This study focuses on the effects of pH and fluoride at different molar ratios of fluoride to Al i.e., aluminum (Al) hydro(oxide) with adsorbed fluoride at R F:Al of below 0.1:1, may be reclaimed as a coagulant after being dissolved.
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 31.0 mg/g, while it was 84.0 and 56.3 mg/g for As(V), respectively. These adsorption capacities were 25-50% lower compared with pristine Al(OH) 3 . Anion exchange of fluoride by H 2 AsO 4 -and HAsO 4 2 -dominated in As(V) removal by Al(OH) 3 -F ads, 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 (<20 mg/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.
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