Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction

Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction 2017-03-23T09:50:58+00:00
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Minimum Cyanide Concentration (8 replies)

Helena Russell
1 year ago
Helena Russell 1 year ago

My problem is with regards to precipitation of Au and Ag at minimum concentration of CN. I need to lower the cyanide concentration to a limit in the Merrill Crowe processto 20 ppm of free cyanide and 50 of WAD, but I have problems with the precipitation of Cu. To compensate we are adding lead nitrate. How we could keep copper ions complexed and continue precipitating Au and Ag?

Obergruppenfuhrer
1 year ago

The Cu will co-precipitate with the Au and Ag if you wish to maintain a low grade barren solution. The heap leach operation must either accept the additional cost of Zn for precipitation of Cu and the cost of refining. Or look at installing a CIC circuit to selectively remove Cu for sulfide precipitation.

Look at the economics of both (current operating cost minus the sum of the capital of a CIC with cold elution and sulfide precipitation of the Cu and an AARL for the Au & Ag loaded on the carbon.). I figure the M-C operation is the best value.

Ace Levy
1 year ago
Ace Levy 1 year ago

Copper is not soluble in very low concentrations of cyanide but gold and silver are. If you have too much copper in solution you are using too high a cyanide concentration in your leaching.

Cleaning the solution of copper is essential for the recycle of the cyanide because copper cyanide will not dissolve gold BUT the zinc cyanide produced by the Merrill Crowe precipitating the gold, silver and copper out of solution will dissolve gold and silver almost as well as sodium cyanide does.

Rahil Khan
1 year ago
Rahil Khan 1 year ago

There are several methods of copper removal from cyanide solutions including ion exchange, direct electrowinning, acidification, volatilization, and recovery (AVR) and sulphide precipitation such as the sulphidization, acidification, recycling, and thickening (SART) process.

As he mentioned, following bench/pilot testing of scenarios with the greatest potential, you would need to validate economic viability.

Victor Bergman
1 year ago
Victor Bergman 1 year ago

20ppm free CN is very low. With CIP about the lowest is 30ppm below which gold will precipitate not sure of the MC limit but I suspect it is similar, If you have any dilution waste going to tails make sure you only add them to tails after the gold is extracted.

Obergruppenfuhrer
1 year ago

The practice of washing the precipitate with acid to remove the Cu is common. But the additional cost of this practice including the recovery of the Cu from the acid solution must be compared to the cost of the additional refining charge of the bullion.

A previous discussion on the same property indicated the Ag:Au ratio was 4. You should have installed a CIC circuit instead of a M-C. But this is history.

If the economics justify the addition of a CIC and elution circuit (prefer AARL to Zadra). The M-C circuit could be used instead of an EW circuit. The Cu can be separated using an ambient temperature elution with cyanide. This should be done on a continuous basis to generate a high grade Cu solution. This solution would be treated by AVR to precipitate a CuCN or CuS via H2S addition. Note that SART was developed in the 1920's and published for the extraction of Cu by Cyania mid in the 1950's. I do not mind helping you. But prepare the economic cost of precipitating the Cu to justify and additional capital and operating costs.

Ace Levy
1 year ago
Ace Levy 1 year ago

The most cost effective approach is to avoid dissolving the copper in the first place by lowering the cyanide concentration in the leach solution. Try it, it works!

Helena Russell
1 year ago
Helena Russell 1 year ago

Ok, as you can optimize the process using the Pourbaix diagram, which type of reagents could maintain acceptable ranges?On the subject of casting, you can reuse the slag mixing it with the fluxes, or cause more problems?

Gruppen
1 year ago
Gruppen 1 year ago

Try cutting back on Zn addition, Au and Ag come down by reduction to metal on the Zn surface and the rest as a result of hydroxide precipitation, try reducing Zn and keep copper in solution, also can look at SART to remove copper prior to Ag and Au recovery and recovery copper upfront.


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