Distinct Behaviors between Gypsum and Silica Scaling in Membrane Distillation
Distinct Behaviors between Gypsum and Silica Scaling in Membrane Distillation
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DOI：
10.1021/acs.est.9b06023
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发表时间：
2020-01-07
影响因子：
11.4
通讯作者：
Tong, Tiezheng
中科院分区：
文献类型：
--
作者：
Christie, Kofi S. S.;Yin, Yiming;Tong, Tiezheng
矿物结垢制约了膜蒸馏技术在高含盐废水处理中的应用。要应对这一挑战，就需要加强对结垢现象的基本认识。然而，使用不同类型的缩放剂进行MD缩放可能具有不同的机制和后果，这些机制和后果在文献中尚未得到系统的研究。在这项工作中，我们比较了石膏和二氧化硅结垢在MD和表明，石膏结垢引起早期的水通量下降，并诱导膜润湿，没有观察到在二氧化硅结垢。显微成像和元素映射显示对比的规模形态和分布石膏和二氧化硅，分别。值得注意的是，虽然石膏晶体生长在膜表面上和膜基质深处，但二氧化硅仅以由连接的亚微米二氧化硅颗粒组成的相对薄的膜的形式形成在膜表面上。我们属性的石膏侵入膜孔的结晶压力作为一个结果，快速，定向晶体生长，这导致孔变形和随后的膜润湿。相比之下，硅垢层是通过柠檬酸聚合和二氧化硅颗粒凝胶化形成的，其侵入性较小，对膜孔结构的影响较小。这一假设得到了拉伸试验结果的支持，拉伸试验结果表明，MD膜被石膏结垢显著削弱。事实上，不同的结垢机制可能会产生不同的后果，膜性能提供了宝贵的见解，为未来发展的成本效益的结垢控制策略。
Mineral scaling constrains membrane distillation (MD) and limits its application in treating hypersaline wastewater. Addressing this challenge requires enhanced fundamental understanding of the scaling phenomenon. However, MD scaling with different types of scalants may have distinctive mechanisms and consequences which have not been systematically investigated in the literature. In this work, we compared gypsum and silica scaling in MD and demonstrated that gypsum scaling caused earlier water flux decline and induced membrane wetting that was not observed in silica scaling. Microscopic imaging and elemental mapping revealed contrasting scale morphology and distribution for gypsum and silica, respectively. Notably, while gypsum crystals grew both on the membrane surface and deep in the membrane matrix, silica only formed on the membrane surface in the form of a relatively thin film composed of connected submicrometer silica particles. We attribute the intrusion of gypsum into membrane pores to the crystallization pressure as a result of rapid, oriented crystal growth, which leads to pore deformation and the subsequent membrane wetting. In contrast, the silica scale layer was formed via polymerization of silicic acid and gelation of silica particles, which were less intrusive and had a milder effect on membrane pore structure. This hypothesis was supported by the result of tensile testing, which showed that the MD membrane was significantly weakened by gypsum scaling. The fact that different scaling mechanisms could yield different consequences on membrane performance provides valuable insights for the future development of cost-effective strategies for scaling control.