Application of Response Surface Methodol

Over the last decade, the use of new alternative lixiviants for gold extraction has been investigated to overcome the environmental concerns resulting from the cyanidation process. Moreover, with gold economic factors causing a declining gold price, it is crucial that novel hydrometallurgical methods of extracting gold minimize operational costs by using low-priced reagents such as thiosulfate. In the current study, the response surface methodology (RSM) approach is used to optimize the kinetic factors (temperature and copper, ammonia, and thiosulfate concentration) affecting gold leaching. Gold ore assayed at 16 g/t was characterized through X-ray fluorescence and X-ray diffraction spectrometric analysis using an energy dispersive spectrometric technique. Gold ore was predominantly siliceous with minor pyritic content. The results indicate a strong relationship between the actual gold leaching recovery data and the RSM model. Correlation coefficients R² and adjusted R² are equivalent to 0.9869 and 0.9781, respectively. Gold leaching in copper-ammonia-thiosulfate media is best described as a surface-controlled reaction-controlled process, suggesting that gold dissolution in thiosulfate is considerably affected by the increase in temperature. The effect of temperature is mostly significant, contributing up to 64.65% of the gold recovery process model. The contribution percentages of the effects of time, thiosulfate [S2O3], ammonia [NH3], and copper [Cu] concentrations were calculated as 12.81%, 5.88%, 5.19%, and 4.65%, respectively. All investigated kinetic parameters were found statistically significant with p-values of <0.05. The optimal concentrations of gold leaching media to achieve potentially complete dissolution of gold from ores in copper-ammonia thiosulfate media based on the effect of the investigated parameters were 0.5 M S2O3, 0.3 M NH3, and 0.003 M Cu²⁺ with a desirability value equivalent to unity (d = 1.000).