摘要
以自配的具有暂时硬度的碳酸盐溶液为水样,使用NF270型和NF-型纳滤膜在5种pH值条件(6·0,6·5,7·0,7·5和8·0)下进行了纳滤实验.结果显示,当压力为1·0MPa,流量为6L·min-1,温度恒定在25℃的条件下,2种膜的通量随进料液pH值的降低而升高,表明对进料液进行酸化可使膜过滤获得相对较高的通量.整个过滤过程中,透过液pH值始终低于浓缩液pH值,即H+表现为负截留,这是因为小体积、荷正电的H+易透过小孔径、荷负电的纳滤膜所致.H+的负截留作用会加速HCO3-离解,生成更多的CO32-,使膜面发生CaCO3结晶的可能性加大,不利于膜操作.荷负电量高的纳滤膜有利于H+的透过,因此在纳滤软化水过程中,应当综合多方面因素考虑膜的选择及相应的预处理,在满足水质处理要求的前提下,采用荷负电量稍低的膜有利于减小H+负截留对纳滤软化水过程的影响,从而延缓膜面结垢.
The experiments of the nanofiltration （NF） of simulated carbonated solution with impermanent hardness were conducted with NF270 and NF- membranes under 5 pH conditions of 6.0, 6.5, 7.0, 7.5 and 8.0. Under experimental conditions the operating pressure was 1.0 MPa, flowrate was 6 L·min^-1, and the sample temperature was 25℃, the flux of two membranes increased with the decrease of the pH of the feeding solution. The results indicated that the acidification to feeding solution could obtain higher flux during the filtration. In the experiments, the pH of the permeate liquid was always lower than the pH of the concentrate liquid, this meant the H^＋ was negative rejected, because the small positive H^＋ could easily permeate the NF membranes having small pores and negative charges. The negative rejection of H^＋ could results in the decomposition from HCO3^- to CO3^2- , and then accelerate CaCO3 crystallization on membrane surface, which was unfavorable for the membrane performance. As the H^＋ is much more permeable through the NF membranes having more negative charges, the membrane selection and the pretreatment have to be considerated simultaneously in the NF softening. Selecting the membranes with less negative charges is beneficial for prevention of scaling on membrane surface when the water quality can meet the demands.
出处
《环境科学学报》
CAS
CSCD
北大核心
2005年第10期1337-1342,共6页
Acta Scientiae Circumstantiae
基金
国家自然科学基金重点项目(No.50238020)~~
关键词
纳滤
负截留
PH值
结垢
硬度
nanofiltmiton
negative rejection
hardness
pH value
scale
