Editing Lead (section)

=== Primary ===

Most lead ores contain a low percentage of lead (rich ores have a typical content of 3–8%) which must be concentrated for extraction.{{sfn|Davidson|Ryman|Sutherland|Milner|2014|p=6}} During initial processing, ores typically undergo crushing, dense-medium separation, [[grinding (abrasive cutting)|grinding]], [[froth flotation]], [[drying]]. The resulting concentrate, which has a lead content of 30–80% by mass (regularly 50–60%),{{sfn|Davidson|Ryman|Sutherland|Milner|2014|p=6}} is then turned into (impure) lead metal.

There are two main ways of doing this: a two-stage process involving roasting followed by blast furnace extraction, carried out in separate vessels; or a direct process in which the extraction of the concentrate occurs in a single vessel. The latter has become the most common route, though the former is still significant.{{sfn|Davidson|Ryman|Sutherland|Milner|2014|p=17}}
<div style="float: right; margin: 2px; font-size:85%; margin-left:18px; margin-bottom:18px>
{| class="wikitable sortable collapsible"
|+'''World's largest mining countries of lead, 2016'''{{sfn|United States Geological Survey|2017|p=97}}
! Country !! data-sort-type="number"|Output<br />(thousand<br /> tons)
|-
| {{flagu|China}} || align="right"|2,400
|-
| {{flagu|Australia}} || align="right"|500
|-
| {{flagu|United States}} || align="right"|335
|-
| {{flagu|Peru}} || align="right"|310
|-
| {{flagu|Mexico}} || align="right"|250
|-
| {{flagu|Russia}} || align="right"|225
|-
| {{flagu|India}} || align="right"|135
|-
| {{flagu|Bolivia}} || align="right"|80
|-
| {{flagu|Sweden}} || align="right"|76
|-
| {{flagu|Turkey}} || align="right"|75
|-
| {{flagu|Iran}} || align="right"|41
|-
| {{flagu|Kazakhstan}} || align="right"|41
|-
| {{flagu|Poland}} || align="right"|40
|-
| {{flagu|South Africa}} || align="right"|40
|-
| {{flagu|North Korea}} || align="right"|35
|-
| {{flagu|Ireland}} || align="right"|33
|-
| {{flagu|Macedonia}}<!--the country was not called North Macedonia in the year for which this data is provided--> || align="right"|33
|-
| Other countries || align="right"|170
|}
</div>

==== 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}}

==== Direct process ====
In this process, lead bullion and [[slag]] is obtained directly from lead concentrates. The lead sulfide concentrate is melted in a furnace and oxidized, forming lead monoxide. Carbon (as coke or [[coal gas]]{{efn|Gaseous by-product of the coking process, containing [[carbon monoxide]], hydrogen and [[methane]]; used as a fuel.}}) is added to the molten charge along with [[flux (metallurgy)|fluxing agents]]. The lead monoxide is thereby reduced to metallic lead, in the midst of a slag rich in lead monoxide.{{sfn|Davidson|Ryman|Sutherland|Milner|2014|p=17}}

If the input is rich in lead, as much as 80% of the original lead can be obtained as bullion; the remaining 20% forms a slag rich in lead monoxide. For a low-grade feed, all of the lead can be oxidized to a high-lead slag.{{sfn|Davidson|Ryman|Sutherland|Milner|2014|p=17}} Metallic lead is further obtained from the high-lead (25–40%) slags via submerged fuel combustion or injection, reduction assisted by an electric furnace, or a combination of both.{{sfn|Davidson|Ryman|Sutherland|Milner|2014|p=17}}

==== Alternatives ====
Research on a cleaner, less energy-intensive lead extraction process continues; a major drawback is that either too much lead is lost as waste, or the alternatives result in a high sulfur content in the resulting lead metal. [[Hydrometallurgy|Hydrometallurgical]] extraction, in which [[anode]]s of impure lead are immersed into an [[electrolyte]] and pure lead is deposited ([[Electrowinning|electrowound]]) onto [[Cathode|cathodes]], is a technique that may have potential, but is not currently economical except in cases where electricity is very cheap.{{sfn|Thornton|Rautiu|Brush|2001|pp=52–53}}