Treatment of aqueous arsenic - A review of biochar modification methods

Arsenic (As) is an ever-present worldwide environmental contamination issue. The process of As sorption for treatment of contaminated waters is regarded as a promising treatment technology approach due to its simplicity and potential for high efficiency. Biochars are carbon-rich porous solids produced by heating of biomasses under low oxygen conditions. Biochars are considered to be environmentally friendly sorbents that can be used to treat various As-containing waters. However, unmodified biochar is generally a poor sorbent for As species due to static repulsion between the As oxyanions and the negatively charged biochar surface. The As sorption capacity of biochars can be substantially improved by treatments using various physical and chemical activation and modification methods. Thus, this review includes 63 research studies using physical and chemical approaches to enhance biochar physicochemical structures and As sorption efficiencies. The effectiveness of each method for altering the characteristics and sorption capacity of biochars is described. This review can help to focus the scope of future As biochar sorption studies and aid researchers in optimization of biochar-based sorbents for As treatment.