ABSTRACT
The molten metal is poured into and withdraws from the kettle by a centrifugal pump carried from kettle to kettle by an overhead travelling crane. Portable stirrers are used to mix the molten metal in the kettle. Bismuth occurs in most lead ores and follows lead all the way during the smelting and refining operations. There are two ways of removing bismuth: electrolytically or by precipitation. Zinc produced by pyrometallurgical reduction is of lower grade than that produced by the hydrometallurgical method. In the precipitation method, crude zinc is melted in a reverberatory furnace of about 150 tonnes capacity and the molten bath is held in a quiescent state at 420°–450°C for 24 to 48 hours. The lead-zine solution then joins the lead layer near the top of the kettle; it displaces an equal amount of lead from the bottom of the kettle, which discharges through the siphon tap passing vertically upward through the central axis of the kettle.
