Application of Response Surface Method and Central Composite Design for Modeling and Optimization of Gold and Silver Recovery in Cyanidation Process

Abstract

In this study, application of the Response Surface Methodology and the Central Composite Design (CCD) technique for modeling and optimization the influence of some operating variables on gold and silver recovery in a cyanidation process were investigated. Three main cyanidation parameters, namely grinding time, sodium cyanide concentration, and alkalinity of solution, were changed during the concentration tests based on CCD. The range of values of the cyanidation process variables used in the design was as follows: grinding time, 32.61–44.39 min, sodium cyanide concentration, 1989–4511 ppm, and pH, 9.32–12.68. A total of 20 cyanidation tests were designed and carried out in the CCD method according to software-based designed matrix. According to the results, i.e., gold and silver recoveries with these three parameters, empirical model equations, were developed. Second-order equations of responses at the base of parameters were achieved by using statistical software. The model equations were then individually optimized by using quadratic programming to maximize both gold and silver recoveries within the experimental range. The optimum conditions were found to be 41.89 min for grinding time, 3665.28 ppm for cyanide concentration, and pH 9.32, for achieving the maximum gold recovery (96.23%). Similarly, the conditions for maximum silver recovery were 65.62% at 44.39 min for grinding time, 4511.34 ppm for cyanide concentration, and pH 12.68. The predicted values for gold and silver recoveries were found to be in a good agreement with the experimental values, with R 2 as correlation factor being 0.91 and 0.94, respectively.