Ores or concentrates of cu, ni, CO, fe, mn, and zn can be leached more selectively and without wasting acid on such minerals as limestone or calcite, if an aqueous solution of an amine polycarboxylic acid chelating agent is used as the extractant instead of a strong mineral acid. The stability constant of the chelate of the metal to be extracted must be >10-3/k, where k is the solubility product constant in h2o of the compound that is the source of the metal leached. Since ethylenediamine tetraacetic acid (edta) forms a chelate with cu having a stability constant 10x greater than that formed with ca in solutions having a ph of approximately 7, this acid is very suitable for leaching cu from an ore having caco3 gangue. It also forms chelates having stability constants >10 10 with all the metals in the group above. The process is generally suitable for carbonate, oxide, hydroxide, and silicate ore materials since they generally have sufficient aqueous solubility. When a mixture of 97 g of caco3 and 3 g cuco3 was leached with 1l of aqueous 10 vol pct edta solution at 30 deg. C and ph 7.8-8 For 30 min, all the cu was dissolved with a 12/88 weight ratio of dissolved ca/cu. In a similar extraction of cu from limestone ore containing 0.8 pct cu, all the cu was dissolved in 1 h at ph 7 by a 2.5 Wt pct edta solution. Cu(oh)2 was precipitated from these solutions by addition of cao or ca(oh)2 to ph 11-13, and filtered out; the filtrate ph was adjusted to approximately 8 and used for further leaching.
U.S. Pat. 3,634,070; Jan. 11, 1972; Chem. Abstr. 76:88,930F