Experimental study on preparation of calcium oxide by coal reduction of calcium sulfate in carbon dioxide atmosphere

Abstract BACKGROUND Recent studies show that CaO is being produced from CaSO 4 by CO reduction using fixed‐bed reactors. However, the product yield is low and the reaction time is long. Furthermore, the high cost of CO hinders its application in industrial processes. Therefore, a new process is proposed for preparing CaO by CaSO 4 decomposition using lignite under CO 2 . The influence of various process conditions on the production of CaO by CaSO 4 decomposition is investigated by combining kinetic and FactSage simulations. Finally, a typical industrial gypsum – phosphogypsum (PG) – is used for experimental verification. RESULTS The study found that adding CO 2 during the coal reduction of CaSO 4 increases the CaO yield. The ideal conditions are 1.75 C/Ca molar ratio, 7.5% CO 2 concentration at 1100 °C with the maximum CaSO 4 decomposition rate and CaO yield of 99.63% and 99.28%, respectively. CaO generation is carried out using a two‐step process. Initially, CaSO 4 is reduced to become CaS and CaO, and CaS interacts with CaSO 4 to produce CaO. Secondly, the reaction between CaS and CO 2 produces CaO. The nucleation and growth model with g ( α ) = −ln(1 − α ) is applicable to both processes. The experimental use of PG confirms the above conclusions, but SiO 2 in PG reacts with CaO to produce Ca 2 SiO 4 and affect the CaO yield. CONCLUSION The addition of CO 2 promotes the conversion process of CaSO 4 to CaO. Increasing the temperature, C/Ca molar ratio and CO 2 concentration favor the decomposition of CaSO 4 into CaO. This study offers advice for using CaSO 4 products like PG as resources. © 2023 Society of Chemical Industry (SCI).