In situ recovery of gold: Column leaching experiments and reactive transport modeling

In situ leaching (ISL) is the dissolution and subsequent recovery of minerals from the subsurface by injection of a chemical solution. Because ISL of gold does not involve bulk rock mining, it has great potential to be substantially more environmentally friendly than conventional methods. However, detailed experiments and modeling are needed before ISL of gold is viable at an operational scale. Therefore, laboratory column tests using an iodide/tri-iodide solution as a proxy for a potential lixiviant were carried out to develop a conceptual and numerical modeling framework for gold ISL operations. The key processes affecting gold ISL for flow-through conditions were identified as (i) dual-domain type transport behavior, i.e., transport occurring mainly along preferential pathways, (ii) reprecipitation of gold, at locations where the tri-iodide decreases to a level where it is too low to keep the gold in solution, thus slowing down gold recovery and (iii) the presence of competing reductants in the ore material, which reduce the effectiveness of ISL and the time needed for gold recovery. These findings are crucial for the design and interpretation of field-scale trials and operations.