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Chemical Equilibrium
Published in Armen S. Casparian, Gergely Sirokman, Ann O. Omollo, Rapid Review of Chemistry for the Life Sciences and Engineering, 2021
Armen S. Casparian, Gergely Sirokman, Ann O. Omollo
Amphoterism refers to the property of certain compounds to act as both acids and bases. For example, the compound Al(OH)3, which is categorically a base, may react with acid to form [Al (H2O)6]3+and with excess base to form [Al(OH)4]−1. Both of these species are termed complex ions and are water-soluble. They are governed by complex-ion equilibrium constants, as explained in Section 4.16 of this chapter. Aluminum oxide, Al2O3, is also amphoteric. The hydroxides, as well as oxides of zinc(II) and chromium(III), are similarly amphoteric.
Fluoride removal from water using alumina and aluminum-based composites: A comprehensive review of progress
Published in Critical Reviews in Environmental Science and Technology, 2021
Sikpaam Issaka Alhassan, Lei Huang, Yingjie He, Lvji Yan, Bichao Wu, Haiying Wang
This section of the paper focused on the use of activated alumina (AA) and aluminum-based composites for adsorption of fluoride. The advantages of activation as well as some defects have also been highlighted and the mechanisms of adsorption and adsorption efficiency of various materials have been reviewed and compared. Activated alumina is a kind of aluminum oxide, semi-crystalline (Rabia et al., 2018) with surface area significantly over 200 m2·g−1 and mostly used as desiccant and sorbent for elements such as fluoride, arsenic and selenium in water. It has a high surface area to weight ratio due to its high porosity with amphoteric properties (Salvador et al., 2015). Its amphoteric nature allows it to behave as an acid in basic medium and as a base in acidic medium. Because of its high affinity, it is mostly a preferable desiccant for moisture removal from air as well as a catalyst in natural gas and refining operations. There are two common methods of activating Al2O3 thus, thermal treatment otherwise called physical activation and chemical treatment with acid in the laboratory.