Copper is extracted from porphyry ores containing <1 pct cu as sulfide with considerable fe that are buried too deeply for openpit mining, if they can be made permeable by explosives or high pressure, by leaching with dilute h2so4 containing an oxidizing agent such as nitrate ion and alkali metal or ammonium ions to form with the dissolved iron a sandy crystalline jarosite having the composition rfe3(so4)2(oh)6, where r is na, k, or nh4. This compound, which is formed at 70 deg-120 deg c, ph 0.5-3, and oxygen overpressure at least 25 psi, does not prevent permeability of a leach solution through shattered rock as precipitation of fe(oh)3 does. This process is especially suited for underground leaching, but less so for leaching above-ground waste piles. Leach solutions containing up to 50 g cu/l and fe <100 ppm were obtained by subsurface leaching of lean chalcopyrite ore in this way, leaving most of the s underground in the elemental form. The no3- ion concentration in the solution used should be 0.05-0.5 pct, but the alkali metal or ammonium ions should be in excess of the amount required to form jarosite from the iron present. In laboratory leach tests at 80 deg c and 1 atm o2 pressure for 2 weeks in 1.8-9.2 pct h2so4 and hno3 up to 1 pct, 43 pct of the cu was extracted with 0.25 pct hno3, irrespective of the h2so4 concentration. With 1 pct hno3 the extraction was improved to approximately 70 pct with 9.2 pct h2so4.
U.S. Pat. 3,912,330; Oct. 14, 1975; Chem. Abstr. 81:P124,651e