CA1097508A

CA1097508A - Recovery of metal values

Info

Publication number: CA1097508A
Application number: CA282,762A
Authority: CA
Inventors: Raymond J. Davidson; David Duncanson
Original assignee: Anglo American Corp of South Africa Ltd
Current assignee: Anglo American Corp of South Africa Ltd
Priority date: 1976-07-15
Filing date: 1977-07-14
Publication date: 1981-03-17
Also published as: IL52438A0; FR2358466A1; BR7704649A; IT1080793B; AU2683477A; CH631488A5; IL52438A; ZA764204B; FR2358466B1; IN147865B; GB1573685A; DE2731029A1; AU508816B2

Abstract

ABSTRACT OF DISCLOSURE
The invention provides a method of recovering metal values selected from gold, silver, copper and nickel from a support such as activated carbon having one or more of these values adsorbed thereon in the form of an alkaline earth metal ionic complex, the metal value forming part of the anionic portion thereof, including the steps of contacting the support with a solution selected from the group of an alkali metal cyanide solution, an alkali metal hydroxide solution and a mixture thereof, followed by desorbing the metal values from the support with water having a low concentration of metal cations, preferably deionised or softened water.

Description

~0~75~i8 This invention relates to metal recovery, in particular to the recovery of gold, silver, nickel or copper metal values.
A method of recovering the above metals from supports on which they are adsorbed as complexes is covered by Canadian Patent Application No. 212,497. According to this method, the metal values are desorbed by contacting the support with water of low metal cation concentration. The water preferably has a low-multi-charged cation (e.g. alkaline earth metal cation) concentra-tion. Concentrations less than 300 ppm, preferably 50 ppm, are preferred. In other words the water is relatively pure and has a low ionic strength. Suitable waters are for example dis-tilled, deionised and softened waters.
The above method has particular application to metal values in the form of cyanide ionic complexes, the metal value forming the anionic portion of the complex. Any suitable adsorbent support may be used, carbon, particularly activated carbon, being preferred.
It is also disclosed that when the cation of the com-plex is an alkaline earth metal, the complex is adsorbed on to

- 2 , ~75~8 the support very much more strongly than when the cation is an alkali metal, particularly when the complex is an aurocyanide one. Accordingly, if the cation of the com-plex is an alkaline earth metal, particularly calcium, the support is preferably pre-treated with an alkali metal salt solution prior to water desorption.

This pretreatment results in an exchange reaction between the alkali metal and the alkaline earth metal. The exchange reaction is enhanced by providing a salt the anion of which forms an insoluble or substantially insoluble salt with the alkaline earth metal so that the latter is effectively removed from the system as exchange takes place.
~uitable salts for this purpose are carbonates, oxalates, sulphites, and fluorides, the alkali metal preferably being sodium, potassium, or lithium.

A preferred pretreatment solution according to the above patent is a potassium carbonate/potassium hydroxide solution having a basic pH.

We have now discovered that improved results are obtained with other pretreatment solutions.

According to the invention there is provided a method of -~0~75Q~3 recovering metal values selected from gold, silver, copper and nickel From a support having one or more oF these metal values adsorbed thereon in the form of an alkaline earth metal ionic complex, the metal value forming part oF the anionic p?rtion thereof including the steps of contacting the support with a solution selected from the group of an alkali metal cyanide solution, an alkali metal hydroxide solution and a mixture thereof, followed by desorbing the , metal values from the support with water having a low con-centration of metal cations.

The solution may be one containing alkali metal cyanide of concentration in the range 1 to 10 percent by weight and alkali metal hydroxide of concentration in the range 1 to 20 percent by weight. It is preferred that the concen-tration of cyanide ions exceeds the concentration of the hydroxyl ions in solution. The preferred mixture is sodium cyanide and sodium hydroxide.

Qne particularly suitable pretreatment solution contains an alkali metal cyanide concentration of about 10 percent by weight and an alkali metal hydroxide concentration of about 1 percent by weight.

Another suitable pretreatment solution is a sodium hydroxide ~q7S~
solution. It has been found that concentrations not exceeding lO percent by weight provide satisfactory results.
Initially the metal values are adsorbed on to the support in the form of an alkaline earth metal ionic complex.
The preferred support is activated carbonr The desorbing, after treatment of the support with the selected solution, is carried out using the conditions and waters as described above and in the above mentioned patent. It is important to note that the process of desorbing involves only physical adsorption/
desorption action and does not involve ion exchange.
The alkaline earth metal will generally be calcium and the complex will generally be a cyanide ionic complex. The invention has particular application to the recovery of gold and other metal values from solutions containing these values obtained in the cyanidation of gold bearing ores with, for example, a sodium cyanide/calcium hydroxide leach solution as described in the above mentioned patent.
The invention is illustrated in the fol]owing Examples:
Example I:
Type G210 granular activated carbon (Le Carbone (Pty) Ltd) ~"~,, ~QC'7S~8 was laden using gold plant cyanidation effluent. The laden charcoal analysed as follows:

Gold 2.9 kg/t Silver 64 g/t Nickel 2.2 kg/t Copper 90 g/t These metals were present on the charcoal in the form of calcium cyanide ionic complexes, e.g. Ca(Au(CN)2)2 .

The original capacity constant of the virgin charcoal was 22 mg gold per gram of charcoal.

Various runs were conducted using different pretreatment solutions and operating conditions. Except where other-wise indicated, in each case 16 g of charcoal were laden using a vibrator into a small glass e1ution column, to provide a charcoal bed of 1 cm internal diameter and 25 cm in length.

The bed was pretreated by pumping a half-bedvolume of pre-treatment solution at a rate of approximately 1 bed-volume per hour (apparent flow velocity 9.2xlO 3 cm/sec~
through the bed, after first draining the column of any surplus water.

16~975~8 The pretreated bed was then eluted using deionised water at 90C, at elution rates in the range 0~5 to 2,0 bedvolumes per hour.
10 bedvolumes were then collected and analysed. Finally the char-coal was removed from the column, ovendried, and analysed and activity tested.
In all the experiments conducted, the pretreatment solution com-prised a mixture of sodium cyanide and sodium hydroxide.
(a) Runs 1 to 11 In a first series of experiments, the effect of variations in the relative proportions of these two components were studied. The results of these experiments are set out in Tables I and II hereunder.
TABLE I

EFFECT OF CHANGE IN SODIUM HYDROXIDE CONCENTRATION USED AS A
PRETREATMENT REAGENT

¦Elution peak Residual concen- charcoal trations harcoal residues activity No. Pretreatment reagent/conditions ( r/t l _ ~ /t) (mg Au/g - o ~ ~ ~ Au ~$_ ~~ ~i_ ~h~r~.l ) 110% NaCN at 90 C 940 40 160 16 <2 4 64 13 2 " /1% NaOH " 862 37 193 15 < 2 7 100 12

3 ~ /5% NaOH " 825 25 143 23 3 8 57 12

4 ~ /14% NaOH " 820 25 135 18 5 1 7 13 ~ /20% NaOH " 7r70 23 126~ 19 11 _ llo 12 .

1l~Ca75~8 TABLE II

EFFECT OF CHANGE IN SODIUM CYANIDE CONCENTRATION USED AS A
PRETREATMENT REAGENT

_ . . Residual Pretreatment Elution peak charcoal reagent/ conce~ration Charcoal residues activity ~o. conditions ~/t) . (g/t) (mg Au/g _ Au _ _ Ni Au ~ Cu Ni charcoal) 6 14% NaOE at go& 550 1]. _ 42 22 17 300 13 7 " /1% NaCN " 630 21 1250 17 5 ~ 9 13 8 " /3% NaCN " 705 28 1560 26 33 18 88 13,5 9 " /5% NaCN " 670 25 1360 18 11 14 64 13 lo " /8% NaCN " 740 24 1560 18 9 6 30 13 11 " /10% NaCN " 820 25 1350 18 5 1 70 13 _ _ _ _ _ It is seen that as the sodium hydroxide concentration was de-creased, and the sodium cyanide concentration increased, the recovery of metal values improved, the best results being obtained using a pretreatment

5 solution comprising 10 percent by weight sodium cyanide and 1 percent by weight sodium hydroxide.

(b) Runs 12 to 14 In a second series of experiments (Runs 12 to 14) the efficiency of the process in regard to high gold loadings was studied. The results are set out in Table III.
G 215 activated charcoal was laden to 4-6 percent gold using ~975~8 clarified gold plant pregnant solutions. The metal values in the solutions were in the form of cyanide ionic complexes.
The laden charcoal was treated with various sodium cyanide/
sodium hydroxide reagents, and eluted at 90C with deionised water.
In Run 12 the analysis of the laden charcoal was:
Gold 4 percent Silver 600 g/t Nickel 2 600 g/t The pretreatment solution comprised 10 percent sodium cyanide/14 percent sodium hydroxide Recoveries of 98,6% gold, ~3% silver, and over 99% nickel were obtained.
After 6 bedvolumes of deionised water (12 hours) the gold eluate contained only 6 g/t of gold.

In Run 13 the analysis of the laden charcoal was:
Gold 6 percent Silver 2 000 g/t Nickel 6 000 g/t The pretreatment solution comprised 12 percent sodium cyanide/l percent sodium hydroxide.

i Recoveries of 99~9 percent gold, 97,1 percent silver, and .

g ..

~q75~8 99,9 percent nickel were obtained. The lower hydroxide concentration is seen to provide better results.
Similar results were obtained in Run 14, wherein the charcoal anal~
ysis was ~ percent gold, 1,000 g/t silver, and 1,700 g/t nickel.
TABLE III
ELUTION DATA AT HIGHER GOLD LOADINGS

_ Residual Original lution Charcoal harcoal Pre- loading eak residue ctivity treatment ( %) (g/t) __ (g/t) _ % Recovery mg Au/g No. conditions Au Ag Ni ~Au Ag Ni Au~ Ag Ni Au Ag Ni charcoal) _ _ _ .
12 1/2 Bed- ,0 O, o6 0,2 ¦ 8500 140 7o 550 125 9 98,8 83 99~ 21 volume 14% NaOH/
lat%lN/a2CN
Bedvolume h elution ure 90 C
13 1/2 Bed- 6 0,2 o,6 4000 1000 5 77 58 8 99~9 97,1 9~9 16 volume 12% NaCN/
1% NaOH
at 1/2 Bed -volume/h elution Temperat-ure 90C
14 As above 4 O,~L 0,1l 8800 47( 720 78 93 12 99,8 91,C 99, 17 (c) Runs 15 to 17 In a third series o~ experiments the process of the invention was compared with two other processes, namely potassium carbonate pretreatment ~ ollowed by elution with deionised water at 90 C, and elution at 65C with sodium sulphide/sodium hydroxide solution.

.
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~Q"75~

The results are set out in Table IV hereunder and graphically illustrated in Figures 1 (Gold), 2 (Silver) and 3 (Nickel).
TABLE IV
COMPARISGN OF DIFFERENT METHODS USED FOR ELUTION OF
GOLD FROM LOADED CHARCOAL
-_ Residual Pretreatment/elution Elution peak charcoal No. reagent/conditions concentration Charcoal residue activity _ (g/t) _ (g/t) (mg Au/g Au Ag Ni Au Ag Cu Ni charcoal) 15 1 Bedvolume 10% K~C03/ ~78 12,6 ~ 27 7 10 340 13,5 5% KOH at 1/2 Bedvolume h followed by deionised water at 90C
16 10 Bedvolumes of 3%1050 0,2 300 81 4 5o 85 10 Na2S/3% NaOH/1/2%
Na2S03 elution at 65C
at 2 Bedvolumes/h fol-lowed by 10 Bedvolumes Followed by 4 Bed-volumes of 5% HNO
Followed by 10 Be~-volumes of H20 17 1/2 Bedvolume 10%862 37 1930 15<2 7 100 12 NaCN/1% NaOH
Followed by deionised water at 1/2 Bed-_ volume/h at 90C _ _ ~ _ h = hour The process employing the sodium cyanide/sodium hydroxide pretreat-ment is seen to be superior to both the other processes.
In the case of gold recovery, the Na2S/NaOH provided marginally bet-ter recovery than NaCN/NaOH, but the unpleasantness of handling Na2S/NaOH so-lutions and the costs thereof make it unacceptable as a pretreatment reagent.
There is no precipitation of by-products on the charcoal, close to 100 percent recoveries are possible. Costs of reagents are relatively low since the regenerated sodium r ~ 11 ~

~ ;

~ 756P8 cyanide and sodium hydroxide solution may be reused in other parts of the gold circuit; elution is fiexible in that it may be effected at a rate between one-half and one bedvolume per hour in 5 to 7 bedvolumes of eluate at 90C, or 4 to 5 bedvolumes at 125C (3 hours elution time); and the highe. the gold loading on the charcoal, the more efficient becomes the elution.

EXAMPLE II
In this example the effect of using sodium hydroxide pre-treatment solutions was investigated. The procedures and materials used were similar to those used in Example I.
lhe metal rich solution, as in Example I, was a cyanidation effluent from a gold recovery process.

Various sodium hydroxide solutions ~ere investigated and the results of these investigations can be found in Table V. From these results it can be seen that there is no appreciable advantage to be gained by using sodium hydroxide solutions of concentration greater than 10 percent by weight. It should also be noted that in all of runs 18 to 21, the loaded charcoal was acid washed with hydrochloric acid to remove calcium carbonate from the carbon prior to treatment with sodium hydroxide.

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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 method of recovering metal values selected from gold, silver, copper and nickel from a support having one or more of these values adsorbed thereon in the form of an alkaline earth metal ionic complex, the metal value forming part of the anionic portion thereof, including the steps of con-tacting the support with a solution selected from the group of an alkali metal cyanide solution, an alkali metal hydroxide solution and a mixture thereof, the concentration of the alkali metal cyanide solution being in the range 1 to 10 percent by weight and the concentration of the alkali metal hydroxide solution being in the range 1 to 20 percent by weight, followed by desorbing the metal values from the support with water having a concentration of metal cations, of less than 300 ppm.

2.
A method according to claim 1 wherein the solution contains both alkali metal cyanide and alkali metal hydroxide.

3.
A method according to claim 2 wherein the concentration of cyanide ions exceeds the concentration of hydroxyl ions.

4.
A method according to claim 2 wherein the solution contains sodium cyanide and sodium hydroxide.

5.

A method according to claim 1 wherein the solution is a sodium hydroxide solution.

6.

A method of recovering metal values selected from gold, silver, copper and nickel from an activated carbon support having one or more of these values adsorbed thereon in the form of an alkaline earth metal cyanide ionic complex, the metal value forming part of the anionic portion thereof, including the steps of contacting the support with a solution selected from the group of an alkali metal cyanide solution, an alkali metal hydroxide solution and a mixture thereof, the concentration of the alkali metal cyanide solution being in the range 1 to 10 percent by weight and the concentration of the alkali metal hydroxide solution being in the range 1 to 20 percent by weight, followed by desorbing the metal values from the support with water having a concentration of metal cations of less than 300 ppm.