Characteristics and mechanisms of aluminum salts on arsenate removal by coagulation: Significance of aluminum speciation distribution and transformation. Issue 1 (February 2022)

• Record Type: Journal Article
• Authors: Kong, Yanli; Ma, Yaqian; Huang, Zhiyan; Ding, Lei; Ma, Jiangya; Chen, Zhonglin; Shen, Jimin; Huang, Yuan
• Is Part Of: Journal of environmental chemical engineering. Volume 10:Issue 1(2022)
• Publication Date: 2022-02
• Subjects: Hydrolyzed aluminum species -- Distribution and transformation -- Coagulation process -- Arsenate removal -- Interface reaction mechanism; Chemical engineering -- Environmental aspects -- Periodicals; Environmental engineering -- Periodicals; Chemical engineering -- Environmental aspects; Environmental engineering; Periodicals; 660.0286
• DOI: 10.1016/j.jece.2021.106805
• Languages: English
• ISSNs: 2213-2929

Abstract

Abstract: It is well known that the hydrolyzed aluminum species of Al-based coagulants play a critical role in coagulation process. So far, however, little information has been collected on arsenate removal from the perspectives of aluminum speciation distribution and transformation. In this study, three different Al-based coagulants have been applied to investigate the distribution and transformation of hydrolyzed aluminum species and their coagulation behaviors for arsenate removal. High levels of in situ Al13 were produced from AlCl3 under weakly acidic conditions. Lab-prefabricated polyaluminum chloride PACl1 was almost entirely preformed Al13 under acidic conditions while large polymeric aluminum species Al14 and Al15 became dominated under alkaline conditions. While for commercial polyaluminum chloride PACl2, large polymeric aluminum species were the dominated in the pH range of 4–9. Results showed that the best coagulation effect occurred at pH 6 for three coagulants with arsenate removal were all above 95%. The distribution and transformation of Al species were variant in different Al-based coagulants, which results in difference of mechanisms on arsenate removal. AlCl3 had synergistic effects on arsenate removal based on charge neutralization of in situ Al13 and sweep flocculation of Al(OH)3 . Charge neutralization of preformed Al13 generated by PACl1 and the bridging adsorption of Al13 aggregates have a key role to play in arsenate removal. The sweep flocculation by Al(OH)3 during PACl2 coagulation process was proved to be the main function for arsenate removal. This study provides a new insight into the interaction and mechanism between arsenate and various aluminum species of Al-based coagulants. Graphical Abstract: Reactivity characteristics and mechanism of As(V) removal by the three coagulants under weakly acidic conditions This study had found that pH has significant influence on aluminum distribution and transformation, which can significantly evaluate their coagulation behaviors and thus plays a determining role on As(V) removal. The optimal As(V) removal by AlCl3 was due to the synergistic effects of the combination of small polymeric aluminum complexation, the Al13 charge neutralization and Al(OH)3 sweep flocculation. The charge neutralization effect of Al13, bridging adsorption of Al13 aggregates and sweep flocculation of Al(OH)3 were involved for As(V) removal by PACl1 . Whereas for PACl2 was mainly dependent on the sweep flocculation of Al(OH)3, charge neutralization of Al13, bridging adsorption of Al13 aggregates and complexation of small polymeric aluminum. ga1 Highlights: The pH has significant influence on aluminum distribution and transformation. As(V) removed by AlCl3 was mainly dependent on charge neutralization of in situ Al13 and sweep flocculation of Al(OH)3 . Charge neutralization of preformed Al13 and the bridging adsorption of Al13 aggregate were the major contributors to As(V) removal by PACl1, whereas for PACl2 was the sweep flocculation of Al(OH)3 .