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We report an alternative technology for the mineralization of CO 2 and production of soluble potash fertilizer via thermal activation of the insoluble K-feldspar with industrial waste of CaCl 2 with lower energy consumption since the activation temperature was about 800−900°C compared with the conventional temperature of 1300°C. A remarkable K-extraction and CO 2 mineralization ratio could be obtained at an appropriate activation temperature and content of additive CaCl 2 , which possessed the exchange of skeletal K + with dissociative Ca 2+ to form soluble K + species, the collapse of K-feldspar framework, and the formation of intermediates (e.g., anorthite, pseudowollastonite, and wollastonite) to react with CO 2 . Characterization results (e.g., XRD, EDS, and SEM) indicated that pseudowollastonite and wollastonite were the major species to fix CO 2 . Moreover, the reaction principles of the K-extraction and CO 2 mineralization were discussed, and a possible mechanism was proposed.

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 CO 2 fixation using the resultant potassium-depleted residue was proposed in our previous studies. The potassium-depleted residue comprises several Ca-bearing phases, namely wollastonite (CaSiO 3 ), pseudowollastonite (Ca 3 Si 3 O 9 ), Clmayenite (Ca 12 Al 14 O 32 Cl 2 ), and anorthite (CaAl 2 Si 2 O 8 ), which are potential materials for fixation of CO 2 via carbonation. In this study, carbonation of the residue was examined with focuses on the effects of reaction temperature, initial CO 2 pressure, particle size of the residue, and reaction duration on the carbonation of these Cabearing phases. The results demonstrated that both the temperature and CO 2 pressure significantly affect the carbonation, while the residue particle size has only minor influence. At 1 MPa CO 2 pressure, the carbonation of these components was dominant at different reaction temperatures. Almost complete carbonation of the pseudowollastonite could be achieved at 75°C, while significant carbonation of the wollastonite takes place above 100°C. However, the Cl-mayenite and anorthite are incapable of carbonation even at 200°C. Increasing the CO 2 pressure to 4 MPa can lead to a distinct carbonation of the Cl-mayenite at 150°C but the anorthite remains untouched. At 1.5 MPa CO 2 pressure and 150°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.

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