The direct conversion of celestite, SrSO4, to strontium carbonate, SrCO3, in leaching solutions of sodium carbonate, Na2CO3 was analyzed using an air-lift loop vessel or Pachuca tank (0.28 m I.D. x 1.36 m total height, 90 degrees conical bottom) as reactor: The kinetics of the process were studied at 353 K (80 degrees C) using 1.1 M Na2CO3 solutions containing 18 wt % celestite particles. Experimental runs were carried out to determine the effects of particle size distribution (-106 and -250 mu m) and geometrical and operating parameters of the reactor such as draft tube diameter-to-reactor diameter ratio, D-d/D-t (0.25 and 0.5) and superficial air velocity, V-sg (0.15 to 0.77 cm/s), respectively. The results showed that leaching rate was improved by increasing air superficial velocity and D-d/D-t ratio, and by decreasing particle size. For the same size distribution and air velocity the kinetics were improved by increasing the D-d/D-t ratio. A shrinking-core model considering diffusion of CO32- ions, through the solution contained in the pores of the strontium carbonate product layer; as the rate limiting stage gave a good description of the kinetics of the leaching process. Furthermore, the model takes into account both the particle size distribution of the treated samples and the depletion of leaching reactant that occurs as reaction proceeds.