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A method was developed for preparing high purity Al30O8(OH)56(H2O)24 18+ (Al30) through elimination of impurities by complexation. Polyaluminum chloride II (PAC30) with Alc content of 75％ was adopted as the source of Al30. The PAC30 was prepared under conditions of total aluminum concentration 0.1 mol/L and OH?/Al ratio 2.2 to obtain the highest content of Al30. A precipitation/metathesis method, organic solvent precipitation method and organic complexation method were examined to separate and purify Al30. It was found that only by the organic complexation method could high purity Al30 products be obtained in large yield economically. In the experiments, benzoic acid was used as the coordinating reagent to decompose the main impurity AlO4Al12(OH)24(H2O)12 7+ (Al13), and the Al30 product could be obtained by precipitation and metathesis operations. It was noteworthy that the decomposition of impurities by benzoic acid could be completed in 2 hr. The Al30 product was characterized by Ferron assay, 27Al-NMR, SEM, XRD and TGA. The results showed that the purity of the Al30 product could exceed 92％.