The ore which is concentrated by leaching  

Leaching is a process in which powdered ore is treated with certain reagents, which dissolves the ore leaving behind impurities in undissolved form. Aluminium ore is concentrated by this method, bauxite ($A{l}_2{O}_3,2H_{2}O)$contain ferric oxide, titanium oxide and silica as impurities. Bauxite is treated with aqueous solution of caustic soda, alumina get dissolved forming soluble sodium aluminate leaving behind impurities.

$A{l}_2{O}_3+6NaOH\to 2N{a}_{3}Al{O}_3+3H_{2}O$