Abstract: An improvement in the process of leaching metal sulfide minerals with an oxidative leaching solution is obtained by adding to the leaching solution over only a portion of the leaching cycle aqueous hydrogen peroxide in an amount ranging from about 2 to about 25 percent by weight of the quantity of hydrogen peroxide required to bring the metal value of the mineral into solution if hydrogen peroxide were used as the sole oxidizing agent.

Abstract: A process for extracting copper from a copper-containing concentrate by comminuting the concentrate in the presence of a liquid dispersing agent which inhibits agglomeration and forms a pulp, and leaching the pulp in the presence of a silver catalyst.

Abstract: Process for receovering copper values (and zinc, if present) from copper bearing materials, optionally in admixture with iron. The feed material is leached with a mixture of nitric and sulphuric acids, after which the dissolved copper is cemented from solution by contact with iron. The solution, containing dissolved iron (and zinc, if present in the feed material) salts is reacted with ZnO to precipitate iron as ferric oxide, which is separated, leaving zinc sulfate in solution. Solid zinc sulfate is recovered from the solution by evaporation, and then calcined to produce SO.sub.2, which is recovered and recycled as H.sub.2 SO.sub.4, and ZnO, which is reused in the process, any excess being recovered as a product.