CA1043572A - Process for separation of tungsten and molybdenum by extraction - Google Patents
Process for separation of tungsten and molybdenum by extractionInfo
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- CA1043572A CA1043572A CA218,219A CA218219A CA1043572A CA 1043572 A CA1043572 A CA 1043572A CA 218219 A CA218219 A CA 218219A CA 1043572 A CA1043572 A CA 1043572A
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Abstract
ABSTRACT OF THE DISCLOSURE
A process for separation of tungsten and molybdenum by extraction involves the addition to an aqueous solution con-taining tungsten and molybdenum nitric or hydrochloric acid to obtain pH from 0.5 to 1.5, introduction of a stabilizer comprising water-soluble phosphorus salts and a complexing agent - hydrogen peroxide in an amount from 1.5 to 2 mol per 1 g-atom of the total content of tungsten and molybdenum.
Then molybdenum is selectively extracted from the resulting aqueous solution with tri-n-butylphosphate with equal volu-metric proportioning of the aqueous and organic solutions.
Re-extraction of molybdenum and partially tungsten is car-ried out from the organic extracting agent with an alkali or soda solution.
The process enables the preparation of tungsten solution containing no more than 0.001 g/1 of molybdenum, and an increase in the degree of extraction of tungsten and molyb-denum.
A process for separation of tungsten and molybdenum by extraction involves the addition to an aqueous solution con-taining tungsten and molybdenum nitric or hydrochloric acid to obtain pH from 0.5 to 1.5, introduction of a stabilizer comprising water-soluble phosphorus salts and a complexing agent - hydrogen peroxide in an amount from 1.5 to 2 mol per 1 g-atom of the total content of tungsten and molybdenum.
Then molybdenum is selectively extracted from the resulting aqueous solution with tri-n-butylphosphate with equal volu-metric proportioning of the aqueous and organic solutions.
Re-extraction of molybdenum and partially tungsten is car-ried out from the organic extracting agent with an alkali or soda solution.
The process enables the preparation of tungsten solution containing no more than 0.001 g/1 of molybdenum, and an increase in the degree of extraction of tungsten and molyb-denum.
Description
1()~;~5~7~
The present invention relates to the hydrometallurgy of rare metals, and more particularly to a process for separa-tion of tungsten and molybdenum by extraction from aqueous solu-tions of chemical compoùnds thereof.
The separation of tungsten and molybdenum in aqueous solutions of salts thereof is one of the most complicated prob- `
lems in the production of pure chemical compounds of tungsten, such as ammonium paratungstate and tungstic acid, and hence, -metallic tungsten.
At present only one commercial process for separation of tungsten and molybdenum from aqueous solutions obtained after the alkali decomposition of molybdenum-containing tungsten con-centrate is known. This process, which is referred to as tri-sulphide purification involves a precipitation of hardly solukle molybdenum trisulphide from solutions containing sodium tung-state and molybdate.
In this process, tungsten mainly remains in the aqueous solution.
However, the process of trisulphide purification cannot provide for a desired separation of tungsten and molybdenum with a high content of molybdenum in tungsten concentrate, such as with 4 - 5 w.% of molybdenum contained in scheelite concentrate.
About 0.1 w.% of molybdenum remains in tungstic acid, whereas tungsten used for electronic and vacuum electronic techniques should contain less than 0.02 w.% of molybdenum as impurity.
In addition, a considerable quantity of tungsten up to 1 - 1.5 w.% of the starting content thereof in the aqueous solution is lost with molybdenum sulphide precipitate.
The disadvantages of this process also include contam-ination of environment with noxious sulphydrates formed in theproduction liquors during the trisulphide purification of tung-sten from molybdenum.
During the decomposition of scheelite concentrates 10~35~;~2 with hydrochloric acid a separation of tungsten and molybdenum also occurs. In this case, tungsten substantially completely precipitates in the form of tungstic acid, and the main part of molybdenum remains in the aqueous solution. It should be, how-ever, noted that tungstic acid obtained after decomposition of such concentrates with hydrochloric acid contains generally from 0.1 to 0.3 w.% of molybdenum, which is undesirable.
It is known the process of separation of tungsten and molybdenum by extracting molybdenum with an organic extracting 13 agent - methyl isobutyl ketone or acetophenon from a sludge of tungstic acid containing also hydrochloric acid. This method permits to reduce the content of molybdenum in tungstic acid up to 0.02 w.%.
The process conducted by this method requires, however, a high consumption of hydrochloric acid of up to 8 tons per 1 ton of tungsten concentrate so that such method cannot have any indus-trial application.
Rapid and widespread development of such important industries as electronic engineering, and electrovacuum technol-ogy, production of pure compounds and the like impose stringentrequirements on the purity of metallic tungsten and molybdenum and their compounds.
Necessity for complex, economic and rational utilization of deposits of difficultly available tungsten and molybdenum con-centrates and products makes very urgent the solution of the problem of the provision of a new efficient process for separa-tion of these metals.
The main difficulty lies in that molybdenum is a perman-ent and difficultly separated impurity in tun~sten ores and pro-duction liquors containing tungsten.
Difficulties in separating tungsten and molybdenum areassociated with the affinity of these metals. This circumstance 1~4~5t7~
explains the fact that none of the above-described processes of separating tungsten and molybdenum can provide for complete sep-aration of the metals.
The attempts to separate tungsten and molybdenum by extraction with organic extracting agents from aqueous solutions of salts thereof have not gained expected results due to affinity of tungsten and molybdenum.
The difficulties become still more serious due to the fact that at pH less than 2 tungstic acid precipitates from aqu-eous solutions containing tungsten, and molybdenic acid is pre-cipitated therewith, while at pH from 2 to 7 tungsten and molyb-denum form polyanions, for example, of the type [H(W,M)6~21-a9]
and of another composition.
It is obvious, that over a large range of pH of an ~-aqueous solution tungsten and molybdenum either precipitate or are strongly bound into polymeric complexes. The both circum-stances witness the impossibility of selecting the conditions for complete separation of tungsten and molybdenum by extraction from conventional aqueous solutions.
On the basis of theoretical and experimental tests, it has been found that the process for separation of tungsten and molybdenum by extraction should be carried out under qualitative-ly new conditions, wherein these metals could be retained in the solution over a wide range of pH without formation common com-plexes in between them and have different chemical properties and extraction ability.
The theoretical and experimental tests have shown that the both conditions are provided by adding to a solution contain-ing tungsten and molybdenum a complexing agent - hydrogen per-oxide and preferably also water-soluble phosphorus compounds.
It has been found,that peroxide complexes of tungsten io435q;~
and molybdenum formed after adding hydrogen peroxide to the 901u-tion exhibit different chemical and extraction properties.
Tungstic acid will never precipitate at a~y pH of an aqueous solution in the presence of hydrogen peroxide.
In addition, the degree of polymerization of tungsten and molybdenum in an aqueous solution and their capability of forming combined polymeric complexes are reduced.
Separation of tungsten and molybdenum by extraction from such solutions is possible using neutral and ion-exchange organic extracting agents.
It is the main object of the invention to provide a process for separation of tungsten and molybdenum by extraction which permits to obtain a solution of chemical compounds of tung-sten containing substantially no mol~bdenum~from an aqueous solution of chemical compounds thereof.
An important object of the invention is to increase the degree of extraction of tungsten from 5 to 10 w.% into the high quality end product - tungsten trioxide containing less than 0.005 w.% of molybdenum.
Still another object of the invention is to increase the degree of extraction of molybdenum from 2 to 3 w.% as com-pared to that obtained with the trisulphide purification.
It is also an object of the invention to simplify the process for separation of tungsten and molybdenum and provide the conditions for automation of the process.
A not least important object of the invention is to eliminate contamination of environment with noxious production wastes occurring with t~e trisulphide purification of tungsten from molybdenum.
These objects are accomplished by the provision of a process for separation of tungsten and molybdenum by extraction with organic extracting agents from an aqueous solution of chem-1(1~3S72 ical compounds thereof, wherein, according to the invention to said solution there is added a complexing agent-hydrogen peroxide in an amount from 1.5 to 2 mol per 1 g-atom of the total content of tungsten and molybdenum and then an inorganic acid selected from the group consisting of nitric, hydrochloric and sulphuric acid to obtain pH of the solution from 0.5 to 1.8, whereafter molybedenum is extracted from the resulting solution with neutral or ion-exchange extracting agents with the volumetric ratio of the aqueous solution to the organic solution of 1:1.5.
The process for separation by extraction according to the invention provides for obtaining a solution containing chemi-cal compounds of tungsten with molybedenum impurity from 0.001 to 0.003 w.%.
Besides, it has been found that it is necessary to strictly maintain the above-described operating conditions in con-ducting the separation of tungsten and molybdenum by extraction.
A decrease in the consumption of hydrogen peroxide below 1.5 mol per 1 g-atom of the total content of tungsten and molybdenum re-sults in a rapid destruction of peroxide complex of tungsten and, hence, in a more rapid precipitation of tungstic acid and hampered extraction conditions. An increase in the consumption of hydro-gen peroxide above 2 mol per 1 g-atom of the total content of tungsten and molybdenum is technologically unreasonable and may only result in a needless consumption of hydrogen peroxide.
The above-specified range of pH provides for the most complete separation of tungsten and molybdenum since maximum ex-traction of molybdenum and minimum extraction of tungsten are obtained within this range.
It has been found that the above-specified ratio be-tween the volumes of organic and aqueous solutions (Vorg :Vfrom 1 to 1.5) is the optimal one since with a lower ratio the coefficient of molybdenum distribution Emo is reduced resulting 104~5'7Z
in an increased number of extraction stages and volume of ex-traction equipment, and with an increase in this ratio the con-sumption of organic extracting agent becomes greater and the con-centration of molybdenum in organic extracting agent is lower.
The above-described complexing agent may be used with water-soluble phosphorus compounds taken in an amount from 0.002 to 0.005 mol/l.
This permits to carry out the separating of tungsten and molybdenum by extraction from production liquors containing silicon, arsenic and phosphorus impurities.
It has also been found that a decrease or increase in the amount of water~soluble phosphorus compounds added to the production liquor as compared to the range from 0.002 to 0.005 mol/l results in an increased rate of destruction of hydrogen peroxide and reduced efficiency of separation of tungsten and molybdenum by extraction.
The separation of tungsten and molybdenum by extrac-tion is preferably conducted using neutral extracting agents, -such as tri-n-butylphosphate or tributylphosphineoxide from aqueous solutions in the presence of nitric acid at pH from 0.5 to 1Ø
This permits to obtain maximum efficiency of purifica-tion of tungsten from molybdenum with minimum number of produc-tion stages.
The separation of tungsten and molybdenum by extrac-tion from aqueous solutions using an ion-exchange extracting agent, such as trioctylamine is preferably conducted in the pre-sence of nitric acid within the pH range from 0.5 to 1.8 since in this pH range an optimal separation of the metals is achieved.
The separation of tungsten and molybdenum by extrac-tion from aqueous solutions using trin-butylphosphate is prefer-ably effected in the presence of hydrochloric acid within the 104;~5'7~
pH range from 1.5 to 1.8 to obtain an efficient separation and sufficient stability of hydrogen peroxide.
The separation of tungsten and molybdenum by extraction from aqueous solutions using trin-butylphosphate may be conduct-ed in the presence of sulphuric acid within the pH range from 0.5 to 1.5 since it is in this range that a satisfactory separa-tion of the metals takes place.
The invention will now be illustrated by examples of specific embodiments of the process according to the invention.
Example 1 From an artificially prepared aqueous solution contain-ing 19 g/l of tungsten and 1 g/l of molybdenum and acidified with nitric acid to pH = 0.5 with a preliminary addition of hydrogen peroxide used in an amount of 1.5 mol per 1 g-atom of the total content of the metals 79 w.% of molybdenum were extracted at one stage with tri-n-butylphosphate with the volumetric ratio of the aqueous to organic solution of 1:1. Substantially no tungsten was extracted.
After three sequential extraction stages with fresh tri-n-butylphosphate with the volumetric ratio of the aqueous to organic solution of 1:1 the content of molybdenum in the aqueous solution was reduced to 0.01 g/l, the content of tungsten being as high as 18.5 g/l.
The separation of tungsten and molybdenum by extraction may be effected with an ion-exchange extracting agent such as a salt of quaternary ammonium base from an aqueous solution in the presence of nitric acid at pH from 2.5 to 2.8 or in the presence of sulphuric acid at pH = 4.3.
In this example the separation by extraction may be effected using an organic extracting agent comprising tri-butyl-phosphineoxide with the same efficiency.
\
Exam~le 2 0.003 mol/l of sodium pyrophosphate were added to an artificially prepared aqueous solution of sodium tungstate and sodium molybdate containing 78.65 g/l of tungsten trioxide, 4.7 g/l of molybdenum and 0.1 g/l of silicon. Then hydrogen peroxide was added to the solution in an amount of 2 mol per 1 g-atom of the total content of tungsten and molybdenum and nitric acid to obtain pH of 0.9. Subsequently the extraction was conducted using trin-butylphosphate with the volumetric ratio of the aqueous to organic solution of 1:1.
The test results have shown that the coefficient of tungsten distribution DW was below 0.0045, whereas the coeffic-ient of distribution for molybdenum DMo was equal to 4. 78.3 g/l of tungsten trioxide and only 0.9 g/l of molybdenum were found in the tungsten solution after the extraction. .
Example 3 0.005 mol/l of sodium pyrophosphate were added to a production liquor obtained after decomposition of scheelite con-centrate with soda containing 109.8 g/l of tungsten trioxide, 9.103 g/l of molybdenum, 0.15 g/l of silicon dioxide, 0.0045 g/l of phosphorus, 0.003 g/l of arsenic, 25 g/l of sodium nitrate and 3.5 g/l of sodium hydroxide. Then nitric acid was added to the resulting solution to obtain pH of 0.5, and hydrogen peroxide in an amount of 2 mol per 1 g-atom of the total content of tung-sten and molybdenum.
The extraction was conducted with tri-n~butylphosphate in a mixing and settling apparatus continuously in counter-cur-rent with the ratio of flows of aqueous and organic solutions of 1:1.5.
Throughput capacity of the apparatus was 6 l/hour of the total flow of the organic and aqueous solutions, with the ~()435r~Z
volume of one section of the apparatus being equal to 2.5 1.
After eight extraction stages in an equilibrium aqueous solution the content of tungsten trioxide was 102.8 g/l and the content of molybdenum was lowered to 0.0033 g/l. The content of tungsten in the organic solution was 7.0 g/l and the content of molybdenum - 9.1 g/l.
The tests of re-extraction of molybdenum and tungsten have shown that the both metals are extracted from tri-n-butyl-phosphate in an aqueous solution containing 10 w.% of water and about 8 w.% of sodium nitrate with four stages with continuous counter-current operation and with the volumetric ratio of aque-ous to organic solution of 1~
The resulting re-extracts contained from 14 to 16 g/l of tungsten trioxide and from 18 to 20 g/l of molybdenum. 0.2 g/l of tungsten trioxide and 0.002 g/l of molybdenum remained in the organic solution.
Example 4 From a production liquor obtained after decomposition of scheelite concentrate with soda containing 120 g/l of tungsten 20 trioxide, 5.8 g/l of molybdenum, 0.15 g/l of silicon dioxide, 0.005 g/l of phosphorus and 0.003 g/l of arsenic, after adding thereto 0.005 mol/l of sodium pyrophosphate, and 1.8 mol of hydrogen per-oxide per 1 g-atom of the total content of tungsten and molybdenum and hydrochloric acid to obtain pH of the solution about 1.5, molybdenum was extracted with tri-n-butylphosphate continuously in counter-current in a mixing and settling apparatus as described ; in Example 3.
With six extraction stages with the volumetric ratio of aqueous to organic solution of 1:1.3 substantially the total content of molybdenum was extracted from the solution. The con-tent of molybdenum in the aqueous solution was lowered to 0.0035 g/l, and the content of tungsten trioxide in the aqueous solution 10435~2 was 113.2 g/l.
6.8 g/l of tungsten trioxide and 5.78 g/l of molybdenum remained in the organic solution.
The re-extraction was conducted as de~cribed above.
Exam~le 5 Hydrogen peroxide was added to an artificially prepared solution containing 98.5 g/l of tungsten and 9.6 g/l of molybdenum in an amount of 2 mol per 1 g-atom of the total content of tung-sten and molybdenum, and hydrochloric acid was then added to ob-tain pH about 1.8. Molybdenum was extracted from the resultingsolution with tri-n-butylphosphate with the volumetric ratio of the aqueous to organic solution of 1:1.86 w.% of moIybdenum and only 2 w.% of tungsten were extracted in a single stage.
With four sequential re-extraction stages with a fresh extracting agent the content of molybdenum in the aqueous solu-tion of tungsten was lowered to 0.0016 g/l.
Example 6 Hydrogen peroxide in an amount of 1.5 mol per 1 g-atom of the total content of tungsten and molybdenum was added to an artificially prepared solution containing 19 g/l of tungsten - and 1 g/l of molybdenum, and then sulphuric acid was added to obtain pH - 0.65. Molybdenum, and partially tungsten were select-ively extracted from the resulting solution using tri-n-butylphos-; phate. Coefficient of molybdenum distribution was DMo = 3, co-efficient of tungsten distribution was DW ~ 0.18. 80 w.% of molybdenum and 15 w.% of'tungsten were transferred into the or-ganic solution at a single extraction stage.
Molybdenum content in the aqueous solution was lowered to 0.2 g/l, and the content of tungsten was as high as 16.5 g/l.
Example 7 ~ itric acid was added to an artificially prepared solu-tion containing 20 g/l of tungsten and 1 g/l of molybdenum to 10435\7;~
obtain p~ , and then hydrogen peroxide was ad~ed to the solu-tion in an amount of l.S mol per l g-atom of the total content of tungsten and molybdenum.
Subsequently the extraction was effected with 15% solu-tion of trioctylamine in kerosene with the volumetric ratio of the aqueous to organic solution of l:l. Up to 80 w.% of molyb-denum and about 3 w.% of tungsten were extracted in a single stage.
We have also conducted physical and chemical studies on the chemical states of molybdenum and tungsten in the pre-sence of hydrogen peroxide and on the mechanism governing the extraction of molybdenum from peroxide solutions.
We have found that, independently of the kind of in-organic acid used, diperoxidemolybdenic acid and diperoxide-tungstic acid of the general formula H2Me20ll(H20)2 are formed in weakly acidic solutions.
It has been shown that the extraction of molybdenum proceeds in conformity with the hydronium mech~nism. Molybdenum is converted into the organic phase in the body of hydrosolvate of the formula [H30 tH2o) 3 3 TBP] 2 [M2ll (H20) 2 ]
Example 8 From an artificially prepared aqueous solution contain-ing 19.6 g/l of tungsten and 0.9 g/l of molybdenum acidified with sulfuric acid to obtain pH = 4.3, to which there was preliminarily added hydrogen peroxide in the amount of 1.5 mole per l g-atom of total content of metals, more than 90 w.% of rnolybdenum and 15 w.% of tungsten were extracted in a single stage with 0.1 molar solution of quaternary ammonium tetraoctylammonium sulfate com-pound in toluene. Coefficient of separation of metals was ~ = 73. Ratio of volumes of aqueous and organic solutions was 43~72 In this example, the separation of the above mentioned metals may be as well carried out from their aqueous solutions of nitric acid with pH from 2.5 to 2.8
The present invention relates to the hydrometallurgy of rare metals, and more particularly to a process for separa-tion of tungsten and molybdenum by extraction from aqueous solu-tions of chemical compoùnds thereof.
The separation of tungsten and molybdenum in aqueous solutions of salts thereof is one of the most complicated prob- `
lems in the production of pure chemical compounds of tungsten, such as ammonium paratungstate and tungstic acid, and hence, -metallic tungsten.
At present only one commercial process for separation of tungsten and molybdenum from aqueous solutions obtained after the alkali decomposition of molybdenum-containing tungsten con-centrate is known. This process, which is referred to as tri-sulphide purification involves a precipitation of hardly solukle molybdenum trisulphide from solutions containing sodium tung-state and molybdate.
In this process, tungsten mainly remains in the aqueous solution.
However, the process of trisulphide purification cannot provide for a desired separation of tungsten and molybdenum with a high content of molybdenum in tungsten concentrate, such as with 4 - 5 w.% of molybdenum contained in scheelite concentrate.
About 0.1 w.% of molybdenum remains in tungstic acid, whereas tungsten used for electronic and vacuum electronic techniques should contain less than 0.02 w.% of molybdenum as impurity.
In addition, a considerable quantity of tungsten up to 1 - 1.5 w.% of the starting content thereof in the aqueous solution is lost with molybdenum sulphide precipitate.
The disadvantages of this process also include contam-ination of environment with noxious sulphydrates formed in theproduction liquors during the trisulphide purification of tung-sten from molybdenum.
During the decomposition of scheelite concentrates 10~35~;~2 with hydrochloric acid a separation of tungsten and molybdenum also occurs. In this case, tungsten substantially completely precipitates in the form of tungstic acid, and the main part of molybdenum remains in the aqueous solution. It should be, how-ever, noted that tungstic acid obtained after decomposition of such concentrates with hydrochloric acid contains generally from 0.1 to 0.3 w.% of molybdenum, which is undesirable.
It is known the process of separation of tungsten and molybdenum by extracting molybdenum with an organic extracting 13 agent - methyl isobutyl ketone or acetophenon from a sludge of tungstic acid containing also hydrochloric acid. This method permits to reduce the content of molybdenum in tungstic acid up to 0.02 w.%.
The process conducted by this method requires, however, a high consumption of hydrochloric acid of up to 8 tons per 1 ton of tungsten concentrate so that such method cannot have any indus-trial application.
Rapid and widespread development of such important industries as electronic engineering, and electrovacuum technol-ogy, production of pure compounds and the like impose stringentrequirements on the purity of metallic tungsten and molybdenum and their compounds.
Necessity for complex, economic and rational utilization of deposits of difficultly available tungsten and molybdenum con-centrates and products makes very urgent the solution of the problem of the provision of a new efficient process for separa-tion of these metals.
The main difficulty lies in that molybdenum is a perman-ent and difficultly separated impurity in tun~sten ores and pro-duction liquors containing tungsten.
Difficulties in separating tungsten and molybdenum areassociated with the affinity of these metals. This circumstance 1~4~5t7~
explains the fact that none of the above-described processes of separating tungsten and molybdenum can provide for complete sep-aration of the metals.
The attempts to separate tungsten and molybdenum by extraction with organic extracting agents from aqueous solutions of salts thereof have not gained expected results due to affinity of tungsten and molybdenum.
The difficulties become still more serious due to the fact that at pH less than 2 tungstic acid precipitates from aqu-eous solutions containing tungsten, and molybdenic acid is pre-cipitated therewith, while at pH from 2 to 7 tungsten and molyb-denum form polyanions, for example, of the type [H(W,M)6~21-a9]
and of another composition.
It is obvious, that over a large range of pH of an ~-aqueous solution tungsten and molybdenum either precipitate or are strongly bound into polymeric complexes. The both circum-stances witness the impossibility of selecting the conditions for complete separation of tungsten and molybdenum by extraction from conventional aqueous solutions.
On the basis of theoretical and experimental tests, it has been found that the process for separation of tungsten and molybdenum by extraction should be carried out under qualitative-ly new conditions, wherein these metals could be retained in the solution over a wide range of pH without formation common com-plexes in between them and have different chemical properties and extraction ability.
The theoretical and experimental tests have shown that the both conditions are provided by adding to a solution contain-ing tungsten and molybdenum a complexing agent - hydrogen per-oxide and preferably also water-soluble phosphorus compounds.
It has been found,that peroxide complexes of tungsten io435q;~
and molybdenum formed after adding hydrogen peroxide to the 901u-tion exhibit different chemical and extraction properties.
Tungstic acid will never precipitate at a~y pH of an aqueous solution in the presence of hydrogen peroxide.
In addition, the degree of polymerization of tungsten and molybdenum in an aqueous solution and their capability of forming combined polymeric complexes are reduced.
Separation of tungsten and molybdenum by extraction from such solutions is possible using neutral and ion-exchange organic extracting agents.
It is the main object of the invention to provide a process for separation of tungsten and molybdenum by extraction which permits to obtain a solution of chemical compounds of tung-sten containing substantially no mol~bdenum~from an aqueous solution of chemical compounds thereof.
An important object of the invention is to increase the degree of extraction of tungsten from 5 to 10 w.% into the high quality end product - tungsten trioxide containing less than 0.005 w.% of molybdenum.
Still another object of the invention is to increase the degree of extraction of molybdenum from 2 to 3 w.% as com-pared to that obtained with the trisulphide purification.
It is also an object of the invention to simplify the process for separation of tungsten and molybdenum and provide the conditions for automation of the process.
A not least important object of the invention is to eliminate contamination of environment with noxious production wastes occurring with t~e trisulphide purification of tungsten from molybdenum.
These objects are accomplished by the provision of a process for separation of tungsten and molybdenum by extraction with organic extracting agents from an aqueous solution of chem-1(1~3S72 ical compounds thereof, wherein, according to the invention to said solution there is added a complexing agent-hydrogen peroxide in an amount from 1.5 to 2 mol per 1 g-atom of the total content of tungsten and molybdenum and then an inorganic acid selected from the group consisting of nitric, hydrochloric and sulphuric acid to obtain pH of the solution from 0.5 to 1.8, whereafter molybedenum is extracted from the resulting solution with neutral or ion-exchange extracting agents with the volumetric ratio of the aqueous solution to the organic solution of 1:1.5.
The process for separation by extraction according to the invention provides for obtaining a solution containing chemi-cal compounds of tungsten with molybedenum impurity from 0.001 to 0.003 w.%.
Besides, it has been found that it is necessary to strictly maintain the above-described operating conditions in con-ducting the separation of tungsten and molybdenum by extraction.
A decrease in the consumption of hydrogen peroxide below 1.5 mol per 1 g-atom of the total content of tungsten and molybdenum re-sults in a rapid destruction of peroxide complex of tungsten and, hence, in a more rapid precipitation of tungstic acid and hampered extraction conditions. An increase in the consumption of hydro-gen peroxide above 2 mol per 1 g-atom of the total content of tungsten and molybdenum is technologically unreasonable and may only result in a needless consumption of hydrogen peroxide.
The above-specified range of pH provides for the most complete separation of tungsten and molybdenum since maximum ex-traction of molybdenum and minimum extraction of tungsten are obtained within this range.
It has been found that the above-specified ratio be-tween the volumes of organic and aqueous solutions (Vorg :Vfrom 1 to 1.5) is the optimal one since with a lower ratio the coefficient of molybdenum distribution Emo is reduced resulting 104~5'7Z
in an increased number of extraction stages and volume of ex-traction equipment, and with an increase in this ratio the con-sumption of organic extracting agent becomes greater and the con-centration of molybdenum in organic extracting agent is lower.
The above-described complexing agent may be used with water-soluble phosphorus compounds taken in an amount from 0.002 to 0.005 mol/l.
This permits to carry out the separating of tungsten and molybdenum by extraction from production liquors containing silicon, arsenic and phosphorus impurities.
It has also been found that a decrease or increase in the amount of water~soluble phosphorus compounds added to the production liquor as compared to the range from 0.002 to 0.005 mol/l results in an increased rate of destruction of hydrogen peroxide and reduced efficiency of separation of tungsten and molybdenum by extraction.
The separation of tungsten and molybdenum by extrac-tion is preferably conducted using neutral extracting agents, -such as tri-n-butylphosphate or tributylphosphineoxide from aqueous solutions in the presence of nitric acid at pH from 0.5 to 1Ø
This permits to obtain maximum efficiency of purifica-tion of tungsten from molybdenum with minimum number of produc-tion stages.
The separation of tungsten and molybdenum by extrac-tion from aqueous solutions using an ion-exchange extracting agent, such as trioctylamine is preferably conducted in the pre-sence of nitric acid within the pH range from 0.5 to 1.8 since in this pH range an optimal separation of the metals is achieved.
The separation of tungsten and molybdenum by extrac-tion from aqueous solutions using trin-butylphosphate is prefer-ably effected in the presence of hydrochloric acid within the 104;~5'7~
pH range from 1.5 to 1.8 to obtain an efficient separation and sufficient stability of hydrogen peroxide.
The separation of tungsten and molybdenum by extraction from aqueous solutions using trin-butylphosphate may be conduct-ed in the presence of sulphuric acid within the pH range from 0.5 to 1.5 since it is in this range that a satisfactory separa-tion of the metals takes place.
The invention will now be illustrated by examples of specific embodiments of the process according to the invention.
Example 1 From an artificially prepared aqueous solution contain-ing 19 g/l of tungsten and 1 g/l of molybdenum and acidified with nitric acid to pH = 0.5 with a preliminary addition of hydrogen peroxide used in an amount of 1.5 mol per 1 g-atom of the total content of the metals 79 w.% of molybdenum were extracted at one stage with tri-n-butylphosphate with the volumetric ratio of the aqueous to organic solution of 1:1. Substantially no tungsten was extracted.
After three sequential extraction stages with fresh tri-n-butylphosphate with the volumetric ratio of the aqueous to organic solution of 1:1 the content of molybdenum in the aqueous solution was reduced to 0.01 g/l, the content of tungsten being as high as 18.5 g/l.
The separation of tungsten and molybdenum by extraction may be effected with an ion-exchange extracting agent such as a salt of quaternary ammonium base from an aqueous solution in the presence of nitric acid at pH from 2.5 to 2.8 or in the presence of sulphuric acid at pH = 4.3.
In this example the separation by extraction may be effected using an organic extracting agent comprising tri-butyl-phosphineoxide with the same efficiency.
\
Exam~le 2 0.003 mol/l of sodium pyrophosphate were added to an artificially prepared aqueous solution of sodium tungstate and sodium molybdate containing 78.65 g/l of tungsten trioxide, 4.7 g/l of molybdenum and 0.1 g/l of silicon. Then hydrogen peroxide was added to the solution in an amount of 2 mol per 1 g-atom of the total content of tungsten and molybdenum and nitric acid to obtain pH of 0.9. Subsequently the extraction was conducted using trin-butylphosphate with the volumetric ratio of the aqueous to organic solution of 1:1.
The test results have shown that the coefficient of tungsten distribution DW was below 0.0045, whereas the coeffic-ient of distribution for molybdenum DMo was equal to 4. 78.3 g/l of tungsten trioxide and only 0.9 g/l of molybdenum were found in the tungsten solution after the extraction. .
Example 3 0.005 mol/l of sodium pyrophosphate were added to a production liquor obtained after decomposition of scheelite con-centrate with soda containing 109.8 g/l of tungsten trioxide, 9.103 g/l of molybdenum, 0.15 g/l of silicon dioxide, 0.0045 g/l of phosphorus, 0.003 g/l of arsenic, 25 g/l of sodium nitrate and 3.5 g/l of sodium hydroxide. Then nitric acid was added to the resulting solution to obtain pH of 0.5, and hydrogen peroxide in an amount of 2 mol per 1 g-atom of the total content of tung-sten and molybdenum.
The extraction was conducted with tri-n~butylphosphate in a mixing and settling apparatus continuously in counter-cur-rent with the ratio of flows of aqueous and organic solutions of 1:1.5.
Throughput capacity of the apparatus was 6 l/hour of the total flow of the organic and aqueous solutions, with the ~()435r~Z
volume of one section of the apparatus being equal to 2.5 1.
After eight extraction stages in an equilibrium aqueous solution the content of tungsten trioxide was 102.8 g/l and the content of molybdenum was lowered to 0.0033 g/l. The content of tungsten in the organic solution was 7.0 g/l and the content of molybdenum - 9.1 g/l.
The tests of re-extraction of molybdenum and tungsten have shown that the both metals are extracted from tri-n-butyl-phosphate in an aqueous solution containing 10 w.% of water and about 8 w.% of sodium nitrate with four stages with continuous counter-current operation and with the volumetric ratio of aque-ous to organic solution of 1~
The resulting re-extracts contained from 14 to 16 g/l of tungsten trioxide and from 18 to 20 g/l of molybdenum. 0.2 g/l of tungsten trioxide and 0.002 g/l of molybdenum remained in the organic solution.
Example 4 From a production liquor obtained after decomposition of scheelite concentrate with soda containing 120 g/l of tungsten 20 trioxide, 5.8 g/l of molybdenum, 0.15 g/l of silicon dioxide, 0.005 g/l of phosphorus and 0.003 g/l of arsenic, after adding thereto 0.005 mol/l of sodium pyrophosphate, and 1.8 mol of hydrogen per-oxide per 1 g-atom of the total content of tungsten and molybdenum and hydrochloric acid to obtain pH of the solution about 1.5, molybdenum was extracted with tri-n-butylphosphate continuously in counter-current in a mixing and settling apparatus as described ; in Example 3.
With six extraction stages with the volumetric ratio of aqueous to organic solution of 1:1.3 substantially the total content of molybdenum was extracted from the solution. The con-tent of molybdenum in the aqueous solution was lowered to 0.0035 g/l, and the content of tungsten trioxide in the aqueous solution 10435~2 was 113.2 g/l.
6.8 g/l of tungsten trioxide and 5.78 g/l of molybdenum remained in the organic solution.
The re-extraction was conducted as de~cribed above.
Exam~le 5 Hydrogen peroxide was added to an artificially prepared solution containing 98.5 g/l of tungsten and 9.6 g/l of molybdenum in an amount of 2 mol per 1 g-atom of the total content of tung-sten and molybdenum, and hydrochloric acid was then added to ob-tain pH about 1.8. Molybdenum was extracted from the resultingsolution with tri-n-butylphosphate with the volumetric ratio of the aqueous to organic solution of 1:1.86 w.% of moIybdenum and only 2 w.% of tungsten were extracted in a single stage.
With four sequential re-extraction stages with a fresh extracting agent the content of molybdenum in the aqueous solu-tion of tungsten was lowered to 0.0016 g/l.
Example 6 Hydrogen peroxide in an amount of 1.5 mol per 1 g-atom of the total content of tungsten and molybdenum was added to an artificially prepared solution containing 19 g/l of tungsten - and 1 g/l of molybdenum, and then sulphuric acid was added to obtain pH - 0.65. Molybdenum, and partially tungsten were select-ively extracted from the resulting solution using tri-n-butylphos-; phate. Coefficient of molybdenum distribution was DMo = 3, co-efficient of tungsten distribution was DW ~ 0.18. 80 w.% of molybdenum and 15 w.% of'tungsten were transferred into the or-ganic solution at a single extraction stage.
Molybdenum content in the aqueous solution was lowered to 0.2 g/l, and the content of tungsten was as high as 16.5 g/l.
Example 7 ~ itric acid was added to an artificially prepared solu-tion containing 20 g/l of tungsten and 1 g/l of molybdenum to 10435\7;~
obtain p~ , and then hydrogen peroxide was ad~ed to the solu-tion in an amount of l.S mol per l g-atom of the total content of tungsten and molybdenum.
Subsequently the extraction was effected with 15% solu-tion of trioctylamine in kerosene with the volumetric ratio of the aqueous to organic solution of l:l. Up to 80 w.% of molyb-denum and about 3 w.% of tungsten were extracted in a single stage.
We have also conducted physical and chemical studies on the chemical states of molybdenum and tungsten in the pre-sence of hydrogen peroxide and on the mechanism governing the extraction of molybdenum from peroxide solutions.
We have found that, independently of the kind of in-organic acid used, diperoxidemolybdenic acid and diperoxide-tungstic acid of the general formula H2Me20ll(H20)2 are formed in weakly acidic solutions.
It has been shown that the extraction of molybdenum proceeds in conformity with the hydronium mech~nism. Molybdenum is converted into the organic phase in the body of hydrosolvate of the formula [H30 tH2o) 3 3 TBP] 2 [M2ll (H20) 2 ]
Example 8 From an artificially prepared aqueous solution contain-ing 19.6 g/l of tungsten and 0.9 g/l of molybdenum acidified with sulfuric acid to obtain pH = 4.3, to which there was preliminarily added hydrogen peroxide in the amount of 1.5 mole per l g-atom of total content of metals, more than 90 w.% of rnolybdenum and 15 w.% of tungsten were extracted in a single stage with 0.1 molar solution of quaternary ammonium tetraoctylammonium sulfate com-pound in toluene. Coefficient of separation of metals was ~ = 73. Ratio of volumes of aqueous and organic solutions was 43~72 In this example, the separation of the above mentioned metals may be as well carried out from their aqueous solutions of nitric acid with pH from 2.5 to 2.8
Claims (8)
1. A process for the separation of tungsten and molybdenum by extraction comprising the steps of: adding to an aqueous solution containing chemical compounds of tungsten and molyb-denum a complexing agent, hydrogen peroxide in an amount of from 1.5 to 2 mol per 1 g-atom of the total content of tungsten and molybdenum; adding to the resulting solution an acid selected from the group consisting of nitric, hydrochloric and sulphuric acid to obtain a pH of the solution from 0.5 to 1.8; selectively extracting molybdenum from the resulting solution with a neutral or ion-exchange organic extracting agent with the volumetric ratio of the aqueous to organic solution of from 1:1 to 1.5.
2. A process as claimed in claim 1, wherein said complex-ing agent is added along with water-soluble phosphorus compounds used in an amount from 0.002 to 0.005 mol/1.
3. A process as claimed in claim 1, wherein the separa-tion of tungsten and molybdenum by extraction is effected with a neutral extracting agent from aqueous solutions in the presence of nitric acid at a pH from 0.5 to 1Ø
4. A process as claimed in claim 1, wherein the separa-tion of tungsten and molybdenum by extraction is effected with an ion-exchange extracting agent from aqueous solutions in the presence of nitric acid at a pH from 0.5 to 1.8.
5. A process as claimed in claim 1, wherein the separa-tion of tungsten and molybdenum by extraction is effected with tri-n-butylphosphate from aqueous solutions in the presence of hydrochloric acid at a pH from 1.5 to 1.8.
6. A process as claimed in claim 1, wherein the separa-tion of tungsten and molybdenum by extraction is effected with tri-n-butylphosphate from aqueous solutions in the presence of sulphuric acid at a pH from 0.5 to 1.5.
7. A process as claimed in claim 3, wherein the neutral extracting agents are selected from the group consisting of tri-n-butylphosphate and tri-butylphosphine oxide.
8. A process as claimed in claim 4, wherein the ion-exchange extracting agent is selected from the group consisting of trioctylamine and a salt of a quaternary ammonium base.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA218,219A CA1043572A (en) | 1975-01-20 | 1975-01-20 | Process for separation of tungsten and molybdenum by extraction |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA218,219A CA1043572A (en) | 1975-01-20 | 1975-01-20 | Process for separation of tungsten and molybdenum by extraction |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1043572A true CA1043572A (en) | 1978-12-05 |
Family
ID=4102092
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA218,219A Expired CA1043572A (en) | 1975-01-20 | 1975-01-20 | Process for separation of tungsten and molybdenum by extraction |
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| Country | Link |
|---|---|
| CA (1) | CA1043572A (en) |
-
1975
- 1975-01-20 CA CA218,219A patent/CA1043572A/en not_active Expired
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