3987169

Tale of two scales: Elucidating the contrast behaviors and mitigation strategies of gypsum and silica scaling in membrane desalination

Date
March 18, 2024
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Mineral scaling is a major constraint that limits the efficiency of membrane desalination. Different types of mineral scales formed via distinct mechanisms might lead to distinctive consequences. Herein, I am presenting a set of investigations that collectively unveil the different behaviors and mitigation strategies between gypsum and silica scaling in reverse osmosis (RO) and membrane distillation (MD), two major membrane technologies of desalination and wastewater reuse. In RO, while membrane surface charge is shown to closely related membrane propensity to silica scaling, surface properties play a minor role in regulating gypsum scaling. Such a difference is likely due to the facts that negatively charged, ionized silicic acid controls the kinetics of silica scaling and that a non-classical nucleation pathway might govern gypsum formation. In MD, gypsum scaling formed via crystallization causes a rapid water vapor flux decline and membrane pore wetting, due to its fast kinetics and intrusive nature. In contrast, slower kinetics and the absence of pore wetting is observed for silica scaling formed via polymerization. These discrepancies lead to distinct scaling mitigation strategies, where tuning membrane surface hydrophobicity is more effective for reducing gypsum scaling and antiscalants of contrasting functionalities are required between these two scaling types. In addition, I will show evidence that the organic-scalant interactions also vary between gypsum scaling and silica scaling, resulting in different behaviors of combined fouling and scaling. Therefore, our work promotes fundamental knowledge on membrane scaling in MD desalination and suggests that scaling mitigation strategies should be tailored to the scale type and formation mechanisms.

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