Abstract Mineral scaling is one key obstacle to membrane distillation (MD) in hypersaline wastewater desalination, but the scaling and fouling mechanism are poorly understood. Addressing this challenge required revealing the foulants layer formation process. In this study, MD was applied for flue gas desulfurization wastewater treatment with a plug flow module, aims at unfolding the foulants accumulation process into three dimensions (3D) space as the flow velocity had significant influence on foulants distribution. Hence, validated offline method was used to detect the formation of foulants layer by SEM-EDS-FTIR-XPS. Mineral scaling was the key fouling mechanism, and the fouling tendency increased along the flow pass by brick-laying process. Hexagonal CaSO4, primarily in the form of α‑calcium sulfate hemihydrate, and lamellate Mg-Si complexes are the leading foulants, acting as “bricks” during the layer-by-layer manufacturing process of scalants. The pioneering foulant, structured by organic matters and Mg-Si complexes, was the key incipient foulant and acted as “concrete”. Heterogeneous nucleation is the primary crystallization mechanism for CaSO4, whereas Mg-Si complexes was formed in bulk. The “brick-laying” process sheds light on the distribution and formation of mineral scaling and membrane fouling in MD, which can be extended to other membrane desalination processes.

中文翻译：

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揭示脱硫废水处理膜蒸馏污垢层的砌砖过程：洞察矿物结垢

摘要 矿物结垢是超含盐废水脱盐中膜蒸馏 (MD) 的主要障碍之一，但对其结垢和结垢机制知之甚少。解决这一挑战需要揭示污垢层的形成过程。在这项研究中，MD 被应用于带有活塞流模块的烟气脱硫废水处理，旨在将污垢积累过程展开到三个维度 (3D) 空间，因为流速对污垢分布有显着影响。因此，使用经过验证的离线方法通过 SEM-EDS-FTIR-XPS 检测污垢层的形成。矿物结垢是主要的结垢机理，在砌砖过程中结垢倾向沿流道增加。六方 CaSO4，主要以 α-硫酸钙半水合物的形式存在，层状Mg-Si复合物是主要的污垢，在逐层阻垢的制造过程中充当“砖块”。由有机物和 Mg-Si 配合物构成的开创性污垢是关键的初期污垢，起到了“混凝土”的作用。非均相成核是 CaSO4 的主要结晶机制，而 Mg-Si 复合物是大量形成的。“砌砖”过程揭示了 MD 中矿物结垢和膜污染的分布和形成，这可以扩展到其他膜脱盐过程。非均相成核是 CaSO4 的主要结晶机制，而 Mg-Si 复合物是大量形成的。“砌砖”过程揭示了 MD 中矿物结垢和膜污染的分布和形成，这可以扩展到其他膜脱盐过程。非均相成核是 CaSO4 的主要结晶机制，而 Mg-Si 复合物是大量形成的。“砌砖”过程揭示了 MD 中矿物结垢和膜污染的分布和形成，这可以扩展到其他膜脱盐过程。