Production of η-alumina from waste aluminium dross

Processing of aluminium dross is one of the most challenging tasks because of its toxic nature. The dross generated while melting at various facilities is generally remelted with salts to recover residual metal values. The remaining residue dross contains mostly aluminium oxide, alloying elements and salts such as NaCl or KCl. This residue dross while stock piling creates pollution of the adjoining area as salts leach out to water stream and also emits harmful gases. In the present study domestic aluminium dross was treated for developing a suitable process flow sheet to obtain η-alumina a high valued product. Initially H2SO4 leaching was carried out for both un-washed and washed dross. With un-washed dross the leaching efficiency achieved was ∼71% but washing of dross followed by leaching raised the recovery to ∼84%. Washing of dross is essential to have higher alumina recovery and also to recover salt for recycling. The liquor obtained after treatment of the dross with acid was further processed to obtain aluminium hydroxide of amorphous nature by hydrolyzing aluminium sulphate with aqueous ammonia. The aluminium hydroxide was then subjected to calcinations which resulted in the formation of η-alumina at 900 °C.