The dissolution kinetics of ulexite in perchloric acid solutions was investigated. The effect of perchloric acid concentration, particle size, stirring speed and reaction temperature on the dissolution rate of ulexite was determined. It was found that the rate of dissolution increased with increasing perchloric acid concentration, stirring speed, reaction temperature and with decreasing particle size. The dissolution rate may describe the Avrami model. The activation energy was calculated 19.12 kJ mol(-1). (c) 2007 Elsevier B.V. All rights reserved.