cyanidation

The presence of copper oxide next to gold increases the consumption of cyanide in the cyanidation process, reduces the absorption of gold on carbon, and causes many problems in the downstream processes of elution, electrowinning, and smelting. In the current research, increasing the recovery of gold dissolution and its selective adsorption on activated carbon using ammonia additive and the effect of different factors such as the type of ammonia additive, changing the system of contact of gold with carbon from CIL to CIC, and adding hydrogen peroxide and cyanide to the filtered solution were studied. The findings showed that adding ammonium chloride or liquid ammonia to the cyanidation solution, in the sample with high copper grade (1% copper), and in the sample with medium copper grade (0.5% copper), increased the dissolution recovery by 60% and 30%, respectively. Also, the recovery of gold adsorption on activated carbon in sample with a grade of 0.5% copper increased from about 25% during the normal CIL process to about 100% during the ammonia cyanidation process in the form of CIC. Results showed that liquid ammonia provides up to 10% higher dissolution recovery and up to 3% higher absorption recovery compared to ammonium chloride, while reduces the consumption of cyanide by half and the amount of copper absorption on carbon by a third.

Nugget effect is a common feature of many vein-style gold deposits. This style of mineralization results in complication in many exploitation stages including resource and average grade estimation, representative sample selection, ore characterization as well as processing. Accurate and reliable ore characterization is a vital stage in any mineral processing project. Ore characterization in high nugget effect gold ores is so complex due to uncertainties associated with representativity of the selected sample. The main challenge is to provide a representative sample for identification of each process mineralogy parameter such as average grade, liberation, grinding size, mineral association, floatability, etc. Here, different protocols are collected and compared to draw a comprehensive picture of the available methods. The results are examined on a high nugget effect gold ore from Northeast of Iran, Azghad mine. Processing experiments were conducted to develop a process suitable for Azghad gold mine. To investigate the feasibility of pre-concentration, gravity methods using a Nelson separator was applied on the oxide sample as the main gold vein. 43.3% of total gold was concentrated in the gravity concentrate with only 2% weight recovery, suggesting gravity concentration can be considered as an efficient method in this ore. Gold preg-robbing experiments were performed for Shale sample due to the organic matter, clay minerals and mica. Preg-robbing potential of the shale ore was determined to be 1.1 ppm. Optimization of operating parameters was performed by central composite design method for the combined oxide and shale samples.

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.