Polyaluminium Chloride and Anionic Polyacrylamide Water Treatment Residuals as a Sorbent for Cd2+ and Zn2+ in Soils

Water treatment residuals produced after addition of polyaluminium chloride and anionic polyacrylamide (PAC-APAM WTRs) were evaluated for the potential to remove Cd2+ and Zn2+ from aqueous solutions by batch adsorption studies. The maximum adsorption capacity obtained from Langmuir modeling was 85.5 mg Cd2+/g PAC-APAM WTRs or 25.6 mg Zn2+/g PAC-APAM WTRs. A Dubinin-Radushkevich (D-R) model study showed that the adsorption process was chemically controlled. The pseudo-second-order model described the adsorption kinetic data better than the pseudo-first-order model, while kinetic studies showed that the adsorption process included external surface adsorption and intraparticle diffusion, which was likely the rate-limiting step. PAC-APAM WTRs adsorbed Cd2+ and Zn2+ in the pH range of 3–9 and in the temperature of 20–40 °C, and the immobilization ability for both ions increased with the increase of pH or an increase in temperature. FT-IR spectroscopy analysis illustrated that the carboxyl groups from APAM in WTRs participated in the adsorption reactions in addition to Fe(Al)-O functional groups and O–H groups. This short-term study showed that PAC-APAM WTRs could be a cost-effective media for the remediation of Cd2+ and Zn2+ contaminated soils. Further studies are needed to examine the slow adsorption mechanisms and determine the optimum mass ratio of soil to PAC-APAM WTRs under various soil conditions.