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Water Science & Technology—WST Vol 59 No 4 pp 823–832 © IWA Publishing 2009 doi:10.2166/wst.2009.066

Modified ferron assay for speciation characterization of hydrolyzed Al(III): a precise k value based judgment

Ye Changqing, Wang Dongsheng, Wu Xiaohong, Qu Jiuhui and John Gregory

Yantai Institute of Coastal Zone Research for Sustainable Development, Chinese Academy of Sciences, Yantai, 264003, China E-mail: cqye@yic.ac.cn
State Key Lab of Environmental Aquatic Chemistry, RCEES, Chinese Academy of Sciences, Beijing, 100085, China E-mail: wgds@rcees.ac.cn; wu_sherry@126.com; jhqu@rcees.ac.cn
Department of Civil and Environmental Engineering, University of College London, WC1E 6BT, London, UK


ABSTRACT

The speciation of Al-OH complexes in terms of Ala, Alb and Alc could be achieved by traditional ferron assay and Alb is generally considered as Al13, however, the inherent correlation between them remains an enigma. This paper presents a modified ferron assay to get precise determination of Al13 using nonlinear least squares analysis, and to clarify the correlation between Alb and Al13. Two parallel reactions conforming to pseudo-first-order kinetics can simulate the complicate reactions between polynuclear complexes and ferron successfully. Four types of experimental kinetic constant (k value) of Al-OH complexes can be observed by this method when investigating three typical aluminium solutions. Comparing with the results of 27Al NMR, the species with moderate kinetics around 0.001 s-1 can be confirmed to resemble to Al13 polycation. The other types of kinetics are also well-regulated in partially neutralized aluminium solutions with various OH/Al ratios (b values) in the range 0 ~ 2.5. It would provide potential means to trace the in-situ formation of Al13 in dilute solutions such as coagulation with Al-based coagulants

Keywords: Al13; coagulation; ferron assay; hydrolyzed Al(III); speciation characterization


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