Journal of Industrial and Engineering Chemistry, Vol.30, 309-321, October, 2015
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.