Comparative molecular characterization of aluminum hydroxy-gels derived from chloride and sulphate salts

BackgroundAluminum (III) hydroxy-gels find important applications in areas such as paint pigments, pharmaceuticals and water treatment or toxic metal sequestration. Since the method of preparation may affect their properties and performance, in this work we prepare aluminum hydroxy-gels from either chloride or sulphate salts and subject them to comparative characterization. ResultsAluminum (III) hydroxy-gels were produced by partial quick neutralization of 2molL(-1) AlCl3 or Al(SO4)(1.5) salt solutions with 5N NaOH at room temperature. The gels were found, following ageing and water washing, to consist of 60-70wt% Al(OH)(3), 5-18wt% Cl or SO4 and approximate to 20wt% water. Both gel materials upon drying were seen to be highly porous formed from aggregates of very fine particles nucleated during the fast neutralization process. The Al(SO4)(1.5)-derived gel was found to differ significantly from the AlCl3-derived gel both in terms of surface area (38m(2)g(-1) vs. 18m(2)g(-1)) and chemical features. The aluminum chloride gel material is probably composed of chains of aluminum octahedra (Al-n(OH)(2.5)Cl-0.5n(H2O)(3n)) while the aluminum sulphate gel of SO4-stabilized Keggin Al-13 structure: AlO4Al12(OH)(24)(SO4)(3.5)(H2O)(12). ConclusionThe distinct molecular structure of the aluminum sulphate-derived gel may provide an effective matrix for hazardous metal containment. (c) 2013 Society of Chemical Industry