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

Abstract

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.

Utilization of annealed aluminum hydroxide waste with incorporated fluoride for adsorptive removal of heavy metals

“…The adsorbents Al(OH) 3 -F ads , Al(OH) 3 -F coag , and pristine Al(OH) 3 were prepared according to the methods described in our previous study [17]. Briefly, the pristine Al(OH) 3 was prepared by the stoichiometric reaction between AlCl 3 and NaOH.…”

“…This may be attributed to the different mechanisms involved in their adsorption. Fluoride incorporated into Al(OH) 3 -F ads and Al(OH) 3 -F coag via different mechanisms, and affected their interfacial characteristics accordingly [17]. The adsorption of positive Cd(II) is achieved by forming surface complexes with surface hydroxyl groups, and fluoride showed little effects therein.…”

“…The reclamation of these two solid wastes not only minimizes their discharge into water environments but also is economically valuable. Our previous study indicated that freeze-dried Al(OH) 3 -F ads and Al(OH) 3 -F coag are potentially attractive for the removal of heavy metals such as arsenic [17]. However, the experimental freezedrying procedure is not practically feasible from an engineering point-of-view.…”

Evaporation‐induced self‐assembly (EISA) synthesized mesoporous bimetallic oxides (MBOs) enabling enhanced co‐uptake of arsenate and fluoride from water

“…A wide range of point‐of‐use treatment techniques has been developed in past decades to remove both anions (i.e. As and F − ) from waters, including reverse osmosis (RO), nanofiltration (NF), ion exchange, electrocoagulation, and adsorption . Of these techniques, adsorption is the most cost‐effective technique with high performance …”

“…Adsorption of As(V) or F − from aqueous solution has been extensively studied over the last two decades with a focus on development of high‐efficiency, low‐cost and environmentally‐benign adsorbents . A wide variety of adsorbents were developed to remove As(V) and F − from drinking water, e.g.…”