Experimental study on preparation of calcium oxide by coal reduction of calcium sulfate in carbon dioxide atmosphere
Dong Ma, Qinhui Wang
Abstract
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).