Iron as a co-additive in refining crude lead bullion Grant US-5223021-A United States of America 29 Jun 1993
Iron and a copper speiss as co-additives in refining crude lead bullion Grant US-5183497-A United States of America 02 Feb 1993
Copper speiss as a co-additive in refining crude lead bullion Grant US-5183496-A United States of America 02 Feb 1993
Process for purifying lead using calcium/sodium filter cake Grant US-5100466-A United States of America 31 Mar 1992