DISSOLUTION OF A CITRIC ACID-HYPERSOLUBLE SILICOPHOSPHATE GLASS OF AGROCHEMICAL IMPORTANCE

In order to determine the dissolution mechanism and the influence of t he concentration of organic ligands on the dissolution rates of a Si - Ca - Mg - P glass, experiments were performed under static conditions at 40-degrees-C, from 1 h to 3 d, in citric acid solutions of various concentrations. Parallel runs in HCl and 0.1 mol/l citric acid were p erformed at the same initial pH value (pH = 2.3) in order to understan d the part played by protons in the dissolution mechanisms. Reacted su rfaces were characterized by SEM and XPS. Leachate compositions were a nalyzed by ICP-AES. The studied glass is soluble in HCl and hypersolub le in citric acid solutions, the dissolution being rapidly completed a fter only several hours. The presence of free SiO4 tetrahedra revealed by Raman investigations on the unaltered glass may explain the enhanc ed solubility in citric acid solutions through formation of a highly s oluble citrate-silica species.