Removal of aluminum from aqueous solution by adsorption on montmorillonite K10, TiO2, and SiO2: kinetics, isotherms, and effect of ions

Montmorillonite K10, TiO2, and SiO2 adsorption capacities for aluminum removal from acidic aqueous solution were studied. The effect of pH, initial aluminum concentration, adsorbent amount, contact time, and ions Ca2+, Mg2+, SO42-, HCO3-, Na+, Cl- were investigated. The experiments showed that tested adsorbents exhibited maximum capacities at pH 4.0. Over the studied adsorbent concentration range of 1.0-5.0 g L-1 the maximum aluminum uptake up to 97.4% was achieved by using 5.0 g L-1 of K10 while the same amount of TiO2 or SiO2 removed 71.9% and 94.6%, respectively. Several isotherm models were examined, and equilibrium data were found matching Freundlich model, whereas K10 data were also reasonably described by Langmuir and Sips isotherm models. The effect of ions on aluminum adsorption by 2.0 g L-1 of K10, TiO2, and SiO2 at pH 4.0 showed that Ca2+ ions presented in the solution lowed the removal efficiency of aluminum by materials tested. The adsorption capacity of K10 was influenced the most-the aluminum removal decreased by more than 50%. For TiO2 and SiO2 the reduction of aluminum removal was less-from 53.7 to 44.5% and from 65.5 to 47.4%, respectively. It was found that aluminum removal by both K10 and SiO2 was also influenced by Mg2+ ions and decreased the efficiency of adsorbents. The presence of HCO3- ions reduced the aluminum removal by TiO2 from 53.7 to 17.5%, while no apparent negative effect of HCO3- ions was observed for K10 and SiO2.