It is an object of this invention to recover gold from carbon


Date & time Oct 29

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Gold-loaded solution 15 is then passed to solids-liq- 'uid separation means such as filter 18 to remove any suspended carbon activated carbon for goldparticles carried from the column. The solution is cooled to a temperature below its normal boiling point by heat exchange means 19, which may be water cooled as indicated on the drawing, and passed from the desorption process through pressure reducing valve 20. Gold may then be recovered from the cooled solution in a variety of conventionalways but it is preferred to use an electrolytic cell to deposit elemental gold and regenerate the stripping solution for reuse in the process.

Water may be used as the stripping liquid but it is preferred to use dilute aqueous caustic (0.1 to 1.0% sodium hydroxide being appropriate) or dilute aqueous caustic cyanide solutions. Since the carbon was exposed to a dilute caustic cyanide solution during adsorption, water will dissolve caustic and cyanide carried by the loaded carbon in any event. Temperatures of the process must not be allowed to exceed the decomposition temperature of the adsorbed gold cyanide complex. Such decomposition begins at about 170C with the deposition of elemental gold on the carbon. A preferred desorption temperature is in the range of 150 to 165C with a most preferred operating temperature being about 160C.

The following examples serve to more fully illustrate the invention.

EXAMPLE 1 A series of batch equilibrium tests were performed on carbon loaded with adsorbed gold cyanide at various temperatures using a dilute caustic cyanide solution as the desorbing liquid. The following results were obtained:

Table 1 Temperature Relative Desorption C Rate EXAMPLE 2 Samples of carbon loaded with gold cyanide were obtained from three different gold mills. The samples were placed in a cylindrical column which was provided with heating means capable of providing a controlled temperature of the carbon within the column.

-An aqueous solution of caustic cyanide containing 1.0% sodium hydroxide and 0.1% sodium cyanide was flowed continuously through the column at a tempera- A sample of activated coconut carbon which had been industrially loaded with cyanide-lime gold-bearing solution to about 560 troy ounces of gold per ton of carbon was split into two parts. One sample portion was stripped of its gold in the conventional fashion using an aqueous solution of 0.1% sodium cyanide and 1.0% sodium hydroxide as the stripping liquid. Desorption of this sample portion was accomplished at atmospheric pressure and a temperature which varied from 88 to 94C which approximates the normal boiling point of the stripping liquid.

The other sample portion was desorbed at elevated temperature and pressure; the temperature being maintained within the range of about C to C over most of the stripping cycle. A stripping solution containing 0.4% sodium hydroxide was used in this test. Results are set out in graphical form as FIG. 2 which is a plot of cumulative percentage of gold stripped versus time; Curve A represents results obtained by the practice of this invention while curve B is typical of results obtained by the prior art.

As may be seen from that figure, the rate of gold desorption is dramatically enhanced by use of this invention. At the end of 10.5 hours of stripping, the carbon of curve A assayed 0.35 ounce gold per ton while at the end of 65.5 hours, the carbon of curve B assayed 2.0


The data and examples presented herein are illustrative of the benefits derived from practice of this invention. Minor modifications and changes in technique will be obvious to those experienced in the 

I claim:

1. A method for recovering gold adsorbed on activated carbon in the form of a gold cyanide complex which comprises:

6 wherein the gold-depleted liquid is recycled to the desorption step.

4. The method of claim 3 wherein the liquid is a dilute caustic.

5. The method of claim 3 wherein the liquid is a dilute caustic cyanide.

6. The method of claim 3 wherein the gold content of said gold-loaded carbon is in the range of 250 to 1000 troy ounces of gold per ton of carbon.

7. The method of claim 4 wherein said dilute caustic contains from about 0.1 to 1.0% sodium hydroxide.


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