Preparation of high purity PCC from medium- and low-grade limestones using the strongly acidic cation exchange resin

Domestic medium-grade limestone(CaO 53%) is calcined to form CaO for use in steel industries. On the other hand, low-grade limestone(CaO 52%) is directly used for stack-gas desulfurization. In this study, the strongly acidic cation exchange resin (SCR) process was used to obtain high purities.X-ray diffraction results indicated that the calcined product from medium-grade limestone was CaO (98.6 wt%) and SiO2 (1.4 wt%), and that the product from low-grade limestone was composed of CaO (97.6 wt%) and SiO2 (2.4 wt%). Hydration reactions revealed 96.7 and 94.0 wt% of Ca(OH)2, and the amount of CaCO3 increased because of the reaction of HCO3− in aqueous solutions during the slaking reaction.To prepare precipitated calcium carbonate (PCC, CaCO3), the adsorption of calcium ion and recovery reaction were conducted with the prepared CaO and cation exchange resin(R-SO3H) (1:24 kg:kg). High-grade PCC was prepared from the reaction with calcium-adsorbed resin(Ca-(R-SO3)2) and NaOH. Although Ca(OH)2 is amorphous, Ca(OH)2 by calcium adsorption is plate-type and can be used as a plastic filler. Calcium ion was recovered as CaCl2 solution by calcium-adsorbed resin(Ca-(R-SO3)2) and HCl. This solution was concentrated and dried to form CaCl2, which was used to form high-grade PCC, Ca(OH)2, and CaO.

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