Adsorption of low-concentration arsenic from water by co-modified bentonite with manganese oxides and poly(dimethyldiallylammonium chloride)

Abstract

Inorgano–organo–bentonite (PMBt) was synthesized through co-modification of bentonite with manganese oxides and poly(dimethyldiallylammonium chloride) (PDMDAAC), and was utilized to remove low-concentration arsenic from water. The hybrid material was characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and N2 adsorption–desorption. It was revealed that the hybrid material possessed an amorphous structure and displayed uneven manganese oxides particles gathering about the bentonite aggregates with a large BET area of 128.90m2/g. The effects of adsorption parameters were investigated, such as stirring time, arsenic concentrations, adsorbent dose, temperature, pH, added anions and ionic strength. The adsorption kinetics and equilibrium of arsenic on the co-modified bentonite were further determined. The results revealed that the adsorption of arsenic was dramatically affected with change in solution pH and significantly suppressed by phosphate anion. The adsorption kinetic data was best fitted with the linear pseudo–second–order model and was well with the non-linear Bangham model. The equilibrium data were well simulated with the Brunauer–Emmett–Teller, Freundlich and Redlich–Peterson isotherms by either non-linear or linear regression, respectively. The non-linear Langmuir isotherm showed best fitting and the maximal adsorption capacity was 9.14–9.99mg/g, dependent on the error function used. It was suggested that the hybrid material had a heterogeneous surface and high affinity towards arsenic, which is highly favorable for arsenic adsorption following a non-ideal monolayer adsorption model. Based on the above comprehensive analysis, the plausible mechanism for arsenic adsorption on PMBt was suggested as a mixed removal mechanism i.e., electrostatic attraction followed by inner-sphere complexation.