Preparation of high purity CaCO3 by carbonation of carbide slag after physical impurity removal: calcination, cyclone and magnetic separation

ABSTRACT The co-production of high-purity CaCO 3 by carbonating CO 2 from carbide slag (CS) has attracted significant attention. However, due to the complex composition of CS and the difficulty in separating Ca element, it is difficult to balance the carbonation cost and quality of the product. In this study, CS was used as raw material, and a method of preparing high-purity CaCO 3 through calcination, cyclone and magnetic separation, named multi-stage impurity removal, was proposed firstly. The effects of calcination time and temperature on mineral phase transformation and the purity and whiteness of CaCO 3 prepared by carbonation during the calcination of carbide slag were studied. The effects of cyclone and magnetic separations were also discussed. The mechanism for the removal of impurities through high-temperature calcination was discussed innovatively. The optimum process conditions for multi-stage impurity removal and carbonation were determined, after calcination at 900 ℃ for 3 h, the CS was transported to cyclone separation at an inlet volumetric flow rate of 80 m³ /h. The separated substrate was then formulated into a pulp with a S/L of 10 % for magnetic separation. The CS pulp obtained after magnetic separation entered the carbonation process, where it was aerated with CO 2 at a flow rate of 0.2 L/min for carbonation. This process resulted in calcite-type CaCO 3 with the purity and whiteness of 97.8 % and 97.4, respectively. Finally, the cost of the process was estimated. The total initial investment cost was approximately CNY 6.51 million, while the total operating cost was CNY 1915.85/t of CaCO 3 .