Abstract
Chromium (Cr(VI)) presence in aqueous systems has become a worldwide health and environmental concern. Here, we compared and explored the Cr(VI) removal potential of novel biochars produced from wheat straw and press mud in aqueous media under varying environmental conditions such as pH (3–10), sorbent dose (0.1–1.3 g L−1), shaking time (0.016–24 h) and initial sorbate concentration (10–250 mg L−1). Sorption batch studies showed that wheat straw biochar (WSB) achieved 97% Cr(VI) removal than 91% of press mud biochar (PMB) with 120 mg L−1 initial metalloid concentration, 0.6 g L−1 sorbent dose and 2 h shaking time. Kinetic modeling showed that pseudo-second order equation (R2=0.99) fitted well the equilibrium kinetic data of both biochars indicating the Cr(VI) sorption was a fast process. Langmuir and Freundlich isotherm models provided the best fit to the equilibrium data of WSB and PMB respectively, showing monolayer and multilayer sorption processes for WSB and PMB, respectively. The FTIR and XPS spectroscopy elucidated that mainly –OH functional groups along with other aromatic and aliphatic carbon- and oxygen-rich functional moieties were responsible for Cr(VI) sorption onto biochars. The XPS analyses also revealed that Cr(VI) was successfully reduced to Cr(III) after sorption onto WSB and PMB. Thus, the developed low-cost WSB and PMB showed promising potential for Cr(VI) removal both by direct sorption and/or after reduction from contaminated aqueous solutions.
•Wheat straw biochar showed maximum sorption of Cr(VI) than press mud biochar.•Langmuir and pseudo-first order models provided the best fit for Cr(VI) sorption.•XPS spectra confirmed the reduction of Cr(VI) to Cr(III) after sorption onto both biochars.