Processing of GOLD ORES with high sulfide minerals is problematic as they consume cyanide and reduce GOLD leaching. Optimization of GOLD leaching and cyanide consumption requires a methodology to estimate the amount of exposed cyanicides, their leaching kinetics, and speciation of cyanide complexes that consume the free cyanide and compete with GOLD. In this paper, a physico-chemical approach is presented to estimate the liberation and exposure of cyanicides to the leaching solution, and then prediction of the speciation of all possible related species in the solution. The results obtained show that this methodology not only could successfully estimate the GOLD leaching and cyanide consumption based on the mineralogical data with a lower number of parameters compared to existing empirical models, but also offers the prediction of formation of all the possible complexes that could be used for optimization purposes.

The presence of copper bearing minerals in cyanidation of GOLD ORES may lead to several challenges in the CIP/CIL circuits. Many solutions have been proposed to address these problems, one being the use of glycine in the cyanidation process. Here, the experimental as well as molecular modelling studies using Density Functional Theory (DFT) have been conducted to investigate the glycine role in cyanidation of copper bearing GOLD ORES. The results show that in the presence of glycine in the solution containing copper-cyanide species and in very low or zero free cyanide content, the dissolution rate of GOLD is significantly improved (3.02 vs. 0.23 ppm), while no improvement is observed in copper free or cyanide enriched solutions. Molecular modeling has been performed to interpret the laboratory results as well as to identify the mechanisms. The modeling results demonstrate that in cyanide deficient solutions, cyanide complex of copper complexes (E = -319 kCal.mol-1) is replaced by glycine, and the free cyanide produced results in higher GOLD cyanidation as well as lower copper cyanide formation.

This study involved preliminary laboratory test work to identify the relative leaching response to cyanidation and thiourea leaching of an oxidized low grade GOLD ore based on characterization studies. Huge reserves of GOLD deposits have been reported from different parts of Iran, especially at Neishaboor area with GOLD grade of approx 4 ppm. For the mineralogical composition, the nature of the minerals, type of GOLD, chemical characters and the suitable mesh of grind which play vital role in finding out suitable flowsheet design, the representative samples were subjected to detailed characterization studies and found that, the ore is oxidized and GOLD is present partly in the from of solution in quartz veins as well as in the form of free particles in iron hydroxide specially hematite which is the product of pyrite oxidation. Quartz, hematite, calcite and feldspar are the main minerals present in the order of abundances. Sieve analysis and distribution of GOLD particles in different sieve fractions shows most of the GOLD are distributed bellow 2000 microns. Therefore based on characterization studies, the potential of an alternative lixiviate like thiourea leach have been determined and found that under optimized conditions cyanide leaching of the ore performs (extraction of 95% after 240 hours) better than thiourea leaching (extraction of 10% after 240 hours and 67% after 662 hours).

In this study preliminary laboratory test work to identify the relative agitation leaching response to cyanidation and thiourea leaching of an oxidized ore have been carried out. The ore deposits of Neishaboor area with GOLD grade of 4ppm are rich enough for beneficiation studies.The characterization studies show that, the ore is oxidized and GOLD is present partly in the form of solution in quartz veins as well as in the form of free particles in iron hydroxide specially hematite which is the product of pyrite oxidation. Quartz, hematite, calcite and feldspar are the main minerals present in the order of abundances. Sieve analysis and distribution of GOLD particles in different sieve fractions shows GOLD particles are distributed bellow 2000 microns.Based on characterization studies, the potential of an alternative lixiviant like thiourea and cyanide leach have been determined and found that under optimized conditions thiourea leaching of the ore performs (extraction of 96.7% after 16 hours) better than cyanide leaching (extraction of 47.3 after 16 hours).

Zarshuran mine located at 35 km north of Takab city in an area of about 37 square kilometers at a distance of 7 km from Zarshuran village and consists of sulfide minerals such as pyrite, ralgar, overpement, arsenopyrite, stebenite, sphalerite, galen and cinnabar. About 55 to 60% of the GOLD in this ore is in solid solution inside the crystal lattices of pyrite and arsenopyrite and this has caused the resistance of GOLD ore in the cyanation process to increase and the percentage of GOLD recovery in the cyanation process to decrease. Therefore, ferric ion oxidation method was investigated to release GOLD from sulfide minerals and under optimal conditions, ion ferric concentration of 11 g / l, time 8 hours, temperature 45 ° C, pH equal to 1 and pulp density 25% recovery GOLD increased to 72%, while under direct cyanation process without oxidation with ferric ion, the maximum recovery of GOLD was 41%, which shows that the oxidation process with ion ferric can increase the recovery of GOLD in the cyanation process by 31%.

By depletion of high-grade and easy-to-treat GOLD ORES and the increase in GOLD price, the extraction of GOLD from low-grade and refractory ORES, such as sulfide ORES has been given attention. Biooxidation is one of the efficient, relatively low-cost and environmentally friendly processes to enhance GOLD extraction by releasing fine GOLD encapsulated in sulfide phases. So, in this research, the efficiency of concentrate biooxidation-flotation system in increasing GOLD recovery from sulfide-refractory low-grade ORES was investigated. Biooxidation experiments with mesophilic and moderate thermophilic microorganisms were conducted on the flotation concentrate. Finally, cyanidation experiments were conducted on the flotation concentrate, and biooxidized flotation concentrate. GOLD recovery from non-biooxidized flotation concentrate was 63.59%, while it increased to 80.21% after biooxidation with mesophilic microorganisms and to 79.84% after biooxidation with moderate thermophilic microorganisms.