Wang Bingqi, Yang Lin, Luo Tong, Cao Jianxin
School of Chemistry and Chemical Engineering, Guizhou University, Guiyang 550025, China.
Guizhou Engineering Research Center for High Efficiency Utilization of Industrial Waste, Guiyang 550025, China.
ACS Omega. 2021 Mar 8;6(11):7342-7350. doi: 10.1021/acsomega.0c05432. eCollection 2021 Mar 23.
The key technology of wet process phosphoric acid recrystallization is phosphogypsum phase transformation. In this study, the hydration of α-hemihydrate phosphogypsum (α-HH) to dihydrate phosphogypsum (DH) and the influence of process parameters on hydration kinetics are performed by modifying a dispersive kinetic model in the simulation of wet process phosphoric acid recrystallization. Results show that the modified dispersive kinetic model is very important in describing the entire kinetic process, indicating that α-HH-DH hydration includes induction of nucleation and growth restriction. The hydration rate of α-HH-DH substantially accelerates with the decrease of temperature and phosphoric acid concentration because the activation entropy of the reaction increases during the induction stage and the growth stage, which reduces the activation energy barrier. Moreover, the hydration rate of α-HH-DH considerably accelerates with the increase of SO ion concentration. Activation entropy increases in the induction stage, causing the activation energy barrier to decrease. Activation enthalpy increases in the growth stage, causing the activation energy barrier to decrease. The influence of process parameters on the rate of the α-HH-DH hydration reaction follows the order SO ion concentration > phosphoric acid concentration > temperature. Therefore, controlling the three parameters of temperature, phosphoric acid concentration, and SO ion concentration are important for improving the conversion rate of α-HH-DH and the purity of DH products in the production of wet process phosphoric acid.
湿法磷酸重结晶的关键技术是磷石膏的相转变。本研究通过在湿法磷酸重结晶模拟中修正分散动力学模型，对α-半水磷石膏（α-HH）水合生成二水磷石膏（DH）以及工艺参数对水合动力学的影响进行了研究。结果表明，修正后的分散动力学模型对于描述整个动力学过程非常重要，这表明α-HH-DH水合包括成核诱导和生长限制。α-HH-DH的水合速率随着温度和磷酸浓度的降低而显著加快，这是因为在诱导阶段和生长阶段反应的活化熵增加，从而降低了活化能垒。此外，α-HH-DH的水合速率随着SO离子浓度的增加而显著加快。诱导阶段活化熵增加，导致活化能垒降低。生长阶段活化焓增加，导致活化能垒降低。工艺参数对α-HH-DH水合反应速率的影响顺序为SO离子浓度＞磷酸浓度＞温度。因此，控制温度、磷酸浓度和SO离子浓度这三个参数对于提高湿法磷酸生产中α-HH-DH的转化率和DH产品的纯度至关重要。
