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Leaching: metallurgy

Leaching is a chemical method for the concentration of the ore. Here the powdered ore is treated with a suitable reagent in which the ore alone dissolves. The impurities are filtered off and from the solution the ore is regenerated by precipitation.

Thus bauxite (Al2O3.2H2O), the ore of aluminum, contain silicon dioxide and oxides of iron and titanium as impurities. The powdered ore is digested with 45% sodium hydroxide solution at 500K and 35 atmosphere pressure. Al2O3 forms soluble sodium aluminate (SiO2 form soluble sodium silicate). The solution is filtered to remove insoluble impurities, diluted with water and seeded with some freshly precipitated Al(OH)3 which induce the precipitation of Al(OH)3 from the solution. The precipitate is filtered and heated to get pure alumina (Sodium silicate remain in solution).


Al2O3.2H2O + 2NaOH ----------> 2NaAlO2 + 3H2O


NaAlO2 + 2H2O -----------> Al(OH)3 + NaOH


2Al(OH)3 ------^-----> Al2O3 + 3H2O


For extraction of Aluminum visit Extraction of aluminium from bauxite


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