Heavy metal removal from aqueous solutions by activated phosphate rock

Abstract

The use of natural adsorbent such as phosphate rock to replace expensive imported synthetic adsorbent is particularly appropriate for developing countries such as Tunisia. In this study, the removal characteristics of lead, cadmium, copper and zinc ions from aqueous solution by activated phosphate rock were investigated under various operating variables like contact time, solution pH, initial metal concentration and temperature. The kinetic and the sorption process of these metal ions were compared for phosphate rock (PR) and activated phosphate rock (APR). To accomplish this objective we have: (a) characterized both (PR) and (APR) using different techniques (XRD, IR) and analyses (EDAX, BET-N 2); and, (b) qualified and quantified the interaction of Pb 2+, Cd 2+, Cu 2+ and Zn 2+ with these sorbents through batch experiments. Initial uptake of these metal ions increases with time up to 1 h for (PR) and 2 h for (APR), after then, it reaches equilibrium. The maximum sorption obtained for (PR) and (APR) is between pH 2 and 3 for Pb 2+ and 4 and 6 for Cd 2+, Cu 2+ and Zn 2+. The effect of temperature has been carried out at 10, 20 and 40 °C. The data obtained from sorption isotherms of metal ions at different temperatures fit to linear form of Langmuir sorption equation. The heat of sorption (Δ H°), free energy (Δ G°) and change in entropy (Δ S°) were calculated. They show that sorption of Pb 2+, Cd 2+, Cu 2+ and Zn 2+on (PR) and (APR) an endothermic process. These findings are significant for future using of (APR) for the removal of heavy metal ions from wastewater under realistic competitive conditions in terms of initial heavy metals, concentrations and pH.