Influence of organic acids on nature and surface reactivities of hydrolytic reaction products of aluminium
| MSI99P0034 | |
| Ng Kee Kwong, K. F. | |
| University of Saskatchewan, Department of Soil Science, Saskatchewan, CA | |
| Influence of organic acids on nature and surface reactivities of hydrolytic reaction products of aluminium | |
| Thesis, Ph.D. | |
| Thesis | |
| 1977 | |
| 150 p. | |
| En | |
| The role of organic acids in the solution and surface chemistry of soil aluminum is not well defined. The influence of citric, malic, tannic, aspartic and p-hydroxybenzoic acids at the concentration range of 0 to 10-4M, as would be expected in soils, on the nature and surface reactivities of the hydrolytic reaction products of AI was therefore studied. The hindrance of the hydrolysis and subsequent precipitation of Al by the organic acids increased with concentration and affinity of the organic acids for Al. This can be interpreted in terms of a side-reaction coefficient which integrates the influence of both the concentration of organic acids and the stability constants of their complexes with Al. The side-reaction coefficient is more accurate than the stability constant for predicting the relative influence of the organic acids on the hydrolytic reactions of Al in systems such as the soil where the concentrations of the organic acids may not follow the same order as their chemical affinity towards Al. The hydrolytic reaction products of Al precipitated in the absence of organic acids were crystalline to X-rays after one day aging. The corresponding products formed in the presence of 10-4M citric, malic, tannic and aspartic acids were still non-crystalline to X-rays after 40 day aging due to structural distortion created on occupation of coordination sites of Al by the organic ligands. The degree of structural distortion in the solid phase reaction products increased with the molar ratio of organic acid to Al and with the affinity of the organic acids towards Al. Electron optical observations revealed that the organic acids imparted a rough fluffy surface to the solid phase. The hydrolytic reaction products precipitated in the presence of individual organic acids were found to be markedly more reactive than those formed in their absence. The enhanced reactivity was reflected by an increase in specific surface, in the development of surface charge, and in the capacity to retain phosphate and Ca. When the organic acids, except tannic acid, were present at the same initial concentration of l0 -6M, their ability to increase the reactivity of the solid phase products followed the sequence of the stability constants of their complexes with Al, namely, Al-citrate > Al-malate > Al-aspartate > Al-p-hydroxybenzoate. Deviations from the sequence occurred when the concentration of the organic acids was raised to 10-4M. The specific adsorption of the organic anions, although favouring the retention of Ca, counteracted the promoting influence of high specific surface on the sorption of phosphate and on the development of the net surface positive charge of the solid phase reaction products. The anomalous influence of tannic acid on the surface reactivities of the solid phase reaction products of Al arose from its susceptibility to significant physical adsorption on the surface of the reaction products. This study has uncovered the importance of the low molecular weight organic acids in the transformations and basic colloidal chemistry of Al. The knowledge gained provides a basis for a better understanding of the nature and physico-chemical properties of non-crystalline inorganic com-ponents of soils, particularly with respect to the transport and fate of nutrients and pollutants in terrestrial ecosystems. | |
| ORGANIC ACIDS ALUMINIUM CHEMISTRY | |
| Chemistry | |
| 1991-10-17 | |
| En | |
| Mauritius Sugar Industry Research Institute | |
| CHEM |