Arsenic sorption on zero-valent iron-biochar complexes

Abstract

Arsenic (As) is toxic to human and is often found in drinking water in India and Bangladesh, due to the natural abundance of arsenides ores. Different removal procedures such as precipitation, sorption, ion exchange and membrane separation have been employed for removal of As from contaminated drinking water (CDW), however, there is a critical need for low-cost economically viable biochar modification methods which can enhance As sorption. Here we studied the effectiveness of zero-valent iron (ZVI)-biochar complexes produced by high temperature pyrolysis of biomass and magnetite for removing As⁵⁺ from CDW. Batch equilibration and column leaching studies show that ZVI-biochar complexes are effective for removing As⁵⁺ from CDW for the studied pH range (pH ∼7-7.5) and in the presence of competing ions. XPS As 3d analysis of ZVI-biochar complexes exposed to As⁵⁺ in the batch and column studies show primarily As³⁺, indicating simultaneous oxidation of Fe° to Fe³⁺ and reduction of As⁵⁺ to As³⁺. SEM-EDS and XRD analyses show isomorphous substitution of As³⁺ for Fe³⁺ in neo-formed α/γ-FeOOH on biochar surfaces, which is attribute to co-precipitation. This study also demonstrates the efficacy of pyrolyzing biomass with low-cost iron ores at 900 °C to rapidly produce ZVI-biochar complexes, which have potential to be used for treatment of As CDW.

Keywords: Arsenic; Biochar; Co-precipitation; Contaminated drinking water; Pyrolysis; Zero valent iron.