Adsorption of Inorganic and Organic Ligands onto Hydrous Aluminum Oxide:  Evaluation of Surface Charge and the Impacts on Particle and NOM Removal during Water Treatment

Abstract

The variable removal from solution of sulfate, orthophosphate, fluoride, five simple organic acids, and natural organic matterfromtwo sources by adsorption on aluminum hydroxide was examined to assess their potential influence on coagulation during drinking water treatment. Measurements of electrophoretic mobility were conducted with adsorption studies to provide means of evaluating the impact of the adsorption of these anions on the removal of particulate material during coagulation at water treatment facilities. The three inorganic ions exhibited widely different trends in terms of removal from solution and effect on the surface charge of the aluminum hydroxide. Phosphate was nearly completely removed from solution across a wide pH range and was observed to lower surface charge and shift the isoelectric point. Sulfate was removed to a lesser extent than phosphate, lowered the surface charge on the precipitate, but did not shiftthe isoelectric point. Fluoride was well-removed through adsorption but exhibited no influence on the charge of the hydrous aluminum oxide. The organic acids similarly displayed varying abilities to be removed through adsorption and different influences on surface charge. The results indicate the importance of the number and location of functional groups and their acid/ base properties. The ability to strongly influence surface charge illustrates the impact that adsorption of these anions can have on particle stability.

Simultaneous removal of arsenic and fluoride by freshly-prepared aluminum hydroxide

“…Our previous study also indicated the adverse effect of fluoride on the coagulation behavior of aluminum chloride (AlCl 3 ) towards kaolin suspensions, and the formation of Al-F complexes at high fluoride levels plays an important role [18]. Besides the formation of Al-F complexes, the attachment of fluoride onto Al hydroxide decreased the surface charge and particles stability [19], and this effect was assumedly to inhibit the removal of negatively-charged arsenate [As(V)]. Additionally, the competitive effect between As(V) and F occurs to affect their adsorption onto AlOxHy, and this adverse effect may be remarkably alleviated by introducing iron oxides to AlOxHy [6].…”

Removal of fluoride from aqueous media by Fe3O4@Al(OH)3 magnetic nanoparticles

“…Several methods have been applied to remove excessive fluoride from aqueous environments, such as adsorption [2,[8][9][10], precipitation [6], ion-exchange [11], electrodialysis [12] and electrochemical methods [13]. Among them, precipitation and adsorption are two most important techniques used for water defluoridation.…”

Effects of fluoride on the removal of cadmium and phosphate by aluminum coagulation

“…The adsorption of fluoride onto hydrous aluminum oxides via ligand exchange, as indicated by Eq. (1), cannot contribute to ζ-potential reversal, although it did decrease the ζ-potential to some extent (Pommerenk and Schafran, 2005). In this study, fluoride significantly lowered the ζ-potential and the reversal of the ζ-potential to negative values was observed.…”

“…Besides Al-F complex formation, the adsorption of fluoride onto Al hydro (oxide) also plays a role. Pommerenk and Schafran (2005) indicated that the attachment of fluoride on hydrous aluminum oxide decreased its surface charge and adversely affected the removal of natural organic matter (NOM) accordingly (Pommerenk and Schafran, 2005). Furthermore, aluminum oxide tends to dissolve in the acidic pH range.…”