CA1053914A

CA1053914A - Metal recovery from sulfate solutions

Info

Publication number: CA1053914A
Application number: CA225,719A
Authority: CA
Inventors: Victor A. Ettel; Andrew J. Oliver; Juraj Babjak
Original assignee: Vale Canada Ltd
Current assignee: Vale Canada Ltd
Priority date: 1975-04-29
Filing date: 1975-04-29
Publication date: 1979-05-08
Also published as: PH11859A; FR2309645A1; AU1324976A; FR2309645B1; JPS51131418A; ZA761148B

Abstract

ABSTRACT

Nickel, cobalt, copper or zinc is recovered from a sulfate solution by mixing the solution with a organic phase containing a chelating reagent and con-trolling the pH with a solid calcium base to a value lower than that at which the metal in question hydrolyzes.

Description

~)53~
PC-lll9 The present invention relates to the recovery of metals from sulfate solutions, and in particular to liquid-liquid extraction processes for recovering one or more of the metals: nickel, cobalt, copper and zinc from such solutions.
The selective extraction of nickel, cobalt, copper or zinc from aqueous solutions is a step of major commercial importance in the production of the pure metals.
Thus, after leaching an ore or concentrate, the leach liquor invariably contains impurities which either preclude direct electrowinninq of the metal from the liquor, or which deleteriously affect the grade of the electrowon metal.
convenient process for selective extraction of the desired ~etal from such a liquor offers a far more attractive com-mercial proposition than~the elimination of all undesirable impurities, which elimination might require an elaborate multi-operation process. For this reason much research has been directed at developing economical processes for extracting these metals, particularly in the case of nickel and cobalt, from aqueous solutions thereo~ with the aid of o~ganic extractants.
Several processes have been proposed, wherein the common feature is the use of organic chelating agents capable of forming organic-soluble complexes with the desired metal, :
and having~different~degrees of selectivity. In carrying ~out such extraction processes, it is necessary to control :: : : :
the pH of the solutions both at the start and durinq the progress of the extraction. This is because the reaction .
between the chelating agent and the metal to be extracted :
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leads to an increase in the acidity of the solution, and unless a suitable alkali were added the p~ of the aqueous solution would be rapidly lowered to a point where the extraction would cease to be effective. The alkali most widely advocated for use in such processes has been ammonia.
~ne important reason for ~he use of ammonia is its ability to form water soluble ammine complexes with nickel or cobalt.
Thus where the metal to be extracted is nickel or cobalt, it has been generally recommended to operate at a pH of 8 or even higher. At such pH values, the nickel or cobalt would tend to precipitate out of the aqueous phase in the absence of a complexing agent such as ammonia. The ammonia therefore fulfills the double role of controlling the pH as well as preventing precipitation of the nickel or cobalt.
The cost of ammonia and of its rçcovery as welI as : ~:
its undesirability from an environmental pollution ~iewpoint are both factors which detract from a wide commercial appli-cation of such processes. -It is an object of the p~xesent invention to provide a process for extracting nickel, cobalt, copper or zinc ~rom a sulfate solution with the aid of a low cost environmentally acceptable base.
According to the present invention, a process or ~ -extracting a metal selected from the group consisting of nickel,cobalt, copper and zinc dissolved in an aqueous sulfate phase comprises contacting the aqueous phase with an~organic phase which comprises a water immiscible organic solvent and a chel~tlng reagent having a solubility of at least 2% in the organic solvent and being effective to ~;
extract said metal by forming an organic-soluble complex therewith,the relative proportions o~ ~he organlc and aqueous '-'-" ' ~; -2- ~

~05~9~4 phases being such that the aqueous phase is continuous in the mixture of phases; introducing lime or limestone into the mix-ture in amounts sufficient to maintain ~he pH within a pre-determined range which is lower than the value at which the metal precipitates as a hydroxide; separating the mixture into a loaded organic phase and an aqueous slurry containing pre-cipitated gypsum; and treating the aqueous slurry to recover substantially any organic phase entrained therein.
It is an essential feature of the invention that the chelating extraction, which is a two-phase liquid-liquid extraction process, is carried out in the presence of a third, solid, phase. The calcium base used is preferably introduced in the form of an aqueous slurry into the extraction vessel, so that the extraction vessel will contain some base solids, i.e. lime or limestone, as well as some solid neutralization product, i.e. gypsum. A major reason why calcium bases, despite their well known cheapness and environmental accept-ability, have never to our knowledge been advorated for use in such chelating extractions, is the generally held view that the presence of solids 'Ln ~he extraction vessel is highly detrimental. Thus it has been th~ught heretofore that the .. .. . .
presence of solid lime or gypsum wo~lld not only prevent e~
cient extraction but also lead to intl~lerable losses ~f organic phase by entrainment. We have found, surprisingly, that the presence in the reaction vessel of ~he a~ove-mentioned solids does not prevent efficient e~4raction from being achieved.
We have also found that the amount of organic phase en-trained with the solids at the end of the process is not high, and that most of such entrained organic is easily recoverable by~a simple treatment such as gas sparging .

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- - f ~0539~4 or flotation, so that actual losses of the expensive organic phase are low enough to be tolerable.
The extraction may be practised in batch or in continuous operation, and may be carried out with a counter-current flow of the organic liquid and aqueous slurry between stages of the operation. Adjustment of the pH by addition of the calcium base may take place as required in some or all of the stages.
Careful control of the pH of the sulfate solution from which the desired metal is to be extracted is essential to the success of the extraction process. The upper limit of the permissible pEI range is dictated hy the need to avoid pxecipitation of the metal ion to be extracted in view of the absence of ammonia to complex the ion. Thus the pH used must be Lower than the value at which the desired metal ion would hydrolyze. However the pH must also be high enough to ensure effective extraction, since the loading effective-ness of the organic phase decreases with decreasing pH of the aqueous phase. It is this need to operate within a ~ specified range of pH values that necessitates the addition o the base directly into the reaction vessel in order to obtain a high level of extraction in a reasonable number of cycles. Thus the process of the invention can be contrasted with an alternative process wherein a portion of the phase mixture is bled from the extraction vessel and neutralized prior to returning it to the vessel. Because the chelating reaction results in the li~eration of hydrogen ions; the pH
can change from the highest permissible value to the lowest n the course of a relatively small level of extraction.
This is the case particularly where the permissib:Le pH range is relatively narrow. In such a case if neutrali~ation ~ -:

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were to be performed outside the reaction vessel the aqueous phase would be recycled a very large number of times prior to completion of the extraction process. An important benefit resulting from the ability to extract substantially all of the ~esired metal value from the aqueous solution is that the gypsum obtained at the end of the process is wetted with barren liquor and can therefore be discarded without the need for solid-liquid separation.
The actual pH values to be maintained during the process will depend of course on the particular metal value to be extracted. Where the metal value is nickel or cobalt, the pH must be maintained within the range 4-7 and preferably within the range 5.5-6.5. In the case of copper extraction, the pH must be within the range 2-5 and is preferably 2.5-3. For zinc extraction, the permissible pH range is 5-10, and a preferred range is 7-9. Within the above-mentioned pH ranges, the most preferred value in any case will depend on the particular chelating reagent used.
The chelating reagent used in the process o~ the invention can be any one of the many known reagents which are capable of forming organic-soluble chelate complexes with one or more of the~metals nickel,cobalt, copper and zinc, so as ~to extract the metal or metals from a solution which contains other metals and in particular calcium and magnesium (since the latter may well be presen~t as impurity in the calcium base used or in the aqueous feed). While the chelating .
. .
~reagent must be selective between on the one hand the desired :: .
metals and on the other hand such metals as calcium and mag-~nesium, it need not necessarily be selective between the : " ",, .
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various desired metals nickel, cobalt, copper and zinc.
Indeed most known chelating reagents are not selective between nickel and cobalt, and it is in fact possible to extract all four of the desired metal values with the same chelating reagent under appropriate pE conditions.
Known chelating reagents which can be used in the process of the invention include many compounds from the class known as beta hydroxyoximes, having the following general formula:

C _ R, R3 R~
where each of Rl, R2, R3, R4 and R5 may be a hydrogen atom or an aliphatic or aromatic hydrocarbon radical.
One such effective extractant, developed by General Mills, Inc., is commonly known as "LIX 65N", and comprises approximately a 50% by volume kerosene solution of 2~hydroxy-benzophenoxime active anti-isomers. Another extractant developed by General Mills is known as "LIX 70". It is a chlorinated derivative of "LI~ 65N" and its structure can be represented by the above general formula where Rl is C6H~Cl, R3 is CgHlg, and R2, R4 and Rs are hydrogen atoms.
A further extractant of this class is available ~rom Shell Chemicals Corp. under the trade name "SheIl ~etal Extractant 5~29". The structure of the active com-ponent of this extractant corresponds ~o the general formula given for beta hydroxyoximes, with Rl being CH3, R3 being C~H19, and R2, R~ and R5 being hydrogen atoms.
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. Another useful reager.t of this class is available from ~corga Limited under the trade name "ACORGA P17". Its structure corresponds to the general formula with Rl being a benzyl radical, R3 being a nonyl radical, while R2, R~
and ~5 are hydrogen atoms.
A second class of chelating reagents useful in the process of the invention comprises 8-hydroxyquinolines, having the following general formula:
~ ~4 0 ~ R~

OH
where each of Rl to ~ may be a hydrogen atom or an aliphatic or aromatic hydrocarbon radical. One such extractant is com-mercially available from Ashland Chemical Co. under the trade name "Kelex 100". The structure of the active component of this rea~ent can be represented by the above general Eormula for 8-hydroxyquinolines wherein Rl is a tetramethyloctenyl radical, while ~2 to R6 are hydrogen atoms.

A third class o compounds effective as chelating reagents in the process of the invention comprises beta diketones, of which a specific example is oleoylacetone:

H H O O
- -:
CH3-(CH2)7-C = C-(cH2)7-c-cH2-c-c~3 The soIvent which constitutes a part of the organic phase i~ the process of the invention may be any organic liquid which is immiscible with the aqueous phase and in which the chalating reagent is at least partially soluble.
The concentration of the chelating reagent in the solvent is .

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chosen in accordance with the amount of metal to be extracted from the aqueous phase. Preferably the solvent used is one in which the solubility of the extractant is 20~ or more.
Typical solvents comprise aliphatic or aromatic hydrocarbons, such as kerosene, as well as alcohols such as isodecanol, and phenols such as para-nonyl phenol, or mixtures of such com-pounds. Whexe the solvent consists of a mixture of organic liquids, one of the component liquids is often termed a modi-fying agent, one of its functions being to improve the phase separation.
After separating the aqueous phase from the organic phase, the latter can be treated in a known manner to recover the extracted metal therefrom. The conditions for stripping the extracted metal are known to one skilled in the art and depend on the particular chelating reagent used. For example ~ ~ ~ .
J nickel can be stripped from the extractant "LIX 65N" by con- ' tacting the loaded organic phase with an aqueous stripping , phase having a low pH, e.g.j 1.5, whereupon nickel passes into the aqueous solution and can be recovered from it ~y electroly~
sis.
In view of the cost of the organic extractant, as well as the value of metals loaded therein, it is essential to the successful operation of a commercial extraction pro~ess that losses of organic liquid, and in particular chelating reagent, be minimizedO Whlle we have found that in extractions according to the invention very little of the chelating reagent is entrained in the aqueous slurry at the end of the extraction, , ~ '' almost all of such entrained organic,phase can be readily re- ',' covered from the aqueous phase. A simple recovery treatment ~, ~comprises subjecting the aqueous slurry to a gaseous sparging. , '- , ' ' .

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A more efficient recovery can be obtained by washing the gypsum solids with organic solvent, or by subjecting the slurry to flotation.
Some specific examples will now be given:
xAMæLE
An aqueous phase was used which consisted of a solution of nickel sulfate and magnesium sulfate in which the nickel and magnesium values were 4.0 and 2.5 g/1 respec-tively. An organic phase was made up by mixing one part C 10 by volume of the reagent "LIX 65N" with nine parts by volume of a commercial solvent known as Escaid 100, the approximate composition o which is, by weight, 44% parafEin, 37%
naphthene and 19% aromatics.
The aqueous and organic phases were mixed, in an extraction vessel, such that the volume ratio of organic phase/aqueous phase was 2/1. The resulting mixture was mechani-.
cally agitated and maintained at 50C for the duration of the extraction. The pH of the aqueous phase was constantly moni-tored and co~trolled by addition o an aqueous slurry of lime as required to keep it constant at about 6.5. When the ex-traction had ceased, as evidenced by a stabilization of the pH, a further 10-15 minutes were allowed for equilibration, ~;
giving an overall extraction time of about 1 hour. The agita-tion was then di~scontinued and the organic phase was separated rom the aqueous slurry by settling and decantation. The aqueous slurry contained gypsum particles of about 230 microns in length and 25 microns in ~idth. The ælurry had good set-tIing properties and yielded an under10w of about 50% solids. ~;
; Analysis of the loaded organic phase showed a nickel content of 2 y/l, indicating virtually complete extraction Y~t ~ a~e ~
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of the nickel from the aqueous phase. In fact analysis of the equilibrated aqueous phase, after settling, showed a nickel content of 0.006 g/l in the overflow solution and a Eurther 0.002 g/l of nickel was detectecl in the underflow slurry by acicl leach of the solids.
The aqueous slurry was also analyzed, after set-tling, ~o determine the amount of chelating agent dissolved or entrained therein. 0.006 g/l of the oxime were found to be in the overflow solution and 0.025 g/l were in the under-flow slurry. This corresponded to a transfer from the organicphase to the aqueous phase of O.n75% by weight of the che-latinq reagent initially present in the organic phase. By subjecting a sample of the aqueous slurry to gas sparging ~-for 5 minutes, 80% of the chelatiny reagent present therein was recovered. By subjecting a further sample of the aqueous slurry to flotation, 98% of the chelating reagent was re-covered.
To examine the ease with which nickel can be stripped from such an organic phase, a similar extraction to that described above was carried out to produce an organic phase comprising one part of "LIX 65N'l to 9 parts of "Escaid 100"
in which 2.62 g/l of nickel wexe loaded. This organic phase was contacted with an aqueous stripping phase which contained 37.5 g/l of nickel present as sulfate, as well as about 40 g/l of sulfuric acid and 5 g/l of boric acid. Four tests were carried out using different ratios of organic phase to aqueous stripping phase and different values oE the pH of aqueous stripping phase -(which was measured in each case at 23C) ': ..
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Each of the st~ipping tests was ~onducted at a temperature of 50GC and anequilibration time of 10 minutes was allowed.
The results of these stripping tests are shown in Table 1 below:
TAB~E 1 . Test ~ ~ ~ % of Ni . . ~ at 23C) ~ _ ~ueaus S~
FOreged ic _ _ 2.62 _ _ :.
FheqUedus _ _ _ 37.5 _ 1 S/l 1.1 0.076 53.0 97.1

2 .10/1 1.5 0.56 61.0 78.6 .

3 15/1 2.7 0.95 66.~ 63.7 . 4 20/l L 1.14 , 5~ 5 ':.

The same chelating reagent, "LIX 6~N", was used :
to extract zinc from a sulfate solution containing 2.4 g~l :~ of zinc. In this case.the organic phase was made up by mixing 1 volume of the chelating reagent with 4 volumes of the solvent~"Escaid 100". Equal volumes of the aqueous and organic phases:wer~e mixed, the mixture was maintained at:50C while a~20% by weight lime slurryiwas added as required to maintain the pH at the desire~ level. Four ests were carried:~ut:a~:different pH:values, w th a 10 minute period being allowed~in each oase for equilibration after he final ~lime addition. The distribution of ~inc be~ween the~;organic~and aqueous phases~;after equilibration is shown in~Table:2~

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TABL~ 2 . pH Zinc Co_ e ~t (q/l) Zinc Distribution :
. _ Organ Aqueous _ Or~anic/~ueous 5.5 0.0~6 2.35 1.95 X 10-2 ~.5 1.9 0.25 7.6 7.5 2.1 0.00$ 2.6 X 102 9.2 2.0 ~ 0.005 ~ 4.0 X 102 ~ ~ ............. .. __ , . ~ , , A similar extraction to those described in the previous Examples was carried out using as an aqueous feed a solution aontaining copper sulfate and nickel sulfate.
The organic phase was idenkical to that used in Example 2, :
as were all other experimental conditions except that the ~- :
ratio of the volume of the aqueous phase to the volume o the organic phase was 2.2. The distribution of copper and ~: -.
nickel between the phases after equilibration is given in Table 3. : :
: ~ ABLE 3 : : _ . . Metal Distrlbution Metal_Contents(q/l) Organia/Aqueous Aquec us ~~ ~ Organic __~ __ ~
. Cu _ _ Ni CU ~ Cu _ Ni Aqueous Feed 1.98 2.63 _ ~ _ Organlc Feed ~:~ 0.i2 0 _ :~
Equilibrated:: ~
Ph~ses ~ 0.004 2.50 4.43 0.11 4.4 X l0 ~ :: -: , . .
It wil]. be seen that at th:e pH~value chosen for good copper :
extraction, the:~oading of nickel into the organic phase was poor.~ ~
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~XAMPLE 4 An aqueous phase containing, in the form of sulfates, 6.46 g/l of nickel, 3.13 g~l of magnesium and 0.32 g/l of calcium was used. The organic phase was made up by mixing sev~n parts by volume of a highly aromatic solvent supplied by Imperial Oil (Canada) under the trade name'~OLVESSO 15Q",with one part by volume of isodecanol and two parts by volume of the chelating reagent "KE~EX 100".
The extraction was performed using a phase ratio of aqueous/
10organic equal to 2, the conditions being otherwise as described in Example 1. Table 4 below shows that exceIlent loading of nickel into the organic phase was achieved with very little coextraction of masnesium or calcium.
. T~3LE 4 _ )ntents ~ l) Mëtal Distribution Ca ~ M-iOr7anlC ~ Ni ~ ou :~
0 82 0 32 3.l4 12.0 10-0l3 1-l l4 6 0 04 0.0003 ~ ~ '; ~.. ' : EXAMPLE 5 . :~
Using the same chelating reagent as in Example 4, ~ .
a test was carried out ko determine the effectiveness of using limestone instead of lime as the oalcium base for pH control~
The aqueous pha;e~:for:this test~cons:isted of a nickel ;ulfate-magne;lum ;ulfate solution contalning 5.0 g/l and 2.S g/l of nickel:and magnesium~re;pectively. ~he organic phase con-;i;ted~of the chel~atlng reaq~nt"KELEX 100",mixed with nonyl- ;
phenol and the solvent'~scaid 100"in the volume ratio 1il~18.
The phases were:mixed in the~valume ratio of organic/aqueous~ ....... .......
~: 27,~ and a ~0% by weight limestone ;lurry was used to maintain ~ r~ J~
i ~ -13--.

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the pH at 4.5 during the extraction. A period of 15 minutes was allowed for equilibration after the final limestone addition. ~nalysis of the equilibrated phases showed a nickel content of 1.8 g/l in the organic phase and 0.75 g/l in the aqueous phase, i.e. a distribution of 2.4. Thus the loading in this case was less efficient than that obtained in the preceding Ex~mple where lime was used to maintain a higher p~.

A series of tests was conducted to extract nickel from a nickel sulfate solution containing 2.5 g/l of nickel with the aid of different chelating reagents. For the first of these tests (Example 6) the organic phase consisted of a 12.4 g/l solution of 8-hydroxyquinoline in chloroform.
In the test of Example 7, the organic phase c~nsisted of a : G 31 g/l solution of oleoylacetone in the solvent "Escaid 100" In Example 8, the organic phase used was a 10~ by volume solution of the chelating reagent "LIX 70" in kerosene.
In Example 9, a 10% by volume solution of the chelating -` reagent "Acorga P17" in the solvent "Escaid 100" was used as the organic phase. In Example lO,the organic phase was a 10% by volume solution of the chelating reagent "Shell Meta~ Extractant 52g" in a~solvent available from Shell Chemicals Corp. under the name "Shell Diluent No. 2 for SME 529".
For eaah of these five tests a lime slurry was used to control the pH to the desired value, and the volwme ratio of the organic and aqueous phases was 1:1~ The results ; ~ of~the extractlans are sho~n in Table 5.
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An aqueous phaae containing 0.055 g/l of cobalt and 4.%0 g/l of nickel in the form o~ sulfates was mixed with an organic phase in a simulation of a two-st~ge countercurrent extraction. The pH was maintained at 6.5 1 in each stage by addition of a lime slurry as required.
The organic phase was made up by mixing 9 parts by volume o the solvent "Escaid lOO" with l part of the chelating-*;reagent "~IX 65N". The extraction was performed using -a phase ratio of organic/aqueous equal to 2 and other aondition~ wexe as described in Exa~ple lo The distribu~
tion of the metals between the phases is shown in ~able 6, fro~ which it can be seen that good~aoextraa~ion:.~o~ ~ 91 and cobalt was achieved under these conditions.

~, _ _ _ _ ~ Metal Distribution .
Metal Contents~ (~/l) Organic/~ueous ~queous orqanlc : , .. ____ W~ ~ Co i ' _ . Co, ~0 ~:~ Agueous Feed~ 4.80 0.~55: - ~ .
Stage l 3.70 0.048 2.64 0.026 0071 Ø54 ~ .
. Stage 2 0.003 O.OOl 2.12 0.024 7.l X lO2 2.4 X lOl OrganLa Feed ~ : ~: 0~ O . :
_~
: The~ab~ve Examples~il1ustrate the wide~applica-bility~of the proo~s~ of the invention, wherein a solld cal-cLum~base Ls Lnt~oducsd~into the Liquid phase mixture Ln the extraction vesse1. :It~wLl1 bs~under~tood that v~rious mo~
Lcations~m`a~:bs~mada to th2 reageN~ and conditions des-cribed in the~e ExampLes without departing from the scope of 30~ ; the~Ln~ent1on, wh1~h Ls defined by the appended claim~3..

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for extracting a metal selected from the group consisting of nickel, cobalt, copper and zinc, dissolved in an aqueous sulfate phase, comprising contacting the aqueous phase with an organic phase which comprises a water-immiscible organic solvent and a chelat-ing reagent selected from the group consisting of beta hydroxyoximes, 8-hydroxyquinolines, and beta diketones, the reagent having a solubility of at least 2% in the organic solvent and being effective to extract said metal by forming an organic-soluble complex therewith, the relative proportions of the organic and aqueous phases being such that the aqueous phase is continuous in the mix-ture of phases; introducing lime or limestone into the mixture in amounts sufficient to maintain the pH within a predetermined range which is lower than the value at which the metal precipitates as a hydroxide; separating the mixture into a loaded organic phase and an aqueous slurry containing precipitated gypsum; and treating the aqueous slurry to recover substantially any organic phase entrained therein.

2. A process as claimed in claim 1 wherein the pH is maintained within the predetermined range by adding an aqueous slurry of lime to the mixture of phases.

3. A process as claimed in claim 1 wherein the step of treating the aqueous slurry comprises subjecting the slurry to flotation.

4. A process as claimed in claim 2 wherein the metal is selected from the group consisting of nickel and cobalt and the predetermined pH range is 4-7.

5. A process as claimed in claim 2 wherein the metal is copper and the predetermined pH range is 2-5.

6. A process as claimed in claim 2 wherein the metal is zinc and the predetermined pH range is 5-10.