Ulexite, sodium-calcium-borate hydrate, has a chemical formula of Na2O center dot 2CaO center dot 5B(2)O(3)center dot 16H(2)O, and is found in great amounts in Turkey. In this study, the dissolution of ulexite in ammonium acetate solutions was investigated in a batch reactor. The effects of the concentration of solution, particle size, solid-to-liquid ratio, stirring speed and reaction temperature on the dissolution rate were determined. It was found that the dissolution rate increased with an increase in concentration and reaction temperature, and with a decrease in particle size and solid-to-liquid ratio. No effect of stirring speed was observed on the conversion. It was determined that the dissolution rate fit the chemical reaction control model. The activation energy of this dissolution process was found to be 55.7 kJ/mol. (C) 2007 Elsevier B.V. All rights reserved.