Pure metals are commonly recovered from sulfide ores by successive processes of

Question

Pure metals are commonly recovered from sulfide ores by successive processes of roasting in air (oxidation), dissolution in sulfuric acid and electrolysis (reduction). Consider the starting ore mineral sphalerite (ZnS). Write balanced chemical reactions for:

(i) the oxidation of sphalerite with O2 to produce zinc oxide,
(ii) dissolution of the gas produced in reaction (i) to form sulfuric acid,
(iii) dissolution of zinc oxide to form an ionic sulfate solution, and
iv) the reduction and oxidation processes that occur during electrolysis of a zinc sulfate solution (note: the oxidation reaction that takes place at the anode may not be obvious ... ).

Explanation / Answer

i) 2 ZnS + 3 O2 ? 2 ZnO + 2 SO2 ii) 2SO2 + 2H2O + O2 -> 2H2SO4 iii)ZnO + H2SO4 ? ZnSO4 + H2O iv) Reduction: 2ZnSO4 + 2 H2? 2Zn + 2H2SO4 Oxidation : 2H2O -> 2H2 + O2 Overall electrolysis reaction: 2 ZnSO4 + 2 H2O ? 2 Zn + 2 H2SO4 + O2

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