed from the system as condensed steam.
  • the process of the invention preferably comprises the steps of i) providing a mass of phosphoric acid having a concentration of at least 50 % P2O5, and containing up to 40 ppm cadmium; ii) admixing to said phosphoric acid of step i) concentrated sulfuric acid to reach a concentration of at least 7 % SO 4 " 2 in the mixture; iii) admixing to said mixture of step ii) a naturally occurring phosphate rock in an amount corresponding to at least the mass of said SO 4 in the mixture; iv) reacting said rock with said sulfuric acid at a temperature of between 80 and 90°C; and v) filtering the suspension of step iv); thereby obtaining a product of low-cadmium phosphoric acid having a concentration of at least 52 % P2O5, and containing at most 0.2 % S0 4 and at most 4 ppm cadmium.
  • Said concentrated sulfuric acid has preferably a concentration of at least 95%.
  • said step v) comprises adding water to the filtered suspension or onto the filter.
  • the process according to the invention provides a low-cadmium product of phosphoric acid, which in addition has a phosphoric acid concentration higher than the initial raw material, and further it has less sulfates than said raw phosphoric acid.
  • sulfates intended are all molecular forms comprising SO4" 2 , whereas their total amount is characterized as weight percent of S0 4 .
  • the phosphoric acid concentration is characterized, as is usual, by weight percent of P2O5.
  • the process steps may be separated in the space and time in various ways.
  • the process according to the invention is performed in more reactors. At least one of the reactors is a temperature-controlled reactor. In a preferred embodiment, said steps i) and ii) are performed in a first stirred reactor, and said steps iii) and iv) in a second stirred reactor.
  • said raw phosphoric acid and said concentrated sulfuric acid may be continuously fed to a first stirred reactor, the mixture from said first reactor may be continuously transferred to a second stirred reactor, and the mixture from said second reactor may be continuously transferred either to the filter or to a collection tank.
  • one part of the reaction mixture from said second reactor is transferred to said filter or tank, and another part of the reaction mixture from said second reactor is recirculated back to said first reactor.
  • Water may be added to various stages of the process, according to the concentration needs. In one embodiment of the invention, water is continually added either onto said filter or into said tank.
  • the invention provides a continuous process for manufacturing low-cadmium phosphoric acid, comprising the steps of i) providing raw phosphoric acid containing up to 40 ppm cadmium and up to 8% sulfate as S0 4 " 2 ; ii) reacting said phosphate rock in the mixture with said sulfuric acid and said raw phosphoric acid at a temperature of between 80 and 90°C; and iii) filtering the reaction mixture; thereby obtaining low-cadmium and low- sulfate phosphoric acid having a P2O5 concentration higher than said raw phosphoric acid.
  • the invention relates to a process for reducing cadmium amounts in phosphoric acid, simultaneously increasing the concentration of P2O5 in said phosphoric acid.
  • some stages of the process are performed in a continuous mode; more preferably the process is a continuous process.
  • the process steps are performed at a temperature between 80 and 90°C.
  • the product has preferably a concentration of P2O5 of 54% or more.
  • the invention relates to an apparatus for reducing the cadmium level in phosphoric acid, comprising i) at least one stirred and temperature-controlled reactor enabling to keep the reaction mixture between 80 and 90°C; ii) a unit for feeding raw phosphoric acid comprising at least 45 % P2O5 and cadmium up to 50 ppm; iii) a unit for feeding concentrated sulfuric acid; iv) a unit for feeding phosphate rock; v) pumps and transferring means for transporting solutions or suspensions between the units and reactors; and vi) at least one filtration unit for removing calcium sulfate from suspension and providing a filtrate of phosphoric acid having at most 5 ppm cadmium.
  • Fig. 1. is a schematic presentation of a process in accordance with one embodiment of the invention, comprising two stirred, flow-through reactors.
  • phosphoric acid containing unacceptably high amounts of cadmium may be efficiently purified by inducing the formation of calcium sulfate in the raw acid at a temperature of between 80 and 90°C followed by filtration.
  • the mechanism is not entirely clear, but without wishing to be bound by any theory, the inventors believe that, under certain conditions, calcium sulfate formed in the mixture binds cadmium which is removed from the solution during the filtration step. Said calcium sulfate may probably be in the anhydrous form, or partially as a hemihydrate.
  • Said special conditions comprise certain temperature range for both the reacting step and the filtration step, a relatively high P2O5 concentration, and the presence of sulfuric acid in the reaction stage. It was observed by the inventors that, under certain conditions, cadmium is removed during the filtration, but the filtration rate was very low. It was found that the kinetics of anhydrite formation affects the structure of the formed calcium sulfate, while leading to much better filterability of the sulfate cake under certain reaction conditions. Another important factor taken onto consideration is the P2O5 concentration, as dilution of phosphoric acid during the purification would increase the process cost.
  • the process according to the invention addresses both the problem of undesired impurities and the problem of undesired dilution.
  • the conditions of the process enable formation of anhydrite from hemihydrate, without involving calcium sulfate dihydrate, so avoiding the excessive water release and product dilution.
  • the present process enables to purify phosphoric acid from various sources and of various purity levels, and containing various impurities; particularly, the instant process enables to lower unacceptably high levels of cadmium.
  • cadmium decreases to 5 ppm or less, preferably to 4 ppm or less, and still more preferably to 3 ppm or less, for example to 2 ppm or less.
  • the process of cadmium removal according to the invention does not lead to the dilution of phosphoric acid, but surprisingly even provides a P2O5 higher than in the raw acid.
  • the process also enables to remove excessive sulfate in the raw acid.
  • the level of sulfates is lowered to less than 1%, preferably to less than 0.5%, still preferably to at most 0.2%.
  • the method of the invention comprises step i) of providing a mass of raw phosphoric acid having a concentration of between 45 and 55 % P2O5, preferably at last 50 %, and containing up to 50 ppm cadmium, preferably up to 40 ppm, or up to 30 ppm.
  • step ii) concentrated sulfuric acid is admixed to said phosphoric acid of step i) to reach a concentration of between 4 and 12% SO4" 2 in the mixture, preferably from 6 to 10%; if the raw acid contained sulfates, such as in an amount of 4%, sulfuric acid is added to increase the SO4" 2 level by only about 4 or 5 %, making totally 8 or 9% SO4" 2 ; excess of sulfuric acid increases the amounts of solids and accelerates sulfate dehydratation, but may lower the concentration of P2O5.
  • a naturally occurring phosphate rock is admixed to said phosphoric acid of step i) in an amount corresponding to between 5 and 15% of said raw acid mass, but preferably in such an amount so as to enable to said rock to completely react with sulfuric acid.
  • the reaction of said rock with said sulfuric acid, step iv) occurs between 80 and 90°C, dehydratation runs best at 90°C, but in many cases it is optimal to keep the mixture at 87°C.
  • a mixture comprising phosphoric acid and suspended particles of calcium sulfate, wherein the conditions are believed to lead to calcium sulfate forms without crystal water.
  • the reaction time, or retention time in a flow-through reactor may be several hours, for example 1.5 hour.
  • Step v) includes filtering the suspension of step iv) at a temperature of at least 80°C; thereby obtaining a filtration cake of calcium sulfate which, in its spatial structure, binds a greater part of the cadmium atoms, whereas the filtrate provides the desired product of low-cadmium phosphoric acid.
  • the temperature should preferably be kept below 85°C during the filtration step; the concentration of monocalcium phosphate (MCP) is preferably 2.5% or more.
  • MCP monocalcium phosphate
  • Perlite may be added in the mixture to improve the use of phosphate rock which is not finely milled, or its admixture, may be helpful.
  • the concentration of the components is controlled in all stages, during the whole process.
  • the product is at least 46 % P2O5, preferably at least 48%, more preferably at least 50%, and still more preferably at least 52%, for example at least 54% but preferably lower than 56.0%, whereas cadmium level is at most 5 ppm, or preferably at most 4 ppm, for example 3 ppm or less, such as 2 ppm or less.
  • the invention provides an apparatus for reducing the cadmium level in phosphoric acid, comprising at least one stirred and temperature-controlled reactor, a raw acid feeder unit, sulfuric acid feeder unit, phosphate rock feeder unit, pumps, a filtration unit, and transferring means for transporting solutions or suspensions.
  • the apparatus has two stirred reactors.
  • Number symbols (1), (2), (3), and (4) represent stocks of raw phosphoric acid, concentrated sulfuric acid, phosphate rock, and water, respectively.
  • the materials (1) and (2) are fed to reactor Rl, whereas rock (3) is fed to reactor R2.
  • filtration cake (7) is removed from filter F, liquid streams comprising (1), (2), (4) (5), (6), (8), and the stream between reactors Rl and R2 are driven preferably by pumps.
  • water vapor is removed from the apparatus as a condensate.
  • some of the liquid streams may be driven by gravity.
  • parts of the process may be performed in a batch mode.
  • Said filtration cake may be removed periodically or continually, eventually washing out acid residues and returning it to the reactors.
  • the apparatus works essentially in a continuous mode.
  • the material transport velocities are selected to ensure equilibrium of the system, including constant volumes of the mixtures in reactors.
  • the velocity of the recirculation stream (5) may contribute to the mixing efficiency of the reaction mixture, it may be, for example, about a half of the feeding velocity of (1).
  • the retention time, affected by the ratio of feeding velocity and the reactor volume, may be, for example, between 1 and 5 hours.
  • a skilled person will select the initial values based on small batch tests, knowing that the values will be affected by the composition of the reagents, including the processed raw phosphoric acid and the used phosphate rock, and later will adjust the values to obtain the highest yield.
  • the process of the invention may incorporate further steps aiming at removing additional undesired component in a raw material, including other toxic elements, or halogens, etc.
  • Phosphoric acid 52.5% P2O5, 5.0% SO4" 2 , 20ppm Cd
  • Phosphoric acid 97.5%) was fed to the same reactor at a velocity of 82.0 g/hr (v2).
  • the mixture was pumped from said first reactor to a second reactor of the same volume, to which phosphate rock was continuously fed at a velocity of 230.0 g/hr (v3).
  • the stirred suspension from the second rector was pumped simultaneously to the filter unit at a velocity of about 2500 g/hr (v6) and back to the first reactor at a velocity of about 1100 g/hr.
  • the velocities were kept in balance so that the volumes of the mixtures in both reactors be kept constant (for example, vl+v2+v3 approximately equals v6 if there are no losses).
  • Water was pumped to the filter unit by a velocity onto the filter at a velocity of about 304 ml/hr.
  • the filtrate was obtained at a velocity of 2190 ml/hr (54.9% P2O5, 0.192 SO4- 2 , 3.65 ppm Cd).
  • About 640 g/hr calcium sulfate with other reagent residues was obtained.
  • the total losses of phosphoric acid were 3%, the total yield of the phosphoric acid production was 97%.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

Abstract

La présente invention concerne un procédé de fabrication d'acide phosphorique à teneur réduite en cadmium et en sulfate, lequel procédé comprend les étapes qui consistent à mélanger de l'acide phosphorique brut, ayant une concentration en P2O5 située entre 45 et 55% et contenant jusqu'à 50 ppm de cadmium, avec de l'acide sulfurique concentré, afin d'obtenir une concentration en sulfate de 4 à 12%; à ajouter au mélange 5 à 15% de roche phosphatée naturelle, de manière à obtenir de l'acide phosphorique et des particules en suspension de sulfate de calcium; puis à filtrer lesdites particules à une température d'au moins 80 degrés C.
PCT/IL2013/050686 2012-08-16 2013-08-12 Procédé de fabrication d'acide phosphorique à teneur en cadmium réduite WO2014027348A1 (fr)

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IL221523 2012-08-16
IL22152312 2012-08-16

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WO2014027348A1 true WO2014027348A1 (fr) 2014-02-20

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022124875A1 (fr) 2020-12-10 2022-06-16 Ocp Sa Procede integre de decadmiation d'acide phosphorique

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4822582A (en) * 1986-07-15 1989-04-18 Stamicarbon B.V. Process for the removal of heavy metals from acid, phosphate-containing, aqueous media
EP0333489A2 (fr) * 1988-03-16 1989-09-20 IMI (TAMI) INSTITUTE FOR RESEARCH & DEVELOPMENT LTD. Procédé d'élimination d'ions de métaux lourds d'acide phosphorique
US5279806A (en) * 1989-07-04 1994-01-18 Office Togolais Des Phosphates Process for eliminating heavy metals from phosphoric acid

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4822582A (en) * 1986-07-15 1989-04-18 Stamicarbon B.V. Process for the removal of heavy metals from acid, phosphate-containing, aqueous media
EP0333489A2 (fr) * 1988-03-16 1989-09-20 IMI (TAMI) INSTITUTE FOR RESEARCH & DEVELOPMENT LTD. Procédé d'élimination d'ions de métaux lourds d'acide phosphorique
US5279806A (en) * 1989-07-04 1994-01-18 Office Togolais Des Phosphates Process for eliminating heavy metals from phosphoric acid

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2022124875A1 (fr) 2020-12-10 2022-06-16 Ocp Sa Procede integre de decadmiation d'acide phosphorique
FR3117476A1 (fr) 2020-12-10 2022-06-17 Ocp Sa Procede integre de decadmiation d’acide phosphorique

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