Editing Metalloid (section)

===Extraction===
The recognised metalloids can be obtained by [[redox|chemical reduction]] of either their oxides or their [[sulfide]]s. Simpler or more complex extraction methods may be employed depending on the starting form and economic factors.<ref>[[#MacKay2002|MacKay, MacKay & Henderson 2002, p.&nbsp;204]]</ref> Boron is routinely obtained by reducing the trioxide with magnesium: B<sub>2</sub>O<sub>3</sub> + 3 Mg → 2 B + 3MgO; after secondary processing the resulting brown powder has a purity of up to 97%.<ref>[[#Baudis|Baudis 2012, pp.&nbsp;207–08]]</ref> Boron of higher purity (> 99%) is prepared by heating volatile boron compounds, such as BCl<sub>3</sub> or BBr<sub>3</sub>, either in a hydrogen atmosphere (2 BX<sub>3</sub> + 3 H<sub>2</sub> → 2 B + 6 HX) or to the point of [[thermal decomposition]]. Silicon and germanium are obtained from their oxides by heating the oxide with carbon or hydrogen: SiO<sub>2</sub> + C → Si + CO<sub>2</sub>; GeO<sub>2</sub> + 2 H<sub>2</sub> → Ge + 2 H<sub>2</sub>O. Arsenic is isolated from its pyrite (FeAsS) or arsenical pyrite (FeAs<sub>2</sub>) by heating; alternatively, it can be obtained from its oxide by reduction with carbon: 2 As<sub>2</sub>O<sub>3</sub> + 3 C → 2 As + 3 CO<sub>2</sub>.<ref>[[#Wiberg2001|Wiberg 2001, p.&nbsp;741]]</ref> Antimony is derived from its sulfide by reduction with iron: Sb<sub>2</sub>S<sub>3</sub> → 2 Sb + 3 FeS. Tellurium is prepared from its oxide by dissolving it in aqueous NaOH, yielding tellurite, then by [[electrolytic reduction]]: TeO<sub>2</sub> + 2 NaOH → Na<sub>2</sub>TeO<sub>3</sub> + H<sub>2</sub>O;<ref>[[#Chizhikov1968|Chizhikov & Shchastlivyi 1968, p.&nbsp;96]]</ref> Na<sub>2</sub>TeO<sub>3</sub> + H<sub>2</sub>O → Te + 2 NaOH + O<sub>2</sub>.<ref>[[#Greenwood2002|Greenwood & Earnshaw 2002, pp.&nbsp;140–41, 330, 369, 548–59, 749: B, Si, Ge, As, Sb, Te]]</ref> Another option is reduction of the oxide by roasting with carbon: TeO<sub>2</sub> + C → Te + CO<sub>2</sub>.<ref>[[#Kudryavtsev1974|Kudryavtsev 1974, p.&nbsp;158]]</ref>

Production methods for the elements less frequently recognised as metalloids involve natural processing, electrolytic or chemical reduction, or irradiation. Carbon (as graphite) occurs naturally and is extracted by crushing the parent rock and floating the lighter graphite to the surface. Aluminium is extracted by dissolving its oxide Al<sub>2</sub>O<sub>3</sub> in molten [[cryolite]] Na<sub>3</sub>AlF<sub>6</sub> and then by high temperature electrolytic reduction. Selenium is produced by roasting the coinage metal selenides X<sub>2</sub>Se (X = Cu, Ag, Au) with [[soda ash]] to give the selenite: X<sub>2</sub>Se + O<sub>2</sub> + Na<sub>2</sub>CO<sub>3</sub> → Na<sub>2</sub>SeO<sub>3</sub> + 2 X + CO<sub>2</sub>; the selenide is neutralized by sulfuric acid H<sub>2</sub>SO<sub>4</sub> to give [[selenous acid]] H<sub>2</sub>SeO<sub>3</sub>; this is reduced by bubbling with [[sulfur dioxide|SO<sub>2</sub>]] to yield elemental selenium. Polonium and astatine are produced in minute quantities by irradiating bismuth.<ref>[[#Greenwood2002|Greenwood & Earnshaw 2002, pp.&nbsp;271, 219, 748–49, 886: C, Al, Se, Po, At]]; [[#Wiberg2001|Wiberg 2001, p.&nbsp;573: Se]]</ref>