If this was reagent grade elemental sulphur then it can be fairly hydrophobic and therefore very slow to react. If you want to observe it in the lab then it helps if the pH is elevated and a surfactant to disperse the sulfur may also assist.

I work for a gold mine using the Biox process for oxidation of gold bearing pyrite/arsenopyrite. One of the side reactions in the process generates elemental sulfur which is in a colloidal form and this reacts extremely quickly with NaCN. Our leach liquor contains significant thiocyanate levels

SO doesn't exist and what is the point here. You will get SCN- due to the complex breakdown of sulphur compounds but nothing as you stated on your formula. Get chemistry right first.

He referred S0 (elemental sulphur), not SO (sulphur oxide). This was just a limitation of the way that characters can be expressed.

It is always worth remembering that text, without the positive context of voice, can very easily be misinterpreted. This is a professional forum for respectful, professional exchanges, and we should all be careful to ensure that our mutual goodwill is evident in everything that we write.

The chemical convention is to express the symbol of an elementary compounds is to write it without any valence indicator like S + CN- = SCN- . This avoids confusion particularly when there is a limited characters possibility.

There are authors (H.Ciftci, A.Akcil, 2010, “Effect of bio-oxidation conditions on cyanide consumption and gold recovery from a refractory gold concentrate” and P. Miller and A.Brown, 2005, “Bacterial oxidation of refractory gold concentrates”) who concluded that the high cyanide consumption in bio oxidation residue was due to the formation of jarosite and they reported high amount of SAD CN- and low SCN-. On your plant is there any relationship between the % sulphides oxidized and cyanide consumption? And how efficient is your washing process? Does it wash off all dissolved sulphur species? According to the bio oxidation reaction only elemental sulphur and unreacted sulphides will be carried over to the cyanidation stage. How is your % cyanide distribution (% CN-,%SCN-,%WAD CN- and %SAD CN-) in the cyanide liquor?

I apologies for a very late response. I didn't see any notification that there were further responses to this conversation.

Yes, I am aware that a number of researchers point to jarosites as a possible cause for cyanide consumption and we no doubt generate this mineral in our own BIOX circuit. I followed elemental sulphur levels for some time and tried to correlate these with cyanide consumption but found that the amount of sulphur present did not account for how much cyanide was used. I have also done numerous tests to try and eliminate other cyanide reactive sulphur species but this did not reduce consumption rates. I can only conclude that something else is also consuming cyanide but can't confirm it is jarosite. Un-oxidized sulphide levels are very low and don't seem to contribute significantly to cyanide use (in our case anyway).

A high washing efficiency is certainly very important. The level of residual iron in solution is quite low and doesn't account for much of the cyanide use either.

I have been wondering if there is some kind of catalytic effect at work that speeds up the decomposition of cyanide.
Sorry, I don't have any of the cyanide distribution data available at the moment.