Removal of arsenic oxy-anions using lanthanum oxide

Batch adsorption tests were conducted to study the mechanism of adsorption of oxy-anions of arsenic (arsenate and arsenite) from solution to lanthanum oxide. The investigation was considered from kinetics and thermodynamics perspectives.; Various thermodynamic parameters such as Gibbs free energy, enthalpy and entropy for adsorption were determined. The thermodynamic calculations indicated that the adsorption of arsenate and arsenite on to lanthanum oxide was spontaneous at all temperatures under consideration. The process of adsorption of arsenate on to lanthanum oxide was endothermic and was temperature dependent. The process of adsorption of arsenite on to lanthanum oxide was exothermic and was less significantly temperature dependent. The activation energy showed a decreasing trend with an increase in the initial arsenic content in both the cases. The dependency of the isosteric heat of adsorption on adsorption density indicated that the active binding sites of the adsorbent were heterogeneous. The effect of pH on the removal of arsenate and arsenite was also studied.