Reusability of Al-F Hydroxide Precipitates Generated in Adsorption and Coagulation Treatment of Fluoride for Adsorptive Removal of Arsenic

This study aims to investigate the feasibility of utilizing Al-F hydroxide precipitates generated in Al hydroxide [Al(OH)(3)] adsorption [Al(OH)(3)-F-ads] and aluminum (Al) coagulation [Al(OH)(3)-F-coag] for adsorptive removal of As(III) and As(V). Al(OH)(3)-F-ads, Al(OH)(3)-F-coag, and pristine Al(OH)(3) were characterized by nitrogen sorption, X-ray photoelectron spectroscopy, and fourier transform infrared spectroscopy (FTIR) before and after arsenic adsorption. The kinetic study indicated that As(III) and As(V) adsorption on these Al-based solid wastes followed the pseudo-second-order model. The calculated adsorption capacity of Al(OH)(3)-F-ads and Al(OH)(3)-F-coag for As(III) was 48.0 and 31.0mg/g, while it was 84.0 and 56.3mg/g for As(V), respectively. These adsorption capacities were 25-50% lower compared with pristine Al(OH)(3). Anion exchange of fluoride by H2AsO4- and HAsO42- dominated in As(V) removal by Al(OH)(3)-F-ads,F- while formation of an As-O complex played a more important role in As(V) removal by Al(OH)(3)-F-coag. The maximum concentration of released fluoride after the adsorption of As(III) and As(V) by Al(OH)(3)-F-ads and Al(OH)(3)-F-coag was below the Chinese Class-II industrial discharge standard for fluoride (<20mg/L). Results from this study indicated that the aluminum hydroxides generated in the fluoride removal process could be reclaimed as an adsorbent for As(III)/As(V) removal from industrial wastewater.