Behaviour and mechanism of enhanced phosphate sorption on loess modified with metals: equilibrium study

Abstract

AbstractBACKGROUND: Phosphate is one of the main contaminants responsible for the eutrophication of surface waters. In developing countries, algae blooming in lakes have threatened the quality of drinking water due to the lack of proper management of phosphate‐containing wastewaters from mining sites and industry.MAJOR RESULTS: The sorption behaviour of phosphate on loess modified by metals (Zn(II), Cu(II) and Pb(II)) was investigated in this paper. Zn(II) and Cu(II) sorption on the loess was attributed to the constituent silicate minerals while the sorption of Pb(II) was assigned to natural carbonate in the loess. The sorption affinity of phosphate towards the modified sorbent was as follows: Pb(II) (221.3–832.2 L g−1) > Cu(II) (20.26 L g−1) > Zn(II) (0.77–1.90 L g−1) > loess (0.11 L g−1) with regard to the partition coefficient. The sorption isotherms were well fitted by an extended Henry's law with multi‐linearity. Several factors including metal loading, pH, sorbent dosage and temperature were investigated and all were found to correlate positively with phosphate sorption. The enthalpy and entropy changes during phosphate sorption on Pb(II) loaded loess were predicted as 14.32 kJ mol−1 and 128.45 J mol−1 K−1, respectively. The sorption mechanism for phosphate on Pb(II) doped loess was investigated by FT‐IR spectra from which the sorption was attributed to chemical bonding with lead carbonate and physisorption with surface adsorbed phosphate as well as diffusion through micropores into the sorbent.CONCLUSIONS: Pb(II) loaded loess shows the best performance for phosphate removal from aqueous solution. The optimum conditions for sorption were pH = 9.5, lead modified loess sorbent dosage = 10 g L−1, temperature = 35 °C and Pb(II) loading 295 mg g−1. Copyright © 2008 Society of Chemical Industry