Extraction of precious metals from technogenic placers of primorye

Intensive development of gold placer deposits in the South Far East of Russia has produced numerous technogenic placers (concentration dump tailings) that contain fine free and bound gold and the platinum group metals. The secondary processing of these technogenic placers makes it possible to extract the whole set of precious metals from the concentration tailings.The authors have elaborated the low-waste technology of extraction of useful components using the methods of gravitation, magnetic and electromagnetic separation, hydrometallurgy, and extraction. Usually, precious metals are leached with cyanide solutions that significantly deteriorate the ecological situation. Instead of them we propose to use thiocarbamide, thiocyanate, and mixed thiocarbamide and thiocyanate solutions in the process of utilization of the technogenic placers. Introduction of thiocyanate ions into the thiocarbamide leaching solutions increases the indices of gold extraction into a leaching solution. Efficiency of the precious metal extraction into leaching solutions is 94%-96%. Our investigations showed that liquid extraction of gold and silver from the leaching solutions permits the precious metals to be extracted with additional separation from admixtures and essential decrease of specific thiocarbamide consumption. Comparatively inexpensive tributyl phosphate and diphenyl thiourea that are manufactured in production quantities, are used as extragents.Utilization of the technogenic placers of Primorye will produce the raw material for repeated extraction of precious metals and will be favorable for the ecological situation in the populous districts of the region where the placers exist.