Oxidized copper minerals in basic carbonate rocks are leached by a naoh solution of a siliceous material (approx. 60-85 Wt pct of the cu ore), e.g., pulverized diatomaceous earth, sodium silicate, silicic acid. The sio2 addition should be made to a naoh leach solution even if the cu ore contains sio2. In a series of experiments with 75-g batches of ore, 800 ml of 25 pct naoh solution was used at 90 deg c for each batch with varying amounts of powdered diatomaceous earth, and the cu extraction into solution is reported after 1, 3, 8, and 40 min of leach, respectively. With no diatomaceous earth, the cu extractions were 37.5 pct in 1 min, 33 in 3, 30 in 8, and 11.7 In 40, showing how cuo was precipitated out of solution. With 40 g of diatomaceous earth/75 g of ore, the results were 60.9, 50.8, 60, and 63.5 pct, respectively; and with 100 g, 89, 86.3, 88.6, and 87.4 pct extraction, respectively.
U.S. Pat. 3,985,855; Oct 12, 1976; Chem. Abstr. 84:138,943A