Characteristics and mechanism of desulfurization gypsum to α-hemihydrate gypsum: Experiments and simulations

doi:10.16085/j.issn.1000-6613.2023-1118

Abstract

Abstract:

The efficient utilization of desulfurized gypsum can effectively alleviate a series of environmental problems and turn waste into treasure. This paper used dihydrate gypsum to prepare α-hemihydrate gypsum in ethylene glycol aqueous solution containing trace anhydrous sodium sulfate, and explored the effects of temperature (94—98℃), ethylene glycol volume fraction (25%—35%), sodium sulfate concentration (0.1—0.3mol/L) on the mole fraction of α-hemihydrate gypsum and kinetic parameters in the dehydration conversion process from dihydrate gypsum to α-hemihydrate gypsum. The results showed that in ethylene glycol aqueous solution, the dehydration conversion process of dihydrate gypsum to α-hemihydrate gypsum conformed to the dispersion kinetic model. With the increase of temperature and ethylene glycol concentration, the kinetic parameter α remained basically unchanged, while the parameter β increased significantly, leading to an increase in the activation entropy (∆S*), which in turn led to a decrease in the energy barrier (E_a) and promoted the dehydration of dihydrate gypsum to α‍-hemihydrate gypsum. The addition of a small amount of anhydrous sodium sulfate significantly shortened the nucleation induction time of α-hemihydrate gypsum. Through molecular dynamics simulation, with increasing the concentration of sodium sulfate, the coordination number of Na⁺ and SO₄^2- increased, and the absolute difference of diffusion coefficient ∆D decreased, resulting in the increase of coordination ability and the decrease of decoupling ability. This study was of great significance for efficient utilization of desulfurized gypsum and mastering its conversion characteristics to α-hemihydrate gypsum.

Key words: dihydrate gypsum, α-hemihydrate gypsum, ethylene glycol, crystallization, kinetic model, molecular simulation

摘要：

脱硫石膏的高效利用可以有效缓解一系列环境问题，变废为宝。本文利用二水石膏在含有微量无水硫酸钠的乙二醇水溶液中制备α-半水石膏，探究温度（94~98℃）、乙二醇体积分数（25%~35%）、硫酸钠浓度（0.1~0.3mol/L）对二水石膏向α-半水石膏脱水转化过程的α-半水石膏摩尔分数和动力学参数变化。研究发现，在乙二醇水溶液中，二水石膏向α-半水石膏脱水转化过程符合分散动力学模型。随着温度和乙二醇浓度的增加，动力学参数α基本保持不变，而参数β显著增加，导致活化熵∆S*增大，进而导致能垒E_a降低，促进了二水石膏向α-半水石膏脱水转化。微量无水硫酸钠的添加，显著缩短了α-半水石膏的成核诱导时间。通过分子动力学模拟，增加硫酸钠的浓度，Na⁺与SO₄^2-的配位数增加，扩散系数绝对差值∆D降低，从而导致配位能力增加，解耦能力降低。本研究对高效利用脱硫石膏、掌握其向α-半水石膏的转化特征具有重要意义。

关键词: 二水石膏, α-半水石膏, 乙二醇, 结晶, 动力学模型, 分子模拟

CLC Number:

TQ177.3⁺7

HUAI Liye, ZHONG Zhaoping, YANG Yuxuan. Characteristics and mechanism of desulfurization gypsum to α-hemihydrate gypsum: Experiments and simulations[J]. Chemical Industry and Engineering Progress, 2024, 43(8): 4694-4703.

怀立业, 仲兆平, 杨宇轩. 脱硫石膏转化α-半水石膏的特征及机理：实验与模拟[J]. 化工进展, 2024, 43(8): 4694-4703.

Figures/Tables 14

References 26

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温度/℃	α/h	β/h^-2	R²	t_ind/h	v/h^-1	t_tot/h	K_sp,DH	K_sp,HH	a_w	S_HH
94	0.2821	0.1393	0.9995	2.01	0.23	5.93	1.61×10^-5	1.83×10^-5	0.853	1.10
95	0.2992	0.2021	0.9992	1.21	0.29	4.35	1.58×10^-5	1.76×10^-5	0.854	1.13
96	0.3177	0.2779	0.9978	0.63	0.39	2.94	1.55×10^-5	1.7×10^-5	0.855	1.15
97	0.2392	0.3783	0.9995	0.53	0.60	2.01	1.53×10^-5	1.63×10^-5	0.855	1.17
98	0.2572	0.6314	0.9998	0.41	0.75	1.61	1.50×10^-5	1.57×10^-5	0.856	1.20

温度/℃	α/h	β/h^-2	R²	t_ind/h	v/h^-1	t_tot/h	K_sp,DH	K_sp,HH	a_w	S_HH
94	0.2821	0.1393	0.9995	2.01	0.23	5.93	1.61×10^-5	1.83×10^-5	0.853	1.10
95	0.2992	0.2021	0.9992	1.21	0.29	4.35	1.58×10^-5	1.76×10^-5	0.854	1.13
96	0.3177	0.2779	0.9978	0.63	0.39	2.94	1.55×10^-5	1.7×10^-5	0.855	1.15
97	0.2392	0.3783	0.9995	0.53	0.60	2.01	1.53×10^-5	1.63×10^-5	0.855	1.17
98	0.2572	0.6314	0.9998	0.41	0.75	1.61	1.50×10^-5	1.57×10^-5	0.856	1.20

乙二醇体积分数/%	α/h	β/h^-2	R²	t_ind/h	v/h^-1	t_tot/h	K_sp,DH	K_sp,HH	a_w	S_HH
25.0	0.2522	0.1093	0.9997	2.59	0.21	6.85	1.55×10^-5	1.7×10^-5	0.872	1.09
27.5	0.2365	0.1810	0.9998	1.80	0.26	5.21	1.55×10^-5	1.7×10^-5	0.866	1.11
30.0	0.2992	0.2421	0.9992	1.21	0.29	4.35	1.55×10^-5	1.7×10^-5	0.854	1.13
32.5	0.2532	0.3234	0.9996	1.06	0.34	3.74	1.55×10^-5	1.7×10^-5	0.839	1.16
35.0	0.2965	0.5798	0.9993	0.77	0.44	2.78	1.55×10^-5	1.7×10^-5	0.823	1.19

乙二醇体积分数/%	α/h	β/h^-2	R²	t_ind/h	v/h^-1	t_tot/h	K_sp,DH	K_sp,HH	a_w	S_HH
25.0	0.2522	0.1093	0.9997	2.59	0.21	6.85	1.55×10^-5	1.7×10^-5	0.872	1.09
27.5	0.2365	0.1810	0.9998	1.80	0.26	5.21	1.55×10^-5	1.7×10^-5	0.866	1.11
30.0	0.2992	0.2421	0.9992	1.21	0.29	4.35	1.55×10^-5	1.7×10^-5	0.854	1.13
32.5	0.2532	0.3234	0.9996	1.06	0.34	3.74	1.55×10^-5	1.7×10^-5	0.839	1.16
35.0	0.2965	0.5798	0.9993	0.77	0.44	2.78	1.55×10^-5	1.7×10^-5	0.823	1.19

Na₂SO₄浓度/mol·L^-1	α/h	β/h^-2	R²	t_ind/h	v/h^-1	t_tot/h	K_sp,DH	K_sp,HH	a_w	S_HH
0.10	0.3364	0.0644	0.9994	3.19	0.16	8.76	1.55×10^-5	1.7×10^-5	0.889	1.06
0.15	0.3132	0.1031	0.9976	2.40	0.20	6.87	1.55×10^-5	1.7×10^-5	0.871	1.09
0.20	0.2992	0.2421	0.9992	1.21	0.29	4.35	1.55×10^-5	1.7×10^-5	0.854	1.13
0.25	0.2760	0.6871	0.9988	0.39	0.47	2.29	1.55×10^-5	1.7×10^-5	0.834	1.22
0.30	0.2967	2.0467	0.9995	0.17	0.83	1.26	1.55×10^-5	1.7×10^-5	0.751	1.37