Copper is precipitated from acid solutions with metallic iron with agitation in a closed vessel at room temperature under 50-300 psig H2 pressure. Under these conditions stronger leach solutions containing 2-10 pct free acid can be used for improved extraction of copper from ore deposits or slag, and the cost of sponge iron or scrap required for copper reduction is reduced. In experiments on the agitation of sponge iron in an excess of 5-pct H2SO4 under different H2 pressures, the iron weight losses in 1 h were 18 pct at atmospheric pressure, 14 pct at 50 psig, and 1.2 pct at 200 or 250 psig H2 pressure. In other experiments with the same acid containing 2 g/l Cu and 1/2-10 times as much iron powder present as there was Cu in solution, reacting for 1-2 h gave a 7.49 ratio of iron loss/lb Cu precipitated with no H2 pressure and 3.42-1.57 with 200 psig H2 pressure, whereas when no iron was present, 250 psig H2 gave no cu precipitation.
U.S. Pat. 3,877,932; Apr. 15, 1975; Chem. Abstr. 83:31,406E