This study has been made of the leaching process to reduce carbonate content in calcareous phosphate rock using lactic acid. The samples mineralogical constituents were apatite, calcite, quartz and dolomite. In this study, the effect of important variables such as reaction time, acid concentration, liquid/solid ratio, particle size and temperature in laboratory scale was optimized. It was found that the leaching rate of carbonate material increased with increasing the acid concentration, temperature, reaction time and decreasing solid/liquid ratio and particle size. The experimental data were tested through graphic and statistical methods and a shrinking core kinetics model was presented to describe the dissolution and to analyze the data. The activation energy for leaching was found to be 43.58 kJ/mol and, consequently, the rate of the reaction based on a chemical reaction-controlled process could be expressed as 1 - (1-alpha)(1/3) = 6.05 x 10(6) e(-43.58/RT)t. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.