Enhanced Fluoride Removal from Water by Nanoporous Biochar-supported Magnesium Oxide

Magnesium oxide was impregnated into biochar (BC) through a simple procedure of one-step pyrolysis, and a hybrid adsorbent MgO-BC was obtained for highly efficient defluoridation from water. The nanoporous BC as the carrier enhanced fluoride adsorption by the loaded MgO. The fluoride adsorption by MgO-BC is pH-dependent and approaches equilibrium within 400 min. MgO-BC exhibits great sorption preference for the target fluoride in the presence of high levels competing anions (chloride, nitrate, sulfate, and carbonate), The maximum adsorption capacity of fluoride onto MgOBC was predicted to be 83.05 mg/g, which is higher than that of other adsorbents, including commercial activated alumina and magnesia based composites with natural carriers. In addition, the MgO-BC can be successfully applied in a fixed-bed column adsorption system for the treatment of simulated fluoride-polluted groundwater, yielding a similar to 250 BV effluent of fluoride concentration less than 1.5 mg L-1. Such satisfactory fluoride adsorption performance of MgO-BC originated from its hybrid structure. In other words, the impregnated MgO shows preferential adsorption to fluoride through the specific inner-sphere complexation, which was been probed by means of Fourier transfrom infrared and X-ray photoelectron spectroscopy analyses, and for the BC support, the nanoporous structure promotes the activity of the loaded MgO by confining their growth and aggregation. All experimental results indicate that MgO-BC has great potential for fluoride sequestration from various water sources.