In this paper, a method was proposed to prepare high-purity CaCO3 to sequester CO2 by means of the cyclic utilization of ammonium chloride and with carbide slag as the raw material was proposed. There was a systematical discussion about the process conditions for carbonation reaction and the effect of different technological conditions on the property of reaction product. The results have shown that the optimum process conditions for the carbonation reaction were as follows: reaction time: 60 min, reaction temperature: 30 °C, and the flow velocity of CO2: 80 mL/min. The optimum carbonated conversion rate was 98.99%. The resulting product was nanoscale spherical vaterite with a CaCO3 content of 99.95%, a whiteness of 99.3% and good self-fluidity and self-pulverability. The carbonation reaction filtrate could be recycled 8 times throughout the preparation process, and the reaction efficiency at this time was greater than 50%. High-purity nanoscale CaCO3 and fibrous CaCO3 could be successfully prepared by the control of process conditions. The study scheme proposed herein is hopeful to be used to the extraction of CO2 from carbide slag and the controlled preparation of CaCO3.