Abstract:

Forward osmosis (FO) is an emerging membrane process for desalination driven by the difference of osmotic pressure between feed solution and draw solution (DS). We previously developed a novel quasi-symmetric thin film inorganic (QSTFI) membrane with several advantages compared with conventional polymeric FO membranes. In this paper, elimination of Cd²⁺ in aqueous solution was investigated by using FO process with QSTFI membrane. Scanning electron microscope (SEM) was used to characterize membrane micro-scale morphology, and energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscope (FTIR) were used to characterize chemical properties of the membrane. Besides, atomic force microscopy (AFM) was used to identify membrane surface electrical potential. The effects of Cd²⁺ concentration, DS concentration and membrane surface potential on Cd²⁺ rejection were examined and discussed. The surface of QSTFI membrane was negatively charged, which promoted formation of electric double layer structure through interacting with Cd²⁺ in bulk solution. The Debye length of electric double layer was positively correlated to Cd²⁺ rejection by the membrane. The FO experiments showed that the QSTFI membrane was able to successfully reject Cd²⁺ with overall efficiency up to 99%, at the same time achieving water flux of 69 L·m^-2·h^-1 at initial Cd²⁺ concentration of 10 mg·L^-1 and DS concentration of 2.0 mol·L^-1 NaCl. This study provides a promising approach to using FO process for elimination of heavy metals in waste water in practical applications.

Key words: QSTFI membrane, forward osmosis, cadmium ion, surface, electric double layer, waste water

摘要：

正向渗透(forward osmosis, FO)是一种以溶液渗透压差为驱动力的新型膜技术。课题组在先前研究中使用微界面溶胶凝胶法制备了一种全新的准对称结构无机薄膜(QSTFI膜), 与传统的有机聚合FO膜相比具有更大的优势。本文考察了QSTFI膜分离去除水中重金属Cd²⁺的效能, 讨论了Cd²⁺浓度、提取液浓度以及膜表面带电性对Cd²⁺去除的影响机制。采用扫描电子显微镜(SEM)表征了QSTFI膜的微观形貌, 使用能量色散光谱(EDS)、傅里叶变换红外光谱(FTIR)表征了膜的化学组成, 并使用原子力显微镜(AFM)表征膜表面带电特性。结果表明, QSTFI膜表面带负电荷, 能够与液相主体中的Cd²⁺通过静电引力形成双电层结构, 双电层的Debye厚度越大越有利于膜对Cd²⁺的截留。FO实验测试中原液Cd²⁺浓度为10 mg·L^-1的条件下, QSTFI膜对Cd²⁺截留率超过99%, 水通量最大值可达到69 L·m^-2·h^-1(提取液为2.0 mol·L^-1 NaCl)。本研究为拓展FO技术在含重金属废水处理的潜在应用前景提供了理论依据和指导。

关键词: QSTFI膜, 正向渗透, 重金属Cd²⁺, 表面, 双电层结构, 废水