荷电性能对纳滤膜盐水软化中膜面结垢过程的影响机制

With the rapid development of membrane technology, charged nanofiltration (NF) membrane shows excellent separating performance and good prospect in saline water softening process. Based on the fact that in this process when inlet bulk solution with low or medium concentration was involved, the scaling was apt to appeared on the NF membrane surface in brine side. Therefore, the development research of influencing mechanism for charge performance on NF membrane surface scaling process or other possible scaling models are very necessary. The project intends to carry out a series of NF membrane surface scaling experiments with different charge properties, build charge performance mechanism roadmap in NF membrane surface scaling process. Then, the streaming potential, Zeta potential and the membrane surface charge density impacts on the scale-prone ions concentration polarization, nucleation rate and membrane surface scaling growth are investigated. In the end, the relationship among charge performance, concentration polarization, nucleation rate and scaling growth is analysed comprehensively. Further, the influencing mechanism on NF membrane surface scaling process by charge property will be clarified. On the basis, the influencing mechanism and the interaction among different relevant factors accomplishes this by parsing charge performance on NF membrane surface scaling formation during saline water softening process, a set of generality and representation influencing mechanism of the evaluation method system is proposed. The results will provide theoretical basis for the evaluating charged NF membrane surface scaling potential and taking anti-scaling measurements in the saline water softening process.

随着膜技术的发展，荷电性纳滤（NF）膜应用于盐水溶液软化显示出良好的前景。基于荷电NF膜在中低浓度范围的进水端主体溶液软化过程中，浓水端的膜面处易出现结垢污染，因此，开展荷电性能对NF膜面结垢过程的影响机制及可能存在的其它结垢机理研究是十分必要的。为此，本项目拟开展不同荷电性能的NF膜面结垢过程实验，构建膜面结垢过程中荷电性能作用机制路线图，研究流动电位、Zeta电位和膜表面电荷密度对构晶离子浓差极化、膜面成核速率和膜面结垢生长的影响，深化对荷电性能、浓差极化、膜面成核速率和膜面结垢生长四者相互作用的机制认识，阐明荷电性能对NF膜盐水溶液体系软化过程中膜面结垢过程的影响机制。通过解析荷电性能对NF膜盐水溶液软化时膜面结垢过程中的影响机制及不同因素之间的交互作用，提出一套具有普适性和代表性的影响机制评估方法体系，为科学评估荷电NF膜盐水溶液软化过程中膜面结垢潜能、制定防垢措施提供依据。

荷电性能对纳滤（NF）膜盐水溶液体系软化具有重要影响，并且前期研究证实了利用NF膜的荷电性能开展盐水溶液体系的截留研究思路是可行的，但其对构晶离子的浓差极化、NF膜面成核和结垢生长等结垢过程的影响机制尚不完全清楚。这在很大程度上制约了NF膜盐水软化技术的规模化应用。为此，本项目开展了不同荷电性能的NF膜在相同研究体系下对膜面结垢过程的影响机制实验，研究了流动电位、Zeta电位和膜表面电荷密度对构晶离子浓差极化、膜面成核速率和膜面平均结垢速率的影响，深化了对荷电性能、浓差极化、膜面成核结晶和膜面结垢生长四者相互作用的机制认识，阐明了荷电性能对NF膜盐水溶液体系软化中膜面结垢过程的影响机制。本研究以DK型NF膜为载体，通过自制的切向流动电位分析仪对临阈浓度时不同进水条件（浓度、pH、压力及离子强度）下进行流动电位测定，代入H−S方程计算了NF膜面Zeta电位值，再采用NF评价仪对盐水溶液在相同条件下进行渗透实验，根据浓差极化模型计算了膜面处构晶离子浓度，并依据经典成核理论进行成核速率和诱导时间的测算。最后，在长达500 h的全闭合循环式结垢实验中，采用Pervov模型对结垢速率进行计算，并采用SEM、XPS及ATR−FTIR技术对NF膜面垢体进行表征和分析。结果表明随构晶离子浓度由0.5增加至18 mol.m−3时，膜面流动电位及Zeta电位绝对值均逐渐减小，膜面电荷密度增加。在临阈浓度时膜面依然存在较弱的流动电位值存在，并未出现零电荷现象。由于膜面浓差极化现象的存在，膜面解离官能团与该边界处成垢离子通过离子键形成的异相晶核，诱发了后续反应并生成无机垢体。本项目的研究结果将为利用NF膜的荷电性能，提出高效的NF膜结垢调控策略和降低NF膜盐水软化成本探索一条新途径。