Leaching kinetics of ulexite in sodium hydrogen sulphate solutions

Abstract The aim of this study was to investigate the dissolution kinetics of ulexite in sodium hydrogen sulphate solutions in a mechanical agitation system and to declare an alternative reactant to produce boric acid. Reaction temperature, concentration of sodium hydrogen sulphate solutions, stirring speed, solid/liquid ratio and ulexite particle size were selected as parameters of the dissolution rate of ulexite. The experimental results were successfully correlated by linear regression using Statistica program. Dissolution curves were evaluated in order to test shrinking core models for solid-fluid systems. It was observed that increase in the reaction temperature and decrease in the solid/liquid ratio cause an increase in the dissolution rate of ulexite. The dissolution extent is highly increased with increase in the stirring speed rate between 100 and 700 rpm experimental conditions. The activation energy was found to be 36.4 kJ/mol. The leaching of ulexite was controlled by diffusion through the ash or product layer. The rate expression associated with the dissolution rate of ulexite depending on the parameters chosen may be summarized as: 1–3(1 −  X ) 2/3  + 2(1 −  X ) = 6.17 ×  C 0.97  ×  W 1.17  ×  D −1.72  × ( S / L ) −0.66  ×  e (−36.4/ RT ) · t .