Preparation of precipitated calcium carbonate using wollastonite and CO2 from industrial exhaust

The production of precipitated calcium carbonate (PCC) from carbonate-free minerals and CO2 from industrial exhaust gas could lower energy consumption and promote CO2 sequestration. The present study proposes a chemical looping process for the production of PCC from wollastonite (calcium silicate) and CO2 from industrial exhaust using ammonium chloride as the looping medium; this study also included a pilot setup with a capacity of 3 kg of carbonate per hour to demonstrate the process. The process consisted of three phases: extraction of calcium from the wollastonite with hydrochloric acid; carbonation of the CO2 in the extract solution in the presence of ammonia to produce calcium carbonate while generating ammonium chloride; and regeneration of hydrochloric acid and ammonia by the decomposition of ammonium chloride. A special air-lift reactor with an integrated settling vessel was designed for the carbonation reaction. The extraction and carbonation conditions were optimized, and fine calcium carbonate with a purity greater than 98% and a particle size of 2 mu m was produced. The overall utilization of the calcium from wollastonite and the CO2 reached 99 and 90%, respectively. This process avoids the high-temperature pyrolysis of limestone and thus consumes less energy. It also sequesters CO2 from industrial exhaust and is a green and high-performing process for the production of PCC.