【作者】 刘景霞；

【导师】 李建新；

【作者基本信息】 天津工业大学 ， 纺织工程， 2007， 硕士

【摘要】 世界水资源短缺和水污染正严重地影响着人类的生存和社会经济的发展，纳滤（NF）和反渗透（RO）膜分离技术在解决水资源短缺和水质净化方面发挥着越来越重要的作用。但在膜分离过程中，膜污染严重影响了膜的分离效果，限制了膜分离技术的进一步推广。膜污染机理研究及膜污染控制受到了科学工作者的广泛关注。本文将磁化水处理技术引入到纳滤过程中，并采用超声时域反射法量化研究磁场对纳滤膜表面无机盐垢沉积和生长的影响。系统研究了磁场对Ca（HCO₃）₂溶液的某些物理化学性质及其结晶形态的影响。实验中所用的永磁和电磁场强度分别为0.4T和0.02T。实验结果表明磁场可以提高溶液的电导率和pH值，且其效果依赖于溶液浓度。随着溶液的浓度的增大，磁化效果有所减弱。实验过程中的流速和溶液的pH值都会影响到磁化效果。另外，磁场可以促进CaCO₃结晶由方解石向文石或球霞石的转变。错流纳滤实验结果表明超声监测与NF膜表面污染层的生长和发展具有良好的关联。随着CaCO₃垢在膜表面沉积，超声信号的振幅不断增高。超声时域信号随着污染层厚度的增加而发生移动。此外，超声监测技术可以监测到不同的磁化条件下，即无磁、永磁和电磁，污染层形成的速率。永磁和电磁作用条件下膜通量下降缓慢，重量法和超声监测结果表明膜表面形成的CaCO₃垢质层厚度较薄。SEM和XRD研究结果表明磁化处理抑制了正六方体方解石的形成，而优先生长松球形的球霞石或针状文石。磁处理后NF膜表面CaCO₃晶体晶型不规则、排列疏松，导致了污染层厚度和密度的减小及NF膜的渗透通量衰减较缓慢，这与超声反射信号的振幅增长较慢相对应。上述磁化效果通常被认为与磁流体动力学机理有关。总之，超声监测与膜通量变化、重量法、SEM和XRD等分析结果具有良好的对应关系，这为膜污染控制方法的评价提供了一种有效手段。更多还原

【Abstract】 The lack of water resource and the serious water pollution in the world are influencing the life and the development of society economic deeply. Nanofiltration and Reverse Osmosis is playing a more and more important role in resolving the lack of water resource and water purification. In the membrane processes, however, membrane fouling weakens the separate effect and limits the further extension of membrane separation technique. The study on the mechanism and the control of membrane fouling has been paid extensive attention to by boffins all over the world. This study introduces the magnetic water treatments into Nanofiltration process, and describes an existing ultrasonic technique for quantitative study of the effect of magnetic fields on the CaCO₃ scale deposition on the membrane surface during crossflow nanofiltration （NF）.The effects of magnetic fields on some physico-chemistry properties of Ca（HCO₃）₂ solutions and the crystal morphology were investigated systematically. The permanent and electro magnetic fields used in the experiments are 0.4T and 0.02T, respectively. Results show that magnetic field enhances the conductivity and pH of the treated solution and its effect depends on the concentration of the solution. The influence of magnetic fields declines with the increase of solution concentration. The magnetic effect also affected by the flow rate and the pH of the solutions. In addition, the magnetic treatments promote the formation of aragonite and vaterite from calcite.The results obtained in the experiments of crossflow nanofiltration show a good relationship between the ultrasonic measurements and the development of CaCO₃ scale on the NF membrane surface. The amplitude of the ultrasonic signal increased with the deposition of the CaCO₃ scale on membrane. Furthermore, the ultrasonic technique is capable of measuring the rate of fouling layer formation under different treatment conditions, i.e. with non-magnetic field, permanent magnetic field and electromagnetic field. The permeate flux of NF membrane declined slower and the thickness of the scale layer obtained by ultrasonic and weight measurements was thinner in the experiments with PMF and EMF. The SEM and XRD analyses imply that the magnetic treatment suppresses the formation of calcite crystals and prefers to vaterite and aragonite. The CaCO₃ crystal deposited on membrane surface is lessregular and looser, resulting in the decrease in the thickness and density of fouling layer and the slower flux-decline of NF membrane. These correspond with the lower increase in the amplitude of the ultrasonic response signals, the effect of magnetic treatments is normally related to the the magnetohydrodynamic （MHD） mechanism.Overall, the independent measurements such as the flux-decline data, weight measurement and SEM analysis corroborate the ultrasonic measurements. The ultrasonic technique has provided an effective measure to evaluate the prevention and control of membrane fouling.更多还原