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Fig. 1. Changes in the concentrations of (a) aluminum tridecamer (Al13), (b) undefined species other than Al13 or AlSYM including aggregated or precipitated Al that cannot be detected by NMR (AlNON), and (c) Al monomer and dimer (AlSYM) and (d) in pH with aging time (10 mmol L–1 hydroxyaluminum [HyA] solution). Humic acid carboxy group versus Al ratios (COOH/Al) are 0 (open square), 0.07 (open triangle), 0.15 (open inverted triangle), and 0.38 (open circle).
