Experimental leaching of atacamite, chrysocolla and malachite: Relationship between copper retention and cation exchange capacity

Copper retention due to chemical and physical interaction with reactive gangue has been studied during sulphuric acid leaching of atacamite, chrysocolla and malachite, using a synthetic rock (57% quartz, 42% reactive gangue and 1% ore). Smectite- and mordenite-rich gangues represent the highest copper retention whereas the lowest is found for kaolinites and illite. During leaching, smectites show the largest change (increase) in volume; no volume change occurred for kaolinites, zeolite and illite. Kaolinite-rich gangue forms barriers due to de-lamination demonstrated by acid accumulation at the top of the columns. ray diffraction patterns of smectite, illite and kaolinite in the residues demonstrate the diminution or complete loss of basal crystal faces accompanied by the neo-formation of alunogen, meta-alunogen, coquimbite and goldichite. These new phases contribute to a temporary reduction of permeability. For all the synthetic rocks assayed, the copper retention is directly proportional to cation exchange capacity (CEC) of the starting materials, and corroborated by the CEC of Cu of the residues determined without water elution prior to analysis. est used represents a predictive tool to evaluate the potential Cu retention and gangues with elevated CEC.