Kinetic study of the conversion of mineral barite to barium carbonate under alkaline hydrothermal conditions

Abstract

The kinetic exchange of SO₄²⁻ ions with CO₃²⁻ ions in natural barium sulphate (barite) mineral under alkaline hydrothermal conditions was investigated. The experiments were performed at several temperatures ranging from 423 to 523 K for different reaction times between 1 and 192 h with molar ratios of CO₃²⁻/SO₄²⁻=1, 5 and 10. Structural characterisation of partially and completely converted witherite (BaCO₃) crystals was conducted by XRD and SEM. X-ray diffraction results showed that under hydrothermal conditions the exchange of CO₃²⁻ ions in barite was complete at 523 K in a Na₂CO₃ solution with a molar ratio of CO₃²⁻/SO₄²⁻=10 for 192 h. Based on the experimental observations, a mechanism for the conversion of barite under hydrothermal conditions is proposed. As the reaction proceeds, a porous layer of barium carbonate forms on the barite surface. The reaction rate is determined by the diffusion of sulphate ions through the porous layer. The apparent activation energy for the conversion of barite to barium carbonate is 22·5 mol⁻¹.