CA1183005A - Ammonium hydroxide stripping of tungsten from organic solvents - Google Patents
Ammonium hydroxide stripping of tungsten from organic solventsInfo
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- CA1183005A CA1183005A CA000394071A CA394071A CA1183005A CA 1183005 A CA1183005 A CA 1183005A CA 000394071 A CA000394071 A CA 000394071A CA 394071 A CA394071 A CA 394071A CA 1183005 A CA1183005 A CA 1183005A
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- stripping
- organic phase
- tungsten
- stripping solution
- aqueous
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Abstract
AMMONIUM HYDROXIDE STRIPPING OF TUNGSTEN
FROM ORGANIC SOLVENTS
ABSTRACT OF THE DISCLOSURE
A process for stripping tungsten values from a tungsten-bearing acidic liquid organic phase into a basic aqueous ammoniacal stripping solution comprises mixing the organic phase and the stripping solution with a high-shear mixing device to maximize the pH gradient between the organic phase and the aqueous solution whereby growth of any precipitated ammonium paratungstate crystals is minimized and the dissolution thereof is maximized and to strip the tungsten values from the organic phase into the stripping solution.
FROM ORGANIC SOLVENTS
ABSTRACT OF THE DISCLOSURE
A process for stripping tungsten values from a tungsten-bearing acidic liquid organic phase into a basic aqueous ammoniacal stripping solution comprises mixing the organic phase and the stripping solution with a high-shear mixing device to maximize the pH gradient between the organic phase and the aqueous solution whereby growth of any precipitated ammonium paratungstate crystals is minimized and the dissolution thereof is maximized and to strip the tungsten values from the organic phase into the stripping solution.
Description
9~7 BACKGROU~D OF TIIE INVENTION
___ . _ ___ _ _ ~ Field of _ e Invention _ The present invention relates to the recovery of tungsten from its ores, particularly as a compound such as ammonium paratungstate (APT). In particular, the present invention relates to the treatment of an aqueous solution containing sodium tungstate (Na2WO4) and dissolved impurities to recover an aqueous solution of ammonium tungstate via extraction of tungstate values from the aqueous sodium tungstate solution into an acidic organic phase, followed by stripping of the tungsten values from the organic.phase into a basic aqueous ammoniacal solution.
More particularly, the present invention relates to improve-ments in the process of stripping the tungsten-rich organic phase with the ammoniacal aqueous solution.
Tungsten is frequently recovered from its ore by a series of steps including alkali digestion of the ore to recover an aqueous solution of sodium tungstate. Following removal of im~urities such as silica and molybdenum from this aqueous solution, it is passed through solvent extrac-tion and stripping steps to produce an aqueous solution of ammonium tun~state that should be essentially free from sodium ions and should contain only minor arnounts of sulphate ion. In the extraction step, the sodium tungstate solution is mixed under acidic conditions in several stages with a water-immiscible organic phase comprising, for instance, .an alkylamine diluted in kerosene, ari(l suLIstantial
___ . _ ___ _ _ ~ Field of _ e Invention _ The present invention relates to the recovery of tungsten from its ores, particularly as a compound such as ammonium paratungstate (APT). In particular, the present invention relates to the treatment of an aqueous solution containing sodium tungstate (Na2WO4) and dissolved impurities to recover an aqueous solution of ammonium tungstate via extraction of tungstate values from the aqueous sodium tungstate solution into an acidic organic phase, followed by stripping of the tungsten values from the organic.phase into a basic aqueous ammoniacal solution.
More particularly, the present invention relates to improve-ments in the process of stripping the tungsten-rich organic phase with the ammoniacal aqueous solution.
Tungsten is frequently recovered from its ore by a series of steps including alkali digestion of the ore to recover an aqueous solution of sodium tungstate. Following removal of im~urities such as silica and molybdenum from this aqueous solution, it is passed through solvent extrac-tion and stripping steps to produce an aqueous solution of ammonium tun~state that should be essentially free from sodium ions and should contain only minor arnounts of sulphate ion. In the extraction step, the sodium tungstate solution is mixed under acidic conditions in several stages with a water-immiscible organic phase comprising, for instance, .an alkylamine diluted in kerosene, ari(l suLIstantial
- 2 -957amounts of tungsten values pass into the organic phase.
The aqueous-organic mixture is then allowed to separate into two discrete phases. The mixing and separating operations of the extraction step can be performed in mixer-settler units of conventional design. rhe tunasten-enriched organic phase is typically washed, and then conveyed to the stripping step.
The stripping step comprises one or more stages each comprisin3 a stripping unit and a phase separation unit such as a settler. In the stripping unit, the tungsten- ~
bearing organic phase is mixed with an aqueous stripping ~ ^~-solution of ammonia which also contains some ammonium tungstate in solution. Tungsten values are stripped from the organic phase into the aqueous ammoniacal stripping solution, forming a mixture of the tungsten-depleted organic phase and a tungstate-enriched aqueous solution.
The mixture is then separated, for instance by allowing the aqueous solution to settle from the organic phase in the settler. The stripped organic phase can be washed and recycled to the extraction step, and the tungstate-rich aqueous solution is processed for the recovery of, e~g., solid ammonium paratungstate ((NH4)10W1241) (APT) crystals-In practice, however, the conditions under which conventional stripping techniques have been carried out previously have favored the formation in the stripping unit of sol;d reaction products, particularly APT, which inter-fere with the normal operation of the set-tler. It is desirable that tne a4ueous and organic pha~es form two g57 sharply divided layers in the settling stage as quickly as possible to maximize efficient recovery of tungsten while minimizing contamination of the product but solid reaction j products that are formed in the stripping unit and are carried into the settler interfere with the separation that ; I must be attained between the organic and aqueous phases.
Since solids that are carried into the settler generally do j not redissolYe there the solids must be dealt with before reaching the settler~ Physlcally removing the solids necessitates additional process time and equipment~ and to the extent that the removed material contains tungsten its removal represents a decrease in the amount of tungsten - which would ptherwise report to subsequent recovery stages.
Thus the formation of APT or other solid reaction products in the stripping unit should be minimized.
Past efforts directed toward minimizing the forma-tion of APT in the stripping unit have met with less than complete success 9 while imposing restrictive and expensive requirements as to equipment size and as to operating conditions and controls. Thus there is a need for a process for stripping a high percentage of tungsten values from the organic phase into the aqueous ammoniacal solution quickly while minimizing the Formation of solid APT.
: .
Description of the Prior Art __ _ _ __ _ Previous techniques for stripping tungsten have dealt with the formation of solids in the stripping unit by increasing the size and~or nu;-ber of mixing compartments g~
g57 so as to provide enough residence time for the solids to redissolve before the liquid passes to the settler. This approach increases overall prvcess time, and ra;ses costs, for a given amount of production.
Also, the prior art has Favored operating the stripping unit with relatively dilute concentrations of ammonium tungstate so as to lessen the proximity to saturation of the aqueous phase with respect to tungsten, and thus minimize formation of APT solids in the stripping unit.
These techniques require the operator to sacriflce rate of produc~ion as well as flexibility of operating condi~ions, and they require wasteful commitment of equipment capacity.
In particular, the load on the APT crystallizer is increased due to the ielatively low l~03 concentrat;on of the ammoniacal liquor fed to the crystallizer and the larger quantity of water that must be evaporated.
South African published patent applicatisn Serial No~ 68~4892 shows the inevitability with which the prior art has viewed both the formation of undesired solids in the stripping column and the need for sizing the equipment so as to allo~ the undesired solids to redissolve in the stripping column. The applicant teaches stripping tungstate from an or~anic-amine phase by feeding the organic phase into the side of a column agitated by a marine-type propeller lying in a hori~ontal plane just above the top of the sid~
inlet. The applicant states that upon initial contact of the loaded organic phase wit~ the stripping solution in accordance with the disclosed ~ethod there occurs some precipitation of a "white, tungsten-containing compound"
... . .
which redissolves before reaching the sektler stage "pro-v;d;ng the column is of sufficient length". It ;s subm;tted that this teaching suggests 7 ncreasing the size and, therefore~
the residence time of the stripping unit in order to keep APT solids from passing into the settler.
According to the aforementloned published South Afri~m application, an aqueous ammcnium tungstate strip liquor containing 350 to 370 gpl of W03 is formed by contacting ~le organic phase with a stripp mg solution having a pH of 10 to 11 and containing 23 to ].25 gpl W03. The preferred W03 concentration in the stripping solution is 100 gpl or less, such as 20 to 40 or 50 gpl; it - ~
is believed that ~he lower W03 concentrations are preferred in order to reduce the formation of solid APT in the stripping unit.
U.5. Patent No. 4,092,400 describes stripping an organic phase containing 100 to 150 gpl of W03 with an aqueous solution containing about 1.3 wt.-~ ammonia. Solid APT forms on contact between the organic and aqueous phases, and a retention tim~ of at least 10 minutes is required to assure that the APT solids that form are redissolved.
The prior art thus has not recognized the particular combination of conditions under which a tungsten-laden acidic organic s,tream can be stripped of ~ungsten values in a short residence' time without passage of undesired solids to the settling unit.
SUMMARY OF THE IN~ENTION
Generally speaking, the present in~e~,tiGn cor~-~rises a Drocess for stri,ping tun~sten ~alues fro~ a I ~
-D-tungsten-bearing acidic liquid organic phase into a basic aqueous ammoniacdl stripping solution comprising mixing the organic phase and the stripping solution with a high-shear mixing device to maximize the pH gradient between the organic phase and the aqueous solution whereby growth of any precipitated ammonium paratungstate crystals is minimized and dissolution thereof is maximized and to strip the tungsten values from the organic phase into the stripping solution.
The invention can be carried out in a stripping unit by feeding an aqueous ammoniacal stripping solution to the stripping unit, establishing a zone of high shear comprising an intimate mixture of the organic and aqueous phases is established with the high-shear mixing device, and, feeding the acidic liquid organic phase to the zone of high shear, wherein high-shear mixing is imparted to the organic phase which is effective to strip tungsten values from the organic phase into the aqueous ammoniacal stripping solution.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic flowsheet of the stripping step.
Figure 2 is a cutaway view of a stripping unit in which the invention is practiced.
DETAILED DESCRIPTION OF THE IN~ENTION
_ __ _ _ _ The present invention relates in particular to the conditions under which the organic and aqueous phases are con-tacted with each other in a stripping unit such that tungsten values are stripped from the organic phase into the aqueous phase in a short residence time without the cArryoYer of unw~nted solid reaction products into the settling unit. By "solid reaction products"
is meant solid APT and solid silica-based compounds that cQn form in the stripping unit during mixing of the acidic organic tungsten-laden stream with the basic aqueous ammoniacal strippir~ solution.
With reference to Figure 19 stream 1 comprises a tungsten-bearing acidic liquid organic phase such as is produced by solvenl~
extraction of an ~queous tungstate leach liquor, and stream 2 com-prises an aqueous ammoniaeal stripping solution. Streams 1 and 2 are fed se?arately to stripping unit 3, which can comprise the mixer section of a mixer-settler unit 4.
- Strea~ 1 can oomprise a tungsten-bearing or~anic phase produced by the extractlon process described in Canadian Patent Application, Serial Niunber 393,845 filed January 8, 1982, entitled "Solvent Extraction of Tungsten from Aqueous Tungstate Solutions", and assigned to the assignee of the present application.
The organic and aqueous phases are mixed in stripping unit 3, ~nd the mixture of liquids is then conveyed to settler unit 5 from which stream 6, comprising the aqueolls stripping solution now enriched in tungstate (the l'strip ~~ liquor"), and stre~m 79 comprising the organic phase now depleted of tungsten values, are recovered. An aqueous recycle stream 8 is drawn off of stream 6 and recycled to stripping unit 3. The remaining portion of the strip liquor is conveyed to crys~allizers in which water is evapo~ated from the strip liquor and APT is recovered. Organic stream 7 is washed at washing stage 9 with deionized water 10 to remove entrained ammonia and tungsten. The washed organic stream 11 is recycled to the solvent extraction step, and a stream 12 of wash water containirlg small amounts of NH3 and tungs~ate is recycled to stripping unit 3.
Stream 1 can comprise a tungsten-loaded organic stream produced by solvent extraction of an aqueous solution of, for instance, sodium tungstate, advantageously followed by a water wash stagP to remove entrained aqueous liquid from the organic stream. Stream 1 typically comprises an organic diluent, such as kerosene or a mixture of linear aliphatic hydrocarbons 10 to 13 carbon atoms in length, in which is dissolved about 2 to about ~0 vol. % of an alkylamine ex-tractant such as ditridecyl amine, and optionally about 2 to about 25 vol. ~ of an alkanol conditioning agent such as isodecyl alcohol. The alkylamine extractant is loaded with about 1 to about 200 gpl of WO3, and can also contain traces of anionic silica impurity that has been loaded along with the tungsten. Advantageously, the WO3 concentration is about 10 to about 140 gpl, and more advantageously about 25 to about 100 gpl, to provide an increased rate of pro-duction of the final tungstate product ~e.~. APT).
Stream 2 comprises an aqueous ammo~iacal stripping solution containing free ammonia, supplied as fresh NH40H in stream 1~. While the ~ree ammonia concentration can be _ 9 _ between about 2 to about 80 gpl, it is advantageously about 10 to about 60 gpl and more advantageously about 15 to about 30 gpl to provide efficient stripping oE tungsten frcm the organic phase. The pH of stream 2 is about 9.0 to about 11.5, and advantageously about 9.5 to about 11.0 to optimize stripping of tungsten values from the organic phase.
It is advantageous that the aqueous stream 2 contain dissolved ammonium tunystate as well as free ammonia~ to permit recovery of a tungstate-laden strip liquor containing a high conc~ntration of tungstate. Again referring to Figure 1, stream 6, containing the aqueous strip liquor, is conveyed from the settling unit to the crystallizers in which water and ammonia are volatilized, and APT is formed;
higher concentrations of tungstate in the strip liquor advantageously require less time and energy to drive off water and ammonia in the APT crystallizers. Thus, to provide a high concentration of tungstate in the strip liquor~
recycle stream 8 comprising ammonium tungstate in solution is drawn off of stream 6 and fed to stripping unit 3 to-gether with fresh ammoniacal feed (e.g. NH40H) and recycled water from washing stage 9. Thus, stream 2 also contains about 25 to about 200 gpl WO3, and advantageously about 100 to about 175 gpl WO3 to optimize recovery of a satisfactory concentration of WO3 in the strip liquor. It is a surprising and advantageous feature of the present invention that a stripping unit can be operated with so high a WO3 concen-tration and a short residence time without passage of solid reaction products out of the stripping unit.
The concentration of tungstate in the strip li~uor (stream 6) is typically about 50 to about 300 gpl W03;
advantageously it is about 100 to about 275 gpl ~l03, and more advantageously about 150 to about 250 gpl W03, to permit more economical operation in the crystallizer.
With reference to Figure 2, the invention w;ll be described as it can be carried out in stripping unit 3.
Organic stream l and aqueous stream 2 are separately fed ~o s~ripping uni~ 3 where they are mixed~ The mixture flows upward and through outlet 14 into settler 5. The ratio of the volume feed rates of the organic and aqueous streams tO/A) is about 0.5 to about 3.0, and advantageously about 0.8 to about 1.2 to optimize strlpping of tungsten in the stripping unit. Advantageously, the -flow rates of streams 1 and 2 are selected with respect to the volume of stripping unit 3 to provide a residence time of less than about 10 minutes, and more advantageously less than about 6 minutes.
The liquid in stripping unit 3 is under agitation by an impeller 15 which is being rota~ed via shaft 16 by externally mounted motor 17.~ Any of several ~ypes of impeller can be used. Yery satisfactory results have been obtained with a "turbine-type" impeller, hàving a plurality of blades mounted around the axis of rotation. The impeller can be-provided with a shroud to increase pumping action.
Impel1er 15 is rotated so a~ to~impart high-shear to a zone 18 around the blades of the impeller. Organic stream 1 is fed into zone 18, and hlgh~shear mixing is
The aqueous-organic mixture is then allowed to separate into two discrete phases. The mixing and separating operations of the extraction step can be performed in mixer-settler units of conventional design. rhe tunasten-enriched organic phase is typically washed, and then conveyed to the stripping step.
The stripping step comprises one or more stages each comprisin3 a stripping unit and a phase separation unit such as a settler. In the stripping unit, the tungsten- ~
bearing organic phase is mixed with an aqueous stripping ~ ^~-solution of ammonia which also contains some ammonium tungstate in solution. Tungsten values are stripped from the organic phase into the aqueous ammoniacal stripping solution, forming a mixture of the tungsten-depleted organic phase and a tungstate-enriched aqueous solution.
The mixture is then separated, for instance by allowing the aqueous solution to settle from the organic phase in the settler. The stripped organic phase can be washed and recycled to the extraction step, and the tungstate-rich aqueous solution is processed for the recovery of, e~g., solid ammonium paratungstate ((NH4)10W1241) (APT) crystals-In practice, however, the conditions under which conventional stripping techniques have been carried out previously have favored the formation in the stripping unit of sol;d reaction products, particularly APT, which inter-fere with the normal operation of the set-tler. It is desirable that tne a4ueous and organic pha~es form two g57 sharply divided layers in the settling stage as quickly as possible to maximize efficient recovery of tungsten while minimizing contamination of the product but solid reaction j products that are formed in the stripping unit and are carried into the settler interfere with the separation that ; I must be attained between the organic and aqueous phases.
Since solids that are carried into the settler generally do j not redissolYe there the solids must be dealt with before reaching the settler~ Physlcally removing the solids necessitates additional process time and equipment~ and to the extent that the removed material contains tungsten its removal represents a decrease in the amount of tungsten - which would ptherwise report to subsequent recovery stages.
Thus the formation of APT or other solid reaction products in the stripping unit should be minimized.
Past efforts directed toward minimizing the forma-tion of APT in the stripping unit have met with less than complete success 9 while imposing restrictive and expensive requirements as to equipment size and as to operating conditions and controls. Thus there is a need for a process for stripping a high percentage of tungsten values from the organic phase into the aqueous ammoniacal solution quickly while minimizing the Formation of solid APT.
: .
Description of the Prior Art __ _ _ __ _ Previous techniques for stripping tungsten have dealt with the formation of solids in the stripping unit by increasing the size and~or nu;-ber of mixing compartments g~
g57 so as to provide enough residence time for the solids to redissolve before the liquid passes to the settler. This approach increases overall prvcess time, and ra;ses costs, for a given amount of production.
Also, the prior art has Favored operating the stripping unit with relatively dilute concentrations of ammonium tungstate so as to lessen the proximity to saturation of the aqueous phase with respect to tungsten, and thus minimize formation of APT solids in the stripping unit.
These techniques require the operator to sacriflce rate of produc~ion as well as flexibility of operating condi~ions, and they require wasteful commitment of equipment capacity.
In particular, the load on the APT crystallizer is increased due to the ielatively low l~03 concentrat;on of the ammoniacal liquor fed to the crystallizer and the larger quantity of water that must be evaporated.
South African published patent applicatisn Serial No~ 68~4892 shows the inevitability with which the prior art has viewed both the formation of undesired solids in the stripping column and the need for sizing the equipment so as to allo~ the undesired solids to redissolve in the stripping column. The applicant teaches stripping tungstate from an or~anic-amine phase by feeding the organic phase into the side of a column agitated by a marine-type propeller lying in a hori~ontal plane just above the top of the sid~
inlet. The applicant states that upon initial contact of the loaded organic phase wit~ the stripping solution in accordance with the disclosed ~ethod there occurs some precipitation of a "white, tungsten-containing compound"
... . .
which redissolves before reaching the sektler stage "pro-v;d;ng the column is of sufficient length". It ;s subm;tted that this teaching suggests 7 ncreasing the size and, therefore~
the residence time of the stripping unit in order to keep APT solids from passing into the settler.
According to the aforementloned published South Afri~m application, an aqueous ammcnium tungstate strip liquor containing 350 to 370 gpl of W03 is formed by contacting ~le organic phase with a stripp mg solution having a pH of 10 to 11 and containing 23 to ].25 gpl W03. The preferred W03 concentration in the stripping solution is 100 gpl or less, such as 20 to 40 or 50 gpl; it - ~
is believed that ~he lower W03 concentrations are preferred in order to reduce the formation of solid APT in the stripping unit.
U.5. Patent No. 4,092,400 describes stripping an organic phase containing 100 to 150 gpl of W03 with an aqueous solution containing about 1.3 wt.-~ ammonia. Solid APT forms on contact between the organic and aqueous phases, and a retention tim~ of at least 10 minutes is required to assure that the APT solids that form are redissolved.
The prior art thus has not recognized the particular combination of conditions under which a tungsten-laden acidic organic s,tream can be stripped of ~ungsten values in a short residence' time without passage of undesired solids to the settling unit.
SUMMARY OF THE IN~ENTION
Generally speaking, the present in~e~,tiGn cor~-~rises a Drocess for stri,ping tun~sten ~alues fro~ a I ~
-D-tungsten-bearing acidic liquid organic phase into a basic aqueous ammoniacdl stripping solution comprising mixing the organic phase and the stripping solution with a high-shear mixing device to maximize the pH gradient between the organic phase and the aqueous solution whereby growth of any precipitated ammonium paratungstate crystals is minimized and dissolution thereof is maximized and to strip the tungsten values from the organic phase into the stripping solution.
The invention can be carried out in a stripping unit by feeding an aqueous ammoniacal stripping solution to the stripping unit, establishing a zone of high shear comprising an intimate mixture of the organic and aqueous phases is established with the high-shear mixing device, and, feeding the acidic liquid organic phase to the zone of high shear, wherein high-shear mixing is imparted to the organic phase which is effective to strip tungsten values from the organic phase into the aqueous ammoniacal stripping solution.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic flowsheet of the stripping step.
Figure 2 is a cutaway view of a stripping unit in which the invention is practiced.
DETAILED DESCRIPTION OF THE IN~ENTION
_ __ _ _ _ The present invention relates in particular to the conditions under which the organic and aqueous phases are con-tacted with each other in a stripping unit such that tungsten values are stripped from the organic phase into the aqueous phase in a short residence time without the cArryoYer of unw~nted solid reaction products into the settling unit. By "solid reaction products"
is meant solid APT and solid silica-based compounds that cQn form in the stripping unit during mixing of the acidic organic tungsten-laden stream with the basic aqueous ammoniacal strippir~ solution.
With reference to Figure 19 stream 1 comprises a tungsten-bearing acidic liquid organic phase such as is produced by solvenl~
extraction of an ~queous tungstate leach liquor, and stream 2 com-prises an aqueous ammoniaeal stripping solution. Streams 1 and 2 are fed se?arately to stripping unit 3, which can comprise the mixer section of a mixer-settler unit 4.
- Strea~ 1 can oomprise a tungsten-bearing or~anic phase produced by the extractlon process described in Canadian Patent Application, Serial Niunber 393,845 filed January 8, 1982, entitled "Solvent Extraction of Tungsten from Aqueous Tungstate Solutions", and assigned to the assignee of the present application.
The organic and aqueous phases are mixed in stripping unit 3, ~nd the mixture of liquids is then conveyed to settler unit 5 from which stream 6, comprising the aqueolls stripping solution now enriched in tungstate (the l'strip ~~ liquor"), and stre~m 79 comprising the organic phase now depleted of tungsten values, are recovered. An aqueous recycle stream 8 is drawn off of stream 6 and recycled to stripping unit 3. The remaining portion of the strip liquor is conveyed to crys~allizers in which water is evapo~ated from the strip liquor and APT is recovered. Organic stream 7 is washed at washing stage 9 with deionized water 10 to remove entrained ammonia and tungsten. The washed organic stream 11 is recycled to the solvent extraction step, and a stream 12 of wash water containirlg small amounts of NH3 and tungs~ate is recycled to stripping unit 3.
Stream 1 can comprise a tungsten-loaded organic stream produced by solvent extraction of an aqueous solution of, for instance, sodium tungstate, advantageously followed by a water wash stagP to remove entrained aqueous liquid from the organic stream. Stream 1 typically comprises an organic diluent, such as kerosene or a mixture of linear aliphatic hydrocarbons 10 to 13 carbon atoms in length, in which is dissolved about 2 to about ~0 vol. % of an alkylamine ex-tractant such as ditridecyl amine, and optionally about 2 to about 25 vol. ~ of an alkanol conditioning agent such as isodecyl alcohol. The alkylamine extractant is loaded with about 1 to about 200 gpl of WO3, and can also contain traces of anionic silica impurity that has been loaded along with the tungsten. Advantageously, the WO3 concentration is about 10 to about 140 gpl, and more advantageously about 25 to about 100 gpl, to provide an increased rate of pro-duction of the final tungstate product ~e.~. APT).
Stream 2 comprises an aqueous ammo~iacal stripping solution containing free ammonia, supplied as fresh NH40H in stream 1~. While the ~ree ammonia concentration can be _ 9 _ between about 2 to about 80 gpl, it is advantageously about 10 to about 60 gpl and more advantageously about 15 to about 30 gpl to provide efficient stripping oE tungsten frcm the organic phase. The pH of stream 2 is about 9.0 to about 11.5, and advantageously about 9.5 to about 11.0 to optimize stripping of tungsten values from the organic phase.
It is advantageous that the aqueous stream 2 contain dissolved ammonium tunystate as well as free ammonia~ to permit recovery of a tungstate-laden strip liquor containing a high conc~ntration of tungstate. Again referring to Figure 1, stream 6, containing the aqueous strip liquor, is conveyed from the settling unit to the crystallizers in which water and ammonia are volatilized, and APT is formed;
higher concentrations of tungstate in the strip liquor advantageously require less time and energy to drive off water and ammonia in the APT crystallizers. Thus, to provide a high concentration of tungstate in the strip liquor~
recycle stream 8 comprising ammonium tungstate in solution is drawn off of stream 6 and fed to stripping unit 3 to-gether with fresh ammoniacal feed (e.g. NH40H) and recycled water from washing stage 9. Thus, stream 2 also contains about 25 to about 200 gpl WO3, and advantageously about 100 to about 175 gpl WO3 to optimize recovery of a satisfactory concentration of WO3 in the strip liquor. It is a surprising and advantageous feature of the present invention that a stripping unit can be operated with so high a WO3 concen-tration and a short residence time without passage of solid reaction products out of the stripping unit.
The concentration of tungstate in the strip li~uor (stream 6) is typically about 50 to about 300 gpl W03;
advantageously it is about 100 to about 275 gpl ~l03, and more advantageously about 150 to about 250 gpl W03, to permit more economical operation in the crystallizer.
With reference to Figure 2, the invention w;ll be described as it can be carried out in stripping unit 3.
Organic stream l and aqueous stream 2 are separately fed ~o s~ripping uni~ 3 where they are mixed~ The mixture flows upward and through outlet 14 into settler 5. The ratio of the volume feed rates of the organic and aqueous streams tO/A) is about 0.5 to about 3.0, and advantageously about 0.8 to about 1.2 to optimize strlpping of tungsten in the stripping unit. Advantageously, the -flow rates of streams 1 and 2 are selected with respect to the volume of stripping unit 3 to provide a residence time of less than about 10 minutes, and more advantageously less than about 6 minutes.
The liquid in stripping unit 3 is under agitation by an impeller 15 which is being rota~ed via shaft 16 by externally mounted motor 17.~ Any of several ~ypes of impeller can be used. Yery satisfactory results have been obtained with a "turbine-type" impeller, hàving a plurality of blades mounted around the axis of rotation. The impeller can be-provided with a shroud to increase pumping action.
Impel1er 15 is rotated so a~ to~impart high-shear to a zone 18 around the blades of the impeller. Organic stream 1 is fed into zone 18, and hlgh~shear mixing is
3~9~3 imparted to the liquid in zone 1~ which is effective to strlp tungsten from the organic phase into-the aqueous phase and effective to permit recovery from the strippin~ unit 3 of the tllngstell-depleted organic phase and the tungsten-enriched aqueous solution as a liquid mlxture which is free of solid reaction products. Such high-shear mixing maximizes the pH grddient between the organic phase and the aqueous solution whereby growth of any precipitated ammonium paratungstate crystals is minimized and the dissolution thereof is maximized. Upon initial contact be~een the organic pha~e and ~he aqueous solution, the aqueous solution is momentarily depleted of ammonia by the stripping reaction and any precipitated ammonium paratungstate crystals can grow to sizes which are not readily redissolved. Effective high-shear mixing instantaneous-ly re-establishes the initial high pH gradient between the organic phase and the aqueous solution therehy minimizing the growth of any precipitated ammonium paratungstate crystals. The effectiver,ess of the high-shear mixing can be ascertained by ohserving the initial contact between the phases. The region of initial contact should either remain clear (i.e., no precipitation of ammonium paratun~state) or become te~porarily clouded follo~ed by rapid clearing (i.e., precipitation of finely divided ammonium paratungstate follo~ed by rapid redissoluti(,n)~ The high-shear mixing should not be so high, ho~ever, as to form an emulsion of the aqueous and organic phases;
in such an event, phase separation ~ould be very slow. The mixture is passed to settler 5, in which the organic and aqueous phases readily separate from each other with a desirable clear, well-defined interface. Tungsten is substantially completely str1pped from the organ;c phase into the aqueous phase in th`e stripping unit; typically, at least about 90~ and advantageously at least about 99% of the tungsten is stripped.
The organic s~ream is fed to th;e stripping unit at a polnk near the blades of the impeller 15. where a zone of h~gh shear can readily be established. Advantageously, to maximize contact hetween the organic phase and the aqueGus ammohiacal stripping solution for more efficient stripping, the stripping solution is separately fed to the zone of high shear. One skilled ln this art will recognize that the location of the zone of high shear can be readily ascertained, and that the location of this zone is relatively static in a unit operating at s~eady state. Thus, a stripping uni~ can be designed by reference to the foregoing descriptlon and the following Examples.
Operating conditions shoilld be established so that the aqueous phase is the continuous phase ln the strlpping unit.
Residence ti~es in the stripping uni~ of less than about 10 minutes, and more advantageously less than about 6 minutes, are preferred so as to increase the rate of production of tungsten-bearing strip liquor, and are feasible by stripping in accordance with this invention. As is well known, the residence t;me is a function of the stripping unit volume and the total flow rate of liquid (organic phase and ~queous stripping solution) into the stripping unit.
The relatively short retention time in the stripping unit minimizes the opportunity for silica to precipitate within the stripping unit and the mixer-~ettlers. If sillca concentration is relatively high in ~he feed ~o the solvent extraction s~ep, significant quantities of silica can enter ~he stripplng operation. In conventional practlce, sllica then precipltates not only after the stripping operatlon, but during stripping, necessitating periodic equipment cleaning and special holding and digestion tanks for precipltation and re~val o f preclpitated sllicaO~ ~
Whlle the apparatus shown in Figure 2 depicts one stripping unit feeding directly to the settler, the present invention is also applicable to the treatment of a tungsten-bearing organic stream with a plurality or stripping units. For example, twostripping units may be operated in series; in such a case the aqueous-organic mixture formed by operation of the first stripping unit in accordance with the present invention con~
stitutes the feed to the second stripping unit, which in turn further agitates the mixture sufficierltly fast to avoid the formation of solid reaction products, and discharges the mixture to the settling unit.
The invention will be further illustrated with reference to the following non-limiting Examples:
EXAMPL_ 1 A organic stream composed of 7~ ditridecyl amine, 12%
isodecanol, ànd 81~ kerosene (by volume), and containing 6801 gpl of tungsten (as WO3~, and an aqueous stream which con-tained 148 gpl WO3 and sufficient free NH3 to establish a pH
of 10.5, were fed separately but simultaneously to a strip-ping unit at an average O/A ratio of 1 to 1.1. The residence time in the stripping unit was 6 minutes. The organic stream was fed into the stripping unit adjacent the outside edges of a 1-3/4 inch diameter shrouded radial turbine impeller which was rotating at about 1400 rotations per minuten The aqueous stream was fed into the bottom of the unit n The unit was operating at a temperature of 40 to 45C. The organic-aqueous mixture leaving the stripping unit contained no solid reaction products. Doubling the total flow rate of the aqueous and organic phases to the unit, e~., decreasing the retention time to 3 minutes, also generated a discharged organic-clqueous mixture containing no solids. Tungsten transfer from the organic to the aqueous phase was essentially complete.
- ~4 -An organic stream composed of 7~ ditridecyl amine, 12%
isod~canol, and 81~ kerosene (vol.%), and containing 67.8 gpl of tungsten (as WO3), and an aqueous s~ream which con-tained 130 gpl WO3 and sufficient free N~3 to establish a pH of 10.5, were fed separately through the bottom of the stripping unit, at an average O/A ratio oE 1 to 1.1. The residPnce time in the stripping unit was 12 minutes. The organic and aqueous streams were fed into the stripping ~ unit underneath the outside edges of a 1~3/4 inch diameter I shrouded radial turbine impeller, which was rotating at about 1400 rotations per minute. The aqueous stream was also fed into the stripping unit underneath the outside edges of the impeller. Because of the physical arrangement of the inlet streams, back-mixing of the two phases occurred in a region of low shear. Copious quantities of white AP~
solids were precipitated, and were carried out into the ; settler compartment. These solids did not redissolve after standing overnight. The problem of solids formation was corrected by relocating the organic inlet such -that the organic phase was injected directly into the high~shear zone of the impeller, such that back-mixing was avoided.
The aqueous stream was also fed into the stripping unit underneath the impeller.
,~
:
.. ~f,.
in such an event, phase separation ~ould be very slow. The mixture is passed to settler 5, in which the organic and aqueous phases readily separate from each other with a desirable clear, well-defined interface. Tungsten is substantially completely str1pped from the organ;c phase into the aqueous phase in th`e stripping unit; typically, at least about 90~ and advantageously at least about 99% of the tungsten is stripped.
The organic s~ream is fed to th;e stripping unit at a polnk near the blades of the impeller 15. where a zone of h~gh shear can readily be established. Advantageously, to maximize contact hetween the organic phase and the aqueGus ammohiacal stripping solution for more efficient stripping, the stripping solution is separately fed to the zone of high shear. One skilled ln this art will recognize that the location of the zone of high shear can be readily ascertained, and that the location of this zone is relatively static in a unit operating at s~eady state. Thus, a stripping uni~ can be designed by reference to the foregoing descriptlon and the following Examples.
Operating conditions shoilld be established so that the aqueous phase is the continuous phase ln the strlpping unit.
Residence ti~es in the stripping uni~ of less than about 10 minutes, and more advantageously less than about 6 minutes, are preferred so as to increase the rate of production of tungsten-bearing strip liquor, and are feasible by stripping in accordance with this invention. As is well known, the residence t;me is a function of the stripping unit volume and the total flow rate of liquid (organic phase and ~queous stripping solution) into the stripping unit.
The relatively short retention time in the stripping unit minimizes the opportunity for silica to precipitate within the stripping unit and the mixer-~ettlers. If sillca concentration is relatively high in ~he feed ~o the solvent extraction s~ep, significant quantities of silica can enter ~he stripplng operation. In conventional practlce, sllica then precipltates not only after the stripping operatlon, but during stripping, necessitating periodic equipment cleaning and special holding and digestion tanks for precipltation and re~val o f preclpitated sllicaO~ ~
Whlle the apparatus shown in Figure 2 depicts one stripping unit feeding directly to the settler, the present invention is also applicable to the treatment of a tungsten-bearing organic stream with a plurality or stripping units. For example, twostripping units may be operated in series; in such a case the aqueous-organic mixture formed by operation of the first stripping unit in accordance with the present invention con~
stitutes the feed to the second stripping unit, which in turn further agitates the mixture sufficierltly fast to avoid the formation of solid reaction products, and discharges the mixture to the settling unit.
The invention will be further illustrated with reference to the following non-limiting Examples:
EXAMPL_ 1 A organic stream composed of 7~ ditridecyl amine, 12%
isodecanol, ànd 81~ kerosene (by volume), and containing 6801 gpl of tungsten (as WO3~, and an aqueous stream which con-tained 148 gpl WO3 and sufficient free NH3 to establish a pH
of 10.5, were fed separately but simultaneously to a strip-ping unit at an average O/A ratio of 1 to 1.1. The residence time in the stripping unit was 6 minutes. The organic stream was fed into the stripping unit adjacent the outside edges of a 1-3/4 inch diameter shrouded radial turbine impeller which was rotating at about 1400 rotations per minuten The aqueous stream was fed into the bottom of the unit n The unit was operating at a temperature of 40 to 45C. The organic-aqueous mixture leaving the stripping unit contained no solid reaction products. Doubling the total flow rate of the aqueous and organic phases to the unit, e~., decreasing the retention time to 3 minutes, also generated a discharged organic-clqueous mixture containing no solids. Tungsten transfer from the organic to the aqueous phase was essentially complete.
- ~4 -An organic stream composed of 7~ ditridecyl amine, 12%
isod~canol, and 81~ kerosene (vol.%), and containing 67.8 gpl of tungsten (as WO3), and an aqueous s~ream which con-tained 130 gpl WO3 and sufficient free N~3 to establish a pH of 10.5, were fed separately through the bottom of the stripping unit, at an average O/A ratio oE 1 to 1.1. The residPnce time in the stripping unit was 12 minutes. The organic and aqueous streams were fed into the stripping ~ unit underneath the outside edges of a 1~3/4 inch diameter I shrouded radial turbine impeller, which was rotating at about 1400 rotations per minute. The aqueous stream was also fed into the stripping unit underneath the outside edges of the impeller. Because of the physical arrangement of the inlet streams, back-mixing of the two phases occurred in a region of low shear. Copious quantities of white AP~
solids were precipitated, and were carried out into the ; settler compartment. These solids did not redissolve after standing overnight. The problem of solids formation was corrected by relocating the organic inlet such -that the organic phase was injected directly into the high~shear zone of the impeller, such that back-mixing was avoided.
The aqueous stream was also fed into the stripping unit underneath the impeller.
,~
:
.. ~f,.
Claims (7)
1. A process for stripping tungsten values from a tungsten-bearing acidic liquid organic phase into a basic aqueous ammoniacal stripping solution and thereby enriching the stripping solution in tungstate, comprising (a) feeding the organic phase and the stripping solution to a stripping unit, (b) mixing the organic phase and the stripping solution with a high-shear mixing device to establish a zone of high shear in the organic-aqueous mixture that is effective to strip the tungsten values from the organic phase into the stripping solution and to maximize the pH gradient between the organic phase and the aqueous solution, said zone comprising an intimate mixture of the acidic liquid organic phase and the aqueous ammoniacal stripping solution, wherein no ammonium paratungstate precipitates, and (c) wherein the acidic liquid organic phase is fed to said zone of high shear.
2. The process of claim 1 wherein the aqueous ammoniacal stripping solution is also fed into said zone of high shear.
3. The process of claim 1 wherein the acidic liquid organic phase contains about 1 to about 200 gpl of tungsten as WO3, the aqueous ammoniacal stripping solution contains about 25 to about 200 gpl of tungstate as WO3 and has a pH of about 9 to about 11.5, and wherein the aqueous ammoniacal stripping solution enriched in tungstate contains about 50 to about 300 gpl of tungstate as WO3.
4. The process of claim 1 wherein the acidic liquid organic phase fed to the stripping unit contains about 25 to about 100 gpl of tungsten as WO3, the aqueous ammoniacal stripping solution fed to the stripping unit contains about 100 to about 175 gpl of tungstate as WO3, and has a pH of about 9 to about 11.5, wherein the aqueous ammoniacal stripping solution enriched in tungstate contains about 150 to about 250 gpl of tungstate as WO3.
5. The process of any of claims 1/3 or 4 wherein the residence time in the stripping unit is less than about 10 minutes.
6. The process of any of claims 1,3 or 4 wherein the residence time in the stripping unit is less than about 6 minutes.
7. A process according to claim 1 for stripping tungsten values from a tungsten-bearing acidic liquid organic phase into a basic aqueous ammoniacal stripping solution and thereby enriching the stripping solution in tungstate, comprising mixing the organic phase and and the stripping solution so as to establish in the organic-aqueous mixture a zone of shear equivalent to the shear that would be imparted to the mixture adjacent the outside edges of a 1-3/4 inch-diameter radial shrouded turbine impeller rotating in the mixture at about 1400 rotations per minute; and feeding the organic phase to the mixture into said zone of shear, wherein no ammonium paratungstate precipitates and tungsten values are stripped from the organic phase into the stripping solution.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US22590381A | 1981-01-19 | 1981-01-19 | |
| US225,903 | 1988-07-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1183005A true CA1183005A (en) | 1985-02-26 |
Family
ID=22846747
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000394071A Expired CA1183005A (en) | 1981-01-19 | 1982-01-13 | Ammonium hydroxide stripping of tungsten from organic solvents |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1183005A (en) |
-
1982
- 1982-01-13 CA CA000394071A patent/CA1183005A/en not_active Expired
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