磷石膏常压制备二水硫酸钙晶须机理研究

摘要/Abstract

摘要： 磷石膏是湿法磷酸工艺产生的大宗固体废弃物,堆存量大且对环境污染严重,因此,亟需对磷石膏进行除杂提纯以实现其高值化利用。本文以盐酸为溶剂对磷石膏进行热析提纯,得到了高品质、高长径比二水硫酸钙晶须,基于分子动力学对晶须生长机理进行了模拟。结果表明:在反应温度80 ℃、反应时间1.5 h、盐酸浓度4 mol/L条件下,热析提纯后磷石膏中二水硫酸钙质量分数由82.50%提升至99.80%,P₂O₅含量由1.78%(质量分数,下同)降低至0.03%,SiO₂含量由7.37%降低至0.02%,氟几乎完全去除,最终得到二水硫酸钙晶须制品。模拟计算表明:298 K条件下,二水硫酸钙在盐酸中比在纯水中更易溶解,且随温度升高,二水硫酸钙溶解度降低。此外,二水硫酸钙(020)面间距最小,该面硫酸钙离子排列更加紧密,有利于形成完整有序的晶体。晶须生长机制为二水硫酸钙在盐酸环境下先逐渐溶解,随着温度升高,溶液开始过饱和,析出硫酸钙晶体并形成晶核,晶体沿二水硫酸钙(020)面螺旋位错生长,形成二水硫酸钙晶须。

关键词: 磷石膏, 二水硫酸钙晶须, 热析提纯, 分子动力学, 生长机制

Abstract: Phosphogypsum(PG) is a bulk solid waste produced during wet phosphoric acid process, which is largely stocked and can cause seriously environmental pollution. Therefore, it is urgent to remove impurities, realizing its high valuable utilization as a resource. In this study, PG was extracted and purified bythermolysis purification using hydrochloric acid to obtain high quality and high lengh-diameter ratio calcium sulfate dihydrate whisker. Besides, the growth mechanism of calcium sulfate dihydrate whisker was simulated based on molecular dynamics. The results show that at 80 ℃, reaction time of 1.5 h and 4 mol/L hydrochloric acid, the mass fraction of calcium sulfate dihydrate in PG increases from 82.50% to 99.80% after thermolysis purification. In addition, after thermolysis purification, the content of P₂O₅ decreases from 1.78% (mass fraction, the same below)to 0.03%, the mass fraction of SiO₂ decreases from 7.37% to 0.02%, and fluorine is almost completely removed. Finally, calcium sulfate dihydrate whisker products are obtained. The simulation calculation results exhibit that calcium sulfate dihydrate is more soluble in hydrochloric acid solution than that in pure water at 298 K. In addition, the solubility of calcium sulfate dihydrate decreases at increased temperature. Moreover, the (020) plane of calcium surfate dihydrate presents the lowest interplanar spacing, in which calcium sulfate ions are more closely arranged and conducive to the formation of orderly and complete crystals. The growth mechanisms of whisker indicate that, firstly, calcium sulfate dihydrate gradually dissolve into hydrochloric acid. At higher temperatures, the solution begins to supersaturate, calcium sulfate crystals precipitate to form crystal nuclei. Subsequently, the crystals grow along the spiral dislocation of (020) plane of calcium surface dihydrate, thereby forming calcium sulfate dihydrate whisker.

Key words: phosphogypsum, calcium sulfate dihydrate whisker, thermolysis purification, molecular dynamics, growth mechanism

中图分类号:

TQ132.32

吴开振, 李瑞, 李育彪, 吴晓勇, 孙旭超, 薛璐韬, 陈新, 池汝安. 磷石膏常压制备二水硫酸钙晶须机理研究[J]. 硅酸盐通报, 2024, 43(12): 4461-4470.

WU Kaizhen, LI Rui, LI Yubiao, WU Xiaoyong, SUN Xuchao, XUE Lutao, CHEN Xin, CHI Ru’an. Mechanism of Preparing Calcium Sulfate Dihydrate Whiskers from Phosphogypsum under Atmospheric[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2024, 43(12): 4461-4470.

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