CS209387B1 - A method of stepwise purification of phosphoric acid extraction acid - Google Patents

Abstract

A method for the stepwise purification of extractive phosphoric acid from cationic impurities by the action of alcohols or ketones miscible with water in the presence of potassium or ammonium ions, the essence of which is that the purification of extractive phosphoric acid with alcohols or ketones miscible with water takes place in the presence of a precipitate separated in the previous stage after the completion of the purification process, containing, in addition to potassium or ammonium ions, also cations of impurities from purified phosphoric acid, whereby the precipitate is added in an amount of 5 to 100 parts by weight per 100 parts by weight of purified extractive phosphoric acid, at a temperature of 40 to 60 °C and the entire procedure is repeated in subsequent stages until the purification ability of the separated precipitate is lost. The precipitate formed by a mixture of potassium, ammonium and cationic phosphates is applied and pure phosphoric acid is isolated from the H3PO4 solution in the organic solvent after its distillation. When the cationic phosphate precipitate is recirculated, impurities accumulate in the precipitate until the cleaning capacity of the precipitate is exceeded. After reaching this state, the precipitate is unable to bind further impurities from the extracted phosphoric acid and its cleaning capacity decreases.

Description

(54) Method for stepwise purification of extractive phosphoric acid

A method for the stepwise purification of extractive phosphoric acid from cationic impurities by the action of alcohols or ketones miscible with water in the presence of potassium or ammonium ions, the essence of which is that the purification of extractive phosphoric acid with alcohols or ketones miscible with water takes place in the presence of a precipitate separated in the previous stage after the completion of the purification process, containing, in addition to potassium or ammonium ions, also cations of impurities from purified phosphoric acid, whereby the precipitate is added in an amount of 5 to 100 parts by weight per 100 parts by weight of purified extractive phosphoric acid, at a temperature of 40 to 60 °C and the entire procedure is repeated in subsequent stages until the purification ability of the separated precipitate is lost. The precipitate formed by a mixture of potassium, ammonium and cationic phosphates is applied and pure phosphoric acid is isolated from the H ₃ PO ₄ solution in an organic solvent after its distillation. When the cationic phosphate precipitate is recirculated, impurities accumulate in the precipitate until the cleaning capacity of the precipitate is exceeded. After reaching this state, the precipitate is unable to bind further impurities from the extracted phosphoric acid and its cleaning capacity decreases.

The invention relates to a method for the stepwise purification of extractive phosphoric acid from cationic impurities with water-miscible alcohols or ketones in the presence of potassium or ammonium cations.

Commercial extraction phosphoric acid contains, in addition to a small proportion of suspended impurities, mainly calcium sulfate hydrates, also soluble impurities, mainly cationic, which adversely affect its properties, quality and processability in technological processes. Soluble cationic impurities, mainly Fe, Al, Mg, are gradually excreted from extraction phosphoric acid during its storage, transport and processing in the form of poorly soluble and difficult to resuspend sludges. In addition to handling and technological problems, sludges also bind a significant proportion of P ₂ O ₅ , which is only slightly resorbable by plants in this form.

The composition of the sludge varies according to the amount and nature of impurities depending on the type of phosphate and the technology of its processing into extractive phosphoric acid. These sludges, except for a small amount of CaSO ₄ hydrates, are predominantly composed of compounds containing Fe, Al, Mg, Si, Na, K, P" and SO ₄ "ions.

Many authors agree that the essential component of sludges are phosphates of the isomorphic series of the type (FeAl) ₃ KH ₁₄ (PO ₄ ) ₈ .4H ₂ O. Potassium is found in small quantities in these compounds, but its presence is essential.

Currently, a large number of papers are published in the professional and patent literature that relate to !

‘ the problem of purifying extractive phosphoric acid from cationic impurities based on the principles of the salting-out effect of organic solvents, on the relatively selective extraction of phosphoric acid by organic solvents, etc. The most widespread purification processes are based on the use of alcohols and ketones, miscible and immiscible with water, on the use of esters, amines, etc., as described, for example, in US patents 1857470, 3318661, 3684438 and 3919396, in English patent 464370 and in DOS 2047261.

;>For the removal of Fe and Al from the extractive phosphoric acid, it is recommended to use dimethyl ketone and ammonia according to US patent 3684438, Kelly ΐ (eng. pat. 1364710) suggests dimethyl ketone in the presence of condensed phosphates. ¹ ₍ The method of purifying the extractive phosphoric acid, according to DOS 2041394 is based on the dechlorination of KC1 with this acid at temperatures of 90—115 °C and under reduced pressure with subsequent methanolic precipitation of the KH _? PO ₄ formed by the reaction together with cationic impurities.

The purification method according to British Patent No. 1342344 consists in dissolving KH ₂ PO ₄ in extractive phosphoric acid and subsequently precipitating the KH ₂ PO ₄ and impurities with methanol.

It has now been found that pure phosphoric acid of the same or better quality as that obtained by the process according to British Patent 1342344 or;

technology according to DOS 2041394 can be obtained in a technologically more advantageous and raw material-saving manner if the extracted phosphoric acid is purified in stages, with the first stage being purified by the action of alcohols and/or ketones miscible with water in the presence of potassium or ammonium ions.

The essence of the invention lies in the fact that the purification of the extractive phosphoric acid with alcohols and/or ketones miscible with water takes place in the presence of the precipitate separated in the previous stage after the completion of the purification process, containing in addition to potassium and/or ammonium ions also cations of impurities from the purified phosphoric acid, the precipitate being added in an amount of 5 to 100 parts by weight per 100 parts by weight of the purified extractive phosphoric acid, at a temperature of 40 to 60 °C and the entire procedure being repeated in subsequent stages until the purification ability of the separated precipitate is lost. The separated precipitate consisting of a mixture of potassium phosphates, ammonium and phosphate cations is applied and pure phosphoric acid is isolated from the H ₃ PO ₄ solution in an organic solvent after its distillation. When recirculating the cation phosphate precipitate, impurities accumulate in the separated precipitate until the cleaning capacity of the precipitate is exceeded. Once this condition is reached, the precipitate is unable to bind further impurities from the extracting phosphoric acid and its cleaning capacity decreases.

Furthermore, it was found that the number of cycles of using the spun and filtered sludge for the purification of the extractive phosphoric acid depends on the mass ratio of the organic solvent: P ₂ O ₅ in H ₃ PO ₄ in each purification cycle and on the type of acid or on the content of impurities in the extractive H ₃ PO ₄ .

The advantages of the process according to the invention are as follows:

— saving of raw material (potassium or ammonium component); i.

— the precipitate, which loses its cleaning ability after several cycles, can be used as a solid or suspension PK, NP or NPK fertilizer slowly releasing nutrients;

-'relatively simple technology without requirements for high temperatures and pressures.

The following examples illustrate but do not limit the scope of the invention.

Example 1: Into a three-necked flask equipped with an electrically heated jacket, a thermometer, an efficient stirrer and a funnel were introduced 230.30 parts by weight of commercial extraction phosphoric acid of the so-called black type with the composition:

1.94% P ₂ O ₅ '0.50% Fe jd.35% AI ln0.08 parts by weight of chemically pure KH ₂ PO ₄ (according to Sørensen), which corresponded to the molar ratio K ₂ O : P ₂ O ₅ in H ₃ PO ₄ = 0.0675 or KjO : P ₂ O ₅ total = 0.0632.

The reaction mixture was heated to 40 °C and 310.6 parts by weight of methanol were added with vigorous stirring, which corresponded to a weight ratio of CH ₃ OH : P ₂ O ₅ total — 2.5 : 1.

The precipitated solid phase was separated from the methanolic solution of purified H ₃ PO ₄ by filtration, methanol was separated from the filtrate by distillation and returned to the process.

The distillation residue was purified phosphoric acid with the composition:

_43.10 % _P2O5

0.038% Fe 0.050% AI which corresponded to a removal of Fe to 90.6% and a removal of AI to 82.2%. The solid phase separated by filtration, i.e. a filter cake containing a mixture of KH ₂ PO ₄ and phosphates of Fe and AI in an amount of 157.50 parts by weight, was added in the second cycle to 230.30 parts by weight of impure extractive phosphoric acid (53.94% P ₂ O ₅ , 0.50% Fe, 0.35% AI), after dissolving the solid phase at 40 °C with intensive stirring, 621.20 parts by weight of methanol were added, which corresponded to a mass ratio of CH ₃ OH : P ₂ O ₅ in H ₃ PO ₄ = 5.

80.21 parts by weight of the solid phase were separated and after filtering it and distilling off methanol from the filtrate, purified H ₃ PO ₄ was obtained with the composition: 44.75% P ₂ O ₅ , 0.19% Fe, 0.17% AI, which represented the degree of purification from Fe SV _Fe = 54.2% and SV _A1 = 41.5%, where a is the mass ratio of Fe : P ₂ O ₅ in the unpurified H ₃ PO ₄ and b is the mass ratio of Fe : P ₂ O ₅ in the purified H ₃ PO ₄

A similar procedure was followed in the third cycle, in which H ₃ PO ₄ was obtained with the following composition: 41.04% P ₂ O ₅ , 0.25% Fe, 0.16% AI, which corresponded to the removal of Fe to 35.6% and AI to 39.9%.

in example 1 while maintaining the molar ratio K ₂ 0 : P ₂ O ₅ in H ₃ PO ₄ = 0.0675 or K ₂ O : P ₂ 0 ₅ total = 0.0632 with the difference that in the first cycle the cationic impurities were precipitated with methanol corresponding to the mass ratio CH ₃ OH : P ₂ O ₅ in H ₃ PO ₄ = 5.0.

In the second cycle and the third cycle, the mass ratio CH ₃ OH : P ₂ O ₅ vH ₃ PO ₄ = 10.0 was used.

Purified phosphoric acids with the following composition were obtained from individual cycles:

1st cycle: 44.13% P ₂ O ₅ ; < 0.01% Fe; 0.04% AI; SV _Fe > 97.6%

SV _A] = 84.7%

2nd cycle: 41.26% P ₂ O ₅ ; < 0.01% Fe; 0.06% AI;

SV _Fe > 97.5% ''

SV^ 73.3%

3rd cycle: 43.08% P ₂ O ₅ ; 0.01% Fe; 0.16% AI; SV _Fe = 97.6%

SV _AI = 28.2%

Example 3

The procedure was analogous to that in Example 1 with the ^same molar ratios of K ₂ O : P ₂ O _{5 ,} with the difference that the amount of dimethyl ketone (acetone) used as the organic solvent was such that the mass ratio (CH ₃ ) ₂ CO : P ₂ O ₅ in H ₃ PO ₄ = 5 in the first cycle, in the second and third cycles (CH ₃ ) ₂ CO : P ₂ O ₅ in H ₃ PO ₄ = 10.0. Purified phosphoric acids with the following composition were obtained:

1st cycle: 48.88% P ₂ O ₅ ; < 0.01% Fe; 0.05% AI; SV _Fe > 97.9%

SV _A1 ' = 82.2%

2nd cycle: 49.30% P ₂ O ₅ ; 0.01% Fe; 0.06% AI; SV _Fe = 97.9%

SV _A1 = 75.3%

3rd cycle: 48.05% P ₂ O ₅ ; < 0.01% Fe; 0.05% AI; SV _Fe > 97.8%

SV _A1 =81.5%

Example 2

The procedure was analogous to that described

Claims (1)

3 The reaction mixture was heated to 40 ° C and 310.6 parts by weight of methanol was added with vigorous stirring, corresponding to the CH 3 OH: P 2 O 5 weight ratio. 2.5: 1. The precipitated solid was separated from the methanolic H3PO4-purified methanol by filtration, the filtrate was separated from the filtrate by distillation and returned to the process. The distillation residue was purified phosphoric acid in the composition: 43.10% P2O5 0.038% Fe0.050% A1, corresponding to Fe removal to 90.6% and removal of AI to 82.2%. Filtration-separated solid phase, ie a filter cake containing a mixture of KH2PO4a Fe and Al phosphates in 157.50 parts by weight in the second cycle was added to 230.30 parts by weight of impure phosphoric extraction acid (53.94% P2O5, 0.50% Fe, 0.35). % Al), after dissolving the solid phase at 40 ° C and intensively stirring, dispensed 621.20 parts by weight of methanol, corresponding to the weight ratio of CH 3 OH: P 2 O 5 in H 3 PO 4 = 5. 80.21 parts by weight of solid phase were precipitated and filtered off and distilling off the methanol in the filtrate to obtain purified H3PO4 of the composition: 44.75% P2O5, 0.19% Fe, 0.17% A1, which represented a purification step from Fe SVFe = 54.2% and SVA1 = 41.5%, wherein where a is the weight ratio of Fe: P2O5 in the non-purified H3PO4 b is the weight ratio of Fe: P2O5 in purified H3PO4 In a similar manner, the third cycle in which H3PO4 was obtained was: 41,04% P2O5,0,25 % Fe, 0.16% Al, corresponding to the removal of Fe to 35.6% and AI to 39.9%. 209387 in Example 1 while maintaining a K 2 O: P 2 O 5 molar ratio in H 3 PO 4 = 0.0675 and 0.0675 respectively. K2O: P205cel. = 0.0632 except that in the first cycle, the sacationic impurities precipitated with methanol corresponding to a CH 3 OH: P 2 O 5 ratio of H 3 PO 4 = 5.0. In the second cycle and the third cycle, the weight ratio of CH 3 OH: P 2 O 5 in H 3 PO 4 was 10.0 = 10.0. Purified phosphoric acids were obtained from the individual cycles of composition: Cycle 1: 44.13% P2O5; <0.01% Fe; 0.04% AI; SVFe> 97.6% SVA] = 84.7% 2nd cycle: 41.26% P2O5; <0.01% Fe; 0.06% Al; SVFe> 97.5% '' SV ^ 73.3% 3rd cycle: 43.08% P2O5; 0.01% Fe; 0.16% Al; SVFe = 97.6% SVAI = 28.2% Example 3 The procedure analogous to Example 1 for the same! K2O: P2O5 molar ratios, except that the amount of dimethyl ketone (acetone) used as the organic solvent was that corresponding to the (CH3) 2CO: P2O5v H3PO4 = 5 weight ratio in the first cycle, the second and the third (CH3) 2CO: P2O5 in H 3 PO 4 = 10.0. Purified phosphoric acids were obtained as follows: 1st cycle: 48.88% P2O5; <0.01% Fe; 0.05% AI; SVFe> 97.9% SVA1 '= 82.2% 2nd cycle: 49.30% P2O5; 0.01% Fe; 0.06% AI; SVFe = 97.9% SVA1 = 75.3% 3rd cycle: 48.05% P2O5; <0.01% Fe; 0.05% Al; SVFe > 97.8% SVA1 = 81.5% EXAMPLE 2 The procedure was analogous to the procedure outlined above. A method for the stepwise purification of phosphoric acid extraction from cationic impurities by the action of potassium or ammonium miscible alcohols or ketones in a further step of purifying the extraction of phosphoric acid with water-miscible alcohols or ketones by the presence of a precipitate precipitated in the previous step of carrying out a purification process comprising, in addition to potassium or ammonium ions, cationic impurities from the purified phosphoric acid, the precipitate being added at 5 up to 100 parts by weight, preferably 10 to 50 parts by weight, per 100 parts by weight of the purified phosphoric acid extraction acid at 40-60 ° C and the entire process is repeated in the subsequent stages until the precipitating capacity of the precipitate is lost.