US Patent 8003581 Iron control agent

An iron control agent capable of reducing ferric iron containing compounds to ferrous iron containing compounds in an acidic solution, such as one used for formation acidizing. The iron control agent comprises a combination of a sulfur dioxide, sulfurous acid, sulfite salts, bisulfite salts, or thiosulfate salts or mixtures thereof, with a source of copper ions and a source of iodine or iodine ions. The iron control agent may also include small amounts of an adjunct such as stannous chloride, 2-mercaptoethanol, and thioglycolic acid and its salts.