Calorimetric study of dissolution kinetics of phosphorite in diluted acetic acid

Abstract

In this report, we present a thermodynamic and kinetic study of the selective dissolution of calcite from low-grade phosphate ores (Epirus area, Greece) by dilute acetic acid at isothermal conditions. A twin calorimeter with two identical membrane vessels, for the acid dissolution process, and for the reference was used. The curves of rate vs. time of the phosphorite dissolution for various temperatures show that the maximum (.qmax) was increased, whereas the time (tpeak) to achieve the corresponding .qmax values was decreased, as the experimental temperature was increased. The dissolution enthalpy was increased from 13.1 to 16.7 kJ mol−1, as the experimental temperature was increased from 10.0 to 28.0°C. The chemical analysis of the supernatant solutions shows that the main process was the calcite dissolution. The reaction model with general form, ln(1/(1-X))=ktm, was found to fitted the experimental data regardless of the experimental temperature. These results were assigned in the presence of two different kinds of particles in the phosphorite. The activation energy of the dissolution process was found 69.7 kJ mol−1. The SEM micrographs of acid dissolution samples showed two different textures after acid dissolution.