Optimizing Synergy between Phosphogypsum Disposal and Cement Plant CO2 Capture by the Calcium Looping Process

In this work, a novel joint processing route that integrates the disposal of phosphogypsum waste with CO2 emissions reduction in a cement plant was proposed. The route mainly includes three parts: direct aqueous carbonation of phosphogypsum, use of the obtained carbonation product for CO2 capture in the calcium looping process (CLP), and manufacture of cement clinker using the spent CaO-based sorbent. The direct use of the CO2 derived from cement plant flue gas (20 vol % CO2) is able to convert 94.5% of CaSO4 in the phosphogypsum into CaCO3. However, a long time of 90 min is required for the completion of the conversion. Therefore, we proposed to introduce a part of the highly concentrated CO2 gas stream separated from the CLP and, hence, to increase the overall CO2 concentration of the carbonation gas stream. It was found that only 45 min is needed to achieve a comparable carbonation level when the gas stream containing 45 (or 60) vol % CO2 was used. Moreover, the solid carbonation residues derived from phosphogypsum carbonation possess relatively good cyclic CO2 capture performance, which is superior to the CaCO3 reagent. It indicates that the joint processing route proposed here is feasible, which can not only recycle the phosphogypsum waste but also reduce the CO2 emissions in the cement plant.