The influence of salinity on the removal of Ni and Zn by sorption onto iron oxide- and manganese oxide-coated sand

The influence of salinity on the single and binary sorption of Ni and Zn onto iron oxideand manganese oxide-coated sand (IOCS and MOCS) was investigated at pH = 5. The single sorption experimental data were fitted to Freundlich, Langmuir, Dubinin-Radushkevich, and Sips models, and a nonlinear sorption isotherm was observed (N_F = 0.309-0.567). The higher Brunauer-Emmett-Teller (BET) surface area (A_BET) and cation exchange capacity (CEC) of MOCS contributed to the higher maximum sorption capacities (q_mL) of Ni and Zn than that of IOCS. The Ni sorption capacities in the single sorption were higher than that in the binary sorption, while the Zn sorption capacities in the single sorption were less than that in the binary sorption. The single and binary sorptions onto both IOCS and MOCS were affected by the salinity, as indicated by the decrease in sorption capacities. Satisfactory predictions were shown by the binary sorption model fitting including P-factor, ideal adsorbed solution theory (IAST)-Freundlich, IAST-Langmuir, and IAST-Sips; among these, the P-factor model showed the best fitting results in predicting the influence of salinity of Ni and Zn in the binary sorption system onto IOCS and MOCS. IOCS and MOCS offer a sustainable reactive media in a permeable reactive barrier (PRB) for removing Ni and Zn in the presence of salinity.