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