A LABORATORY STUDY OF THE LEACHING OF CELESTITE IN A PACHUCA TANK

The direct conversion of celestite, SrSO4, to strontium carbonate, SrC O3, in leaching solutions of sodium carbonate, Na2CO3 was analyzed usi ng 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 pr ocess were studied at 353 K (80 degrees C) using 1.1 M Na2CO3 solution s containing 18 wt % celestite particles. Experimental runs were carri ed out to determine the effects of particle size distribution (-106 an d -250 mu m) and geometrical and operating parameters of the reactor s uch as draft tube diameter-to-reactor diameter ratio, D-d/D-t (0.25 an d 0.5) and superficial air velocity, V-sg (0.15 to 0.77 cm/s), respect ively. The results showed that leaching rate was improved by increasin g air superficial velocity and D-d/D-t ratio, and by decreasing partic le 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 limit ing stage gave a good description of the kinetics of the leaching proc ess. Furthermore, the model takes into account both the particle size distribution of the treated samples and the depletion of leaching reac tant that occurs as reaction proceeds.