Kinetics and Adsorption Isotherms Study of Cyanide Removal from Gold Processing Wastewater Using Natural and Impregnated Zeolites

The extraction of gold involves using cyanide which has the potential to impact the environment. Many studies have been done to reduce the environmental effects of cyanide. In this research, the cyanide adsorption on zeolite from gold processing plant tailing dam wastewater was investigated. Results indicated that the pH of the solution, contact time duration, temperature, zeolite amount and size of zeolite particles were the most important parameters in the adsorption process. Zeolite was used in two fraction sizes; (100-300)m and (300-1000)m in two types of natural and impregnated with copper sulfates. The optimum amounts of both natural and impregnated zeolite in the solutions and the maximum cyanide adsorption percentage were determined as 30, 24g/L and 50.2, 86.1% for small fraction size, and 36, 24g/L and 39.5, 64% for large fraction size, respectively. The optimum values of pH were 10.5 and 10 for natural and impregnated types in both fraction sizes. Contact time duration in equilibrium conditions for fraction sizes of (100-300)m and (300-1000)m were 40 and 50 min, respectively. The optimum temperature in all situations was 22 ºC. The adsorption process in a size of (100-300)m for natural zeolite was fit into the Freundlich model and for impregnated zeolite type there was no significant difference between two models, although, the Langmuir model was more accurate. In a fraction size of (100-300)m for two types of zeolites, the kinetic adsorption was fit into the Lagergren second-order kinetic model. In a fraction size of (300-1000)m, the adsorption kinetics for the natural type has no sensible difference between the first and second Lagergren kinetic model, but for the impregnated zeolite type it follows the second-order kinetic model. The results showed that the cyanide adsorption on impregnated zeolite was more than the natural type.