The Dissolution Kinetics of Ulexite in Sulphuric Acid Solutions

M. Tunç, S. Yapici, M. Kocakerim and A. Yartasi

Abstract
This technical note presents an investigation on the dissolution kinetics of ulexite, a boron mineral, in H2SO4 solutions as a function of particle diameter, mass concentration, stirring speed, acid concentration, and reaction temperature. It was determined that the dissolution rate increased with increasing reaction temperature and decreasing particle diameter, mass concentration and acid concentration, while no important effect of stirring speed was observed. Ulexite could be dissolved up to 100 percent in the sulphuric acid solutions. The following overall reaction was suggested for the process Na2O · 2CaO · 5B2O3 · 16H2O(s)+ 6H3O+ + 3SO42–(aq) → → 2Na+(aq) + 2CaSO4 · 2H2O(s) + 10H3BO3(aq) + 6H2O(l) + SO42–(aq) The analysis of the experimental data showed that the dissolution process was controlled by the diffusion of H3O+ ions to the mineral surface through the product and by-product layer, and the reaction kinetics can be expressed as –1n (1–x) = ktn where x is the dissolution amount fraction, k the function of the experimental quantities, and rate coefficient and t the reaction time.

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Keywords
dissolution kinetics, ulexite, boron minerales