摘要
选用典型疏松型纳滤膜NF270对离子强度为1.5~24 mmol·L^(-1)的3种无机盐(MgCl_(2)、CaCl_(2)、NaCl)的单一盐溶液、混合盐溶液(MgCl_(2)/CaCl_(2)+NaCl)及某地下水进行纳滤实验,解析该膜在不同离子环境中的阳离子截留特性,并考察Ca^(2+)/Mg^(2+)在膜表面的吸附及对膜表面电荷的屏蔽作用对静电效应和盐离子截留率的影响.结果表明,NF270膜表面负电荷密度较高,对Ca^(2+)和Mg^(2+)都具有较强的吸附效应.NF270过滤相同离子强度的3种单一盐溶液时(特别是离子强度为1.5~6 mmol·L^(-1)),道南效应较为显著,限定性离子Cl^(-)发挥了重要作用,截留率关系为NaCl>MgCl_(2)≈CaCl_(2).混合盐溶液中,Ca^(2+)/Mg^(2+)显著降低了膜表面电势的绝对值,在道南效应、空间位阻效应和介电效应的综合作用下,Ca^(2+)/Mg^(2+)在反离子竞争中占据优势,截留率关系为Ca^(2+)/Mg^(2+)>Na^(+).地下水中同样存在反离子竞争效应,且由于SO_(4)^(2-)的存在,提高了各反离子的截留率.
A loose nanofiltration(NF) membrane(NF270) was chosen to test the rejection of single electrolyte solutions(MgCl_(2), CaCl_(2), NaCl), binary electrolytes solutions(MgCl_(2)/CaCl_(2)+ NaCl) and real groundwater, in order to study the cation rejection behavior in different salt conditions. The effect of adsorption of Ca^(2+)/Mg^(2+) by membrane fixed charges as well as the shielding effect of general ions on electrostatic effect and ions rejection were also investigated. Results showed that NF270 membrane featured a plentiful negative charges on surface, with these fixed charges having a strong adsorption ability for both Ca^(2+) and Mg^(2+). For three single salt solution of the same ionic strength(especially in the range of 1.5~6 mmol·L^(-1)), Donnan effect was the main mechanism for salt rejection, so that the limiting ion Cl- played an important role, resulting in a decreasing order of rejection that was NaCl>MgCl_(2)≈CaCl_(2). In the binary electrolyte solutions, membrane surface potential was primarily controlled by Ca^(2+)/Mg^(2+) ions, and under the combination of Donnan effect, steric hindrance effect and dielectric effect, Ca^2+/Mg^2+ dominated the counter-ion competition, leading to a decreasing order of rejection as Ca^(2+)/Mg^(2+)>Na^(+). There was also a counter-ion competition when filtering groundwater, and the presence of high concentration SO_(4)^(2-) was responsible to enhance the retention of all type of counter-ions.
作者
高晓琪
俞开昌
王小
GAO Xiaoqi;YU Kaichang;WANG Xiaomao(School of Environment,Tsinghua University,Beijing 100084;Beijing Origin Water Technology Co.,Ltd.,Beijing 102206)
出处
《环境科学学报》
CAS
CSCD
北大核心
2020年第8期2700-2707,共8页
Acta Scientiae Circumstantiae
基金
国家自然科学基金(No.51978367)。
关键词
纳滤膜
截留率
膜表面电势
道南效应
nanofiltration membrane
rejection
membrane potential
Donnan effect
作者简介
高晓琪(1994-),女,E⁃mail:gxq17@mails.tsinghua.edu.cn;责任作者:王小[亻毛],E⁃mail:wangxiaomao@tsinghua.edu.cn。
