Removal of Cr(VI) from water by adsorption using low cost clay-perlite-iron membranes

Abstract

Due to commercial membranes are costly and the energy required to operate them is high, there is an urgent need to develop alternative technologies based on earth’s crust abundant materials, low operating and maintenance costs and that do not require post processing of residues. Thus, in this work, first removal of Cr(VI) in clay, perlite and clay-perlite-iron suspensions was assessed. Then, ceramic type membranes made of clay-perlite-iron were prepared to remove Cr(VI) from surface water for human consumption. Membranes of 7 cm in diameter and 1 cm in thickness were prepared varying the amount of iron filings in the clay-perlite matrix from 0, 0.5, 1 and 1.5 wt.%, all sintered at 950 °C. Then, Cr(VI) surface water solutions were filtered under vacuum (50.7 K Pa). Performance of membranes was evaluated based on the Cr(VI) adsorption capacity and removal efficiency. Additionally, other parameters such as turbidity, pH, electrical conductivity, cations and anions content were monitored. Results show that membranes prepared with 1.5 wt.% of iron filings reached the highest adsorption capacity (0.122 mg/g) and the greatest removal efficiency (> 99%), similar to that obtained in clay-perlite-iron suspensions where a removal efficiency of 100% was obtained at pH 2, when the content of iron filings was greater than 1 g. The adsorption process in the ceramic membrane modules was better described by the Langmuir model, furthermore, the Cr(VI) adsorption in the clay-perlite-iron ceramic membranes is a multilayer physisorption process occurring in the outer surface of the membrane material.