Aqueous carbonation of the potassium-depleted residue from potassium feldspar-CaCl2 calcination for CO2 fixation

摘要

Based on the academic thought of carbon capture and utilization, a novel process to integrate the potassium extraction from the insoluble potassium feldspar, industrial waste utilization, and the subsequent CO2 fixation using the resultant potassium-depleted residue was proposed in our previous studies. The potassium-depleted residue comprises several Ca-bearing phases, namely wollastonite (CaSiO3), pseudowollastonite (Ca3Si3O9), Cl-mayenite (Ca12Al14O32Cl2), and anorthite (CaAl2Si2O8), which are potential materials for fixation of CO2 via carbonation. In this study, carbonation of the residue was examined with focuses on the effects of reaction temperature, initial CO2 pressure, particle size of the residue, and reaction duration on the carbonation of these Ca-bearing phases. The results demonstrated that both the temperature and CO2 pressure significantly affect the carbonation, while the residue particle size has only minor influence. At 1 MPa CO2 pressure, the carbonation of these components was dominant at different reaction temperatures. Almost complete carbonation of the pseudowollastonite could be achieved at 75 A degrees C, while significant carbonation of the wollastonite takes place above 100 A degrees C. However, the Cl-mayenite and anorthite are incapable of carbonation even at 200 A degrees C. Increasing the CO2 pressure to 4 MPa can lead to a distinct carbonation of the Cl-mayenite at 150 A degrees C but the anorthite remains untouched. At 1.5 MPa CO2 pressure and 150 A degrees C, with the increasing reaction time, the following Ca-bearing species were successively carbonated: first the pseudowollastonite in 5 min after the reaction started, the wollastonite in 5-15 min, and then simultaneously the wollastonite and the pseudowollastonite in 15-45 min, while the carbonation of Cl-mayenite do not begin even after 120 min. A priority sequence of carbonation of these Ca-bearing minerals was determined as follows: pseudowollastonite > wollastonite > Cl-mayenite > anorthite. The trend is in agreement with the results of thermodynamic calculation. Compared to the carbonation of natural wollastonite, the synthesized wollastonite contained in the potassium-depleted residue seems to be more active in carbonation.