Editing Lead (section)

==== Two-stage process ====

First, the sulfide concentrate is [[Roasting (metallurgy)|roasted]] in air to oxidize the lead sulfide:{{sfn|Thornton|Rautiu|Brush|2001|p=51}}

: 2&nbsp;PbS(s) + 3&nbsp;O<sub>2</sub>(g) → 2&nbsp;PbO(s) + 2&nbsp;SO<sub>2</sub>(g)↑

As the original concentrate was not pure lead sulfide, roasting yields not only the desired lead(II) oxide, but a mixture of oxides, sulfates, and silicates of lead and of the other metals contained in the ore.{{sfn|Davidson|Ryman|Sutherland|Milner|2014|pp=11–12}} This impure lead oxide is reduced in a [[coke (fuel)|coke]]-fired blast furnace to the (again, impure) metal:{{sfn|Thornton|Rautiu|Brush|2001|pp=51–52}}

: 2&nbsp;PbO(s) + C(s) → 2&nbsp;Pb(s) + CO<sub>2</sub>(g)↑

Impurities are mostly arsenic, antimony, bismuth, zinc, copper, silver, and gold. Typically they are removed in a series of [[Pyrometallurgy|pyrometallurgical processes]]. The melt is treated in a [[reverberatory furnace]] with air, steam, sulfur, which oxidizes the impurities except for silver, gold, bismuth. Oxidized contaminants float to the [[dross|top of the melt]] and are skimmed off.{{sfn|Davidson|Ryman|Sutherland|Milner|2014|p=25}}{{sfn|Primary Lead Refining}} Metallic silver and gold are removed and recovered economically by means of the [[Parkes process]], in which zinc is added to lead. Zinc, which is immiscible in lead, dissolves the silver and gold. The zinc solution can be separated from the lead, and the silver and gold retrieved.{{sfn|Primary Lead Refining}}{{sfn|Pauling|1947}} De-silvered lead is freed of bismuth by the [[Betterton–Kroll process]], treating it with metallic [[calcium]] and [[magnesium]]. The resulting bismuth dross can be skimmed off.{{sfn|Primary Lead Refining}}

Alternatively to the pyrometallurgical processes, very pure lead can be obtained by processing smelted lead electrolytically using the [[Betts electrolytic process|Betts process]]. Anodes of impure lead and cathodes of pure lead are placed in an electrolyte of lead [[Hexafluorosilicic acid|fluorosilicate]] (PbSiF<sub>6</sub>). Once electrical potential is applied, impure lead at the anode dissolves and plates onto the cathode, leaving the majority of the impurities in solution.{{sfn|Primary Lead Refining}}{{sfn|Davidson|Ryman|Sutherland|Milner|2014|p=34}} This is a high-cost process and thus mostly reserved for refining bullion containing high percentages of impurities.{{sfn|Davidson|Ryman|Sutherland|Milner|2014|p=23}}