Biochar accelerated Fenton process for roxarsone oxidation, inorganic arsenic adsorption and simultaneous immobilization of arsenic-iron sludge

Abstract

Complete remediation of organoarsenics from environmental matrix hits the bottleneck, that is, the sluggish efficiency of oxidative degradation towards organoarsenics and unsatisfying immobilization performance towards generated inorganic arsenic. Herein, we establish a biochar accelerated Fenton (BA-Fenton) process to decontaminate water from roxarsone (ROX). In comparison with Fe2+/H2O2 process (10 μΜ/0.2 mM), the incorporation of 0.5 g L-1 biochar promoted ROX degradation from 48.2% to 98.2% and total arsenic elimination from 67.6% to 97.3%, respectively. In BA-Fenton process, •OH as the dominant reactive oxygen species (ROS), exhibited a cumulative concentration of 0.42 mM, three times higher than that in classical Fenton process. Crucially, the presence of biochar in Fenton process significantly enhanced the stability of arsenic-iron sludge, whereas the secondary leaching of total arsenic decreased from 433.8 μg-As L-1 to 13.9 μg-As L-1, meeting the prescribed environmental quality standards for surface water in China (50 μg-As L-1, GB 3838-2002). Mechanistic studies unveiled ROX remediation mechanism by BA-Fenton process, highlighting the dual functionality of biochar. On one hand, biochar efficiently reduced Fe3+ to Fe2+ with a rate constant of 0.225 min-1, overcoming the rate-determining step of classical Fenton process for •OH production, consequently promoting the transformation of ROX to As(V). On the other hand, molecular spectroscopy analysis elucidated that in-situ formed As(V) was adsorbed by ferric hydroxides with the formation of arsenic-iron sludge. Subsequently, biochar immobilized arsenic-iron sludge through hydrogen bonds, electrostatic attraction and surface complexation. Furthermore, real water studies demonstrated the effective remediation of organoarsenics by BA-Fenton process in tap water, lake water and chicken manure leachate. This “Two Birds with One Stone” strategy with low-cost, environmental-friendly and sustainable biochar holds great promise for the ultimate disposal of industrial wastewater containing organoarsenics.