INFLUENCE OF SELECTED ORGANIC-LIGANDS ON THE FORMATION OF ALLOPHANE AND IMOGOLITE

The role of organic ligands of different ability to complex with Al**3** plus in affecting the formation of allophane and imogolite and the nature of the precipitation ( greater than 0. 01 mu m) and soluble ( less than 0. 01 mu m) products was investigated at initial Si concentration of 1. 6 multiplied by 10** minus **3 mol. L** minus **1, Si/Al molar ratios of 0. 5 and 1. 0, OH/Al molar ratios of 2. 0, and 3. 0, and organic ligand/Al molar ratios of 0 to 0. 2. DL-aspartic and p-hydroxybenzoic acids showed a very weak impeding effect on the formation of allophane and imogolite; salicylic acid showed a weak to moderate impeding effect on the formation. Tannic, DL-tartaric, citric, and DL-malic acids with a strong affinity for Al greatly perturbed the interaction of hydroxy-Al ions with orthosilicic acid at Si/Al ratio of 0. 5, OH/Al ratio of 2. 0, organic ligand/Al ratios of 0. 03 to 0. 1, and thus hindered the subsequent formation of imogolite, leading to the formation of pseudoboehmites, hydroxy-Al-organic complexes, and/or ill-defined aluminosilicate complexes. The objective of the present study was to investigate the role of selected organic ligands in affecting the formation of allophane and imogolite, and the nature of the reaction products.