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

BACKGROUND: Recent studies show that CaO is being produced from CaSO4 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 CaSO4 decomposition using lignite under CO2. The influence of various process conditions on the production of CaO by CaSO4 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 CO2 during the coal reduction of CaSO4 increases the CaO yield. The ideal conditions are 1.75 C/Ca molar ratio, 7.5% CO2 concentration at 1100 degrees C with the maximum CaSO4 decomposition rate and CaO yield of 99.63% and 99.28%, respectively. CaO generation is carried out using a two-step process. Initially, CaSO4 is reduced to become CaS and CaO, and CaS interacts with CaSO4 to produce CaO. Secondly, the reaction between CaS and CO2 produces CaO. The nucleation and growth model with g(alpha) = -ln(1 - alpha) is applicable to both processes. The experimental use of PG confirms the above conclusions, but SiO2 in PG reacts with CaO to produce Ca2SiO4 and affect the CaO yield. CONCLUSION: The addition of CO2 promotes the conversion process of CaSO4 to CaO. Increasing the temperature, C/Ca molar ratio and CO2 concentration favor the decomposition of CaSO4 into CaO. This study offers advice for using CaSO4 products like PG as resources. (c) 2023 Society of Chemical Industry (SCI).