CA1141939A - Production of alkali metal phosphate solutions free from zinc - Google Patents
Production of alkali metal phosphate solutions free from zincInfo
- Publication number
- CA1141939A CA1141939A CA000342849A CA342849A CA1141939A CA 1141939 A CA1141939 A CA 1141939A CA 000342849 A CA000342849 A CA 000342849A CA 342849 A CA342849 A CA 342849A CA 1141939 A CA1141939 A CA 1141939A
- Authority
- CA
- Canada
- Prior art keywords
- alkali metal
- solution
- zinc
- sulfide
- phosphoric acid
- 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
Links
Abstract
PRODUCTION OF ALKALI METAL PHOSPHATE SOLUTIONS FREE FROM ZINC
ABSTRACT OF THE DISCLOSURE
The invention relates to the production of alkali metal phosphate solutions free of zinc, from phosphoric acid solu-tions contaminated with zinc. To this end, feed solution is admixed with alkali metal hydroxide or carbonate so as to establish in the resulting suspension a pH-value within the range 8 to 14. Next, resulting suspension is reacted under pressure and with thorough agitation with H2S or an alkali metal sulfide solution; and decontaminated alkali metal phos-phate solution is separated from solid matter, the pressure being maintained.
ABSTRACT OF THE DISCLOSURE
The invention relates to the production of alkali metal phosphate solutions free of zinc, from phosphoric acid solu-tions contaminated with zinc. To this end, feed solution is admixed with alkali metal hydroxide or carbonate so as to establish in the resulting suspension a pH-value within the range 8 to 14. Next, resulting suspension is reacted under pressure and with thorough agitation with H2S or an alkali metal sulfide solution; and decontaminated alkali metal phos-phate solution is separated from solid matter, the pressure being maintained.
Description
3~3 This invention relates to a process for making alkali metal phosphate solutions free of zinc, from phosphoric acid solutions contaminated with zinc, especially from wet~processed phosphoric acid solutions or ~ m alkali metal phosphate solutions having contaminants originating ~rom crude wet-processed phosphoric acid at least partially precipitated therein.
In industry, alkali metal phospha~tes are chiefly made into condensed phosphates, especially pentasodium triphos-phate, which is an important ingredient of almost all current detergent compositions. These are alkali metal phosphates which are often made by neutralizing a wet-pro-cessed phosphoric acid obtained by subjecting crude phos-phates to wet-processing treatment with mineral acid. This gives crude phosphoric acid which is normally contaminated with relatively high proportions of iron, aluminium, magne-sium and zinc salts, and can be subjected to a single or multl-stage neutralization with the use of an alkali metal hydroxide or carbonate. By the neutralization ~ust described, which is often allowed to proceed to the dial~ali hydrogen phosphate stage, it is, however, not possible reliably to remove zinc,an~ the resulting phosphate salt solutions contain indeed up to 600 ppm of zinc (based on P205), depending on the quality of the crude acid used in each particular case.
It has been described that metallic contamina~ts, and especially zinc are liable to impair certain properties of sodium tripolyphosphate, e.g. its hydration behaviour.
.~
33~
All processes described heretofore for the remo~al, by precipitation, of metallic contaminants ~rom wet-pro-cessed phosphoric acid comprise subjecting phosphoric acid which is to undergo purification to treatment with hydrogen sulfide or a sulfide solution in an acid medium, i~ desired, and then neutralizing it by means of an alkali, and sepa-rating precipitated contaminants therefrom, Canadian Patent 380 394, for example, describes a pro-cess wherein phosphoric acld is partially neutralized to a stage where less than 50 ~ of sodium dihydrogen phosphate has undergone conversion to disodium hydrogen phosphate (pH 6.5) and then treated with hydrogen sulfide or an alka-li metal sul~ide to cause precipitation o~ contaminants originating from wet-processed phosphoric acid.
As can be in~erred from Example 1 o~ that Patent,about 1.5 kg of Na2S is required to be used per 100 kg of P205.
Despite this, the contaminants are removed incompletely only. This results from the 0.16'7 % overall concentration o~ contam~nants determined after neutralization and preci-pitation with sulfide. In other words, complete precipita-tion of contaminants would necessitate the use of` conside-rably more H2S or Na2S.
In this prior process, relatively expensive H2S or Na2S is not exclusively used for precipitating ZnS. It is also used ~or separating iron norma1ly contained in phos-phoric acid in proportions 5 to 20 times as large as the proportion of zinc therein. As can be seen, the process just described would not permit zinc to be separated quan-titati~ely under commercially attracti~e conditions. In addition to this, it is necessary in the process just des-~ 9 3~
cribed, ~irst to cool the suspension which is to undergoneutralization and then to add the precipitant in order to avoid he2vy loss of H2S volatile at elevated temperature.
This however is expensi~e in respect of machinery and has adverse ef~ects on the filterability o~ the suspension.
A series of further processes have been described in U.S. Patent 2 977 191, South A~rican Patents 69/5253 and 6g/8290, and U.S, Patents 3 305 305 and 3 421 410. These are processes which relate to the removal of metallic im-purities, such as manganese or vanadium, from phosphoricacid solutions, and which are based on principles analo-gous to those described in Canadian Patent 380 394.
More specifically, ~rocesses are concerned which pro-vide for the su~fide compound to be added to a more or less acidic feed solution, the sulfide compound being used as a medium effectingthe precipitation of relatively large proportions of iron, and also the reduction of those metal ions which are present in a higher stage of oxidation. Zinc is not removed, or to an insignificant extent only, in the process just described.
A method widely used in analytical chemistry for re-moving zinc from an aqueous solution comprises precipita-ting the zinc with H2S or Na2S in a slightl~ acidic or al-kaline medium, the precipitation of zinc from a slightly ~cidic solution being generally preferred because of the poor filterability of matter which is precipitated from an alkaline solution.
It is therefore highly desirable to have a commercially attractive and simple process for making alkali metal phos-phate solutions free of zinc, from zinc-containing phospho-ric acid or alkali metal phosphate solutions.
.
The present invention now unexpectedly provides a pro-cess for making alkali metal phosphate solutions free of zinc, from phosphoric acid solutions contaminated with zinc and more especially from wet-processed phosphoric acid so-lutions or alkali metal phosphate solutions having conta-minants originating from wet-processed phosphoric acid at least partially precipitated therein, which comprises:
a) admixing the solution with alkali metal hydroxide or carbonate so as to establish in the resulting suspen-sion a pH-value within the range 8 to 14, preferably 9 to 9.5, b) reacting the suspension under pressure and with thorough agitation with H2S or an alkali metal sulfide solution; and c) separating decontaminated alkali metal phosphate solu-tion from all solid matter, the pressure ~eing main-tained.
A preferred ~eature of the present invention provides for hydroge~ sul~ide or alkali metal sulfide, especia~ly sodium sulfide, to be used in a proportion of 150 to 300 mol%, based on the zinc present in the feed solution. It 1s also preferable in accordance with this invention to react the suspension with hydrogen sul~ide or alkali metal sulf~de solution under a pressure of 0.1 to 10 bars and to separate solid matter fl~om the alkali metal phosphate so-lution with the use of a pressure filter under approxi-mately the same pressure, A further preferred feature of the present invention provides for hydrogen sulfide or alkali metal sulfide solution to be introduced directly 30 into a pump, or directly upstream thereof, the pump forming part of a pressure filter being positioned directly ahead of the filter.
The present process offers technically beneficial effects in respect of the ~ollowing points:
1) It enables æinc to be precipitated and separated practically quantitatively, in sulfide form.
The precipitant (commonly Na2S or H2S)is used in pro-portions o~ 150 to 300 mol%, based on zinc in the solution, and gives filtrate containing less than 5 ppm of zinc.
In industry, alkali metal phospha~tes are chiefly made into condensed phosphates, especially pentasodium triphos-phate, which is an important ingredient of almost all current detergent compositions. These are alkali metal phosphates which are often made by neutralizing a wet-pro-cessed phosphoric acid obtained by subjecting crude phos-phates to wet-processing treatment with mineral acid. This gives crude phosphoric acid which is normally contaminated with relatively high proportions of iron, aluminium, magne-sium and zinc salts, and can be subjected to a single or multl-stage neutralization with the use of an alkali metal hydroxide or carbonate. By the neutralization ~ust described, which is often allowed to proceed to the dial~ali hydrogen phosphate stage, it is, however, not possible reliably to remove zinc,an~ the resulting phosphate salt solutions contain indeed up to 600 ppm of zinc (based on P205), depending on the quality of the crude acid used in each particular case.
It has been described that metallic contamina~ts, and especially zinc are liable to impair certain properties of sodium tripolyphosphate, e.g. its hydration behaviour.
.~
33~
All processes described heretofore for the remo~al, by precipitation, of metallic contaminants ~rom wet-pro-cessed phosphoric acid comprise subjecting phosphoric acid which is to undergo purification to treatment with hydrogen sulfide or a sulfide solution in an acid medium, i~ desired, and then neutralizing it by means of an alkali, and sepa-rating precipitated contaminants therefrom, Canadian Patent 380 394, for example, describes a pro-cess wherein phosphoric acld is partially neutralized to a stage where less than 50 ~ of sodium dihydrogen phosphate has undergone conversion to disodium hydrogen phosphate (pH 6.5) and then treated with hydrogen sulfide or an alka-li metal sul~ide to cause precipitation o~ contaminants originating from wet-processed phosphoric acid.
As can be in~erred from Example 1 o~ that Patent,about 1.5 kg of Na2S is required to be used per 100 kg of P205.
Despite this, the contaminants are removed incompletely only. This results from the 0.16'7 % overall concentration o~ contam~nants determined after neutralization and preci-pitation with sulfide. In other words, complete precipita-tion of contaminants would necessitate the use of` conside-rably more H2S or Na2S.
In this prior process, relatively expensive H2S or Na2S is not exclusively used for precipitating ZnS. It is also used ~or separating iron norma1ly contained in phos-phoric acid in proportions 5 to 20 times as large as the proportion of zinc therein. As can be seen, the process just described would not permit zinc to be separated quan-titati~ely under commercially attracti~e conditions. In addition to this, it is necessary in the process just des-~ 9 3~
cribed, ~irst to cool the suspension which is to undergoneutralization and then to add the precipitant in order to avoid he2vy loss of H2S volatile at elevated temperature.
This however is expensi~e in respect of machinery and has adverse ef~ects on the filterability o~ the suspension.
A series of further processes have been described in U.S. Patent 2 977 191, South A~rican Patents 69/5253 and 6g/8290, and U.S, Patents 3 305 305 and 3 421 410. These are processes which relate to the removal of metallic im-purities, such as manganese or vanadium, from phosphoricacid solutions, and which are based on principles analo-gous to those described in Canadian Patent 380 394.
More specifically, ~rocesses are concerned which pro-vide for the su~fide compound to be added to a more or less acidic feed solution, the sulfide compound being used as a medium effectingthe precipitation of relatively large proportions of iron, and also the reduction of those metal ions which are present in a higher stage of oxidation. Zinc is not removed, or to an insignificant extent only, in the process just described.
A method widely used in analytical chemistry for re-moving zinc from an aqueous solution comprises precipita-ting the zinc with H2S or Na2S in a slightl~ acidic or al-kaline medium, the precipitation of zinc from a slightly ~cidic solution being generally preferred because of the poor filterability of matter which is precipitated from an alkaline solution.
It is therefore highly desirable to have a commercially attractive and simple process for making alkali metal phos-phate solutions free of zinc, from zinc-containing phospho-ric acid or alkali metal phosphate solutions.
.
The present invention now unexpectedly provides a pro-cess for making alkali metal phosphate solutions free of zinc, from phosphoric acid solutions contaminated with zinc and more especially from wet-processed phosphoric acid so-lutions or alkali metal phosphate solutions having conta-minants originating from wet-processed phosphoric acid at least partially precipitated therein, which comprises:
a) admixing the solution with alkali metal hydroxide or carbonate so as to establish in the resulting suspen-sion a pH-value within the range 8 to 14, preferably 9 to 9.5, b) reacting the suspension under pressure and with thorough agitation with H2S or an alkali metal sulfide solution; and c) separating decontaminated alkali metal phosphate solu-tion from all solid matter, the pressure ~eing main-tained.
A preferred ~eature of the present invention provides for hydroge~ sul~ide or alkali metal sulfide, especia~ly sodium sulfide, to be used in a proportion of 150 to 300 mol%, based on the zinc present in the feed solution. It 1s also preferable in accordance with this invention to react the suspension with hydrogen sul~ide or alkali metal sulf~de solution under a pressure of 0.1 to 10 bars and to separate solid matter fl~om the alkali metal phosphate so-lution with the use of a pressure filter under approxi-mately the same pressure, A further preferred feature of the present invention provides for hydrogen sulfide or alkali metal sulfide solution to be introduced directly 30 into a pump, or directly upstream thereof, the pump forming part of a pressure filter being positioned directly ahead of the filter.
The present process offers technically beneficial effects in respect of the ~ollowing points:
1) It enables æinc to be precipitated and separated practically quantitatively, in sulfide form.
The precipitant (commonly Na2S or H2S)is used in pro-portions o~ 150 to 300 mol%, based on zinc in the solution, and gives filtrate containing less than 5 ppm of zinc.
2) It ensures optimum utilization o~ precipitant for pre-cipitation o~ ZnS (no co~precipitation of FeS, no loss o~ H2S by escape of readily volatile hydrogen sulfide via gas phase) and naturally low consumption of pre-cipitant.
3) Addit~onal machinery and investment of capital are not necessary~ The process can be carried out with the use of apparatus of the kind commonly used for decontamina-ting wet-processed phosphoric acid.
The fact that the present process permits 7inc sulfide to be precipi~ated quantitatively withi~ the short period of t.ime during which the suspension is passed through the ~ilter, namely ~ to 5 minutes, depending on the filling volume of the ~ilter, is a very unexpected result as is also the good filterability of zinc sulfide precipitated in an alkaline medium.
Even in those cases in which use was made of a suspen-sion in which about 20 % of the solid matter was zinc sul fide, the filtration capacity was not affected or to an insignificant extent only.
The following Examples illustrate the invention.
~ 3 EXAMPL~ 1:
Wet-processed phosphoric acid (25.3 % P205; 0~15 ~/0 Fe203;
0,13 % Al203; 0.03 % Zn) made ~rom Morocco phosphate was used.
30 m3/h of acid was subjected to single-stage neutralization with sodium hydroxide solution and neutralized to give Na2HP04 (pH = 9). The suspension which was so obtained was filtered using two identical filtration units (1A and 1 B~ respectivè-ly) of which each was comprised of a horizontal pressure fil-; ter ( 70 m2 filter area) and a circulating pump (Q = up to 100 m3/h). Filtration ~it lA was operated without additionof Na2S to suspension. Suspension delivered to filtration unit 1B was admixed, directly upstream of the circulating pump, with 8 l/m3 o~ a 12 % Na2S-solution (0.4 % Na2S/P205;
this corresponded to 250 mol %, based on Zn), intimately mixed therewith at a pressure of about 7 bars, andfiltered~
Each o~ the 1A and 1B units had a filtration capacity of 0.2 m3/h , m2, under pressure of 7 bars, Clear diphosphate filtrates were obtained in the two cases. In case 1A (no sul-~ide precipitation), the filtrate contained 110 ppm of zinc and in case 1B (with sul~ide precipitation), the filtrate contained less than 5 ppm o~ zinc, EXAMPLE 2:
The procedure was as described in Example 1B, but Na2S-solution was introduced into a reservoir containing the suspension to undergo neutralization~ A~ter sulfide addition, the suspension was allowed to remain in the reser~oir for an average period o~ 2 hours at 90~ and then filtered. 80 l of a 12 % Na2S-solution (4 % Na2S/P205~ was used per m3 of suspension, The filtered disodium phosphate solution was found to contain 30 ppm of zinc. As a result of the Z hour ~ 3~
so~ourn time of the suspension in the reservoir, the filtra-te contained 6 times more Zn than the filtrate of Example 1B, despite the use of a 10 times ~arger proportion of Na2S in the present Example.
EXAMPLE ~:
Wet~processed phosphoric acid, the same as that used in Example 1, was treated with sodium hydroxide solution and neutralized initially to the monophosphate stage (pH = 4.5).
Resulting zinc-containing precipitate was filtered off.
NaH2P04-solution was obtained as the filtrate. It contained 190 ppm of zinc and was neutralized in a second stage to diphosphate (pH = 9). As in Example 1, filtration unit 3A
was operated without Na2S-addition to suspension. Suspension delivered to filtration unit 3B (3A and 3 B unlts provided with ~ilter and pump same as in Example 1B) was admixed, inside unit 3B, directly upstream o~ circulating pump, with 250 mol~ ~based on zinc content o~ monophosphate solution which was Q,3 % Na2S/P205) of an aqueous Na2S-solution, and suspension and solution were mixed together under a pressure of about 7 bars~ Unit 3A operated without Na2S-addition had a filtration capacity o~ 0.24 m3/h 1 . m 2 and gave a di-sodium phosphate solution which contained 90 ppm of zinc.
Unit 3B operated with sulfide precipitation had a slightly reduced ~lltration capacity of 0.22 m3/h 1 . m 2 but gave filtrate containing less than 5 ppm of zinc. ~omparison with Example 1B shows that it is possible for less sulfide to be used provided that neutralization is ef~ected in two stages and that precipitate ~ormed in first neutralization stage is removedO
33~
EXAMPLE 4:
The procedure was as in Example 3B. Wet-processed phos-phoric acid was neutralized to monophosphate stage, but NaH2P04-solution obtained a~ter filtration (21 % P205;
190 ppm zinc; 160 ppm iron) was neutralized to diphosphate content of 46 % only (pH = 6.5). Prior to separating precipi-tated matter, suspension was admixed with 0.8 % Na2S/P205, which was used in the form of a 12 % Na2S-solution and in-troduced upstream of a feed pump forming part of a pressure filter. Suspension and solution were mixed together under a pressure of about 4 bars. The resulting clear filtrate still contained 35 ppm of ~inc. rnis indicated that zinc was not satisfactorily removed within pH-range disclosed, e.g. in Canadian Pa~ent 380 394, even ~ith use of increased quan-tity of Na2S.
EXAMPLE 5:
Wet-processed phosphoric acid made from North African phosphate was sub~ected to two-stage neutralization at pH
of 9. This ga~e decontaminated di~odium phosphate solution which still contained 420 ppm o~ zinc 7 based on P~05, as well as material which consisted essentially of magnesium phosphates post-precipitated after storage for some pro~
longed time. Prior to making the solution into sodium tri-phosphate, zinc was precipitated therefrom in the form o~
zinc sulfide which was filtered off together wi~h the magn~-sium salts. To this end, 3.9 l of a 10 /0 Na2S-solution (0.17 % Na2S/P205) was added per m3 of suspension, imme-diately upstream of circulating pump ~orming part of pres-sure filter. 300 mol % of sulfide, based on Zn, was used.
Solution and suspension were mixed together under a pressure of 9 bars. Filtration was effected under approximately t'ne same pressure with filtration capacity o~ 0.4 m3/h . m2.
A clear disodium phosphate solution containing less than 1 ppm of zinc was obtained.
It is possible for the phosphate solution to be ad-mixed prior to sulfide precipitation, with a filtration aid, e.g. active carbonS so as to improve filtration pro-perties in the presence of minor or complete absence of post-precipitated matter.
. . .
The fact that the present process permits 7inc sulfide to be precipi~ated quantitatively withi~ the short period of t.ime during which the suspension is passed through the ~ilter, namely ~ to 5 minutes, depending on the filling volume of the ~ilter, is a very unexpected result as is also the good filterability of zinc sulfide precipitated in an alkaline medium.
Even in those cases in which use was made of a suspen-sion in which about 20 % of the solid matter was zinc sul fide, the filtration capacity was not affected or to an insignificant extent only.
The following Examples illustrate the invention.
~ 3 EXAMPL~ 1:
Wet-processed phosphoric acid (25.3 % P205; 0~15 ~/0 Fe203;
0,13 % Al203; 0.03 % Zn) made ~rom Morocco phosphate was used.
30 m3/h of acid was subjected to single-stage neutralization with sodium hydroxide solution and neutralized to give Na2HP04 (pH = 9). The suspension which was so obtained was filtered using two identical filtration units (1A and 1 B~ respectivè-ly) of which each was comprised of a horizontal pressure fil-; ter ( 70 m2 filter area) and a circulating pump (Q = up to 100 m3/h). Filtration ~it lA was operated without additionof Na2S to suspension. Suspension delivered to filtration unit 1B was admixed, directly upstream of the circulating pump, with 8 l/m3 o~ a 12 % Na2S-solution (0.4 % Na2S/P205;
this corresponded to 250 mol %, based on Zn), intimately mixed therewith at a pressure of about 7 bars, andfiltered~
Each o~ the 1A and 1B units had a filtration capacity of 0.2 m3/h , m2, under pressure of 7 bars, Clear diphosphate filtrates were obtained in the two cases. In case 1A (no sul-~ide precipitation), the filtrate contained 110 ppm of zinc and in case 1B (with sul~ide precipitation), the filtrate contained less than 5 ppm o~ zinc, EXAMPLE 2:
The procedure was as described in Example 1B, but Na2S-solution was introduced into a reservoir containing the suspension to undergo neutralization~ A~ter sulfide addition, the suspension was allowed to remain in the reser~oir for an average period o~ 2 hours at 90~ and then filtered. 80 l of a 12 % Na2S-solution (4 % Na2S/P205~ was used per m3 of suspension, The filtered disodium phosphate solution was found to contain 30 ppm of zinc. As a result of the Z hour ~ 3~
so~ourn time of the suspension in the reservoir, the filtra-te contained 6 times more Zn than the filtrate of Example 1B, despite the use of a 10 times ~arger proportion of Na2S in the present Example.
EXAMPLE ~:
Wet~processed phosphoric acid, the same as that used in Example 1, was treated with sodium hydroxide solution and neutralized initially to the monophosphate stage (pH = 4.5).
Resulting zinc-containing precipitate was filtered off.
NaH2P04-solution was obtained as the filtrate. It contained 190 ppm of zinc and was neutralized in a second stage to diphosphate (pH = 9). As in Example 1, filtration unit 3A
was operated without Na2S-addition to suspension. Suspension delivered to filtration unit 3B (3A and 3 B unlts provided with ~ilter and pump same as in Example 1B) was admixed, inside unit 3B, directly upstream o~ circulating pump, with 250 mol~ ~based on zinc content o~ monophosphate solution which was Q,3 % Na2S/P205) of an aqueous Na2S-solution, and suspension and solution were mixed together under a pressure of about 7 bars~ Unit 3A operated without Na2S-addition had a filtration capacity o~ 0.24 m3/h 1 . m 2 and gave a di-sodium phosphate solution which contained 90 ppm of zinc.
Unit 3B operated with sulfide precipitation had a slightly reduced ~lltration capacity of 0.22 m3/h 1 . m 2 but gave filtrate containing less than 5 ppm of zinc. ~omparison with Example 1B shows that it is possible for less sulfide to be used provided that neutralization is ef~ected in two stages and that precipitate ~ormed in first neutralization stage is removedO
33~
EXAMPLE 4:
The procedure was as in Example 3B. Wet-processed phos-phoric acid was neutralized to monophosphate stage, but NaH2P04-solution obtained a~ter filtration (21 % P205;
190 ppm zinc; 160 ppm iron) was neutralized to diphosphate content of 46 % only (pH = 6.5). Prior to separating precipi-tated matter, suspension was admixed with 0.8 % Na2S/P205, which was used in the form of a 12 % Na2S-solution and in-troduced upstream of a feed pump forming part of a pressure filter. Suspension and solution were mixed together under a pressure of about 4 bars. The resulting clear filtrate still contained 35 ppm of ~inc. rnis indicated that zinc was not satisfactorily removed within pH-range disclosed, e.g. in Canadian Pa~ent 380 394, even ~ith use of increased quan-tity of Na2S.
EXAMPLE 5:
Wet-processed phosphoric acid made from North African phosphate was sub~ected to two-stage neutralization at pH
of 9. This ga~e decontaminated di~odium phosphate solution which still contained 420 ppm o~ zinc 7 based on P~05, as well as material which consisted essentially of magnesium phosphates post-precipitated after storage for some pro~
longed time. Prior to making the solution into sodium tri-phosphate, zinc was precipitated therefrom in the form o~
zinc sulfide which was filtered off together wi~h the magn~-sium salts. To this end, 3.9 l of a 10 /0 Na2S-solution (0.17 % Na2S/P205) was added per m3 of suspension, imme-diately upstream of circulating pump ~orming part of pres-sure filter. 300 mol % of sulfide, based on Zn, was used.
Solution and suspension were mixed together under a pressure of 9 bars. Filtration was effected under approximately t'ne same pressure with filtration capacity o~ 0.4 m3/h . m2.
A clear disodium phosphate solution containing less than 1 ppm of zinc was obtained.
It is possible for the phosphate solution to be ad-mixed prior to sulfide precipitation, with a filtration aid, e.g. active carbonS so as to improve filtration pro-perties in the presence of minor or complete absence of post-precipitated matter.
. . .
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for making alkali metal phosphate solutions free of zinc, from phosphoric acid solutions contaminated with zinc which comprises:
a) admixing the solution with alkali metal hydroxide or carbonate so as to establish in the resulting suspension a pH-value within the range 8 to 14, b) reacting the suspension under pressure and with thorough agitation with H2S or an alkali metal sulfide solution; and c) separating decontaminated alkali metal phosphate solution from solid matter, the pressure being maintained.
a) admixing the solution with alkali metal hydroxide or carbonate so as to establish in the resulting suspension a pH-value within the range 8 to 14, b) reacting the suspension under pressure and with thorough agitation with H2S or an alkali metal sulfide solution; and c) separating decontaminated alkali metal phosphate solution from solid matter, the pressure being maintained.
2. The process as claimed in claim 1, wherein a pH within the range 9 to 9.5 is established.
3. The process as claimed in claim 1, wherein hydrogen sulfide or alkali metal sulfide is used in a proportion within the range 150 to 300 mol%, based on zinc in feed solution.
4. The process as claimed in claim 1, wherein Na2S is used as the alkali metal sulfide.
5. The process as claimed in claim 1, wherein the suspen-sion is reacted with hydrogen sulfide or alkali metal sulfide solution under a pressure within the range 0.1 to 10 bars.
6. The process as claimed in claim 1, wherein the solid matter is separated from the alkali metal phosphate solution with the aid of a pressure filter.
7. The process as claimed in claim 6, wherein the hydrogen sulfide or alkali metal sulfide solution is introduced directly into a pump, or directly upstream thereof, the pump forming part of, and being positioned ahead of, the pressure filter.
8. The process as claimed in claim 1 wherein said phosphoric acid solution is a wet-processed phosphoric acid solution.
9. The process as claimed in claim 1 wherein said phos-phoric acid solution is an alkali metal phosphate solution having contaminants originating from wet-processed phosphoric acid at least partially precipitated therein.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000342849A CA1141939A (en) | 1979-12-31 | 1979-12-31 | Production of alkali metal phosphate solutions free from zinc |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000342849A CA1141939A (en) | 1979-12-31 | 1979-12-31 | Production of alkali metal phosphate solutions free from zinc |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1141939A true CA1141939A (en) | 1983-03-01 |
Family
ID=4115945
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000342849A Expired CA1141939A (en) | 1979-12-31 | 1979-12-31 | Production of alkali metal phosphate solutions free from zinc |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1141939A (en) |
-
1979
- 1979-12-31 CA CA000342849A patent/CA1141939A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US3420622A (en) | Process for obtaining fluorine compounds from digestion solutions of crude phosphates with nitric acid or hydrochloric acid | |
| FI66162C (en) | FOERFARANDE FOER RENING AV FOSFORSYRA MED AVSEENDE PAO TUNGMETALLER | |
| US4028237A (en) | Method and apparatus for treatment of fluorine-containing waste waters | |
| US3993733A (en) | Food grade alkali metal phosphates from wet process H3 PO4 | |
| CA1071836A (en) | Food grade phosphoric acid from wet process phosphoric acid | |
| IE49648B1 (en) | Conversion of extraction residues originating from phosphoric acid decontamination to solid deposition products | |
| US4299803A (en) | Production of alkali metal phosphate solutions free from zinc | |
| CA1045339A (en) | Process and apparatus for purifying wet-processed phosphoric acid | |
| US4713229A (en) | Process for purifying phosphoric acid | |
| JPS62191409A (en) | Removal of heavy metals from inorganic acids | |
| CA1141939A (en) | Production of alkali metal phosphate solutions free from zinc | |
| US4053562A (en) | Production of alkali metal phosphate solutions of low vanadium content | |
| FR2551047A1 (en) | PRODUCTION OF PHOSPHATES FROM ALKALINE-TREATED PHOSPHATE ORE | |
| CA1261115A (en) | Process for dearsenifying phosphoric acid solutions | |
| US3685964A (en) | Purification of alkali phosphate solution | |
| US3993735A (en) | Cleanup of wet process phosphoric acid | |
| US4134962A (en) | Production of pure alkali metal phosphate solutions from wet-processed phosphoric acids | |
| US3305305A (en) | Purification of phosphate solutions | |
| US4134964A (en) | Process and apparatus for purifying wet-processed phosphoric acid | |
| US4379132A (en) | Process for sodium hypophosphite | |
| CA1043535A (en) | Process for the preparation of purified phosphoric solutions from phosphoric acid in a wet way | |
| US1002603A (en) | Purification of water. | |
| US4640824A (en) | Process for making alkali metal phosphate solutions containing little fluorine | |
| US20070166217A1 (en) | Method for producing strong base phosphates | |
| US4620966A (en) | Process for defluorinating alkali metal phosphate solutions |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |