2 replies to this topic

[shasha]

Is there any simple method to determine the amount of NaCN needed to leach the gold content in an ore?

[kkala]

Theoretical chemical reaction for gold cyanidation can be seen in http://en.wikipedia.org/wiki/Gold_cyanidation, indicating two kgmol NaCN per kgmol Au (0.5 kg NaCN / kg Au). Gold can precipitate from resulting Au(CN)2^- by adding Zn to form Zn(CN)4^2-, or elsewhere (see "recovery of gold from cyanide solutions" in mentioned link).
Any ore beneficiation or floatation upstream of cyanidation results in Au losses, while during cyanidation there are CN^- losses (due to Fe, S, see "pre-aeration and ore washing" in the link). I have no experience on these losses.
An example in "Au Recovery.pdf" (attached to post No2 in http://www.cheresources.com/invision/topic/16197-mass-and-energy-balance-calculations-for-gold-processing) indicates Au losses of 0.5% in the (post beneficiation) ore (this could be up to 10%), but does not mention NaCN losses (despite mass balance requested from students).
On the other hand http://osdir.com/patents/Metallurgical-processes/Reducing-cyanide-consumption-gold-recovery-finely-ground-sulphide-ores-concentrates-07488370.html indicate NaCN consumption of 1.5-2.5 kg/t in commercial methods, versus 12-20 kg/t in the patented method, where apparently t=tonne of ore. Even supposing that ore contains 31.25 g Au /t (really high, per 2nd link above), NaCN consumption is 48-80 kg / kg Au in commercial methods, too high compared to stoichiometry. A lot of NaCN seems to be spent in "parasitic" reactions.
Another source reports NaCN consumption as 1.0 kg/t, [url="http://www.unep.org/hazardoussubstances/Portals/9/Mercury/Documents/PartneshipsAreas/HylanderEtal_CLEAN-07.pdf"]http://www.unep.org/...al_CLEAN-07.pdf [url] (ore pretreated using Hg).
If I need precise consumption of NaCN, I would ask process technology suppliers, hoping of their response. Complete chemical (and if possible mineralogical) analysis of the ore should be given.
Alternatively for a student project, one can assume a value based on reasonable assumptions, in collaboration with Instructor.
If some more precise answer is received from knowledgeable members, above can change.

Edited by kkala, 07 January 2013 - 02:38 AM.

[shasha]

thank you so much for the information...we are planning to put up a small scale mining operation and we would like to assess the quantities of materials needed.