Homoionic soda-activated bentonite for batch-mode removal of Pb(II) from polluted brackish water

Abstract

Homoionic soda-activated BNT’s (M-SABNT’s) were prepared by replacing the exchangeable cations of a commercial SABNT with the eco-friendly and cheap cations, Na+, K+, NH4+, Mg2+ or Ca2+. The M-SABNT samples were characterized by X-ray diffraction, Fourier-transform infrared spectrometry, X-ray fluorescence, potentiometric titration, pH of zero point charge measurement, and chemical and thermogravimetric analysis. The adsorption of Pb(II) on the homoionic sorbents were studied at different pH values, time of shaking and initial concentration. The models of kinetics and adsorption isotherms of Pb(II) on K-, Mg- and Ca-SABNT’s were examined and suggested to follow the pseudo- 2nd order and Langmuir adsorption models, respectively. The Mg-SABNT was recommended for the application process because it was assumed as an applicable ion exchanger over a wide range of pH (5–9), equilibrated within a suitable time (30 min) and has the highest monolayer Pb(II) capacity (67.11 mg g−1). The process was successfully applied on Pb(II)-spiked brackish water samples. The results confirmed the validity of the homoionic Mg-SABNT as a potential sorbent for the removal of Pb(II) from aqueous media of different salinity levels exceeding 3000 times the spiked Pb(II) contents with removal efficiencies of 55.5–95.3%.