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Optimized coagulation pathway of Al13: Effect of in-situ Aggregation of Al13

Wang, Pin, Jiao, Ruyuan, Liu, Libing, Xiao, Feng, An, Guangyu, Wang, Dongsheng
Chemosphere 2019 v.230 pp. 76-83
aluminum, coagulation, neutralization, pH, silica
The coagulation mechanism for removing particles by Al13 has been extensively investigated for water treatments. It was widely accepted that Al13 played important roles in coagulation mainly by charge neutralization and electrostatic patch. However, the discovery of Al13 aggregates (Al13agg) in flocs indicated that the real coagulation process should be different from the previous understanding, including when Al13agg were generated and how it interacted with negative particles. The aggregation process of Al13 during coagulation and its micro-interfacial effect on particle coagulation remains to be explored. In this study, to investigate the aggregation of Al13 and its effect on coagulation performance, two parallel coagulation jar tests were conducted on silica suspensions by preformed Al13agg and Al13, respectively. The results showed that optimized coagulation for particle removal by Al13 occurred from pH 7 to pH 9, which was dominated by the in-situ aggregation of Al13. The results confirmed that Al13agg were both present in flocs generated in two tests, however, the morphology and distribution of surface Al of flocs were different for two tests. The in-situ formed Al13agg covered all over the silica particles in flocs, resulting in compact structure with rough surfaces, while the preformed Al13agg mainly distributed on joint sites between particles, generating denser flocs with smooth surfaces. This difference verified that the in-situ aggregation of Al13 was the key factor to optimized particle coagulation. The overall optimized particle coagulation by Al13 should undergo the following pathway: charge neutralization – in-situ aggregation of Al13 – inter-particle bridging.