On the acid–base stability of Keggin Al13 and Al30 polymers in polyaluminum coagulants

Abstract

The acid-base stabilities of Al 13 and Al 30 in polyaluminum coagulants during aging and after dosing into water were studied systematically using batch and flowthrough acid-base titration experiments. The acid decomposition rates of both Al 13 and Al 30 increase rapidly with the decrease in solution pH. The acid decompositions of Al 13 and Al 30 with respect to H ? concentration are composed of two parallel first-order and second-order reactions, and the reaction orders are 1.169 and 1.005, respectively. The acid decomposition rates of Al 13 and Al 30 increase slightly when the temperature increases from 20 to ca. 35°C, but decrease when the temperature increases further. Al 30 is more stable than Al 13 in acidic solution, and the stability difference increases as the pH decreases. Al 30 is more possible to become the dominant species in polyaluminum coagulants than Al 13 . The acid catalyzed decomposition and followed by recrystallization to form bayerite is one of the main processes that are responsible for the decrease of Al 13

Removal of Azo dyes with Xanthan

“…It was proposed [46,47], that glucuronate group attached to XANT molecules binds to Al 3+ in such way that this ion act as a linker between XANT molecules, resulting in a polymeric network that can be seen in a macroscopic way as a "strong gel". However, recently it has been encountered that Al +3 in aqueous solution, has a high tendency to form the following polyhydroxyoxoaluminum clusters: [Al13O4(OH)24(H2O)12][SO4]4•19 H2O (which will be denominated as CAL-13) and [Al30O8 (OH)56 (H2O)26][SO4]9 •x H2O (this cluster will be named CAL-30) , which is approximately 2 nm in length) [48,49]. These findings suggest that when pH is increased, the affinity of XANT to CAL-13 and CAL-30 clusters is strongly elevated as a consequence of the electrostatic interaction between clusters and the XANT molecules.…”

A Stochastic Model for Adsorption Kinetics

“…This product is a gel that, when lyophilized, produces a powder with a strong ability to remove different anions. [46,47]. These clusters act as linkers between xanthan molecules to form a polymeric network that possesses a net positive charge that is variable and depends on the proportions of CAL-13 and CAL-30 in Xant-Al.…”

Density functional theory study and kinetic analysis of the formation mechanism of Al30O8(OH)56(H2O)2618+ (Al30) in aqueous solution

“…Vibrational frequency calculations were carried out to confirm the stable structures at the same computational level. Al 30 always occurs at low pHs (Son et al, 2003;Shafran et al, 2004;Chen et al, 2006), therefore, the species we concerned here mainly exist as totally protonated states at these pHs (Francois, 1987;Furrer et al, 1992;Chen et al, 2009). The optimization and vibration calculations of Al(H 2 O) 6 3+ , Na(H 2 O) 6 + and H 2 O were performed at B3LYP/6-311+G (d, p) to compute reaction energy.…”