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.

中文翻译：

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膜蒸馏中石膏和二氧化硅结垢之间的不同行为。

矿物水垢限制了膜蒸馏（MD）并限制了其在处理高盐废水中的应用。解决这一挑战需要增强对结垢现象的基本了解。但是，使用不同类型的洗剂进行MD洗牙可能具有独特的机制和后果，文献中尚未对此进行系统研究。在这项工作中，我们在MD中比较了石膏和二氧化硅的结垢，并证明了石膏结垢导致较早的水通量下降并引起了膜结垢，而在二氧化硅结垢中没有观察到。显微成像和元素映射分别显示了对比的鳞片形态和石膏和二氧化硅的分布。值得注意的是，尽管石膏晶体既在膜表面又在膜基质的深处生长，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膜的形式形成在膜表面上。我们将石膏进入膜孔的原因归因于快速定向的晶体生长的结晶压力，这导致孔变形和随后的膜润湿。相反，二氧化硅垢层是通过硅酸的聚合和二氧化硅颗粒的凝胶化而形成的，其侵入性较小并且对膜孔结构的影响较小。拉伸试验的结果支持了该假设，该试验表明MD膜因石膏结垢而明显减弱。