Heap leaching of gold with in-situ bacterial formation of the leach lixiviant. The case for the bio-formation of (1) cyanide lixiviant, and (2) thiosulfate lixiviant

传统的金浸出和提取方法依赖于使用氰化物（或硫代硫酸盐）作为金浸出剂。在这个过程中，矿石中的金在氰化物（或高浓度硫代硫酸盐）溶液中浸出，然后从溶液中回收为不纯金，最后纯化为99.99%的金。**氰化物是一种毒性极强的试剂；但它对金的浸出具有很强的选择性，浸出效率非常高。因此，在黄金工业中，用其他浸出剂替代氰化物是非常困难的。尽管如此，氰化物盐的运输和处理一直引起人们的关注。这个拟议的项目涉及发展一种就地生成氰化物用于金浸出的替代途径，从而消除在黄金工业中使用氰化物作为“购买试剂”的情况。提出在金堆浸过程中利用产氰菌生产氰化物。在金堆浸出作业中就地形成氰化物将消除从氰化物生产设施购买和运输氰化物到世界各地金矿地点的需要。**作为次要目标，拟议的研究还将研究原位生产硫代硫酸盐的选择，硫代硫酸盐是一种非常有吸引力的金浸出剂，类似于氰化物。硫代硫酸盐金浸出工艺的挑战是硫代硫酸盐试剂的高成本（该工艺需要大量的硫代硫酸盐进行金浸出）。在这个研究项目中，我们还将研究在金堆浸操作中从硫化矿石中原位生产硫代硫酸盐的可能性，从而为金浸出提供一种非常低成本的浸出剂。****

The conventional method for gold leaching and extraction relies on the use of cyanide (or thiosulfate) as the gold leaching lixiviant. In this process gold from the ore is leached in a cyanide (or highly concentrated thiosulfate) solution, and later is recovered from the solution as impure gold, and finally purified to 99.99% gold.**Cyanide is known to be an extremely toxic reagent; however, it is highly selective for gold leaching with very attractive leaching efficiency. Thus the replacement of cyanide with alternative lixiviants is very difficult in the gold industry. Nonetheless, the shipping and handling of cyanide salts to the gold operations have always raised concerns. This proposed project pertains to the development of an alternative route for the in-situ generation of cyanide for gold leaching thus eliminating the use of cyanide as a "purchased-reagent" in the gold industry. Herein, it is proposed to use cyanide producing bacteria in gold heap leaching operations to produce cyanide. The in-situ formation of cyanide in the gold heap leaching operations would eliminate the need for the purchase and shipping of cyanide from the cyanide production facilities to the gold mines sites around the world.**As a secondary objective, the proposed research will also investigate the option for the in-situ production of thiosulfate, which is known to be a very attractive lixiviant for gold leaching, similar to cyanide. The challenge with the thiosulfate gold leaching process is the high cost of the thiosulfate reagent (the process requires large volumes of thiosulfate salt for gold leaching). In this research project we will also investigate the possibility of the in-situ thiosulfate production from the sulfide ores in the gold heap leaching operations, thus providing a very low cost lixiviant for gold leaching.****