Cyanide processing has been the mainstay of hydrometallurgical gold recovery for over a century. The perception of a cyanide issue in relation to gold recovery seems to take little account of the number of people have been harmed by it over the past century, or that gold recovery only consumes around 66,000 t/y out of the 1-2 Mt/y of global HCN production. A couple of key differences are that most of the current non-gold applications involve no off-site transport of the HCN and convert it into products with little potential for HCN release unless they are combusted.
Despite decades of research there is still no clear universal replacement in sight. Perhaps one has to remember that initial driving force for application of cyanide was the high costs for chlorine processing of ‘lower grade’ ‘less oxidized’ ores. This led to its use before its almost universal applicability was recognised, while the potential to dissolve gold in cyanide had been identified by researchers a century earlier. Our current understanding of thermodynamics and electrochemistry suggests there is little prospect of identifying a universal challenger to cyanide. However as the remaining gold ores become more complex, more areas are identified where there are issues with the application of cyanide. Hence it is quite likely that some of the possible cyanide replacements can be developed to commercialisation for niche applications, as has been the case for thiosulfate at Barrick Goldstrike.
This paper reviews the current status of potential replacements for cyanide as well as the issues and the possible drivers for various niche applications.
In the absence of a cost effective replacement for cyanide fixing the cyanide issue requires industry wide commitment to consistently addressing the real and perceived issues. The development and implementation of the International Cyanide Management Code has been a good start. Unfortunately it will not be the 99% of compliance that attracts public, but the issues that slip through the net. Transport to site will continue to be viewed with concern, but the more significant issues are likely to be cyanide containing tailings and best practice water treatment for off-site disposal of excess water.