CA1115483A - Preparation of monocalcium phosphate and phosphoric acid - Google Patents
Preparation of monocalcium phosphate and phosphoric acidInfo
- Publication number
- CA1115483A CA1115483A CA326,914A CA326914A CA1115483A CA 1115483 A CA1115483 A CA 1115483A CA 326914 A CA326914 A CA 326914A CA 1115483 A CA1115483 A CA 1115483A
- Authority
- CA
- Canada
- Prior art keywords
- phosphoric acid
- phosphate
- solution
- monocalcium phosphate
- potassium
- 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.)
- Expired
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Classifications
-
- 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
- C01F11/20—Halides
- C01F11/22—Fluorides
-
- 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
- C01B25/223—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 only one form of calcium sulfate being formed
- C01B25/225—Dihydrate 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
- C01B25/26—Phosphates
- C01B25/32—Phosphates of magnesium, calcium, strontium, or barium
- C01B25/328—Defluorination during or after the preparation
-
- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05B—PHOSPHATIC FERTILISERS
- C05B11/00—Fertilisers produced by wet-treating or leaching raw materials either with acids in such amounts and concentrations as to yield solutions followed by neutralisation, or with alkaline lyes
- C05B11/04—Fertilisers produced by wet-treating or leaching raw materials either with acids in such amounts and concentrations as to yield solutions followed by neutralisation, or with alkaline lyes using mineral acid
- C05B11/10—Fertilisers produced by wet-treating or leaching raw materials either with acids in such amounts and concentrations as to yield solutions followed by neutralisation, or with alkaline lyes using mineral acid using orthophosphoric acid
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Fertilizers (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
- Removal Of Specific Substances (AREA)
- Silicon Compounds (AREA)
- Crystals, And After-Treatments Of Crystals (AREA)
Abstract
PREPARATION OF MONOCALCIUM
PHOSPHATE AND PHOSPHORIC ACID
ABSTRACT OF THE DISCLOSURE
Monocalcium phosphate, phosphoric acid and/or potassium phosphate containing fertilizers are produced in a process involving acidulation of phosphate rock with phosphoric acid in the presence of added silicon dioxide and potassium ion whereby fluorides contained in the rock are converted to K2SiF6, wherein monocalcium phosphate dis-solved in phosphoric acid is formed during acidulation. In an important feature, the K2SiF6 is separated and hydrolyzed to regenerate the K20 from K2SiF6 as recycled KH2P04/H3P04 solution for further reaction with fluoride from fresh phosphate rock feed. A portion of the MCP/H3P04 solution and/or crystallized monocalcium phosphate can then be reacted with potassium sulfate, potassium bisulfate, or mixtures thereof, to form KH2P04, or KH2P04/H3P04 solutions, and gyp-sum. In a closely related embodiment, the remaining MCP/H3P04 solution is reacted with sulfuric acid to produce phosphoric acid product and/or the recycle phosphoric acid required in the phosphate rock acidulation step.
PHOSPHATE AND PHOSPHORIC ACID
ABSTRACT OF THE DISCLOSURE
Monocalcium phosphate, phosphoric acid and/or potassium phosphate containing fertilizers are produced in a process involving acidulation of phosphate rock with phosphoric acid in the presence of added silicon dioxide and potassium ion whereby fluorides contained in the rock are converted to K2SiF6, wherein monocalcium phosphate dis-solved in phosphoric acid is formed during acidulation. In an important feature, the K2SiF6 is separated and hydrolyzed to regenerate the K20 from K2SiF6 as recycled KH2P04/H3P04 solution for further reaction with fluoride from fresh phosphate rock feed. A portion of the MCP/H3P04 solution and/or crystallized monocalcium phosphate can then be reacted with potassium sulfate, potassium bisulfate, or mixtures thereof, to form KH2P04, or KH2P04/H3P04 solutions, and gyp-sum. In a closely related embodiment, the remaining MCP/H3P04 solution is reacted with sulfuric acid to produce phosphoric acid product and/or the recycle phosphoric acid required in the phosphate rock acidulation step.
Description
~ll,'j4~
This invention relates to a method for the production of monocalcium phosphate and phosphoric acid by the acidulation of phosphate rock with phosphoric acid in the presence of silicon dioxide and potassium ion wherein fluorides are converted to potassium fluosilicate and the calcium is converted to monocalcium phosphate from which potassium dihydrogen phosphate may be formed.
Phosphoric acid plants are currently operated utilizing a basic and well known process for the acidulation of phosphate rock which comprises reaction of the rock with sulfuric acid to form phosphoric acid with subsequent reaction of the phosphoric acid, with for example ammonia to produce monoammonium phosphate tMAP) and diammonium phosphate (DAP). The phosphoric acid formed in this process is called wet process phosphoric acid. In this reaction, a by-product is gypsum having the chemical formula CaSO4 2H2O. Essentially, all phosphate rock contains some fluoride, normally in the 3.0 to 4.0~ range, and the acidulation reaction usually generates gaseous fluorides.
Because of the fluoride content, an important problem in the operation of these wet process phosphoric acid plants has been in the expensive methods for handling the large amounts of fluorine compounds which are liberated in the gaseous and aqueous effluents from such plants. It is only in recent years that studies have been made on the effects of fluorides contained in the final product and indications seem clear that they may have a deleterious effect on the long range producing ability of the soil when present in fertilizers.
lllS4~;3 It i5 accordingly an object of this invention to produce relatively pure phosphoric acid and relatively pure monocalcium phosphate which are essentially free of fluorides, iron, aluminum, magnesium and other impurities, in such manner as to eliminate or greatly reduce K2O losses and concentrate insoluble fluoride compounds in recoverable form so that they can be processed for fluorine and K2O recovery and reuse, and minimize contamination of the environment and final products by the presence of fluorine compounds.
Thus, by one aspect of the present invention there is provided a process for the acidulation of phosphate rock and the production of phosphoric acid and monocalcium phosphate which may subsequently be converted to potassium dihydrogen phosphate, a valuable fertilizer, as well as the recovery and isolation of the fluoride compounds initially as K2SiF6 and ultimately as calcium fluoride. This process comprises, in its broadest embodiment, acidulating phosphate rock with an excess of phosphoric acid in the presence of added silicon dioxide and potassium ion to produce a first slurry of insoluble potassium fluosilicate in a solution of monocalcium phosphate in phosphoric acid; subjecting this mixture to separation to produce a clarified solution of monocalcium phosphate in phosphoric acid and a second slurry comprisin~ monocalcium phosphate in phosphor-ic acid which contains insoluble potassium fluosilicate; subject-ing said second slurry to hydrolysis at an elevated temperature to regenerate a KH2PO4/H3PO4 solution and produce calcium fluoride and silicon dioxide; recovering the calcium fluoride and silicon dioxide and recycling the KH2PO4/H3PO4 solution to .~ - 3 -, 4~3 the acidulation reaction. Preferably, a major portion of the monocalcium phosphate/phosphoric acid solution is reacted with sulEuric acid to precipitate calcium sulfate hydrate which is removed from the system, and phosphoric acid, a portion of which may be removed as product, with the balance being recycled to the acidulation reactor as determined by material balance considerations.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference is now made to the drawings accompanying this application which are diagrammatic flow sheets wherein:
Figure 1 shows the main embodiment of the process of this invention; and Figure 2 shows alternative embodiments for further processing of the monocalcium phosphate/phosphoric acid product.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As indicated above, this invention is concerned with a multi-step procedure for the preparation of essentially fluoride-free products, preferably alkali metal phosphates and phosphoric acid, by the acidulation of phosphate rock, which procedure is conducted in the substantial absence of fluorine pollution and wherein the fluorides may be recovered in usable form, and wherein phosphoric acid may be regenerated for reuse in the system and/orseparated as product.
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As is known, most of the commercially important phosphate ores mined in this country, and particularly those mined in Florida, contain 3-4% fluorine after beneficiation.
The fluorine is a constituent of fluoapatite which is commonly expressed as Ca9(PO4)6 CaF2 and may also be present as calcium fluosilicate (CaSiF6). Silica is a component of phosphate rock and is usually abundant in most grades of rock that are commonly used in the production of wet process phosphoric acid. In usual processes the fluorine compounds in the phosphate rock react with sulfuric acid during the attack on the rock so that the fluorine appears in vapor form as hydrofluoric acid (HF), silicon tetrafluoride (SiF4), or other gas, and in the phosphoric acid solution as fluosilicic acid (H2SiF6) and/or fluosilicate salts or other forms. Acids from a rock low in reactive silica may also contain free hydrogen fluoride. The present invention provides a significant solution to problems of fluoride pollu-tion by providing a procedure for minimizing fluoride evolution while recovering substantially all of the fluorides in usable form thereby preventing the fluorides form contaminating the environment and desired products. The present invention also provides a series of substantially purer and useful products as well as novel procedures for obtaining these products without pollution.
In one aspect, the process of this invention is concerned with the preparation of alkali metal phosphates and/or phosphric acid and in a main embodiment of the invention, the alkali metal phosphate is an alkali metal dihdyrogen phosphate.
A preferred product is KH2PO4 and/or its admixture with phosphoric acid, which contain high plant food S~3 nutrients, and is hi~hly valued as a ertilizer. Na~l2PO~, an alternative product, is widely used in tile detergent industry and other areas. However, potassium products are preferred and the reaction is described with respect to potassium reactants and products. The process of the present invention is carried out in a continuous manner in the optimum embodiment.
In the initial step of the process of this invention, - phosphate rock from any origin, but usually of the type described above containing at least some fluorides, is acidulated with a solution of phosphoric acid containing potassium ion recycle values from room temperature up to about 95C., and preferably about 70 to 90C., for a sufficient time to achieve substantially complete acidulation, usually about 1/2 to 4 hours depending on the reaction temperature and using a sufficient amount of the phosphoric acid solution to completely solubilize the calcium phosphate formed. Sufficient potassium ion is present in the mixture to cause precipitation of the fluorides as a precipitate, primarily as K2SiF6 together with SiO2 and impurities. In the preferred embodiment, the potassium ion values are provided by KH2PO4 salts contained in recycle phosphoric acid solution.
In conducting this initial step, the phosphoric acid solution is utilized in sufficiènt excess to effect subs-tantially complete acidulation and solubilization oE the calcium in phosphate rock. The P2O5 content of the phosphoric acid should range from about 20-55~ and preferably about 25~~0~ by weight.
In general, there should be used an excess of phosphoric acid and preferably about 35 to 90 moles of phosphoric acid for each 6 moles of phosphate in phosphate rock, or a molar ratio of P2O5 in the acid to P2O5 in the rock, of about 6:1 to 15:1, respectively. Also, about 1.0 to 10 moles of K2O, preferably 4~3 more than about one mole, to provide a slight excess of K2O, should be present for each three moles of phosphate rock of the formula ca9(po4)6 CaF2 The K2O or potassium ion is preferably added as KH2PO4.
As pointed out, the phosphoric acid is present in sufficient amounts to solubilize the calcium phosphate contained in the phosphate rock. Further, the K2O values such as the KH2PO4 salt are contained in the phosphoric acid in a sufficient amount to precipitate the fluorides present as dense crystalline solids which may be recovered readily. Thus, during the acidulation step, while the calcium phosphates are solubilized, there is precipitated a mixture of solids from which the fluorides may be recovered. This precipitate contains the fluorides essentially as K2SiF6.
It is to be appreciated that the phosphoric acid as the treating acid is to be distinguished from the stronger mineral acids such as sulfuric acid, nitric acid, hydrochloric acid, and the like. As is shown in many standard reference books, phosphoric acid has a weaker ionization constant than stronger mineral acids. By use of the term phosphoric acid, it is meant that it is an acid that is ionized at less than 90~ at a strength of concentration of 0.1 Normal, and has an ioni~ation constant of no more than 7.5 x 10 3.
11 154~3 In conducting the initial step of the reaction, the phosphate rock and phosphoric acid are reacted in the plesence of reactive silica. There is also present a recycle solution comprising a solution of potassium dihydrogen phosphate and phosphoric acid. In general, there is sufficient potassium ion and reactive silica present in this initial reactor to convert fluorides contained in phosphate rock to potassium fluosilicate.
The silica added during the reaction of this in-vention may be amorphous silicon dioxide in any suitable formso long as it is not delete~ious to the reaction under con-sideration. The silica is preferably obtained from materials combinable with the phosphate rock, such as slag, or commerci-ally available products such as those sold under the trade mark "Dicalite,"~ sold by Grafco Corporation.
The product resulting from the initial reaction comprises a relatively low concentration of suspended solids (e.g., in the range of 3 to 15 wt.%), in the solution of monocalcium phosphate and phosphoric acid. This mixture is preferably passed to a thickener for separation of the solids and solution to produce a clarified monocalcium phosphate solution. This clarified monocalcium phosphate may then be treated as described herein to produce phosphoric acid and/or potassium dihydrogen phosphate.
An important feature of the invention is the utilization of the calcium ion from phosphate rock to remove j"':~' ......
::~ ', . :
: ~ '' . :
11154~3 fluorides as 3CaF2 and/or 3CaF2/SiO2 and thereby eliminate the need of using an external source of calcium such as limestone. While the potassium ion is a critical component of this system, it is not consumed, but simply recycled to perform the required fluoride removal function. As a con-sequence, the cost of K2O in fluoride removal is no longer a significant factor since only makeup K2O will be needed as governed by losses.
It is also within the scope of the invention to utilize an external source of phosphoric acid and/or an ex-ternal source of K2SiF6 in the initial acidulation reaction.
However, in the preferred embodiment, recycle of these mater-ials is especially preferred for purposes of economics.
The underflow, when a thickener is used, is a slurry of monocalciurn phosphate/phosphoric acid solution which con-tains the fluorides, usually as potassium fluosilicate, and any slirnes. A feature of this invention is that this mix-ture is hydrolyzed, preferably by heatin~ at 100-115C. or up to the reflux point, to form potassium dihydrogen phos-phate in phosphoric acid and convert the fluorides to cal-cium fluoride and silicon dioxide. As shown, this hydrolysis reaction proceeds as illustrated by the following equation:
This invention relates to a method for the production of monocalcium phosphate and phosphoric acid by the acidulation of phosphate rock with phosphoric acid in the presence of silicon dioxide and potassium ion wherein fluorides are converted to potassium fluosilicate and the calcium is converted to monocalcium phosphate from which potassium dihydrogen phosphate may be formed.
Phosphoric acid plants are currently operated utilizing a basic and well known process for the acidulation of phosphate rock which comprises reaction of the rock with sulfuric acid to form phosphoric acid with subsequent reaction of the phosphoric acid, with for example ammonia to produce monoammonium phosphate tMAP) and diammonium phosphate (DAP). The phosphoric acid formed in this process is called wet process phosphoric acid. In this reaction, a by-product is gypsum having the chemical formula CaSO4 2H2O. Essentially, all phosphate rock contains some fluoride, normally in the 3.0 to 4.0~ range, and the acidulation reaction usually generates gaseous fluorides.
Because of the fluoride content, an important problem in the operation of these wet process phosphoric acid plants has been in the expensive methods for handling the large amounts of fluorine compounds which are liberated in the gaseous and aqueous effluents from such plants. It is only in recent years that studies have been made on the effects of fluorides contained in the final product and indications seem clear that they may have a deleterious effect on the long range producing ability of the soil when present in fertilizers.
lllS4~;3 It i5 accordingly an object of this invention to produce relatively pure phosphoric acid and relatively pure monocalcium phosphate which are essentially free of fluorides, iron, aluminum, magnesium and other impurities, in such manner as to eliminate or greatly reduce K2O losses and concentrate insoluble fluoride compounds in recoverable form so that they can be processed for fluorine and K2O recovery and reuse, and minimize contamination of the environment and final products by the presence of fluorine compounds.
Thus, by one aspect of the present invention there is provided a process for the acidulation of phosphate rock and the production of phosphoric acid and monocalcium phosphate which may subsequently be converted to potassium dihydrogen phosphate, a valuable fertilizer, as well as the recovery and isolation of the fluoride compounds initially as K2SiF6 and ultimately as calcium fluoride. This process comprises, in its broadest embodiment, acidulating phosphate rock with an excess of phosphoric acid in the presence of added silicon dioxide and potassium ion to produce a first slurry of insoluble potassium fluosilicate in a solution of monocalcium phosphate in phosphoric acid; subjecting this mixture to separation to produce a clarified solution of monocalcium phosphate in phosphoric acid and a second slurry comprisin~ monocalcium phosphate in phosphor-ic acid which contains insoluble potassium fluosilicate; subject-ing said second slurry to hydrolysis at an elevated temperature to regenerate a KH2PO4/H3PO4 solution and produce calcium fluoride and silicon dioxide; recovering the calcium fluoride and silicon dioxide and recycling the KH2PO4/H3PO4 solution to .~ - 3 -, 4~3 the acidulation reaction. Preferably, a major portion of the monocalcium phosphate/phosphoric acid solution is reacted with sulEuric acid to precipitate calcium sulfate hydrate which is removed from the system, and phosphoric acid, a portion of which may be removed as product, with the balance being recycled to the acidulation reactor as determined by material balance considerations.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference is now made to the drawings accompanying this application which are diagrammatic flow sheets wherein:
Figure 1 shows the main embodiment of the process of this invention; and Figure 2 shows alternative embodiments for further processing of the monocalcium phosphate/phosphoric acid product.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As indicated above, this invention is concerned with a multi-step procedure for the preparation of essentially fluoride-free products, preferably alkali metal phosphates and phosphoric acid, by the acidulation of phosphate rock, which procedure is conducted in the substantial absence of fluorine pollution and wherein the fluorides may be recovered in usable form, and wherein phosphoric acid may be regenerated for reuse in the system and/orseparated as product.
~: , . ' . ~ ... ~,. . ' : -~. - . . :
; ., ; ~ : ~ .:
:. . : ~
As is known, most of the commercially important phosphate ores mined in this country, and particularly those mined in Florida, contain 3-4% fluorine after beneficiation.
The fluorine is a constituent of fluoapatite which is commonly expressed as Ca9(PO4)6 CaF2 and may also be present as calcium fluosilicate (CaSiF6). Silica is a component of phosphate rock and is usually abundant in most grades of rock that are commonly used in the production of wet process phosphoric acid. In usual processes the fluorine compounds in the phosphate rock react with sulfuric acid during the attack on the rock so that the fluorine appears in vapor form as hydrofluoric acid (HF), silicon tetrafluoride (SiF4), or other gas, and in the phosphoric acid solution as fluosilicic acid (H2SiF6) and/or fluosilicate salts or other forms. Acids from a rock low in reactive silica may also contain free hydrogen fluoride. The present invention provides a significant solution to problems of fluoride pollu-tion by providing a procedure for minimizing fluoride evolution while recovering substantially all of the fluorides in usable form thereby preventing the fluorides form contaminating the environment and desired products. The present invention also provides a series of substantially purer and useful products as well as novel procedures for obtaining these products without pollution.
In one aspect, the process of this invention is concerned with the preparation of alkali metal phosphates and/or phosphric acid and in a main embodiment of the invention, the alkali metal phosphate is an alkali metal dihdyrogen phosphate.
A preferred product is KH2PO4 and/or its admixture with phosphoric acid, which contain high plant food S~3 nutrients, and is hi~hly valued as a ertilizer. Na~l2PO~, an alternative product, is widely used in tile detergent industry and other areas. However, potassium products are preferred and the reaction is described with respect to potassium reactants and products. The process of the present invention is carried out in a continuous manner in the optimum embodiment.
In the initial step of the process of this invention, - phosphate rock from any origin, but usually of the type described above containing at least some fluorides, is acidulated with a solution of phosphoric acid containing potassium ion recycle values from room temperature up to about 95C., and preferably about 70 to 90C., for a sufficient time to achieve substantially complete acidulation, usually about 1/2 to 4 hours depending on the reaction temperature and using a sufficient amount of the phosphoric acid solution to completely solubilize the calcium phosphate formed. Sufficient potassium ion is present in the mixture to cause precipitation of the fluorides as a precipitate, primarily as K2SiF6 together with SiO2 and impurities. In the preferred embodiment, the potassium ion values are provided by KH2PO4 salts contained in recycle phosphoric acid solution.
In conducting this initial step, the phosphoric acid solution is utilized in sufficiènt excess to effect subs-tantially complete acidulation and solubilization oE the calcium in phosphate rock. The P2O5 content of the phosphoric acid should range from about 20-55~ and preferably about 25~~0~ by weight.
In general, there should be used an excess of phosphoric acid and preferably about 35 to 90 moles of phosphoric acid for each 6 moles of phosphate in phosphate rock, or a molar ratio of P2O5 in the acid to P2O5 in the rock, of about 6:1 to 15:1, respectively. Also, about 1.0 to 10 moles of K2O, preferably 4~3 more than about one mole, to provide a slight excess of K2O, should be present for each three moles of phosphate rock of the formula ca9(po4)6 CaF2 The K2O or potassium ion is preferably added as KH2PO4.
As pointed out, the phosphoric acid is present in sufficient amounts to solubilize the calcium phosphate contained in the phosphate rock. Further, the K2O values such as the KH2PO4 salt are contained in the phosphoric acid in a sufficient amount to precipitate the fluorides present as dense crystalline solids which may be recovered readily. Thus, during the acidulation step, while the calcium phosphates are solubilized, there is precipitated a mixture of solids from which the fluorides may be recovered. This precipitate contains the fluorides essentially as K2SiF6.
It is to be appreciated that the phosphoric acid as the treating acid is to be distinguished from the stronger mineral acids such as sulfuric acid, nitric acid, hydrochloric acid, and the like. As is shown in many standard reference books, phosphoric acid has a weaker ionization constant than stronger mineral acids. By use of the term phosphoric acid, it is meant that it is an acid that is ionized at less than 90~ at a strength of concentration of 0.1 Normal, and has an ioni~ation constant of no more than 7.5 x 10 3.
11 154~3 In conducting the initial step of the reaction, the phosphate rock and phosphoric acid are reacted in the plesence of reactive silica. There is also present a recycle solution comprising a solution of potassium dihydrogen phosphate and phosphoric acid. In general, there is sufficient potassium ion and reactive silica present in this initial reactor to convert fluorides contained in phosphate rock to potassium fluosilicate.
The silica added during the reaction of this in-vention may be amorphous silicon dioxide in any suitable formso long as it is not delete~ious to the reaction under con-sideration. The silica is preferably obtained from materials combinable with the phosphate rock, such as slag, or commerci-ally available products such as those sold under the trade mark "Dicalite,"~ sold by Grafco Corporation.
The product resulting from the initial reaction comprises a relatively low concentration of suspended solids (e.g., in the range of 3 to 15 wt.%), in the solution of monocalcium phosphate and phosphoric acid. This mixture is preferably passed to a thickener for separation of the solids and solution to produce a clarified monocalcium phosphate solution. This clarified monocalcium phosphate may then be treated as described herein to produce phosphoric acid and/or potassium dihydrogen phosphate.
An important feature of the invention is the utilization of the calcium ion from phosphate rock to remove j"':~' ......
::~ ', . :
: ~ '' . :
11154~3 fluorides as 3CaF2 and/or 3CaF2/SiO2 and thereby eliminate the need of using an external source of calcium such as limestone. While the potassium ion is a critical component of this system, it is not consumed, but simply recycled to perform the required fluoride removal function. As a con-sequence, the cost of K2O in fluoride removal is no longer a significant factor since only makeup K2O will be needed as governed by losses.
It is also within the scope of the invention to utilize an external source of phosphoric acid and/or an ex-ternal source of K2SiF6 in the initial acidulation reaction.
However, in the preferred embodiment, recycle of these mater-ials is especially preferred for purposes of economics.
The underflow, when a thickener is used, is a slurry of monocalciurn phosphate/phosphoric acid solution which con-tains the fluorides, usually as potassium fluosilicate, and any slirnes. A feature of this invention is that this mix-ture is hydrolyzed, preferably by heatin~ at 100-115C. or up to the reflux point, to form potassium dihydrogen phos-phate in phosphoric acid and convert the fluorides to cal-cium fluoride and silicon dioxide. As shown, this hydrolysis reaction proceeds as illustrated by the following equation:
2 4)2 + lOH3PO4 + K2SiF6 + R2O3/P2O5 + 2 H O >
2/3caF2 + R2O3/P2O5 + 2KH2PO4 + 14H PO
wherein R is a metal such as Fe or Al.
As may be seen from this equation, the fluorides, lli54~3 in the form of K2SiF6, are converted to SiO2/3CaF2as a solid in admixture with A12O3, Fe2O3, etc. This solid mixture is separated from the solution of 2KH2PO4 + 14H3PO4 and valuable fluorides may be recovered from the solids as described here-in.
The resulting solution is suitable for recycle to the system to provide at least a portion of the potassium ion necessary to produce additional potassium fluosilicate and also provide a source of phosphoric acid. As a result, some of the SiO2 and K2O are not consumed in the reaction but rather are recycled in the continuous process. It is, of course, to be understood that additional amounts of potassium ion and SiO2 from external sources may be added to the acidula-tion reactor as may be required by the system. An external source of phosphoric acid may also be used.
In one embodiment, a portion of the resulting clari-fied monocalcium phosphate and phosphoric acid solution is reacted wlth potassium sulfate, potassium bisulfate or mix-tures thereof to produce KH2PO4/H3PO4 solutions from which KH2PO4 may be recovered as a fertilizer grade material. Phos-phoric acid may also be produced in this embodiment and may be recovered or recycled as makeup phosphoric acid.
The remaining monocalcium phosphate/phosphoric acid solution is reacted with sulfuric acid to produce calcium sulfate hydrate which may be recovered and the phosphoric acid regenerated as a result of this reaction may be recovered as product and/or recycled to the main reactor to effect acidulation of the phosphate rock feed.
: ..... : ;.. : - . .
lllX4~3 The essential steps described above for the reaction provide a number of advantages in the process. Thus the process serves to regenerate valuable hydrogen ions as illustrated by the following equation:
K2SiF6+ 3Ca(H2PO4)2~ 10H3PO4 ~ 3caF2 + SiO2+ 2KH2PO4+ 14H3PO4 Thus the phosphoric acid concentration increases from 10 to 14 moles or an increase of 40%. More importantly, this 14 moles of free H3PO4 can now accommodate additional unreacted phosphate rock. In effect, approximately 3CaO/30CaO or 10%
of the original rock feed can be acidulated in this manner;
2/3caF2 + R2O3/P2O5 + 2KH2PO4 + 14H PO
wherein R is a metal such as Fe or Al.
As may be seen from this equation, the fluorides, lli54~3 in the form of K2SiF6, are converted to SiO2/3CaF2as a solid in admixture with A12O3, Fe2O3, etc. This solid mixture is separated from the solution of 2KH2PO4 + 14H3PO4 and valuable fluorides may be recovered from the solids as described here-in.
The resulting solution is suitable for recycle to the system to provide at least a portion of the potassium ion necessary to produce additional potassium fluosilicate and also provide a source of phosphoric acid. As a result, some of the SiO2 and K2O are not consumed in the reaction but rather are recycled in the continuous process. It is, of course, to be understood that additional amounts of potassium ion and SiO2 from external sources may be added to the acidula-tion reactor as may be required by the system. An external source of phosphoric acid may also be used.
In one embodiment, a portion of the resulting clari-fied monocalcium phosphate and phosphoric acid solution is reacted wlth potassium sulfate, potassium bisulfate or mix-tures thereof to produce KH2PO4/H3PO4 solutions from which KH2PO4 may be recovered as a fertilizer grade material. Phos-phoric acid may also be produced in this embodiment and may be recovered or recycled as makeup phosphoric acid.
The remaining monocalcium phosphate/phosphoric acid solution is reacted with sulfuric acid to produce calcium sulfate hydrate which may be recovered and the phosphoric acid regenerated as a result of this reaction may be recovered as product and/or recycled to the main reactor to effect acidulation of the phosphate rock feed.
: ..... : ;.. : - . .
lllX4~3 The essential steps described above for the reaction provide a number of advantages in the process. Thus the process serves to regenerate valuable hydrogen ions as illustrated by the following equation:
K2SiF6+ 3Ca(H2PO4)2~ 10H3PO4 ~ 3caF2 + SiO2+ 2KH2PO4+ 14H3PO4 Thus the phosphoric acid concentration increases from 10 to 14 moles or an increase of 40%. More importantly, this 14 moles of free H3PO4 can now accommodate additional unreacted phosphate rock. In effect, approximately 3CaO/30CaO or 10%
of the original rock feed can be acidulated in this manner;
3 4)2 14H3Po4 = 3ca(H2P4)2 + 10H3P
The process of the invention also removes unreacted phosphate rock from the acidulation reaction and subjects this rock to much more vigorous acidulation conditions to provide:
~ 15 ; a) increased phosphate acid concentration as illustrated above,and b) increased temperatures from 80-90C. The process accomplishes these functions using a relatively modest defluo-rination/hydrolysis loop which is only 10% of the main loop or system. Further it permits recovery of the considerably more dense Fluorspar component, and will also separate unhydrolyzed K2SiF6 with the ÇaF2. In this instance, subsequent - treatment with NH~OH can be utilized to produce a chemical grade Fluorspar. The process also eliminates the R2O3 component after removal of the dense CaF2/K2SiF6 components - preferably by the addition of clean gypsum to assist in the separation (centrifuge) step and to simulate the 0-20-0 NSP grade. The 110 115C. temperatures involved in hydrolysis will help ::`
li:lS4~3 flocculate the R2O3 component and simplify separation.
Reference is now made to Figure 1 accompanying the application wherein there is shown a schematic diagram of the main embodiment of the process of the present invention.
In the drawing, phosphate rock from line 1 and phosphoric acid from line 2 are reacted in acidulation reactor 3. The reaction is conducted at a temperature in the range of about 40-95C. and the materials are reacted utilizing an excess of the phosphoric acid. The phosphoric acid contains potas-sium, usually added as KH2PO4, in sufficient amounts to react with fluoride contained in the phosphate rock and pro-duce potassium fluosilicate. In addition, reactive silica is added by line 4 to provide sufficient reaction with potassium to form the potassium fluosilicate. In this reactor 3, monocalcium phosphate is formed as a solution in phosphoric acid with an insoluble precipitatecomprising slimes and a portion of the potassium fluosilicate. Sufficient phosphoric acid is present to dissolve the monocalcium phos-phate.
The reaction mixture is then passed by line 5 directly to defluorination reactor or thickener 6 for re-.
moval of the fluorides.
In defluorination thickener 6, a product or under-flow is removed which is a slurry of potassium fluosilicate, sio2 slimes, and other solids in a solution of monocalcium phos-phate in phosphoric acid. In accordance with a main embodi-ment of the invention, the potassium fluosilicate in the slurry is withdrawn by line 7 to hydrolyzer 8. The hydrolysis ! .: ', ' , ,' ;, , ~;, , ' ' :
~llS4~;~
reaction in hydrolyzer 8 is conducted by heating at a temperature in the range of 100-115C. or at the reflux point of the system preferably by introduction of steam at 9, to convert the potassium fluosilicate to silicon dioxide, calcium fluoride, and potassium dihydrogen phosphate and/or phos-phoric acid-using monocalcium phosphate. The resulting mixture is passed by line 10 to separator 11 where calcium fluoride and some silicon dioxide are recovered at line 12. In a preferred embodiment, the mixture from separator 11 is passed to separator lS by line 13 after addition of a suit-able amount of gypsum by line 13. Thereafter, there is recovered from separator 15 an 0-20-0 fertilizer by line 16 which contains most of the R2O3 components or slimes.
The gypsum is added primarily as substrate to provide a filterable solid 0-20-0 (N-P-K) product, and to facilitate the separation of slimes from the solution in separator 15.
KH2PO4/H3PO4 solution, which may contain some SiO2, is then recycled by line 17. While the bulk of the R2O3 is removed here, it can also be expected that portions will be removed with other products.
In the meantime, the overflow or solution from de-fluorinator or thickener 6 is recovered in line 18 as a solution of monocalcium phosphate in phosphoric acid. This product may be processed by any of several alternative embodiments to recover valuable products, including mono-calcium phosphate, phosphoric acid including recycle H3PO4, and gypsum, all of which are substantially free of fluoride contamination.
The process of the invention also removes unreacted phosphate rock from the acidulation reaction and subjects this rock to much more vigorous acidulation conditions to provide:
~ 15 ; a) increased phosphate acid concentration as illustrated above,and b) increased temperatures from 80-90C. The process accomplishes these functions using a relatively modest defluo-rination/hydrolysis loop which is only 10% of the main loop or system. Further it permits recovery of the considerably more dense Fluorspar component, and will also separate unhydrolyzed K2SiF6 with the ÇaF2. In this instance, subsequent - treatment with NH~OH can be utilized to produce a chemical grade Fluorspar. The process also eliminates the R2O3 component after removal of the dense CaF2/K2SiF6 components - preferably by the addition of clean gypsum to assist in the separation (centrifuge) step and to simulate the 0-20-0 NSP grade. The 110 115C. temperatures involved in hydrolysis will help ::`
li:lS4~3 flocculate the R2O3 component and simplify separation.
Reference is now made to Figure 1 accompanying the application wherein there is shown a schematic diagram of the main embodiment of the process of the present invention.
In the drawing, phosphate rock from line 1 and phosphoric acid from line 2 are reacted in acidulation reactor 3. The reaction is conducted at a temperature in the range of about 40-95C. and the materials are reacted utilizing an excess of the phosphoric acid. The phosphoric acid contains potas-sium, usually added as KH2PO4, in sufficient amounts to react with fluoride contained in the phosphate rock and pro-duce potassium fluosilicate. In addition, reactive silica is added by line 4 to provide sufficient reaction with potassium to form the potassium fluosilicate. In this reactor 3, monocalcium phosphate is formed as a solution in phosphoric acid with an insoluble precipitatecomprising slimes and a portion of the potassium fluosilicate. Sufficient phosphoric acid is present to dissolve the monocalcium phos-phate.
The reaction mixture is then passed by line 5 directly to defluorination reactor or thickener 6 for re-.
moval of the fluorides.
In defluorination thickener 6, a product or under-flow is removed which is a slurry of potassium fluosilicate, sio2 slimes, and other solids in a solution of monocalcium phos-phate in phosphoric acid. In accordance with a main embodi-ment of the invention, the potassium fluosilicate in the slurry is withdrawn by line 7 to hydrolyzer 8. The hydrolysis ! .: ', ' , ,' ;, , ~;, , ' ' :
~llS4~;~
reaction in hydrolyzer 8 is conducted by heating at a temperature in the range of 100-115C. or at the reflux point of the system preferably by introduction of steam at 9, to convert the potassium fluosilicate to silicon dioxide, calcium fluoride, and potassium dihydrogen phosphate and/or phos-phoric acid-using monocalcium phosphate. The resulting mixture is passed by line 10 to separator 11 where calcium fluoride and some silicon dioxide are recovered at line 12. In a preferred embodiment, the mixture from separator 11 is passed to separator lS by line 13 after addition of a suit-able amount of gypsum by line 13. Thereafter, there is recovered from separator 15 an 0-20-0 fertilizer by line 16 which contains most of the R2O3 components or slimes.
The gypsum is added primarily as substrate to provide a filterable solid 0-20-0 (N-P-K) product, and to facilitate the separation of slimes from the solution in separator 15.
KH2PO4/H3PO4 solution, which may contain some SiO2, is then recycled by line 17. While the bulk of the R2O3 is removed here, it can also be expected that portions will be removed with other products.
In the meantime, the overflow or solution from de-fluorinator or thickener 6 is recovered in line 18 as a solution of monocalcium phosphate in phosphoric acid. This product may be processed by any of several alternative embodiments to recover valuable products, including mono-calcium phosphate, phosphoric acid including recycle H3PO4, and gypsum, all of which are substantially free of fluoride contamination.
4~33 As a result of this process, there is recovered from the defluorinator 6 by line 18 the product from the reaction of this invention. This reaction product comprises a solution of monocalcium phosphate in phosphoric acid, which is a valuable reaction product of high quality sub-stantially free of fluoride contamination. This product solution may be treated by various alternative processing techniques to recover monocalcium phosphate and/or phosphoric acid, which products may also be converted to other valuable products including KH2PO4and recycle phosphoric acid. Pre-ferred further processing techniques are shown in Figure 2.
In the embodiment of Figure 2, the monocalcium phos-phate/phosphoric acid solution product from line 18 is passed to intermediate storage 19 where the stream may be divided into two portions for further processing. The division of the ~CP/H3PO4 stream at this point may be in a desired ratio, ~ e.g., about 40 to 60 wt. ~ of the stream may be removed, and ; ~ processed to recover XH2PO4/H3PO4. In this aspect, a portion of the stream is withdrawn by line 20 and passed to reactor 21. In reactor 21, the stream is reacted with a potassium ` sulfate reactant such as potassium sulfate, potassium hydro-gen sulfate or a mixture thereof, added by line 22. The potassium sulfate reactant may be added as a solid or aque-ous solution and is added in sufficient stoichiometric amounts to react with all the monocalcium phosphate present.
As necessary, for solution purposes, water may be added by line 23. This reaction is conducted at a temperature of about 50 to 100C. with agitation.
11~54?;33 In reactor 21, the monocalcium phosphate and potassium sulfate react to produce potassium dihydrogen phosphate as product together with gypsum and phosphoric acid as illustrated by the following equation when the re-actant is potassium sulfate:
2 4 2 (YH3PO4) where Y is the amount of phosphoric acid in the system.
The resulting reaction slurry is then transferred by line 24 to separator or filter 25 and a solution of KH2PO4 in phosphoric acid is removed by line 26 and the gypsum is removed by line 27. The solid filter cake is washed by water from line 23 and the wash water may be re-cycled by line 29 to reactor 21.
The product recovered at line 26 contains potassium dihydrogen phosphate and has a fertilizer value of 0-24-6.
The KH2PO4 may be recovered from this solution by evapora-tion and precipitation with a water miscible solvent such as methanol or extraction with a water immiscible solvent such as butanol.
In the meantime, the other portion of the clarified monocalcium phosphate/phasphoric acid solution from inter-mediate storage l9 is passed by line 30 to crystalli~er 31 and reacted with at least a stoichiometric amount of-sulfuric acid from line 32. The sulfuric acid reacts with the MCP/H3PO4 solution to produce phosphoric acid and calcium sulfate hydrate and this slurry is passed by line 33 to thickener 34 wherein concentration of the slurry is achieved and the under-flow slurry is then passed by line 35 to filter 36. The solid ll.i 54~3 calcium sulfate hydrate in substantially pure form is re-covered by line 37.
After removal of the calcium sulfate hydrate, the phosphoric acid solution/filtrate is transferred by line 39 to evaporator 40 where water is removed from the system at 41 as required. The remaining phosphoric acid may then be recovered as product by line 42 or may be combined with line 38 overflow from thickener 34 via dotted line 43 to meet the recycle phosphorlc acid needs of line 2 in the phosphate rock acidulation carried out in reactor 3.
In a further embodiment of the present invention (not shown), the monocalcium phosphate/phosphoric acid solu-tion may be processed to recover solid monocalcium phosphate from the phosphoric acid and each product may then be re-covered or further processed. In one aspect, the monocal-cium phosphate/phosphoric acid clarified solution from de-1uorinator 6 is passed to a crystallizer. Up to this point, the monocalcium phosphate/phosphoric acid solution has been maintained at a temperature in the range of 80-95C. to main-tain the solution. However, in the crystallizer, the solutionis cooled via evaporation to about 25-55C., preferably about 40C., to cause crystallization of solid monocalcium phos-phate from the phosphoric acid solution. Therefore, it is preferred that the mixture be cooled by a temperature differ-ence of about 35-55C. The resulting slurry is then passed from the crystallizer to a separator where a separation is effected between solid monocalcium phosphate and the mother liquor MCP/H3PO4. The solid monocalcium phosphate from the separator is then passed,for example to reactor 21,wherein ~.1154~3 reaction is carried out with a potassium sulfate reactant such as potassium sulfate, potassium hydrogen sulfate, or a mixture thereof as described above for the MCP/H3P04 solu-tion. In this reactor 21, the monocalcium phosphate and K2S04and/or KHS04 reactant produce potassium dihydrogen phosphate and/or phosphoric acid as a product together with gypsum~ The resulting mixture is then filtered and the gyp-sum removed by line 27. The product recovered at line 26 is an aqueous solution of potassium dihydro~en phosphate and/or phosphoric acid. This solution may be further pro-cessed into desired products.
In this reaction, the monocalcium phosphate reacts with the potassium sulfate or potassium hydrogen sulfate as -~ illustrated by the following equations:
2 4)2 8K2S4~ 16~12P04 + 8CaS04 2H2o b) 8ca(H2P4)2 + 8KHS04 ~ 8KH2P04 + 8H3 4 4 2 .-In reaction (a) with K2S04, the KH2P04 product is a liquid 0-15-10 fertilizer which may be further concentrated, and in reaction (b) with KHS04, the KH2P04/H3P04 product is ~ .
`~ 20 a liquid 0-24-8 fertilizer.
~ In the meantime, the MCP/phosphoric acid from the ;~ separator is passed to the calcium sulfate hydrate crystal-~, lizer and reacted with sulfuric acid to produce phosphoric acid product and/or recycle mother liquor and calcium sul-~i 25 fate hydrate as described above for the process of Figure 2.
-` This reaction for recycle is illustrated by the following equation:
4~3 ~ 2 4)2 9~l3Po4~l9~l2so4+38l~2) > 128H3PO4+l9caso4 21120 The "128 H3PO4" portion represents the phosphoric acid available for recycle.
It will therefore be understood that this approach also leads to valuable fertilizer products and recycle phosphoric acid.
The following example is presented to illustrate the invention but it is not considered to be limited thereto.
:~n this example and throughout the specification, parts a by weight unless otherwise indicated.
EXAMPL~ I
In this example, l,278 grams (= 9 moles) P2O5 in phosphate rock are reacted with 10,224 grams (= 72 moles) P2O5 as 35~ recycle phosphoric acid for a P2O5 (acid) /P2O5 (rock) weight ratio of 8/l. This reaction mixture provides enough excess phosphoric acid to dissolve essentially all of the calcium i~n~the phosphate rock as monocalcium phosphate whereln the P2O5/CaO weight ratio should approach 6.75/l. ~The acidulation reactio~ ls conducted at 80-90C. and contains a minimum of l mole o~ K2O and sufficient external reactive silica (SiO2) to remove substantially all of the fluoride as insoluble potassium Eluosilicate. Sand, some R2O3 slimes and unxeacted phosphate roc]c also remain insoluble.
Small amounts (up to 3-4 ppm) of a flocculatin~ agent such as Nalcalite 670 are helpful in the settling the solids from this sys teM.
. .
, ,., . . . . ~ : -ll~S4F~3 This thin reaction slurry, still at 90C., is then separated via a decanter/thickener (separatory funnel may be used in the laboratory) wherein approximately 10% of the MCP/H3PO4 solution remains with the underflow insolubles.
The now thickened slurry, is directed into the hydrolysis sector wherein the temperature is raised to 110-115C., e.g., by use of low pressure steam. Under these conditions, the hydrolysis reaction is essentially completed in 1 to 2 hours.
The slurry now contains dense crystalline Fluorspar (CaF2) ; 10 which is readily separated from the unreactive but somewhat flocculated R2O3/P2O5 components such as by a hydraclone or by suitable gravity separation means. Sufficient clean gypsum is then added to the remaining finely dispersed R2O3/P2O5 to achieve a 0-20-0 grade fertilizer which simu-lates NSP. This requires approximately 3.64 grams of CaSO4 per gram of P2O5 slimes to be recovered. The R2O3/P2O5 component has alread~ been flocculated/coalesced to a con-~; siderable degree during the 110-115~C. hydrolysis step.
:
1 However, the utilization of clean gypsum provides additional .
substrate so that separation of this material presents no undue difficulties. The product is readily separated via suitable means, e.g., a centrifuge or a precoat filter.
After separation of the solids, the remaining solu-tion of 2KH2PO4 + 14 H3PO4, which also contains a small amount of silicon dioxide, is recycled to the acidulation reactor as regenerated phosphoric acid containing potassium ion.
EXAMPLE II
The clarified monocalcium phosphate/phosphoric acid overflow from the K2SiF6 thickener is thus passed to a crystal-lizer wherein the temperature is lowered to 40C. to crystal-lize monocalcium phosphate. The solid monocalcium phosphate and the remaining MCP/H3PO4 solutions are then separated via a filter, centrifuge or other separator. The solid monocalcium phosphate is removed and reacted with a stoichiometric amount of potassium hydrogen sulfate in an aqueous medium at ~ a temperature of 90C. In this reaction, the monocalcium ; 10 l~hGsphate is converted to KH2PO4 + H3PO4 and gypsum- The gypsum is removed and the IC~l2PO4 + H3PO4 liquor separated and recovered as a 0-24-8 fertilize solution.
The phosphoric acid solution which still contains mono-calcium phosphate from the separator is reacted with sulfuric acid in stoichiometric amounts at85C. to produce calcium sulfate hydrate which crystallizes from solution. This solid is then filtered and removed from the system. The resulting phosphoric acid ; is then recycled to the acidulation reactor.
EXAMPLE III
In an alternative reaction, the solid monocalcium phQsphate is reacted with potassium sulfate to yield primarily KH2PO4 with little or no H3PO4 coproduct. Conversely, if a portion of the (uncrystallized) MCP/H3PO4 liquor is reacted with potassium sulfate the resulting KH2PO4/H3PO4 solution will have a plant food value of 0-24-6. A portion of any of the K2O products may b~
recycled back to the acidulation vessel to provide makeup for the K2O lost in the hydrolysis sector.
In the embodiment of Figure 2, the monocalcium phos-phate/phosphoric acid solution product from line 18 is passed to intermediate storage 19 where the stream may be divided into two portions for further processing. The division of the ~CP/H3PO4 stream at this point may be in a desired ratio, ~ e.g., about 40 to 60 wt. ~ of the stream may be removed, and ; ~ processed to recover XH2PO4/H3PO4. In this aspect, a portion of the stream is withdrawn by line 20 and passed to reactor 21. In reactor 21, the stream is reacted with a potassium ` sulfate reactant such as potassium sulfate, potassium hydro-gen sulfate or a mixture thereof, added by line 22. The potassium sulfate reactant may be added as a solid or aque-ous solution and is added in sufficient stoichiometric amounts to react with all the monocalcium phosphate present.
As necessary, for solution purposes, water may be added by line 23. This reaction is conducted at a temperature of about 50 to 100C. with agitation.
11~54?;33 In reactor 21, the monocalcium phosphate and potassium sulfate react to produce potassium dihydrogen phosphate as product together with gypsum and phosphoric acid as illustrated by the following equation when the re-actant is potassium sulfate:
2 4 2 (YH3PO4) where Y is the amount of phosphoric acid in the system.
The resulting reaction slurry is then transferred by line 24 to separator or filter 25 and a solution of KH2PO4 in phosphoric acid is removed by line 26 and the gypsum is removed by line 27. The solid filter cake is washed by water from line 23 and the wash water may be re-cycled by line 29 to reactor 21.
The product recovered at line 26 contains potassium dihydrogen phosphate and has a fertilizer value of 0-24-6.
The KH2PO4 may be recovered from this solution by evapora-tion and precipitation with a water miscible solvent such as methanol or extraction with a water immiscible solvent such as butanol.
In the meantime, the other portion of the clarified monocalcium phosphate/phasphoric acid solution from inter-mediate storage l9 is passed by line 30 to crystalli~er 31 and reacted with at least a stoichiometric amount of-sulfuric acid from line 32. The sulfuric acid reacts with the MCP/H3PO4 solution to produce phosphoric acid and calcium sulfate hydrate and this slurry is passed by line 33 to thickener 34 wherein concentration of the slurry is achieved and the under-flow slurry is then passed by line 35 to filter 36. The solid ll.i 54~3 calcium sulfate hydrate in substantially pure form is re-covered by line 37.
After removal of the calcium sulfate hydrate, the phosphoric acid solution/filtrate is transferred by line 39 to evaporator 40 where water is removed from the system at 41 as required. The remaining phosphoric acid may then be recovered as product by line 42 or may be combined with line 38 overflow from thickener 34 via dotted line 43 to meet the recycle phosphorlc acid needs of line 2 in the phosphate rock acidulation carried out in reactor 3.
In a further embodiment of the present invention (not shown), the monocalcium phosphate/phosphoric acid solu-tion may be processed to recover solid monocalcium phosphate from the phosphoric acid and each product may then be re-covered or further processed. In one aspect, the monocal-cium phosphate/phosphoric acid clarified solution from de-1uorinator 6 is passed to a crystallizer. Up to this point, the monocalcium phosphate/phosphoric acid solution has been maintained at a temperature in the range of 80-95C. to main-tain the solution. However, in the crystallizer, the solutionis cooled via evaporation to about 25-55C., preferably about 40C., to cause crystallization of solid monocalcium phos-phate from the phosphoric acid solution. Therefore, it is preferred that the mixture be cooled by a temperature differ-ence of about 35-55C. The resulting slurry is then passed from the crystallizer to a separator where a separation is effected between solid monocalcium phosphate and the mother liquor MCP/H3PO4. The solid monocalcium phosphate from the separator is then passed,for example to reactor 21,wherein ~.1154~3 reaction is carried out with a potassium sulfate reactant such as potassium sulfate, potassium hydrogen sulfate, or a mixture thereof as described above for the MCP/H3P04 solu-tion. In this reactor 21, the monocalcium phosphate and K2S04and/or KHS04 reactant produce potassium dihydrogen phosphate and/or phosphoric acid as a product together with gypsum~ The resulting mixture is then filtered and the gyp-sum removed by line 27. The product recovered at line 26 is an aqueous solution of potassium dihydro~en phosphate and/or phosphoric acid. This solution may be further pro-cessed into desired products.
In this reaction, the monocalcium phosphate reacts with the potassium sulfate or potassium hydrogen sulfate as -~ illustrated by the following equations:
2 4)2 8K2S4~ 16~12P04 + 8CaS04 2H2o b) 8ca(H2P4)2 + 8KHS04 ~ 8KH2P04 + 8H3 4 4 2 .-In reaction (a) with K2S04, the KH2P04 product is a liquid 0-15-10 fertilizer which may be further concentrated, and in reaction (b) with KHS04, the KH2P04/H3P04 product is ~ .
`~ 20 a liquid 0-24-8 fertilizer.
~ In the meantime, the MCP/phosphoric acid from the ;~ separator is passed to the calcium sulfate hydrate crystal-~, lizer and reacted with sulfuric acid to produce phosphoric acid product and/or recycle mother liquor and calcium sul-~i 25 fate hydrate as described above for the process of Figure 2.
-` This reaction for recycle is illustrated by the following equation:
4~3 ~ 2 4)2 9~l3Po4~l9~l2so4+38l~2) > 128H3PO4+l9caso4 21120 The "128 H3PO4" portion represents the phosphoric acid available for recycle.
It will therefore be understood that this approach also leads to valuable fertilizer products and recycle phosphoric acid.
The following example is presented to illustrate the invention but it is not considered to be limited thereto.
:~n this example and throughout the specification, parts a by weight unless otherwise indicated.
EXAMPL~ I
In this example, l,278 grams (= 9 moles) P2O5 in phosphate rock are reacted with 10,224 grams (= 72 moles) P2O5 as 35~ recycle phosphoric acid for a P2O5 (acid) /P2O5 (rock) weight ratio of 8/l. This reaction mixture provides enough excess phosphoric acid to dissolve essentially all of the calcium i~n~the phosphate rock as monocalcium phosphate whereln the P2O5/CaO weight ratio should approach 6.75/l. ~The acidulation reactio~ ls conducted at 80-90C. and contains a minimum of l mole o~ K2O and sufficient external reactive silica (SiO2) to remove substantially all of the fluoride as insoluble potassium Eluosilicate. Sand, some R2O3 slimes and unxeacted phosphate roc]c also remain insoluble.
Small amounts (up to 3-4 ppm) of a flocculatin~ agent such as Nalcalite 670 are helpful in the settling the solids from this sys teM.
. .
, ,., . . . . ~ : -ll~S4F~3 This thin reaction slurry, still at 90C., is then separated via a decanter/thickener (separatory funnel may be used in the laboratory) wherein approximately 10% of the MCP/H3PO4 solution remains with the underflow insolubles.
The now thickened slurry, is directed into the hydrolysis sector wherein the temperature is raised to 110-115C., e.g., by use of low pressure steam. Under these conditions, the hydrolysis reaction is essentially completed in 1 to 2 hours.
The slurry now contains dense crystalline Fluorspar (CaF2) ; 10 which is readily separated from the unreactive but somewhat flocculated R2O3/P2O5 components such as by a hydraclone or by suitable gravity separation means. Sufficient clean gypsum is then added to the remaining finely dispersed R2O3/P2O5 to achieve a 0-20-0 grade fertilizer which simu-lates NSP. This requires approximately 3.64 grams of CaSO4 per gram of P2O5 slimes to be recovered. The R2O3/P2O5 component has alread~ been flocculated/coalesced to a con-~; siderable degree during the 110-115~C. hydrolysis step.
:
1 However, the utilization of clean gypsum provides additional .
substrate so that separation of this material presents no undue difficulties. The product is readily separated via suitable means, e.g., a centrifuge or a precoat filter.
After separation of the solids, the remaining solu-tion of 2KH2PO4 + 14 H3PO4, which also contains a small amount of silicon dioxide, is recycled to the acidulation reactor as regenerated phosphoric acid containing potassium ion.
EXAMPLE II
The clarified monocalcium phosphate/phosphoric acid overflow from the K2SiF6 thickener is thus passed to a crystal-lizer wherein the temperature is lowered to 40C. to crystal-lize monocalcium phosphate. The solid monocalcium phosphate and the remaining MCP/H3PO4 solutions are then separated via a filter, centrifuge or other separator. The solid monocalcium phosphate is removed and reacted with a stoichiometric amount of potassium hydrogen sulfate in an aqueous medium at ~ a temperature of 90C. In this reaction, the monocalcium ; 10 l~hGsphate is converted to KH2PO4 + H3PO4 and gypsum- The gypsum is removed and the IC~l2PO4 + H3PO4 liquor separated and recovered as a 0-24-8 fertilize solution.
The phosphoric acid solution which still contains mono-calcium phosphate from the separator is reacted with sulfuric acid in stoichiometric amounts at85C. to produce calcium sulfate hydrate which crystallizes from solution. This solid is then filtered and removed from the system. The resulting phosphoric acid ; is then recycled to the acidulation reactor.
EXAMPLE III
In an alternative reaction, the solid monocalcium phQsphate is reacted with potassium sulfate to yield primarily KH2PO4 with little or no H3PO4 coproduct. Conversely, if a portion of the (uncrystallized) MCP/H3PO4 liquor is reacted with potassium sulfate the resulting KH2PO4/H3PO4 solution will have a plant food value of 0-24-6. A portion of any of the K2O products may b~
recycled back to the acidulation vessel to provide makeup for the K2O lost in the hydrolysis sector.
Claims (14)
1. A process for the production of monocalcium phosphate and phosphoric acid which comprises acidulating phosphate rock with an excess of phosphoric acid in the presence of added silicon dioxide and potassium ion to produce a first slurry of insoluble potassium fluosilicate in a solution of mono-calcium phosphate in phosphoric acid; subjecting this mixture to separation to produce a clarified solution of monocalcium phos-phate in phosphoric acid and a second slurry comprising monocalcium phosphate in phosphoric acid which contains insoluble potassium fluosilicate; subjecting said second slurry to hydrolysis at an elevated temperature to regenerate a KH2P04/H3P04 solution and produce calcium fluoride and silicon dioxide; recovering the calcium fluoride and silicon dioxide and recycling the KH2P04/H3P04 solution to the acidulation reaction.
2. A process according to claim 1 wherein the acidulatior.
of the phosphate rock is carried out at a temperature in the range of about 25 - 95°C.
of the phosphate rock is carried out at a temperature in the range of about 25 - 95°C.
3. A process according to claim 2 wherein the mixture recovered from the acidulation reaction is separated in a decanter/thickener to produce an overflow comprising the clarified solution of monocalcium phosphate in phosphoric acid and an underflow slurry of K2SiF6 in a solution of monocalcium phosphate and phosphoric acid.
4. A process according to claim 3 wherein the under-flow is subjected to hydrolysis by heating at a temperature in the range of about 95°C. to the reflux temperature of the sys-tem to convert the K2SiF6 to calcium fluoride and silicon dioxide.
5. A process according to claim 1 wherein the calcium fluoride is initially separated from the hydrolysis reaction product, gypsum is then added to the remaining mixture, a solid 0-20-0 fertilizer is removed, and the remaining solution is re-cycled to the acidulation reaction.
6. A process according to claim 1 wherein about 1.0 to 10 moles of potassium ion are present in the acidulation reactor for each three moles of phosphate rock.
7. A process according to claim 6 wherein the potassium ion is added as KH2PO4.
8. A process according to claim 1 wherein the mono-calcium phosphate and phosphoric acid clarified solution is cooled to precipitate at least a portion of the monocalcium phosphate as a solid product, and separating the remaining solution of monocalcium phosphate and phosphoric acid.
9. A process according to claim 8 wherein the solid monocalcium phosphate is reacted with a member selected from the group consisting of potassium sulfate, potassium hydrogen sulfate, and/or mixtures thereof to produce KH2PO4, KH2PO4/H3PO4 mixtures and gypsum.
10. A process according to claim 8 wherein the solid monocalcium phosphate is reacted with K2SO4 in aqueous medium to produce KH2PO4 and gypsum, or the solid monocalcium phosphate is reacted with KHS04 in an aqueous medium to produce a solution of KH2PO4 in H3PO4, and solid gypsum.
11. A process according to claim 8 wherein the monocalcium phosphate/phosphoric acid solution is reacted with sulfuric acid to produce gypsum solids and phosphoric acid, the gypsum solids are filtered off and the phosphoric acid is recycled to the acidulation reactor.
12. A process according to claim 1 wherein the clarified solution of monocalcium phosphate in phosphoric acid is divided into two portions for separate processing.
13. A process according to claim 12 wherein one portion of the clarified solution is reacted with a member selected from the group consisting of potassium sulfate, potassium hydrogen sulfate and/or mixtures thereof at a temperature in the range of 60-80°C. to produce a solution of KH2PO4 in phosphoric acid and insoluble gypsum.
14. A process according to claim 12 wherein the remaining portion of clarified solution is reacted with sulfuric acid to produce gypsum solids and phosphoric acid, the gypsum solids are filtered off, and the phosphoric acid is recycled to the acidulation reactor.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US930,147 | 1978-08-02 | ||
| US05/930,147 US4160657A (en) | 1978-01-19 | 1978-08-02 | Preparation of monocalcium phosphate and phosphoric acid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1115483A true CA1115483A (en) | 1982-01-05 |
Family
ID=25458980
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA326,914A Expired CA1115483A (en) | 1978-08-02 | 1979-05-04 | Preparation of monocalcium phosphate and phosphoric acid |
Country Status (13)
| Country | Link |
|---|---|
| JP (1) | JPS5827207B2 (en) |
| BE (1) | BE876325A (en) |
| BR (1) | BR7903045A (en) |
| CA (1) | CA1115483A (en) |
| DE (1) | DE2930825A1 (en) |
| ES (1) | ES480523A1 (en) |
| FR (1) | FR2432477A1 (en) |
| GB (1) | GB2026996B (en) |
| IL (1) | IL57301A (en) |
| IN (1) | IN150442B (en) |
| IT (1) | IT1194869B (en) |
| MA (1) | MA18439A1 (en) |
| ZA (1) | ZA792199B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS586530B2 (en) * | 1976-09-06 | 1983-02-04 | ライオン株式会社 | composite emulsion |
| JPS58143831A (en) * | 1982-02-22 | 1983-08-26 | Taihoo Kogyo Kk | W/o/w composite emulsion |
| JPS6016542A (en) * | 1983-07-07 | 1985-01-28 | Meiji Milk Prod Co Ltd | Coffee cream and its preparation |
| JPS6016546A (en) * | 1983-07-07 | 1985-01-28 | Meiji Milk Prod Co Ltd | Whipping cream and its preparation |
| JPS60102137A (en) * | 1983-07-08 | 1985-06-06 | Meiji Milk Prod Co Ltd | Synthetic milk and synthetic condensed milk and their production |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2218382C3 (en) * | 1972-04-15 | 1975-08-21 | Gebrueder Giulini Gmbh, 6700 Ludwigshafen | Process for the production of pure calcium sulphate in phosphoric acid wet digestion |
| DE2543632A1 (en) * | 1974-10-07 | 1976-04-08 | Pennzoil Co | PROCESS FOR PREPARATION OF FLUORIDE-FREE PHOSPHATES |
| US4055626A (en) * | 1976-06-15 | 1977-10-25 | Pennzoil Company | Method of producing fluoride-free phosphoric acid |
-
1979
- 1979-05-04 CA CA326,914A patent/CA1115483A/en not_active Expired
- 1979-05-08 ZA ZA792199A patent/ZA792199B/en unknown
- 1979-05-14 FR FR7912214A patent/FR2432477A1/en active Granted
- 1979-05-14 ES ES480523A patent/ES480523A1/en not_active Expired
- 1979-05-16 IL IL57301A patent/IL57301A/en unknown
- 1979-05-17 BE BE0/195218A patent/BE876325A/en not_active IP Right Cessation
- 1979-05-17 GB GB7917161A patent/GB2026996B/en not_active Expired
- 1979-05-17 BR BR7903045A patent/BR7903045A/en unknown
- 1979-05-18 MA MA18633A patent/MA18439A1/en unknown
- 1979-05-19 IN IN522/CAL/79A patent/IN150442B/en unknown
- 1979-05-21 JP JP54062556A patent/JPS5827207B2/en not_active Expired
- 1979-06-01 IT IT12625/79A patent/IT1194869B/en active
- 1979-07-30 DE DE19792930825 patent/DE2930825A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| IN150442B (en) | 1982-10-09 |
| FR2432477B1 (en) | 1984-05-11 |
| GB2026996B (en) | 1982-09-02 |
| JPS5827207B2 (en) | 1983-06-08 |
| ES480523A1 (en) | 1980-01-16 |
| MA18439A1 (en) | 1979-12-31 |
| JPS5523087A (en) | 1980-02-19 |
| IL57301A (en) | 1982-07-30 |
| FR2432477A1 (en) | 1980-02-29 |
| BE876325A (en) | 1979-11-19 |
| BR7903045A (en) | 1980-03-18 |
| IT1194869B (en) | 1988-09-28 |
| DE2930825C2 (en) | 1988-01-07 |
| ZA792199B (en) | 1980-05-28 |
| IT7912625A0 (en) | 1979-06-01 |
| DE2930825A1 (en) | 1980-02-21 |
| GB2026996A (en) | 1980-02-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |