Abstract
Removal of heavy metals by electrocoagulation generates substantial amount of electrocoagulated metal hydroxides sludge (EMHS). This paper reports calcined EMHS as an effective adsorbent for removal of PO 4 3− from aqueous solutions. Cumulative % removal of PO 4 3− is investigated in a batch adsorber with different initial adsorbate concentrations, adsorbent dose, pH of the solution and adsorption temperature. Adsorption of PO 4 3− is due to ligand exchange between the OH group on oxide surface and PO 4 3− in the aqueous medium with formation of inner surface complex. Removal of PO 4 3− is found to be high at lower pH values and higher temperatures indicating strong positively charged metal oxide surface at acidic pH (<pH zpc) and the endothermic nature of adsorption. The experimental results preferably fitting the Langmuir isotherm suggest monolayer coverage of adsorbed molecules. Pseudo-second-order kinetic model provides the best fitting to experimental results at different adsorbent dose and adsorption temperature. The magnitude of the activation energy (10.33 kJ/mol) is calculated based on pseudo-second-order rate constants from Arrhenius equation indicates removal of PO 4 3− corresponds to activated chemisorption.
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