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

Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction2017-04-04T06:57:36-04:00
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Thiourea in elution circuits (1 reply and 1 comment)

4 months ago
ksherren 4 months ago

I am looking for information from anyone who is using thiourea in conjunction with NaCN and NaOH in their Au/Ag elution circuits. We are experiencing problems with eluting Ag and I am wondering if Thiourea could be the problem? If not, any thoughts on what may be the problem. We use an atmospheric Zadra process with NaCN also running 2-4%.

3 months ago
Jorge 3 months ago

I think, you should evaluate the effect of temperature on the elution efficiency. For example, you can perform some tests from 80 to 140 oC. Some pilot tests using thiourea employed an eluant whose composition was 2-3 wt% thiourea, 2-4 wt% NaOH and 1-3 wt% NaCN. Other point to keep in mind is the addition of NaCN, it could be positive if you add it in two or three stages.

3 months ago

Thanks Jorge. We perform an atmospheric strip at approximately 98 C. Higher temperatures would undoubtedly increase performance however not possible with the present infrastructure. There is thinking that the thiourea is forming a silver sulphide that is 'welding' to the carbon and which is very difficult to strip. There is anecdotal evidence only that the thiourea is behaving as a strip accelerator which needs testing for accuracy.

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