Adsorption of inorganic and organic arsenic from aqueous solutions by polymeric Al/Fe modified montmorillonite

Adsorption of arsenite [As(III)], arsenate [As(V)] and dimethylarsinate (DMA) from aqueous solutions onto polymeric Al/Fe modified montmorillonite was studied. Batch adsorption studies were carried out on the adsorption of As(III), As(V) and DMA as a function of contact time, pH, adsorbent dose and initial metal concentration. Fourier transform infrared spectrometry (FT-IR) and scanning electron microscopy (SEM) were used to analyze the functional groups and surface morphology of the montmorillonite or polymeric Al/Fe modified montmorillonite, respectively. SEM images show that modification with polymeric Al/Fe species reduces the clay particle size and aggregation. The results indicate that the maximum adsorption of polymeric Al/Fe modified montmorillonite was obtained in the pH range 3.0–6.0 for As(V), 7.0–9.0 for As(III) and 3.0–7.0 for DMA. The adsorption data was analyzed by both Freundlich and Langmuir isotherm models and the data was well fit by the Freundlich isotherm model. Kinetic data correlated well with the pseudo-second-order kinetic model, suggesting that the adsorption process might be chemical sorption. Thermodynamic studies showed that the adsorption process was endothermic and spontaneous in nature. The presence of phosphate and iron reduced the adsorption efficiency of arsenic, whereas other common coexisting ions had no significant effect on arsenic adsorption. The desorption studies were carried out using dilute NaCl solution.