Pine cone derived polyethersulfone/biochar-Fe₃O₄ mixed matrix membranes for removal of arsenic from acid mine drainage

In this study novel type of mixed matrix membranes (MMMs) were prepared through phase inversion. This fabricated MMMs were impregnated with biochar (BC) and biochar-Fe3O4 (FBC) composites for selective removal of As(V) ions from acid mine drainage through the adsorptive-filtration processes. Scanning electron microscopy (SEM) images revealed that the BC and FBC adsorbents had heterogeneous surface morphologies with varying particle diameters. Fourier transform infrared spectroscopy (FTIR) analysis confirmed the existence of polar functional groups, which aided the improvements in the adsorptive removal of As(V) ions. BET surface area increased from 8.32 m(2)/g of pristine BC adsorbent to 19.90 m(2)/g for the FBC adsorbents. Pure water flux increased from 239.9 L/m(2).h (M0) to 359.4 L/m(2).h (M6), and the water contact angle decreased from 70.7 degrees (M0) to 51.4 degrees (M6). The maximum adsorption capacity achieved was 34.92 mg/g and 49.54 mg/g for BC and FBC MMMs, respectively, at pH 10. The adsorption isotherms and kinetics were analyzed using the Freundlich model and Pseudo-first-order model, respectively, which provided the best-fit to the experimental data. Consequently, the adsorption isotherm data indicated that the removal of As(V) ions was influenced by electrostatic interaction, hydrogen bonding, diffusion (pore filling), and inner-sphere complexation mechanisms. Furthermore, the leaching rate of FBC from membrane labelled M6 was investigated at various pH levels, showing rates of 2.01 mu g/m(2).h, 0.09 mu g/m(2).h, and 0.08 mu g/m(2).h at pH 2, pH 7 and pH 10, respectively. The decrease in leaching rate observed under neutral (pH 7) and basic (pH 10) conditions is ascribed to the improved stability of Fe3O4 NPs within the membranes. The membrane containing 1.5 wt% of FBC demonstrated enhanced effectiveness in removing toxic metals not only for As (99.9 %) but also Cr (99.8 %). These findings indicate that the membrane has great potential towards the treatment of acid mine drainage.