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Effect of Lead Nitrate Concentration on Gold Leaching (3 replies)

9 months ago
Standartenfurer 9 months ago

How to effectively identify overdosing of lead nitrate [Pb(NO3)2] in gold cyanidation.

I'm interested in optimizing the lead nitrate addition at a standard 4000 tpd gold mill using conventional cyanidation. We currently add -240g/t lead nitrate to try to maintain our 'reducing power' (ppm SCN/S2O3) between leach and grinding at 60ppm. Can anyone elaborate on how to identify overdosing, specifically with respect to formation of insoluble lead hydroxides at the operating pHs between 10.7-11.3.

Raje Singh
9 months ago
Raje Singh 9 months ago

Grind sample in lab ball mill to desired size using mill process water & alkaline pH; add 0.2, 0.3, 0.4 & 0.5 lb/stPb(NO3)2 (4-tests) during milling; transfer slurry to bottle leach, add desired cyanide content, pH, carbon etc& leach for predetermined time; kinetic samples (solution/solids) should be assayed for Pb content, SCN/S2O32- etc. Repeat above tests w/o adding Pb(NO3)2 to grinding instead to leach. Ensure control tests are conducted.

Note that a certain amount of soluble Pb (<10-mg/L) is beneficial in Merrill Crowe as it is reduced on Zn localizing Au deposition & preventing passivation of the Zn surface by a coating of Au or Zn(OH)2; it will also remove soluble sulfides from Merrill-Crowe solutions.

Victor Bergman
9 months ago
Victor Bergman 9 months ago

Lead does not stay in solution. Lead addition can be controlled with the reducing power as you mentioned but the concentration of lead in solution is not an indication of overdosing. There is more to it.

Marshal Meru
9 months ago
Marshal Meru 9 months ago

I recommend some bench scale tests to come up with the optimized conditions.

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