Characterization of Al30 in commercial poly-aluminum chlorohydrate by solid-state 27Al NMR spectroscopy

Investigation of commercially produced hydrolysis salts of aluminum by solid-state Al-27 NMR spectroscopy and size-exclusion chromatography (SEC) reveals well-defined and distinct Al environments that can be related to physicochemical properties. Al-27 MAS and MQ-MAS NMR spectroscopic data show that the local structure of the solids is dominated by moieties that closely resemble the Al-30 polyoxocation (Al30O8(OH)(56)(H2O)(23)(18+)), accounting for 72-85% of the total Al. These Al-30-like clusters elute as several size fractions by SEC. Comparison of the SEC and NMR results indicates that the Al-30-like clusters includes intact isolated clusters, moieties of larger polymers or aggregates, and possibly fragments resembling delta-Al-13 Keggin clusters. The coagulation efficacy of the solids appears to correlate best with the abundance of intact Al-30-like clusters and of smaller species available to promote condensation reactions. (C) 2016 Elsevier Inc. All rights reserved.