4.2.3. Aluminium industry waste (re

4.2.3. Aluminium industry waste (red mud)
Red mud, a solid waste product of aluminium industry produced during bauxite processing, was explored as adsorbent by López et al. for wastewater treatment. The maximum adsorption capacities for Cu2+, Zn2+, Ni2+ and Cd2+ were found to be 19.72, 12.59, 10.95 and 10.57 mg/g, respectively for a contact time of 48 h. Red mud has also been explored as an adsorbent for the removal of lead and chromium by Gupta et al.. Freundlich and Langmuir models were found to fit the sorption data. The maximum adsorption capacity for Pb(II) by red mud was reported 64.79 mg/g (batch capacity) and 88.20 mg/g (column capacity). The maximum adsorption capacity for Cr(VI) was 35.66 mg/g (batch capacity) and 75.00 mg/g (column capacity). Red mud has been explored as an adsorbent for arsenic removal from water. It was found by the researchers that an alkaline aqueous medium (pH 9.5) favored As(III) removal, whereas the acidic pH range (1.1–3.2) was effective for As(V) removal. The capacities were reported as 4.31 mol/g at pH 9.5 for As(III) and 5.07 mol/g at pH 3.2 for As(V). The workers reported that heat and acid treatments on red mud increased its adsorptive capacity. Arsenic adsorption on acid and heat treated red mud was also found pH dependent, with an optimum range of 5.8–7.5 for As(III) and 1.8–3.5 for As(V).