Dissolution of a citric acid-hypersoluble silicophosphate glass of agrochemical importance

Abstract

In order to determine the dissolution mechanism and the influence of the concentration of organic ligands on the dissolution rates of a Si-Ca-Mg-P glass, experiments were performed under static conditions at 40°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 performed at the same initial pH value (pH = 2.3) in order to understand the part played by protons in the dissolution mechanisms. Reacted surfaces were characterized by SEM and XPS. Leachate compositions were analyzed by ICP-AES. The studied glass is soluble in HCl and hypersoluble in citric acid solutions, the dissolution being rapidly completed after only several hours. The presence of free SiO4 tetrahedra revealed by Raman investigations on the unaltered glass may explain the enhanced solubility in citric acid solutions through formation of a highly soluble citrate-silica species.