Cyanide removal for ultrafine gold cyanide residues by chemical oxidation methods

Because of the highly toxic cyanide in the gold cyanide residues, cyanide must be removed for environmental protection. The process mineralogy of residues was studied firstly, and then cyanide removal was carried out by three chemical methods. The results showed that the residue mainly contained Si, S and Fe. Pyrite was the main metallic mineral, and the iron-complex cyanides make cyanide removal difficult. The minerals in residues were in ultrafine particle size with high monomer dissociation degrees. In H2O2 oxidation process, the self-decomposition and side reactions resulted in high consumption of H2O2. In Na2S2O5-air oxidation process, the time for complete process was long because of the reactions between Na2S2O5 and O-2. Na2SO3 oxidation method was found to be a new method for cyanide removal without air inflation device. The cyanide content was reduced to the national standard level in 90 min at pH 9.0 with optimum Na2SO3 dose of 2.0 g/L.

Automated summary

This study investigated the process mineralogy of gold cyanide residues and carried out cyanide removal using three chemical methods. The results revealed that the residues primarily contained Si, S, and Fe, with pyrite being the main metallic mineral. The presence of iron-complex cyanides made the removal process difficult. The study also found that Na2SO3 oxidation method was a new and efficient approach for removing cyanide in the residues.