Zhao He, Liu Huijuan, Qu Jiuhui
State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
J Colloid Interface Sci. 2009 Feb 1;330(1):105-12. doi: 10.1016/j.jcis.2008.10.020. Epub 2008 Oct 17.
Effect of pH on the aluminum chloride hydrolysis at low concentration was investigated in detail by electrospray ionization (ESI) mass spectrometry. In particular, formation and decomposition processes of polymeric aluminum species were discussed. When coagulant AlCl(3) was diluted to normal coagulant dose (1.5 x 10(-4) mol/L), hydrolysis occurred immediately. Monomeric and dimeric aluminum species were the main products at pH 4.0. With pH increasing, hydrolysis and polymerization processes were accelerated. Monomeric and dimeric aluminum species hydrolyzed and polymerized into small polymeric aluminum species (Al(3)-Al(5) species) at pH 4.8. Through aggregation and self-assembly, the small polymeric aluminum species polymerized into median polymeric species (Al(6)-Al(10) species) at pH 5.0. In the same way, small and median polymeric aluminum species further aggregated into large polymeric species (Al(11)-Al(21) species). When pH was up to 5.8, metastable median and large polymers species decomposed into small aluminum species, then further disaggregated into dimeric species. With pH increased to 6.4, majority of aluminum species formed to Al(OH)(3) amorphous flocs. Accordingly, coagulant hydrolysis mechanism from polymerization toward decomposition was proposed. Furthermore, formation and decomposition of polymeric aluminum species in AlCl(3) solution followed the "Core-links" model, while those of Keggin-Al(13) species in polyaluminum solution was based on the "Cage-like" model.
采用电喷雾电离（ESI）质谱详细研究了低浓度下pH对氯化铝水解的影响。特别讨论了聚合铝物种的形成和分解过程。当将混凝剂AlCl₃稀释至正常混凝剂剂量（1.5×10⁻⁴mol/L）时，立即发生水解。在pH 4.0时，单体和二聚体铝物种是主要产物。随着pH升高，水解和聚合过程加速。在pH 4.8时，单体和二聚体铝物种水解并聚合成小的聚合铝物种（Al₃ - Al₅物种）。通过聚集和自组装，小的聚合铝物种在pH 5.0时聚合成中等聚合物种（Al₆ - Al₁₀物种）。同样，小的和中等的聚合铝物种进一步聚集成大的聚合物种（Al₁₁ - Al₂₁物种）。当pH达到5.8时，亚稳的中等和大聚合物物种分解成小的铝物种，然后进一步解聚成二聚体物种。随着pH升高至6.4，大多数铝物种形成Al(OH)₃无定形絮体。据此，提出了混凝剂从聚合到分解的水解机理。此外，AlCl₃溶液中聚合铝物种的形成和分解遵循“核 - 链”模型，而聚铝溶液中Keggin - Al₁₃物种的形成和分解基于“笼状”模型。
