In addition to its primary component, calcium sulfate, industrial by-product gypsum also contains trace amounts of heavy metals and soluble salts. When accumulated or landfilled over an extended period, this can lead to soil and groundwater pollution. Utilizing the H2 reduction decomposition of industrial by-product gypsum not only addresses the challenge of managing this waste but also offers a low CO2 emission method for producing quicklime. This study investigates the influence of reaction temperature, H2 concentration, and the PCO2/PH2 partial pressure ratio on the reductive decomposition of CaSO4 through experimental analysis. Subsequently, it delves into the kinetic characteristics of CaO production from the reductive decomposition of CaSO4 by H2, employing isothermal kinetic approaches. Finally, the feasibility of employing industrial by-product gypsum reduction and decomposition technology for quicklime preparation is explored. The results reveal that CaSO4 can be entirely decomposed into CaO when the temperature exceeds 1000 °C, H2 concentration is ≥ 2%, and the PCO2/PH2 ≥ 8. The interaction of CaS with CaSO4 is identified as the primary secondary reaction within the intermediate product CaS. When CaSO4 is decomposed in an atmosphere comprising 2% H2, 20% CO2, and N2, the apparent activation energies for the reaction, as determined by both the model-free and model-fitting methods, are 41.56 kJ/mol and 49.34 kJ/mol, respectively, with a modified reaction order of n = 1.748 and a modified model function of G(α) = [−ln (1-α)]0.572. Furthermore, the overall reaction rate is governed by the nucleation and growth rates of CaO. Lastly, the product quicklime obtained from the reductive decomposition of desulfurization gypsum and phosphogypsum using H2 contains over 90% CaO, complete absence of CaS, and conforms to the first-grade construction quicklime standards.
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