Davey Desilverizing Process at Penarroya’s Noyelles-Godault Lead Refinery

Summary

The Davey desilverizing procedure was introduced at the Noyelles-Godault lead refinery in 1976–1977, following earlier small-scale tests. The procedure is a two-stage, one-kettle operation which completely eliminates the labor associated with skimming second-stage (low-grade) crusts, or scraping the kettle sides during the final cooling stage. The second-stage crusts are formed as a bridge in the kettle by cooling the bath surface with a water-cooled steel tray and simultaneously stirring the lead at a controlled rate.

The main advantage of the new procedure is a reduction in labor. In addition, crane requirements, zinc consumption, total time of treatment, and kettle maintenance are reduced; the refinery is cleaner (due to elimination of return crusts); and more consistent low final silver figures are obtained. Fuel consumption may be slightly increased, and two extra pieces of equipment are required — the tray cooler, and a stirrer with a modified impellor or a variable-speed drive.

Over half a million tons** The figures given as “tons” in this paper all refer to metric tons. of lead have been desilverized by this procedure at Noyelles-Godault. The process is covered by a U.S. patent¹ and applications in other countries.