Kinetics of the dissolution of magnetite in thioglycolic acid solutions

Abstract

The kinetics of the dissolution of magnetite by thioglycolic acid (mercaptoacetic acid) have been studied at different acid concentrations and specific surface areas, and as a function of pH and temperature. The experimental evidence points to the overall rate of reaction depending on the instantaneous surface area of the magnetite particles and that the probable reaction mechanism is the decomposition of the species formed by the interaction of thioglycolate anion with the protonated OH groups located on the surface of the magnetite particles. This mechanism explains the sharp maximum in the dissolution rate constant obtained at pH ca, 4.5, as it takes into account two phenomena which are sensitive to pH in opposite directions, the increase in thioglycolate anion concentration as the pH is increased and the increase in the amount of protonated superficial OH groups as the pH is lowered. The activation enthalpy for this reaction was found to be 15.5 kJ mol^–1.