Use of activated Red Mud for removal of Phosphate and Selenite from Aqueous Solutions

Abstract

Red mud,a voluminous waste produced from alumina industry, mainly consist of oxides of aluminium, iron, titanium and silicon as major and oxides of calcium and sodium as minor constituents. Due to its fineness and active surface sites it can be used to absorb heavy metal ions present in industrial effluents. It is activated by different methods and used for r emoval of phosphate and selenite ions from aqueous solutions. Adsorption experiments were conducted to obtain the optimum conditions of pH, temperature, concentration of absorbate and amount of adsorbent. Applicability of Langmuir as well as Freundlich isotherms to the process was studied. Activated red mud samples produced from simple treatment with 20% HCl with and subsequent ammonia precipitation showed highest adsorption capacity for both the ions. An increase in absorption capacity with increase in adsorbate concentration and vice-versa were also observed. However, with increase in temperature, an increase in the percentage of adsorption for phosphate and decrease for selenite ions were observed. The adsorption capacity of the activated sample was correlated with the surface properties. The activated sample can be effectively used for the removal of phosphate and selenite ions from aqueous solutions.