Microporous Hematite-Loaded Composite Membrane for Arsenic(III) and Arsenic(V) Removal

Abstract

In this work, adsorption and membrane separation were combined to remove adsorbable contaminants from water at lower energy requirements. Such an approach was investigated for arsenic (As) removal with hematite nanoparticles (70 ± 20 nm) immobilized in a microporous (0.2 μm pore size) poly(vinylidene fluoride) (PVDF) membrane. Hematite loading and hydraulic residence time with the role of speciation were investigated for As(III) and As(V) removal using hematite-loaded composite membrane (HLCM). During the flow-through filtration, it was observed 50% removal for As(III), while only 15% As(V) was removed at pH 8 with 2.6 mg/cm2 hematite loading, equivalent to uptakes of 5.5 ± 0.8 μgAs(III)/cm2 and 3.9 ± 0.6 μgAs(V)/cm2. Varying the pH from 2 to 12 and, ultimately, As(III, V) speciation showed a significant impact on the uptake, especially for As(V). In this case, increasing the NaCl concentration from 0.58 to 20 g/L hindered the charge attraction. Arsenic uptake increased with increasing the hematite loading from 0.7 to 3.9 mg/cm2, while the impact of the hydraulic residence time (flux) was observed. Arsenic uptake by this composite membrane requires further improvement in terms of adsorption capacity. Increasing the loading of hematite in the membrane or chemical modifications of hematite to achieve enhanced affinity for As(III, V) will be part of further material modification. From the water treatment perspective, the composite membrane potentially provides effective removal with a lower specific energy consumption compared to nanofiltration.