Weirton Steel Corporation

John L Swanson

Lowell W Austin

Stannous electrolytic tinplating baths utilized in flat-rolled steel tinplating operations contain non-filterable lead in solution at undesirable levels because of the lead content of commercially available tin anode materials. As taught herein, lead in the electrolyte is controllably incapacitated for deposition with the tin by chemical treatment of the bath which establishes, in solid phase, an insoluble bivalent metal compound having an affinity for lead which is adsorbed. In a preferred halogen-system embodiment, calcium fluoride presents an extended surface area for adhesion of lead and not only incapacitates lead in the bath for deposition purposes but also enables separation of such adsorbed lead from the plating bath as part of sludge removal. Quantitatively increasing, within an established range, the concentration of such a lead-absorbent solid-phase bivalent metal compound in the plating bath quantitatively decreases the percent by weight of lead deposited as part of the tin plating on the substrate.

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Pittsburgh, PA, United States of America

John L Swanson