Effect of multistage solution-mineral contact in in-situ recovery for low-grade natural copper samples: Extraction, acid consumption, ganguemineral changes and precipitation

Recent decreases in the grades of copper reserves have stimulated interest in alternative mining technologies, such as in-situ recovery (ISR), which may be an attractive mining approach for low-grade ores. In ISR operations, lixiviant contacts subsurface ore when it is pumped through the deposit. Continuous flow of lixiviant with suitable properties (such as pH and solution potential, Eh) is required from the wellfield injection point through the ore to the recovery point. Leach solution pH and Eh adjustment is not possible between boreholes and therefore, undesired precipitate formation may result, which could produce blockages and restrict solution flow. Our experiments aimed to simulate the chemical processes that may occur when leach solution travels through an ore deposit from the injection to the recovery well by contacting a pregnant leach solution with fresh ore over multiple stages. Low-grade natural ore that contained refractory copper sulfides mixed with gangue minerals was leached with iron (III) as an oxidant in sulfuric, hydrochloric or methanesulfonic acid at 90 degrees C. The leach solution was contacted for 72 h with fresh ore in five successive stages, without acid or oxidant replenishment. Although copper extraction continued for the duration of the five stages, the copper extraction dropped off after two contact stages. Precipitates formed in all solutions after three contact stages; akaganeite precipitated in the chloride systems and jarosite and gypsum formed in the sulfate systems after the second contact stage. The extent of precipitation is predicted to increase with an increase in temperature and pH. These findings provide insights into the behaviour that could be expected in ISR operations and factors that influence borehole spacing and ensure continuous lixiviant-ore contact subsurface.