CA1061574A - Solvent extraction recovery of metals using quinoline derivative - Google Patents

Abstract

SOLVENT EXTRACTION RECOVERY OF METALS
USING QUINOLINE DERIVATIVE

Abstract of the Disclosure A novel procedure is described for stepwise, selective extraction of metal values selected from molybdenum, copper, cobalt and zinc, using a substituted 8-hydroxyquino-line as solvent extraction reagent. By controlling the equilibrium pH and other extraction conditions, it is possible to stepwise, selectively extract molybdenum and copper from aqueous, acidic solutions containing these along with other metal values. Where cobalt and/or zinc are also present, these can also be stepwise selectively extracted using the same reagent. It was previously believed that the substituted 8-hydroxyquinolines were selective only for copper over a wide pH range.

Description

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BACKGROUND OF THE INVENTION
-1. Field of the Invention This invention relates to a soiven~ extraction process for the stepwise recovery of metal values from an aqueous acidic solution in which they are dissolved, and particularly for the stepwise selective recovery of molyb-denum, copper and other metal values from an acid leach solution.

2. Description of the Prior Art The recovery of copper and other metals by smel-ting has been practiced for many years, but late:ly with the discovery of large copper oxide deposits, as well as the restriction of air pollution imposed upon smelters, many studies are being made on the possibility of treating copper ores, residues and concentrates by hydrometallurgical methods.
Commercial plants are presently in operation in the United States for the treatment of low grade copper solu~ions resulting Erom sulfuric acid heap leaching of low grade copper ores. The copper is subsequently separated and recovered by solvent extraction and electrowinning.
Of course, copper ores appear in many other forms than copper oxides and there are, for instance, very large :~, copper deposits in the form of chalcopyrite. The copper ores contain, in addition to copper, a variety of metal values such as nickel, zinc, manganese, cobalt and iron.

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` Another source of copper and various other metal values, including molybdenum, is deep sea nodules.

It would, therefore, be highly desirable if a - hydrometallurgical method could be developed in which an ore ., .
concentrate is subjected to leaching to dissolve the metal values and these metal values are then selectively removed '7~
from the leach liquor by stage-wise extraction, using the same organic extractant.
The solvent extraction reagents previously used in copper plants have tended to suffer from low loading capacity and poor stripping characteristics. A quite recent copper extraction reagent which gives good results is a ~~alkenyl-8-hydroxyquinoline which is available from Ashland Chemicals under the trade mark KELEX lO0. This reagent is described as being capable of extracting copper over a wide range of pH, e.g. 1 - 7. However, there is no discussion of KELEX 100 in relation to stepwise recovery and separation of a series of ~- different metal values.
It is, therefore, the object of the present inven-tion to provide a novel liquid-liquid extraction procedure whereby the extractant KELEX 100 can be used for the stepwise recovery and separation of molybdenum, copper9 zinc and cobalt from each other and from other metals in a solution resulting from leaching ores or concentrates.
SUMMARY OF T~E INVENTION
: According to the present invention, it has surprisingly been found that by using KELEX 100 as extrac-tant and controlling the equilibrium pH, it is possible to stepwise, selectively extract molybdenum and copper from aqueous acidic solutions containing these along with other metal values. It has also been found that when one or more of molybdenum and copper are present in aqueous acid solutions together with one or more of cobalt and zinc, along with other metal values, it is possible to stepwise selec-tively extract any of the molybdenum, copper9 cobalt and :. .

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zinc values present by equilibrium pH adjustment.
The extractant KELEX 100 is a typical substituted 8-hydroxyquinoline extraction reagent of the formula;

C}l~=C~-CH ~ l ~ ¦
OH

wherein R is an alkyl group having from 5 to 14 carbon atoms.
It is used dissolved in an inert organic diluent.
DESCRIPTION OF THE PREF~RRED EMBODIM~NTS
According to one embodiment of the invention, the above reagent can be used to selectively separately extract molybdenum from an aqueous acidic solution contain-ing this along with dissolved copper values and other dissolved me~al values. The process comprises contacting the aqueous, acidic solution with the e~traction reagent at .~
an equilibrium pH of O to about 2, whereby molybdenum values are selectively extracted from the aqueous phase into the organic phase. The resultant molybdenum loaded organic phase - is separated from the remaining aqueous raffinate phase ~ containing the remaining metal values in solution.

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In order to achieve a high degree of purity of molybdenum in the loaded organic, it is desirable to control the extraction conditions such that saturation loading of molybdenum is obtained. In this manner no sites are avail-able on the extraction reagent to receive copper if the molybdenum in the aqueous, acidic solution is depleted.
These extraction conditions can be controlled by the aqueous to organic ratio, number of contact stages, contact time, etc. as is well known to those skilled in the art.

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T~e molybdenum values can be removed from the organic phase by stripping with an alkaline agent. If there is some co-extraction of copper with the molybdenum, these are separated during the stripping stage since the alkaline agent strips only the molybdenum values. The copper values present can be stripped using an acid stripping agent.
After the molybdenum extraction, the same extrac-tion reagent can be used for solvent extraction of copper values present in the raffinate. This extraction can be carried out over a wide pH range as is already known in the art. As mentioned above, the copper values extracted can then be stripped from the organic phase by acid stripping.
According to another embodiment of the invention, the substituted 8-hydroxyquinoline can be used to stepwise selectively extract cobalt and Yinc from aqueous acidic solutions containing these together with at least one of molybdenum and copper as well as other metal values. The cobalt values commence extracting at about pH 3 while zinc values commence extracting at about pH 4.
Thus, if the initial solution contains molybdenum, copper, cobalt and æinc along with other metal values, the - molybdenum can be extracted at pH 0 to 2 as described above.
Then the copper can be extracted in the absence of molybdenum at a pH below 3. Next the cobalt can be extracted in the :, , absence of molybdenum and copper at pH 3 to 4 and zinc can be extracted in the absence of molybdenum, copper and cobalt ` at a pH above ~. If desired, ~he same extraction reagent ?i can be recycled for each extraction.

Of course, other modifications can include the , ! separation of molybdenum for aqueous acid solutions contain-, . ~

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ing no copper, or such solution containing one or mor~ of cobalt and zinc along with other metal values. Also, in ~he absence of molybdenum, the process can be used to selectively extract copper and one or more of cobalt and zinc.
When no copper is present in the aqueous acid solution ~ogether with molybdenum, the molybdenum can be extracted over a wider pH range and may in some instances be extracted at a pH as high as 5.
It has also been found that molybdenum and copper can be selectively co-extracted, e.g. at a pH in the 2 - 4 range. The extracted molybdenum and copper values, in the absence of other metal values, can then be selectively recovered from the extraction reagent by selective stripping.
When a reagent loaded with molybdenum and copper is contacted with sulfuric acid, e.g. 150 - 200 g H2S04/1, substantially - all of the copper is removed with substantially no molyb-denum. Following copper removal, the molybdenum can be removed by stripping with sodium hydroxide solution. The molybdenum is recovered as sodium molybdate.
The aqueous acidic feed solution can be a solution resulting from acid leaching of ores or it can be obtained from various effluents, wastes, etc. from mineral and metallurgical processing plants.
Typical of the ores that can be used are copper-.
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molybdenum ores, copper-lead-zinc ores, copper-nickel ores, copper-nickel-cobalt ores, etc. Of course, the particular procedure that is carried out ultimately depends on the types of metal values present in any aqueous, acidic solution to be treated.
The procedure of this invention has the important advantages of being capable of producing high purity products with minimum pollution, minimum processing steps and minimum production costs as compared to present practice. This is made possible particularly because of the fact that the same organic reagent can be re-used for the separate extraction of each metal value.
Usually the ore being processed is first concen-trated by a suitable preconcentration technique and following preconcentration, the concentrate is leached by atmospheric or pressure leaching. The resultant leach slurry is filtered, and the filtrate, together with washings is sent to the solvent extraction circuit. The leach liquor thus obtained ... .
can be an acidic nitrate, chloride or sulfate solution and a typical such solution may contain for instance from S to . 50 g Cu/l.

Some iron will normally be present in any of the . , - commercial ores and this can present problems in the aqueous `- acidic solut:Lon if it is not first remov~d or converted ., .
to an innocuous form. Thus, iron in the ferric form will extract below about pH 2.5 and any of this present should first either be removed by precipitation or converted to the ferrous form which only extracts above about pH 4.

A wide v~ariety of organic diluents ln which the extraction reagent is dissolved can be used according to the invention. The minimum requirements of the diluent that . .1 .
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is to be used is that it be substantially water-immiscible, that it will dissolve the extraction reagent and that it will provide an adequate phase separation. The diluent can be an aliphatic or aromatic hydrocarbon, halogenated hydro-carbon, etc. Examples of these diluents include toluene, carbon tetrachloride, benzene, etc. The preferred dilùents are liquid aromatic hydrocarbons boiling in the kerosene range. A variety of mixed commercial solvents of this type are available. The extraction reagent preferably also contains a modifier which aids in solubilizing the metal species in the organic phase and improves phase disengage-ment. A variety of known modifiers can be used, including TBP (tributyl phosphate), isodecanol, 2-ethyl hexanol an~
nonylphenol.
It has also been found to be desirable to pre-treat the extraction reagent before using it in the process of this invention. This pre-treatment is a cleaning procedure to remove undesirable impurities and can be-accomplished by contacting the solvent mixture of extractant, modifier and ~ 20 diluent with a metal sulfate solution such as copper sulfate, - followed by stripping with sulfuric acid and water washing.
~ The contacting of the metal-bearing aqueous acidic . , .
solution with the solvent extraction reagent can be carried out by any of the well known procedures employed in liquid-!
liquid extraction. Although continuous counter-current !
; me~hods are preferred, batch, continuous batch,and batch `
` counter-current methods are also useful. Any suitable liquid-liquid contacting system may be employed such as a pulse column, a mixer-settler or highly agitated column such as a Mixco column. The temperature at which the mixing and extraction is carried out is not critical and will typically , ' :
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be in a range of about 20 to 40~.
The ratio of the volume of organic phase to the aqueous phase can be varied considerably and the most 1, efficient ratio in each case can be readily determined by one skilled in the art. However, generally the aqueous to organic ratio will be within the range of ab~ut 115 to 5/1, dependlng upon the metal concentration, concentration of extraction reagent, etc.
Copper, cobalt or zinc values can be stripped from the loaded organic phase by a variety of strong acids such as - nitric, hydrochloric or sulphuric acid. The copper values are preferably stripped with sulphuric acid having a strength of about 150 to 200 g/l H2S04. This removes the copper as copper sulfate solution which is amenable to electrolysis.
A substantial quantity of-this acid remains with the solvent ` but this can readily be removed by water washing so that the ; solvent system can then be used once again for a further extraction.
- Particular embodiments of the invention are illustrated by the attached drawings in which:
Figure 1 is a schematic flow sheet for the treat-ment of chalcopyrite concentrates by pressure leaching and solvent extraction;
`~ Flgure 2 is a plot showing the effect of stage-wise extraction and equilibrium pH on the purity of the product;
~ Figure 3 is a plot showing extraction coefficients -~ for various metals in the pH range 0.5 to 6.0;
Figure 4 is a plot showing solvent loading for molybdenum and copper at various pH values;
Figure 5 is a plot showing the effects of _ g --. .

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retention times on the extraction o~ molybdenum and copper.
As is illustrated in Figure 1, a chalcopyrite ore concentrate 10 and sulfuric acid 11 are fed into a pressure leaching tank 12 and the leaching :is continued for 8 hours at 230 F under 80 psig 0 . The leach slurry is then fil-tered and washed in unit 13 and the filtrate is collected in surge tank 14. This filtrate or leach liquor containing dissolved metal values flows via line 15 to a solvent extrac-tion unit 17. Also being fed into the solvent extraction unit is an extraction reagent 16 and this can Eor instance be 20~ KELEX 100 and 10% isodecanol in Solvesso 150 (trade-mark), an aromatic diluent.
The extraction is conducted at ambient temperatures in three stages with the loaded organic phase being removed by an upper line 18 and the aqueous raffinate being removed by line 19. The loaded organic goes to a stripping unit 20 while the raffinate proceeds to a collector vessel 29. In the stripping unit 20 the loaded organic is contacted with 150g/1 H2SO4 from vessel 21 and this stripping is conducted in two or three stages at ambient temperatures. The aqueous acid phase is removed by line 24 while the stripped organic ; proceeds via line 22 to water washing unit 23. In this unit the organic is contacted with a stream of water 26 to remove residual H2S04. This residual H2SO4 is collected by line 28 while the clean extraction reagent is returned to vessel 16 via line 27.
Preferred embodiments of the invention are further - illustrated by the following non-limiting examples.
Example 1 (a) Preparation of Solvent Composition A solvent extraction composition was prepared con~

sisting of a 0.5 molar solution of KELEX 100 plus 10 v/o ~ ' - 10 -'7~

iæodecanol in an aromatic diluent, Solvesso 150. This solvent composition was then contacted with a copper sulfate solution, followed by stripping with 150 g/l H2S04 and water washing. Any impurities in the original solvent mixture were aqueous soluble and were discarded with the raffinate.
(b) Extraction of ~Ietals To determine the effect of stage-wise extraction on selectivity of one metal over another metal, a series of tests were conducted on four feed solutions at varying equilibrium pH levels. Using the above solvent composition, loaded solvent was contacted 8 successive times with fresh aqueous feed solutions. Extraction was at a phase ratio (A/0) of 3/1, at room temperature and for 0.5 minutes contact time. The results are shown in Table 1 and these indicate that at pH 1.0 copper is loaded in preference to nickel, cobalt, manganese, magnesium, zinc and iron. At pH

3.0, in the absence of copper and iron, very little total metals were extracted, but with some selectivity .. . . ..
~ for cobalt. However, at pH 4 a very high degree .. . . .
of selectivity is shown for the ex~raction of cobalt while at ` pH 5 there is a preference for zinc even in the presence of cobalt. With the removal of cobalt at pH 4, there is a ~; very high degree of preference for the extraction of -i zinc at pH 5. No detectable nickel was extracted over the above pH range.
This is very graphically illustrated by the lines plotted in Figure 2 of the drawings. These show the purity of extracted metal values in a loaded æolvent after an 8-stage contact with fresh feed at the various equilibrium pH values.

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(c) Recovery of Metal Values The metal values were recovered by acid stripping, using 150 - 200 g/l H2S04. However, the cobalt values could be stripped with H2S04 only by keeping the cobalt in the cobaltous form. This was done by keeping the cobalt loaded solvent under a blanket of nitrogen before and during extraction and stripping.

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j Example 2 In order to further determine the effects of pH
on the extractability of various metal values with KELEX
100, extraction tests were conducted on single, pure sulfate solutions of the following metals, containing, in g/l:
5.0 Mo : 5.0 Cu : 5.0 Co; 5.0 Ni; 5.0 Zn; 5.0 Mn, 5.05 Mg;
5.0 Fe ; 5.0 Fe and 5.0 Ca.
The same solvent composition was used as in Example 1 and the extraction was at ambient temperature for 5 10 minutes at a phase ratio A/0 of 3/1 over the pH range of 0.5 to ~. The results are plotted on Figure 3 of the drawings.
; This plot clearly illustrates the selectivity - for molybdenum, copper, cobalt and zinc at the different pH values. What is particularly noteworthy and highly - surprising is the very high extraction coefficient for - molybdenum at a pH below 2. It will also be noted that ; only infinitesimal amounts of manganese, magnesium, calcium and nickel were extrac*ed over the pH range of 0 - ~.
Exam~le 3 .- , (a) To further illustrate the highly surprising selecti~ity between molybdenum and copper, a further series -~
of extractlons were conducted on a mixed suIfate feed solution containing 5 g/l copper and 5 g/l molybdenum~
Again the same solvent composition was used as in Example 1 and the extractions were at room temperature at a phase ratio A/0 of 3/1. The contact time was 5 minutes.
The amounts of the metal values in the loaded . solvent were determined for extractions at different ;~ pH values-between 0.5 and 4 and the results are plotted on , 30 Figure 4. These show a strong preference for molybdenum over copper at pH values below 1 while at pH 3 - 4 there is a , - 14 -.
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strong preference for Cu.
(b) In order to illustrate the effects of kinetics on the system, extractionsof part (a) were con-ducted with different contact times. The results are plotted in Figure 5, showing changes in separation factor with increased contact time.
It will be seen that as the contact time is increased from 10 seconds to 3600 seconds at pH 0.5, the separation factor Mo/Cu increased from 170 to 18,000. On the other hand, at pH 2.5 the maximum Cu/Mo separation factor occurred at 60 - 120 seconds, while the Mo/Cu separation factor increased from 0.4 to 2.7 as the contact time was increased from 120 seconds to 3600 seconds.
These results further illustrate the strong preference of substituted 8-hydroxyquinolines extraction reagents for molybdenum over copper. Even at pH 2.5, apart from a contact time of 60 - 120 seconds9 the separation of molybdenum in preference to copper is kinetically controlled.

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Claims (14)

I claim:

1. A process for the recovery of molybdenum values from an aqueous acid solution containing dissolved molybdenum along with other metal values, which comprises contacting said aqueous solution with a substituted 8-hydroxyquinoline extraction reagent of the formula:

wherein R is an alkyl having from 5 to 14 carbon atoms, dissolved in an inert organic solvent, at an equilibrium pH of 0 to about 5, whereby molybdenum values are selectively extracted from the aqueous phase into the organic phase, the resultant molybdenum loaded organic phase is separated from the remaining aqueous raffinate phase containing the remaining metal values in solution, and the molybdenum is stripped from the loaded organic phase.

2. A process according to claim 1 wherein the aqueous acid solution contains molybdenum, copper and other metal values and wherein the molybdenum is extracted at pH 0 - 2 and the aqueous raffinate phase is further contacted with said extraction reagent, whereby copper values are selectively extracted from the aqueous phase into the organic phase, the resultant copper loaded organic phase is separated from the remaining aqueous raffinate phase containing the remaining metal values in solution, and the copper is stripped from the loaded organic phase.

3. A process according to claim 2 wherein the extracting conditions are controlled such that saturation loading of molybdenum is obtained.

4. A process according to claim 1 wherein the molybdenum is stripped from the loaded organic phase by alkaline stripping.

5. A process according to claim 2 wherein the copper is stripped from the loaded organic phase by acid stripping.

6. A process according to claim 2 wherein the aqueous acid solution contains molybdenum, copper, cobalt and other metal values and wherein the copper extraction is conducted at a pH below about 3, after which the aqueous raffinate phase is further contacted with said extraction reagent at pH greater than 3 to selectively extract cobalt values.

7. A process according to claim 6 wherein the cobalt in cobaltous form is stripped from the loaded organic phase by acid stripping.

8. A process according to claim 6 wherein the aqueous acid solution contains molybdenum, copper, cobalt and zinc along with other metal values and wherein the cobalt extraction is conducted at pH 3-4, after which the aqueous raffinate phase is further contacted with said extraction reagent at pH greater than 4 to selectively extract zinc values.

9. A process according to claim 8 wherein the zinc is stripped from the loaded organic phase by acid stripping.

10. A process according to claim 1 wherein the aqueous acid solution contains molybdenum, copper and other metal values and wherein the molybdenum and copper are co-extracted, after which the copper and molybdenum values in the loaded organic phase are selectively stripped by acid and alkaline stripping respectively.

11. A process according to claim 1 wherein any ferric iron in the initial aqueous acid solution is removed by precipitation or conversion to the ferrous form prior to solvent extraction.

12. A process according to claim 1 wherein the ex-traction reagent is KELEX 100.

13. A process according to claim 1 wherein the aqueous acid solution is an acid leach solution.

14. A process according to claim 2 wherein the aqueous acid solution contains molybdenum, copper and zinc, along with other metal values which exclude cobalt and wherein the copper extraction is conducted at a pH
of O to about 3, after which the aqueous raffinate phase is further contacted with said extraction reagent at pH
greater than 4 whereby zinc values are selectively extracted from the aqueous phase into the organic phase, the resultant zinc loaded organic phase is separated from the remaining aqueous raffinate phase containing the remaining metal values in solution and the zinc is recovered by acid stripping.