Process for the acid digestion of metal-containing compounds

A process comprising:

• providing a metal-containing compound;
• and
• subjecting the metal-containing compound to an acid digestion comprising contacting the metal-containing compound with an aqueous leachant;
• wherein the aqueous leachant comprises a mixture selected from the group consisting of:
• (i) sulfuric acid and one or more alkanesulfonic acids having alkane moieties selected from the group consisting of propyl, ethyl and methyl groups, at a weight ratio of alkanesulfonic acid to sulfuric acid of 1:1000 to 1:1;
• (ii) sulfuric acid and one or more salts of alkanesulfonic acids having alkane moieties selected from the group consisting of propyl, ethyl and methyl groups, at a weight ratio of salt of alkanesulfonic acid to sulfuric acid of 1:9 to 1:99.

An aqueous leachant comprising:

• (a) 0,001-50% by weight of one or more alkanesulfonic acids having a propyl, ethyl or methyl moiety;
• (b) 0.1-50% by weight of sulfuric acid;
• and
• (c) 0-5% by weight of one or more nonionic, anionic, cationic, or amphoteric surfactants;
• wherein the weight ratio of alkanesulfonic acid to sulfuric acid is 1:1000 to 1:1.

An aqueous leachant comprising:

• (a) 1-10% by weight of one or more salts or alkanesulfonic acids having a propyl, ethyl or methyl moiety;
• (b) 90-99% by weight of sulfuric acid;
• and
• (c) 0-5% by weight of one or more nonionic, anionic, cationic or amphoteric surfactants,
• wherein the weight ratio of salt of alkanesulfonic acid to sulfuric acid is 1:9 to 1:99.