عنوان مقاله [English]
Natural degradation of cyanide is one of the oldest methods used to remove the cyanide present in industrial wastewater of electroplating and extraction processes in gold and silver industries. The most important mechanism involved in the natural degradation of cyanide is volatilization which is affected by parameters such as impoundment surface, soil porosity and density, initial concentration, and atmospheric conditions. The objective of the present study was to determine the effects of those parameters involved in natural degradation that can be varied to optimize the design or operation of tailings impoundment. The experiments carried out in this study were of the completely random, statistical factorial, and time-split design using the four major variables of time, surface to depth ratio, tillage operations, and soil cyanide initial concentration. The experiments included 3 levels for surface-depth ratio, 2 levels for tillage operation, and 2 levels for initial concentration with three replications to yield a total number of 36 pilots. Cyanide measurements were performed at four intervals. Statistical analysis and variance of the data obtained on soil cyanide concentration showed that time had the highest effect on soil cyanide removal. Tillage and increased initial contamination both increased cyanide removal efficiency. For a given volume of cyanide contaminated soil, increased surface-depth ratio led to a faster reduction of soil cyanide residual. The regression analysis of the data obtained from this study resulted in the development of a model that can be used to predict soil cyanide concentration with respect to such parameters as time, initial contamination, and surface-depth ratio.