Regeneration and Reuse of Water Treatment Plant Sludge: Adsorbent for Cations

This study applies sintering technology to convert water sludge to a useful and stable adsorption material. The properties of the sintered materials were characterized using SEM and BET. Additionally, adsorption experiments were conducted to elucidate interactions of Cr(III) and Hg(II) at the interface between water and sintered material. Elemental analysis of original water sludge indicates its main constituents to be SiO₂ (54%), Al ₂O₃ (21%), and Fe₂O₃ (6.6%). The BET measurement indicated that the specific surface area of the sintered material is 4.6 m²/g. Since the SiO₂ content exceeds 50%, the surface of the sintered material becomes negatively charged. Adsorption of Cr(III) and Hg(II) on sintered material shows that sorption depends on the systems' pH. The sorption densities are 1.40 mg Cr/g at equilibrium pH 4.6 and 0.43 mg Hg/g at equilibrium pH 6.0. Background electrolyte does not affect the sorption of Cr(III) but markedly affects the sorption of Hg(II). The affinity of Cr(III) for surface reacting sites seem to exceed that of Hg(II). Competitive adsorption experiments were performed to determine the magnitude of the variations in adsorption due to competitive interactions among Cr(III) and Hg(II). The experimental results indicate that a higher competitive solute concentration results in a more significant competitive effect on Hg(II).