真空碳热还原分解硫酸钙热力学分析及实验探究

Decomposition of Calcium Sulphate by Carbothermic Reduction at Reduced Pressures

采用＂物质吉布斯自由能法＂讨论在常压和体系压强为50 Pa条件下,硫酸钙碳热还原分解的热力学条件并进行了实验探究。计算得出：在常压条件下,在500～800 K时,硫酸钙与碳反应生成CaS,当温度升至1400 K以上时,CaS与CaSO4发生反应生成CaO;当系统压强为50 Pa时,第一步反应温度为400～600 K,第二步则降至1100 K以下。实验结论：反应明显分两步发生,第一阶段在400～600 K,第二阶段反应起始于950～1000 K,最终固体产物主要为CaO,含有少量CaS。实验验证了理论计算的正确性,为硫酸钙真空碳热分解提供热力学理论依据和实验基础。

Decomposition of CaSO4 by carbothermic reduction in vacuum was modeled,analytically calculated in scheme of ＂Substance Gibb＇s Free Energy Functional Determinant＂,and experimentally evaluated. The impacts of the decomposition conditions,including the pressure,temperature,and C-content,on CaSO4 deposition were studied. The slag was characterized with X-ray diffraction. The calculated results show that at 100 kPa,the decomposition experienced two stages： CaSO4 first reacted with C to produce CaS at a temperature between 500 ～ 800 K at 100 kPa,and then,CaO formed at 1400 K because CaS went on reacting with the remaining CaSO4,and that the pressure strongly affected the reaction temperature in the two stages. For example,at 50 Pa,the temperatures dropped to 400 ～ 600 K in the first stage and 1100 K in the second. The measured reaction temperatures,around 400 ～ 600 K for the first stage and 950 K for the 2nd,agree fairly well with the calculated ones. We suggest that carbothermic reduction at a reduced pressure be feasible for recycling CaSO4 pollutant.