Thiocarbamoyl derivatives of polyallylamine for gold and silver recovery from ammonia-thiosulfate leachates

Due to the decreasing number of reach placer gold deposits in Russia and in the world, there is growing interest to the recovery of fine gold from wastes of gold industry [1]. Typically, application of gravitation separation to this type of raw materials is of low efficacy, while cyanide leaching is limited by the presence of refractory minerals [2]. Besides, serious concern regar ding ecological safety of gold leaching promotes interest to cyanide-free alternatives, first of all, to ammoniathiosulfate leaching [3–6]. In contrast to cyanides, thiosulfates are biodegradable and low toxic that makes them applicable in-situ underground and heap leaching, moreover, they are cheaper and more efficient in case of carbonaceous ores and ores, containing copper, lead and zinc [4]. Depending on the type of raw material and leaching solution composition efficacy of ammonia-thiosulfate leaching reaches 50–95% [7]. However, optimization of leaching conditions is rather complicated due to the number of side reactions of oxidation and disproportionation involving thiosulfates [5]. Recovery of gold from ammonia-thiosulfate solutions is also not simple. Cementation is not efficient due to coprecipitation of copper and other metals [8]. Electrowinning allows in principle separation of copper and gold due to the difference in deposition potentials [9], but, in most cases, low purity product is obtain, moreover, low current efficiency markedly increases energy consumption [6]. Organic solvents extraction of gold with high efficacy (up to 97%) [10] is an example of expensive and limitedly applicable technology. Sorption of gold from cyanide leaching solution is the most simple and economically sound method, however, Thiocarbamoyl derivatives of polyallylamine for gold and silver recovery from ammonia-thiosulfate leachates*