CA1075878A - Phosphate purification process - Google Patents
Phosphate purification processInfo
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- CA1075878A CA1075878A CA259,986A CA259986A CA1075878A CA 1075878 A CA1075878 A CA 1075878A CA 259986 A CA259986 A CA 259986A CA 1075878 A CA1075878 A CA 1075878A
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- phosphoric acid
- acid
- alkali metal
- aqueous phase
- extraction
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Abstract
ABSTRACT OF THE DISCLOSURE
A continuous process for purifying phosphoric acid by mixing the crude phosphoric acid and an organic solvent, which is infinitely miscible with water, in the presence of alkali metal ions, whereupon the organic phase in extraction vessels is brought into contact with an aqueous phase containing alkali metal ions while aluminium ions are added in one of the extraction vessels.
A continuous process for purifying phosphoric acid by mixing the crude phosphoric acid and an organic solvent, which is infinitely miscible with water, in the presence of alkali metal ions, whereupon the organic phase in extraction vessels is brought into contact with an aqueous phase containing alkali metal ions while aluminium ions are added in one of the extraction vessels.
Description
~L~)7587~3 The subject matter of the present invention is a con-tinuous process for purifyiny crude phosphoric acid by extracting the phosphoric acid with an organic solvent, which is infinitely miscible with water and phosphoric acid, ln the presence of alkali metal or ammoni~m ions, and recovering the organic solvent dissolved in the phosphoric acid by distilling the solvent or adding an alkali metal or ammonium compound and separating, in an aqueous phase, the mono-, di- or tri-ortho-phosphate formed.
The purification of phosphoric acid by means or organic solvents, which are infinitely or at least partially miscible with water and phosphoric acid is already known and, like the extraction of phosphoric acids with solvents which are not misci-ble with water, it is the subject matter of patents. However, it has been found that the phosphoric acids purified by means of known processes do not have the degree of purity required in specific fields of application, such as food chemistry and pharma-ceutical chemistry.
The new process is characterized in that the crude phosphoric acid, which is prepurified if required, and the organic solvent are fed into an extraction vessel, wherein they are mixed with one another in the presence of alkali metal or ammonium ions while an organic phase and an aqueous phase are formed, that the organic phase is brought into contact with an aqueous ` phase in a countercurrent in a series of several extraction vessels, while the organic hase or the aqueous phase in at least one of these extraction vessels is mixed with aluminium ions and the aqueous phase in at least the last extraction vessel:ismixed with alkali metal and/or ammonium ions, whereupon the solvent phase which contains phosphoric acid 30 and water and is obtained in ~he coun~ercurrent extraction is -l~ ~
., .
~0~5~8 separated in a manner known per se into phosphoric acid or salt solution of phosphoric acid and solvent. The separation is carried out preferably by distilling the solvent or by adding metallic salts, oxides or hydroxides, particularly alkali metal and ammonium compo~nds, while the corresponding mono-, di or tri-ortho-phosphates are formed in an aqueous phase and a solvent phase. The water-containing organic solvent separated from the purified phosphoric acid or from the pure phosphate solution by overflow is returned to the puriEication process and is used again for extracting the crude phosphoric acid from its aqueous solution. This process is particularly suitable for the removal of fluorine as well as for the removal o heavy metals.
The aqueous phase separated in the first extraction vessel contains the inorganic compounds separated iErom the crude phosphoric acid in a dissolved form as phosphates, fluorides, etc. Its P2O5 content is between approximately 8 and 16% by weight, relative to the P2O5 content of the phosphoric acid ~ applied. Said aqueous phase can be processed in the fertilizer ;~ industry by means of known processes but according to a preferred embodiment of the present invention it is processed-upon libera~
ting the phosphoric acid bonded in the phosphates - by means of ` sulphuric acid in a second series of extraction vessels by adding ; solvents which are iniEinitely miscible with water and phosphoric acid, particularly isopropanol. In this afterextraction - as in the first vessel of the main extraction - the phosphoric acid is extracted fxom its agueous or sulphuric-acid solution while forming a phase. The separated aqueous phase, which then contains only 2 to 4% by weight of P~O5, relative to the P2O5 content of the starting acid, is removed from the purification cycle and, iiE necessary, it is further processed to fertilizers.
~'''' ' . , .
75~37t~
In the other extraction vessels of the second series (afterextraction) the organic phase formed-which contains phosphoric acid, sulphuric acid and water is brought into contact with the aqueous, alkali metal- or ammonium-ions-containing phase from the main extraction (extraction vessel 2), washed and finally returned to the first vessel of the main extraction.
In the afterextraction the aqueous, alkali metal- or ammonium-ions-containing phase also is in a countercurrent to the organic phase. It is returned with advantage to the main extraction process, for example, along with the crude phosphoric acid. As mentioned hereinbefore, if required the crude phosphoric acid is subjected to a prepurification, which is known per se and can be carried out, for example, in such a way that the crude phosphoric acid along with the recycled aqueous, alkali metal-or ammonium-ions-containing phase is mixed with an amount of calcium ions which is equivalent to that of the sulphate ions as well as with an amount of SiO2 which is at least equivalent to the fluorine content. If necessary, active carbon and sodium sulphide are added for the removal of the organic impurities~
The sulphate ions absorbed from the organic phase are precipitated as calcium sulphate like those from the crude phosphoric acid~-suitably by adding phosphate ores. If necessary, the precipitated gypsum is separated from the phosphoric acid by filtering and decantingO
The subject matter of the invention is explained hereafter in greater detail with reference to the attached draw-ing, which represents the course of the process diagrammatically.
In~the drawing the first series of extraction vessels has the numbers 1 to 6 and the second series the numbers 11 to 15. The crude phosphoric acid and the water-soluble solvent, :~075~37~3 preferably isopropanol, which is recycled, are ~ed into the extraction vessel 1. The overflow from the ext~action vessel 15, i.e., isopropanol, phosphoric acid and water, are added to this mixture. Moreover, the aqueous phase from the extraction vessel 13 is fed along with the phosphoric acid to said mixture.
As mentioned hereinbefore, crude phosphate is added in order to precipitate the sulphate ion;, i.e., in an amount equivalent to that of the sulphate ions to be removed. After the separation ; of the phases the organic phase in the extraction vessel 3 is mixed with a compound yielding aluminium ions, preferably in aqueous solution or phosphoric-acid solution, is passed through several extraction vessels, i.e., the vessels 4, 5 and 6, and brought into contact with an aqueous phase in a countercurrent.
Said aqueous phase contains alkali metal or ammonium compounds and is formed in the extraction vessel 6 in the presence of one or several water-soluble alkali metal or ammonium compounds, particularly a sodium compound. Ortho-phosphates, particularly acid ortho-phosphates are particularly suitable. However, the corresponding carbonates, oxides, hydroxides, etc., can also be used. Relative to the P2O5 content of the phosphoric acid, the alkali metai compounds should be added in amount of 0.5 to 6% by weight (computed as alkali metal oxide)`, preferably 1.5 to 4% by weight.
For example, A12(SO4)3, Al(H2PO~3 and NaAlO2 are suitable aluminium compounds. Finely divided aluminium oxides and hydroxides are also suitable. They can be added in a solid form or in a dissolved form. Amounts of 0.05 to 3.0% by weight (computed as A12O3), preferably 0.2 to 1.5% by weight, relative to the P2O5 content of the acid, were found to be adequate.
~LQ75~378 The puriEied phosphoric acid is separated from the solvent either by distillinq the organic solvent or in the ~orm of aqueous solutions as mono-, di- or tri-ortho-phosphates.
If the phosphoric acid is separated by adding alkali metal or ammonium in the form of aqueous mono-, di- or tri-ortho-phosphate solution, then this is carried out in the reaction vessel 7, from which the water-soluble organic solvent is returned to extraction vessels l and 11.
According to the embodiment shown in the Figure the aqueous phase from the extraction vessel 2 is fed not into the extrac-tion vessel l but directly into the extraction vessel 15. This has the advantage that the particularly strongly polluted aqueous phase separated out in the extraction vessel 1 can be ~- -fractionally separated and processed. The aqueous phase from the extraction vessel l contains the impurities in the form of ' phosphates and, thereforer it is rendered soluble with mineral acid, preferably with ~ SO4, and then fed into the extraction ; vessel 12, where it is extracted with the isopropanol coming from the extraction vessel 11. The extract thus obtained which contains phosphoric acid, water and isopropanol is passed in an overflow through the extraction vessels 13, 14 and 15- and washed in a countercurrent process with the aqueous phase, which comes from the main extraction and is fed into the extraction vessel 15. The impurities are discharged from the extraction vessel 11 as salts, preferably sulphates, and are rejected or processed to fertilizers. The aqueous phase obtained in the extraction vessel 13 is passed into the extraction vessel l along with the phosphoric acid. The organic phase consisting of phosphoric acid, water and isoprop-anol is passed into the extraction vessel l directly from the ~5-.
, ~: , ~ .
~:375i87~
vessel 15. Suitable solvents which are miscible with water are isopropanol, ethanol and acetone.
It is obvious that the subject matter of the invention is not restricted to the embodiment shown in the Figure. The number of series-connected extraction vessels is optional and always depends on the degree of impurit~ of the starting acid as well as on the desired degree of purity of the phosphoric acid or of the ortho-phosphates.
-5a-. .
. .
.
~0758~8 Exam~p~ (Cornparison Example) 20 cu m of crude phosphoric acid produced by rendering Morocco phos-phate soluble with sulphuric acid and containing 52% by weight of P205 are treated along with 4 cu m of aqueous phase from the extraction vessel 13 5 cu m of wash water J 2.2 tons of Morocco sulphate 130 kg of silica 1.5 kg of sodium sulphide.
On separating the washed precipitate this phosphoric acid contains 45.5% by weight of P205 and the following impurities in p.p.M. relative to P205:
Fe2037,200 V 720 alkali metal oxides 27,000 A12312,900 S03 18,000 MgO12,500 F 2,000 CaO12,600 As 1000 litres/h of this prepurified acid are treated in a mixer-settler with 5000 litres/h of recycle isopropanol and 1000 litres of alcohol-water-phosphoric acid phase from the processing stage of the aqueous phas~ with sulphuric acid (from extraction vessel 15) at temperatures between 20 and 30C. In this operation 200 litres/h of aqueous phase containing the im-purities of the phosphoric acid are obtained continuously. In a counter-current in a set of 5 mixer-settler vessels the upper alcohol-water-phosphoric acid phase is brought into contact and washed with 280 litres/h of a saturated monoalkali phosphate solution, which is produced in the mixer-settler 6 of the Figure by adding 40 litres/h of a 50% sodium hydroxide solution. The purified alcohol-water-phosphoric acid phase is neutralized in a mixer-settler 7 with a 50% solution of caustic soda until the monosodium-phosphate stage is ` attained. The separated alcohol phase is cooled and reused for the purifica-tion of the phosphoric acid.
200 litresih of the aqueous phase obtained by mixing the phosphoric acid with alcohol in the extraction vessel 1 are mixed with 70 litres/h of a 75% sulphuric acid and treated with 1000 litres/h of recycled isopropanol in ~' - 6 -~17587~3 a system of two ~nixer-settler vessels. In this operation 116 litres/h of an aqueous phase are obtained. The phase containing 3.0% by weight of the P205 applied is rejected or processed to fertilizers. The alcohol-water-phosphoric acid-sulphuric acid phase is washed in a countPrcurrent in a set of three mixer-settler vessels with 280 litres/h of saturated monoalkali metal phosphate solution in order to remove the sulphuric acid from the alcoholic phase. During this treatment 200 litres/h of an aqueous phase are obtained.
Said aqueous phase is fed to the main extraction along with the crùde phos-phoric acid. The alcohol-water-phosphoric acid phase, which still contains a small amount of sulphuric acid, is also fed to the ~irst extraction vessel of the main extraction.
The analytical results of the purified monosodium phosphate solution in p.p.m., relative to P205 are:
Fe 20 Mg <20 F 150 Al C 50 V 3 Ca < 20 S03 ~ 400 Example 2 A crude phosphoric acid according to example l is processed analogous-- ly to the process described but with the difference that 50 litres/h of aluminium sulphate solution (80 g of A1203 per litre) are additionally fed into the mixer-settler 2 of the washing set consisting of 5 mixer-settler vessels in order to remove the fluoride ions still present despite the pre-- purification.
The anlysis of the purified monosodium phosphate solution shows the following result in p.p.m. relative to P205:
Fe 12 V 3 Al ~ 50 S03 ~ 500 Ca C 20 F 17 Mg ~ 20 Example 3 (Comparison Example) ` 20 cu m of crude phosphoric acid obtained by rendering calcined North-Carolina phosphate soluble with sulphuric acid and containin~ 52.8/~
~75~37~3 of P205 are treated along with 4 cu m of recycled aqueous phase from the extraction vessel 13 5 cu m of wash water 3.0 tons of calcined North-Carolina phosphate and 1.5 kg of sodium sulphide.
On separa~ing the precipitate this phosphoric acid contains 44.7%
by weight of P205 and the follo~ing impurities in p.p.m. relative to P205:
Fe203 26,500 so3 16,700 A1203 13,600 As MgO 20,200 F 7,000 CaO 11,800 alkali metal oxides 29,000 The pretreated phosphoric acid was processed analogously to the process described in example 1, but with the difference that 45 1itres/h of a 50%
solution of caustic soda were fed into the last stage of the washing set of ; 5 mixer-settler vessels and that the aqueous phase formed by mixing the phos-phoric acid with alcohol is mixed with 130 litres/h of a 75% sulphuric acid.
The loss of P205 in the phosphoric acid, relative to the amount of P205 applied, is 3.4% by weight.
The analytical results of the purified monosodium phosphate solution are shown hereafter in p.p.m. relative to P205:
Fe 21 S03 ~ lOOO
Al C 50 F 700 Mg 20 Ca 6 .
Example 4 The same crude phosphoric acid as in example 3 is processed analogous-ly to the process described in example 3 but with the difference that 55 litres/h of monoaluminium phosphate solution (Al203 content 7.5% by weight) are additionally fed into the second.stage of the washing set of 5 mixer-settler vessels.
The purified monosodium phosphate solution shows the following ana-lytical results in p.p.m. relative to P~05:
_ ~ _ . . .
107587~3 Fe 15 . 3 Al ~ 50 F 20 Mg 20 Ca C 10 The examples show that the fluorine content of phosphoric acid and of the phosphates produced therefrom can be reduced in a non-predictable manner by the process according to the in~ention.
'~' ~',' ~.''
The purification of phosphoric acid by means or organic solvents, which are infinitely or at least partially miscible with water and phosphoric acid is already known and, like the extraction of phosphoric acids with solvents which are not misci-ble with water, it is the subject matter of patents. However, it has been found that the phosphoric acids purified by means of known processes do not have the degree of purity required in specific fields of application, such as food chemistry and pharma-ceutical chemistry.
The new process is characterized in that the crude phosphoric acid, which is prepurified if required, and the organic solvent are fed into an extraction vessel, wherein they are mixed with one another in the presence of alkali metal or ammonium ions while an organic phase and an aqueous phase are formed, that the organic phase is brought into contact with an aqueous ` phase in a countercurrent in a series of several extraction vessels, while the organic hase or the aqueous phase in at least one of these extraction vessels is mixed with aluminium ions and the aqueous phase in at least the last extraction vessel:ismixed with alkali metal and/or ammonium ions, whereupon the solvent phase which contains phosphoric acid 30 and water and is obtained in ~he coun~ercurrent extraction is -l~ ~
., .
~0~5~8 separated in a manner known per se into phosphoric acid or salt solution of phosphoric acid and solvent. The separation is carried out preferably by distilling the solvent or by adding metallic salts, oxides or hydroxides, particularly alkali metal and ammonium compo~nds, while the corresponding mono-, di or tri-ortho-phosphates are formed in an aqueous phase and a solvent phase. The water-containing organic solvent separated from the purified phosphoric acid or from the pure phosphate solution by overflow is returned to the puriEication process and is used again for extracting the crude phosphoric acid from its aqueous solution. This process is particularly suitable for the removal of fluorine as well as for the removal o heavy metals.
The aqueous phase separated in the first extraction vessel contains the inorganic compounds separated iErom the crude phosphoric acid in a dissolved form as phosphates, fluorides, etc. Its P2O5 content is between approximately 8 and 16% by weight, relative to the P2O5 content of the phosphoric acid ~ applied. Said aqueous phase can be processed in the fertilizer ;~ industry by means of known processes but according to a preferred embodiment of the present invention it is processed-upon libera~
ting the phosphoric acid bonded in the phosphates - by means of ` sulphuric acid in a second series of extraction vessels by adding ; solvents which are iniEinitely miscible with water and phosphoric acid, particularly isopropanol. In this afterextraction - as in the first vessel of the main extraction - the phosphoric acid is extracted fxom its agueous or sulphuric-acid solution while forming a phase. The separated aqueous phase, which then contains only 2 to 4% by weight of P~O5, relative to the P2O5 content of the starting acid, is removed from the purification cycle and, iiE necessary, it is further processed to fertilizers.
~'''' ' . , .
75~37t~
In the other extraction vessels of the second series (afterextraction) the organic phase formed-which contains phosphoric acid, sulphuric acid and water is brought into contact with the aqueous, alkali metal- or ammonium-ions-containing phase from the main extraction (extraction vessel 2), washed and finally returned to the first vessel of the main extraction.
In the afterextraction the aqueous, alkali metal- or ammonium-ions-containing phase also is in a countercurrent to the organic phase. It is returned with advantage to the main extraction process, for example, along with the crude phosphoric acid. As mentioned hereinbefore, if required the crude phosphoric acid is subjected to a prepurification, which is known per se and can be carried out, for example, in such a way that the crude phosphoric acid along with the recycled aqueous, alkali metal-or ammonium-ions-containing phase is mixed with an amount of calcium ions which is equivalent to that of the sulphate ions as well as with an amount of SiO2 which is at least equivalent to the fluorine content. If necessary, active carbon and sodium sulphide are added for the removal of the organic impurities~
The sulphate ions absorbed from the organic phase are precipitated as calcium sulphate like those from the crude phosphoric acid~-suitably by adding phosphate ores. If necessary, the precipitated gypsum is separated from the phosphoric acid by filtering and decantingO
The subject matter of the invention is explained hereafter in greater detail with reference to the attached draw-ing, which represents the course of the process diagrammatically.
In~the drawing the first series of extraction vessels has the numbers 1 to 6 and the second series the numbers 11 to 15. The crude phosphoric acid and the water-soluble solvent, :~075~37~3 preferably isopropanol, which is recycled, are ~ed into the extraction vessel 1. The overflow from the ext~action vessel 15, i.e., isopropanol, phosphoric acid and water, are added to this mixture. Moreover, the aqueous phase from the extraction vessel 13 is fed along with the phosphoric acid to said mixture.
As mentioned hereinbefore, crude phosphate is added in order to precipitate the sulphate ion;, i.e., in an amount equivalent to that of the sulphate ions to be removed. After the separation ; of the phases the organic phase in the extraction vessel 3 is mixed with a compound yielding aluminium ions, preferably in aqueous solution or phosphoric-acid solution, is passed through several extraction vessels, i.e., the vessels 4, 5 and 6, and brought into contact with an aqueous phase in a countercurrent.
Said aqueous phase contains alkali metal or ammonium compounds and is formed in the extraction vessel 6 in the presence of one or several water-soluble alkali metal or ammonium compounds, particularly a sodium compound. Ortho-phosphates, particularly acid ortho-phosphates are particularly suitable. However, the corresponding carbonates, oxides, hydroxides, etc., can also be used. Relative to the P2O5 content of the phosphoric acid, the alkali metai compounds should be added in amount of 0.5 to 6% by weight (computed as alkali metal oxide)`, preferably 1.5 to 4% by weight.
For example, A12(SO4)3, Al(H2PO~3 and NaAlO2 are suitable aluminium compounds. Finely divided aluminium oxides and hydroxides are also suitable. They can be added in a solid form or in a dissolved form. Amounts of 0.05 to 3.0% by weight (computed as A12O3), preferably 0.2 to 1.5% by weight, relative to the P2O5 content of the acid, were found to be adequate.
~LQ75~378 The puriEied phosphoric acid is separated from the solvent either by distillinq the organic solvent or in the ~orm of aqueous solutions as mono-, di- or tri-ortho-phosphates.
If the phosphoric acid is separated by adding alkali metal or ammonium in the form of aqueous mono-, di- or tri-ortho-phosphate solution, then this is carried out in the reaction vessel 7, from which the water-soluble organic solvent is returned to extraction vessels l and 11.
According to the embodiment shown in the Figure the aqueous phase from the extraction vessel 2 is fed not into the extrac-tion vessel l but directly into the extraction vessel 15. This has the advantage that the particularly strongly polluted aqueous phase separated out in the extraction vessel 1 can be ~- -fractionally separated and processed. The aqueous phase from the extraction vessel l contains the impurities in the form of ' phosphates and, thereforer it is rendered soluble with mineral acid, preferably with ~ SO4, and then fed into the extraction ; vessel 12, where it is extracted with the isopropanol coming from the extraction vessel 11. The extract thus obtained which contains phosphoric acid, water and isopropanol is passed in an overflow through the extraction vessels 13, 14 and 15- and washed in a countercurrent process with the aqueous phase, which comes from the main extraction and is fed into the extraction vessel 15. The impurities are discharged from the extraction vessel 11 as salts, preferably sulphates, and are rejected or processed to fertilizers. The aqueous phase obtained in the extraction vessel 13 is passed into the extraction vessel l along with the phosphoric acid. The organic phase consisting of phosphoric acid, water and isoprop-anol is passed into the extraction vessel l directly from the ~5-.
, ~: , ~ .
~:375i87~
vessel 15. Suitable solvents which are miscible with water are isopropanol, ethanol and acetone.
It is obvious that the subject matter of the invention is not restricted to the embodiment shown in the Figure. The number of series-connected extraction vessels is optional and always depends on the degree of impurit~ of the starting acid as well as on the desired degree of purity of the phosphoric acid or of the ortho-phosphates.
-5a-. .
. .
.
~0758~8 Exam~p~ (Cornparison Example) 20 cu m of crude phosphoric acid produced by rendering Morocco phos-phate soluble with sulphuric acid and containing 52% by weight of P205 are treated along with 4 cu m of aqueous phase from the extraction vessel 13 5 cu m of wash water J 2.2 tons of Morocco sulphate 130 kg of silica 1.5 kg of sodium sulphide.
On separating the washed precipitate this phosphoric acid contains 45.5% by weight of P205 and the following impurities in p.p.M. relative to P205:
Fe2037,200 V 720 alkali metal oxides 27,000 A12312,900 S03 18,000 MgO12,500 F 2,000 CaO12,600 As 1000 litres/h of this prepurified acid are treated in a mixer-settler with 5000 litres/h of recycle isopropanol and 1000 litres of alcohol-water-phosphoric acid phase from the processing stage of the aqueous phas~ with sulphuric acid (from extraction vessel 15) at temperatures between 20 and 30C. In this operation 200 litres/h of aqueous phase containing the im-purities of the phosphoric acid are obtained continuously. In a counter-current in a set of 5 mixer-settler vessels the upper alcohol-water-phosphoric acid phase is brought into contact and washed with 280 litres/h of a saturated monoalkali phosphate solution, which is produced in the mixer-settler 6 of the Figure by adding 40 litres/h of a 50% sodium hydroxide solution. The purified alcohol-water-phosphoric acid phase is neutralized in a mixer-settler 7 with a 50% solution of caustic soda until the monosodium-phosphate stage is ` attained. The separated alcohol phase is cooled and reused for the purifica-tion of the phosphoric acid.
200 litresih of the aqueous phase obtained by mixing the phosphoric acid with alcohol in the extraction vessel 1 are mixed with 70 litres/h of a 75% sulphuric acid and treated with 1000 litres/h of recycled isopropanol in ~' - 6 -~17587~3 a system of two ~nixer-settler vessels. In this operation 116 litres/h of an aqueous phase are obtained. The phase containing 3.0% by weight of the P205 applied is rejected or processed to fertilizers. The alcohol-water-phosphoric acid-sulphuric acid phase is washed in a countPrcurrent in a set of three mixer-settler vessels with 280 litres/h of saturated monoalkali metal phosphate solution in order to remove the sulphuric acid from the alcoholic phase. During this treatment 200 litres/h of an aqueous phase are obtained.
Said aqueous phase is fed to the main extraction along with the crùde phos-phoric acid. The alcohol-water-phosphoric acid phase, which still contains a small amount of sulphuric acid, is also fed to the ~irst extraction vessel of the main extraction.
The analytical results of the purified monosodium phosphate solution in p.p.m., relative to P205 are:
Fe 20 Mg <20 F 150 Al C 50 V 3 Ca < 20 S03 ~ 400 Example 2 A crude phosphoric acid according to example l is processed analogous-- ly to the process described but with the difference that 50 litres/h of aluminium sulphate solution (80 g of A1203 per litre) are additionally fed into the mixer-settler 2 of the washing set consisting of 5 mixer-settler vessels in order to remove the fluoride ions still present despite the pre-- purification.
The anlysis of the purified monosodium phosphate solution shows the following result in p.p.m. relative to P205:
Fe 12 V 3 Al ~ 50 S03 ~ 500 Ca C 20 F 17 Mg ~ 20 Example 3 (Comparison Example) ` 20 cu m of crude phosphoric acid obtained by rendering calcined North-Carolina phosphate soluble with sulphuric acid and containin~ 52.8/~
~75~37~3 of P205 are treated along with 4 cu m of recycled aqueous phase from the extraction vessel 13 5 cu m of wash water 3.0 tons of calcined North-Carolina phosphate and 1.5 kg of sodium sulphide.
On separa~ing the precipitate this phosphoric acid contains 44.7%
by weight of P205 and the follo~ing impurities in p.p.m. relative to P205:
Fe203 26,500 so3 16,700 A1203 13,600 As MgO 20,200 F 7,000 CaO 11,800 alkali metal oxides 29,000 The pretreated phosphoric acid was processed analogously to the process described in example 1, but with the difference that 45 1itres/h of a 50%
solution of caustic soda were fed into the last stage of the washing set of ; 5 mixer-settler vessels and that the aqueous phase formed by mixing the phos-phoric acid with alcohol is mixed with 130 litres/h of a 75% sulphuric acid.
The loss of P205 in the phosphoric acid, relative to the amount of P205 applied, is 3.4% by weight.
The analytical results of the purified monosodium phosphate solution are shown hereafter in p.p.m. relative to P205:
Fe 21 S03 ~ lOOO
Al C 50 F 700 Mg 20 Ca 6 .
Example 4 The same crude phosphoric acid as in example 3 is processed analogous-ly to the process described in example 3 but with the difference that 55 litres/h of monoaluminium phosphate solution (Al203 content 7.5% by weight) are additionally fed into the second.stage of the washing set of 5 mixer-settler vessels.
The purified monosodium phosphate solution shows the following ana-lytical results in p.p.m. relative to P~05:
_ ~ _ . . .
107587~3 Fe 15 . 3 Al ~ 50 F 20 Mg 20 Ca C 10 The examples show that the fluorine content of phosphoric acid and of the phosphates produced therefrom can be reduced in a non-predictable manner by the process according to the in~ention.
'~' ~',' ~.''
Claims (8)
1. A continuous process for purifying crude phosphoric acid by extracting the phosphoric acid with an organic solvent, which is infinitely soluble with water and phosphoric acid, in the presence of alkali metal or ammonium ions and recovering the organic solvent dissolved in the phosphoric acid by distilling off the solvent or by adding an alkali metal or ammonium com-pound and separating the mono-, di-, or tri- ortho-phosphate in an aqueous phase, characterized in that the crude phosphoric acid, which is prepurified if required, and the organic solvent are fed into an extraction vessel, where they are mixed with one another in the presence of alkali metal or ammonium ions while an organic phase and an aqueous phase are formed and that the organic phase is brought into contact with an aqueous phase in a countercurrent in a set of several series-connected extrac-tion vessels, the organic phase or the aqueous phase in at least one of these extraction vessels being mixed with aluminium ions and the aqueous phase in at least the last extraction vessel being mixed with alkali metal and/or ammonium ions, and the solvent phase which is obtained in the countercurrent extraction and contains pure phosphoric acid and water is separated in a manner known per se into phosphoric acid or salt solutions of the phosphoric acid and solvent, said process further characterized in that 0.05 to 3.0% by weight of an aluminium compound, computed as Al2O3, relative to the P2O5 content of the acid, are added, and in that 0.5 to 6% by weight of an alkali metal compound, computed as alkali metal oxide, relative to the P2O5 content of the acid, are added.
2. A process according to Claim 1, characterized in that the aqueous phase formed on mixing the phosphoric acid with solvent is mixed with sulphuric acid while phosphoric acid is set free and that the solution thus formed which contains phosphoric acid, sulphuric acid and water is continuously treated with a water-soluble organic solvent while two phases are being formed.
3. A process according to Claim 2, characterized in that the aqueous phase which is in a countercurrent in a first set of extraction vessels is used in a second set of extraction vessels for purifying the organic phase which contains sulphuric acid, phosphoric acid and water and that both the organic phase and the aqueous phase are returned to the first extraction vessel of the first set.
4. A process according to Claim 1, 2 or 3, characterized in that 0.2 to 1.5% by weight of an aluminium compound, computed as A1203, relative to the P205 content of the acid, are added.
5. A process according to Claim 1, 2 or 3, characterized in that 1.5 to 4% by weight of an alkali metal compound, com-puted as alkali metal oxide, relative to the P205 content of the acid are added.
6. A process according to Claim 1, 2 or 3, characterized in that the fluorine compounds dissolved in the starting acid are precipitated as alkali silicofluorides in a manner known per se by adding SiO2 and an alkali metal compound prior to the mixing with the solvent.
7. A process according to Claim 1, 2 or 3, characterized in that the free sulphate ions present in the starting acid are precipitated with calcium in a manner known per se as gypsum.
8. A process according to Claim 1, 2 or 3, characterized in that the organic impurities contained in the crude phosphoric acid are removed with active carbon in a manner known per se.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19752538720 DE2538720C2 (en) | 1975-08-30 | 1975-08-30 | Process for purifying wet process phosphoric acid |
| DE19752538721 DE2538721C2 (en) | 1975-08-30 | 1975-08-30 | Process for the production of pure alkali phosphates by extraction of raw phosphoric acid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1075878A true CA1075878A (en) | 1980-04-22 |
Family
ID=25769327
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA259,986A Expired CA1075878A (en) | 1975-08-30 | 1976-08-27 | Phosphate purification process |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU502400B2 (en) |
| BR (1) | BR7605683A (en) |
| CA (1) | CA1075878A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4806324A (en) * | 1987-02-18 | 1989-02-21 | Hoechst Aktiengesellschaft | Process for making phosphoric acid free from titanium |
-
1976
- 1976-08-27 CA CA259,986A patent/CA1075878A/en not_active Expired
- 1976-08-30 BR BR7605683A patent/BR7605683A/en unknown
- 1976-08-30 AU AU17273/76A patent/AU502400B2/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4806324A (en) * | 1987-02-18 | 1989-02-21 | Hoechst Aktiengesellschaft | Process for making phosphoric acid free from titanium |
Also Published As
| Publication number | Publication date |
|---|---|
| AU502400B2 (en) | 1979-07-26 |
| BR7605683A (en) | 1977-08-23 |
| AU1727376A (en) | 1978-03-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |