The solubility of magnesite ore in citric acid, an environmentally friend and natural reagent, was investigated. The effects of reaction temperature, particle size and acid concentration were examined. The leaching rate increased with decreasing particle size and with increasing temperature. The dissolution in terms of acid concentration increased initially and then fell with increasing concentration. By testing shrinking core models for fluid-solid systems, it was observed that the dissolution of magnesite was controlled by chemical reaction. The following semi-empirical model was developed: 1 - (1 - x)(1/3) = 6.4 x 10(7)(D)(-0.17)(C)(0.11)e(-61.35/RT)t, where D is the particle size, C the acid concentration, T the reaction temperature and t the reaction time. The activation energy of the process was 61.35 kJ.mol(-1).