optimization of Effective factors in cyanide leaching of gold ore

A sample from "Zaylik" exploration area were taken. Microscopic studies (polished thin sections and polished sections), XRD, XRF and SEM showed that this ore is an oxidized zone. The main mineral is quartz and other minerals consist of clay, secondary hydrous iron oxides and rarely Pyrite, Chalcopyrite, Gold, Azurite and Malachite. Due to the dispersion of fine gold, cyanidation process was conducted without any pre-processing. Cyanidation experiments with effective factors concluding pH, d80, cyanide concentration and leaching time were conducted in a CCD design using the DX8 software. The software proposed models for gold recovery and remaining free cyanide respectively with R2 values of 0.77 and 0.83. In the next step, the optimum conditions obtained from the models were validated experimentally and improved by oxidation and kinetics tests. Pre-aeration was done with flow rate 0.6 lit /min in 3 hours and this was found suitable. Periodic addition of sodium cyanide was found preferable rather than instant adding at time zero. Considering the fact that the recovery did not differ significantly in 24 hours and 12 hours, the optimum leaching time was considered 12 hours. In 12 hours, 1050 ppm sodium cyanide was consumed and in order to achieve optimum recovery of %93.93, pH of 10.15 and d80 of 106 microns should exist in the system.