Coagulation Behavior of Aluminum Salts in Eutrophic Water:  Significance of Al₁₃ Species and pH Control

Abstract

The coagulation behavior of aluminum salts in a eutrophic source water was investigated from the viewpoint of Al-(III) hydrolysis species transformation. Particular emphasis was paid to the coagulation effect of Al 13 species on removing particles and organic matter. The coagulation behavior of Al coagulants with different basicities was examined through jar tests and hydrolyzed Al(III) speciation distribution characterization in the coagulation process. The results showed that the coagulation efficiency of Al coagulants positively correlated with the content of Al 13 in the coagulation process rather than in the initial coagulants. Aluminum chloride (AlCl 3 ) was more effective than polyaluminum chloride (PACl) in removing turbidity and dissolved organic matter in eutrophic water because AlCl 3 could not only generate Al 13 species but also function as a pH control agent in the coagulation process. The solidstate 27 Al NMR spectra revealed that the precipitates formed from AlCl 3 and PACl were significantly different and proved that the preformed Al 13 polymer was more stable than the in situ formed one during the coagulation process. Through regulating Al speciation, pH control could improve the coagulation process especially in DOC removal, and AlCl 3 benefited most from pH control.

Coagulation behaviors of aluminum salts towards fluoride: Significance of aluminum speciation and transformation

“…Al 13 can also be in situ generated in AlCl 3 coagulation at pH 5.5, with the in situ Al 13 species exhibiting better removal of haloacetic acid precursors than preformed PACl does, as indicated from our previous study [20]. AlCl 3 is also observed to be more effective than PACl in removing turbidity and dissolved organic matter in eutrophic water, and this is not only attributed to the generation of in situ Al 13 species but to AlCl 3 functioning as a pH control agent [21]. These results indicate that Al species play a determining role in the coagulation behaviors of Al salts, and their species distribution and transformation is critically important in evaluating their coagulation behaviors.…”

“…Our previous study indicated that pH significantly affected the Al species distribution of AlCl 3 and preformed PACl, and in acidic or alkaline pH region the ratios of monomeric Al increased whereas polymeric and colloidal Al species decreased as compared to the near-neutral pH region [21]. In pH 6-7, the transformation of monomeric Al 3+ within AlCl 3 into polymeric Al occurred, and the ratios of medium and large polymeric Al as expressed by Al b were reported to increase from 71% to 82% with elevated pH from 5 to 7 [21]. Consequently, polymeric Al, i.e., Al b or Al 13 , was inferred to play an important role in the removal of fluoride by Al salts over wide pH range from 4 to 9, and their fluoride removal efficiency increased in the order: PACl 2 > PACl 1 > AlCl 3 .…”

“…In addition, Al 13 also contributed most to the amount of Al species for PACl in basicity range from 1.5 to 2.5 [26,27]. Our previous study indicated that pH significantly affected the Al species distribution of AlCl 3 and preformed PACl, and in acidic or alkaline pH region the ratios of monomeric Al increased whereas polymeric and colloidal Al species decreased as compared to the near-neutral pH region [21]. In pH 6-7, the transformation of monomeric Al 3+ within AlCl 3 into polymeric Al occurred, and the ratios of medium and large polymeric Al as expressed by Al b were reported to increase from 71% to 82% with elevated pH from 5 to 7 [21].…”

Deposition behavior of residual aluminum in drinking water distribution system: Effect of aluminum speciation

“…The coagulation efficiency of PACl is highly related to its aluminum speciation, and Al 13 is claimed as the most efficient species for coagulation in PACl (Hu et al, 2006). The detrimental effects of aluminum on humans are also highly related to its specific species (Wang et al, 2010a).…”

Removal of direct dyes by coagulation: The performance of preformed polymeric aluminum species

“…PACl contains polymeric Al species formed by partially neutralization. The preformed Al species in PACl are relatively stable after dosing, and thus their effectiveness can be less influenced by the specific water quality conditions [13][14][15][16][17] 12 ] 7+ ) is considered as the most important species in PACl and has long been research interest.…”