A review of thiocyanate gold leaching - Chemistry, thermodynamics, kinetics and processing

Thiocyanate is among the most promising alternative gold lixiviants for gold leaching and has not been extensively covered in the literature. Thiocyanate is 1000 times less toxic than cyanide and is a very strong gold leaching lixiviant. This review paper provides an overview of the chemistry, thermodynamics, kinetics, and processing of gold leaching using thiocyanate as well as gold recovery from the pregnant leach solution.One main reason that the thiocyanate gold leaching process has not yet been commercialized is that the process requires a reduction-oxidation (redox) potential higher than that required of cyanide gold leaching. The oxidant, mostly ferric, is needed to leach gold. However, the redox potential must be lowered by removing oxidants to allow gold recovery from the pregnant leach solution. The molar ratio of oxidant to thiocyanate is considered an effective parameter for gold oxidation kinetics and should range between 2 and 20. Thiocyanate gold leaching is an electrochemical reaction which occurs at pH 1.5-2.5 and electrochemical potential of 600-700 mV. The literature shows fast gold leaching kinetics in well-designed thiocyanate systems. The solubilized gold-thiocyanate species can be recovered from the pregnant leach solution by a variety of methods including conventional activated carbon adsorption, solvent extraction, ion exchange, and cementation. Leaching can be performed in both heaps and tanks.

硫氰酸盐是最有前景的可替代金浸出剂之一，用于金的浸出，但在文献中尚未被广泛涵盖。硫氰酸盐的毒性比氰化物低1000倍，是一种非常强的金浸出剂。这篇综述论文概述了使用硫氰酸盐浸出金的化学、热力学、动力学和工艺过程，以及从富金浸出液中回收金的方法。硫氰酸盐浸金工艺尚未商业化的一个主要原因是，该工艺所需的氧化还原电位比氰化浸金所需的电位高。需要氧化剂（主要是三价铁）来浸出金。然而，必须通过去除氧化剂来降低氧化还原电位，以便从富金浸出液中回收金。氧化剂与硫氰酸盐的摩尔比被认为是金氧化动力学的一个有效参数，其范围应在2到20之间。硫氰酸盐浸金是一种电化学反应，发生在pH值为1.5 - 2.5以及电势为600 - 700 mV的条件下。文献表明，在设计良好的硫氰酸盐体系中，金的浸出动力学很快。溶解的金 - 硫氰酸盐物质可以通过多种方法从富金浸出液中回收，包括常规的活性炭吸附、溶剂萃取、离子交换和置换沉淀。浸出既可以在堆浸中进行，也可以在槽浸中进行。