Adsorptive removal of arsenic from groundwater using a novel high flux polyacrylonitrile (PAN)–laterite mixed matrix ultrafiltration membrane

Abstract

A flat sheet mixed matrix membrane, made of polyacrylonitrile (PAN) copolymer, impregnated with laterite, was fabricated for the removal of arsenic from water. The permeability and molecular weight cut-off of the selected membrane were 3.4 × 10−11 m s−1 Pa and 48 kDa, respectively. Morphological analysis showed macrovoids constricted by laterite particles. Surface characteristics assessed by atomic force microscopy revealed the increase in roughness with laterite concentration. The presence of different forms of iron oxide (laterite) and nitrile groups (polyacrylonitrile) in membrane M25 was confirmed by X-ray diffraction. Incorporation of arsenic within the membrane matrix was demonstrated by subsequent lowering of transmittance peaks at different wavelengths of FTIR. Maximum adsorption capacity of the selected membrane was 1.4 mg g−1 at 298 K. Under the optimum operating conditions, the pristine mixed matrix membrane resulted in a filtrate with a concentration below 10 μg l−1 for 17 hours in cross flow mode with a 0.01 m2 filtration area. The stability of the membrane was demonstrated for three regeneration cycles. The effect of pH and coexisting anions like phosphate, sulphate, carbonate and bicarbonate on the removal efficiency of arsenic was studied. The performance of the membrane in the presence of arsenic-contaminated groundwater was also tested.