Initial biochar properties related to the removal of As, Se, Pb, Cd, Cu, Ni, and Zn from an acidic suspension

Abstract

This study tests the influence of a diverse set of biochar properties on As(V), Se(IV), Cd(II), Cu(II), Ni(II), Pb(II), or Zn(II) removal from solution at pH 4.5. Six commercial biochars produced using different feedstock and pyrolysis conditions were extensively characterized using physical, chemical, and spectroscopic techniques, and their properties were correlated to anion and cation removal using multiple linear regression. H/total organic C (TOC) ratio and volatile matter were positively correlated to cation removal from solution, which indicate interactions between metals and non-aromatic C. Defining the correlation of ion removal with specific OC functional groups was hindered by the inherent limitations of the spectroscopic techniques, which was exacerbated by the heterogeneity of the biochars. Ash was negatively correlated to Se(IV) and positively correlated to Cd(II), Cu(II), and Ni(II) removal from solution. Interference from soluble P in biochars may partly explain the low Se(IV) removal from solution; and Ca-, P-, and Fe- containing compounds likely sorbed or precipitated Pb(II), Cd(II), Cu(II), Ni(II) and Zn(II). Furthermore, Ca-oxalate identified using X-ray diffraction in willow, may be responsible for willow's increased ability to remove Cd(II), Ni(II), and Zn(II) compared to the other 5 biochars. It was clear that both OC and inorganic biochar components influenced metal(loid) and Se(IV) removal from solution. The non-aromatic and volatile OC correlated to removal from solution may be readily available for microbial degradation, while Mg, N, P, and S are required for biological growth. Biological metabolism and uptake of these compounds may inhibit or destabilize their interaction with contaminants.

Keywords: Batch sorption; Biochar; Fourier transform infrared spectroscopy; Metal removal; Nuclear magnetic resonance spectroscopy; X-ray diffraction.