Abstract: In a process of producing copper(I) oxide by the action of an aqueous solution of a mineral acid and of oxygen-containing gas on small-lump copper metal with continuous agitation, a temperature from 10.degree. to 40.degree. C., preferably from 15.degree. to 35.degree. C., is maintained to effect a formation of particulate yellow copper(I) oxide (Cu.sub.2 O). An organic acid of the group consisting of formic acid, acetic acid, ascorbic acid, preferably ascorbic acid, may be used in addition to the mineral acid.

Abstract: A process for extracting copper from a compact mass, such as bulk metallic copper and/or copper highly contaminated with insoluble substances, in which the mass of metallic copper is leached with a liquor containing Cu.sup.2+ ions and SO.sub.4.sup.2- ions, the liquor being oxidized separately from the leaching stage, e.g. with oxidizing agents including oxygen-containing gases such as air. At least part of the oxidized liquor is recycled to the leaching stage for the metallic copper. The copper sulfate solution which thus results is recovered.