Yoon J, Amy G, Yoon Y
International Water & Wastewater Research Center, Korea Institute of Water and Environment, KOWACO, 462-1, Jeonmin-Dong, Yusung-Gu, Daejon, Korea 305-730.
Water Sci Technol. 2005;51(6-7):327-34.
Rejection and transport of chromate (Cr (VI)), arsenate (As (V)), and perchlorate (ClO4-) by and through reverse osmosis, nanofiltration, and ultrafiltration were found to be affected by solution pH and ionic strength. In this study, the rejection of these target ionic contaminants increased with increasing pH at the same conductivity (ionic strength) for the tested membranes, regardless of salt type. General trends showed that the rejection followed the order: CaCl2 < KCl < or = K2SO4, at the same pH and conductivity condition. The rejection also significantly decreased as conductivity was increased regardless of the salt type. These results support the notion that a more negative surface charge due to increasing pH and/or decreasing ionic strength (conductivity) enhances rejection; lower molecular weight cut-off also enhances rejection. Measured values of hindered diffusion coefficient through the membrane pores (Dp) for the target contaminants significantly decreased as pH was increased, regardless of salt type at the same conductivity. At the same pH and conductivity, the Dp of the target contaminants follows the order: CaCl2 > KCl > K2SO4, in the presence of different types of salts. The Dp of the target contaminants significantly increased as conductivity was increased regardless of the salt type. The rejection data were modeled by application of a non-equilibrium thermodynamic model. The rejection model has five transport parameters: the molecular transport coefficient (omega), osmotic pressure gradient (deltaII), molecular reflection coefficient (sigma), the average bulk fluid interfacial concentration between the feed and permeate side (C(avg)), and the solvent flux (Jv). The transport parameters were determined by independent measurements (and calculation with minimum assumptions.) Measurements and predictions of the target contaminant transport were in good agreement.
研究发现，反渗透、纳滤和超滤对铬酸盐（Cr(VI)）、砷酸盐（As(V)）和高氯酸盐（ClO4-）的截留及透过情况受溶液pH值和离子强度的影响。在本研究中，对于所测试的膜，在相同电导率（离子强度）下，这些目标离子污染物的截留率随pH值升高而增加，与盐的类型无关。一般趋势表明，在相同pH值和电导率条件下，截留率顺序为：CaCl2 < KCl < 或 = K2SO4。无论盐的类型如何，截留率也会随着电导率的增加而显著降低。这些结果支持了这样一种观点，即由于pH值升高和/或离子强度（电导率）降低导致的表面电荷更负会增强截留率；较低的分子量截留值也会增强截留率。对于目标污染物，通过膜孔的受阻扩散系数（Dp）的测量值在相同电导率下，无论盐的类型如何，都会随着pH值的升高而显著降低。在相同pH值和电导率下，在不同类型盐存在的情况下，目标污染物的Dp顺序为：CaCl2 > KCl > K2SO4。无论盐的类型如何，目标污染物的Dp会随着电导率的增加而显著增加。通过应用非平衡热力学模型对截留数据进行了建模。截留模型有五个传输参数：分子传输系数（ω）、渗透压梯度（δII）、分子反射系数（σ）、进料侧和渗透侧之间的平均本体流体界面浓度（C(avg)）以及溶剂通量（Jv）。传输参数通过独立测量（并以最少假设进行计算）来确定。目标污染物传输的测量值和预测值吻合良好。
