Tsinghua University, Beijing, China.
Water Sci Technol. 2012;65(2):296-302. doi: 10.2166/wst.2012.833.
A combination treatment of Ca-precipitation and nanofiltration membrane was studied to remove arsenate from water. The selected nanofiltration membrane was an amphoteric charged membrane, proved by the results of ATR-FTIR spectra and zeta potential. The arsenate and calcium removal efficiencies had the lowest values at the isoelectric point of the nanofiltration membrane, attributed to the loosest steric hindrance and the weakest electrostatic repulsion. Above the isoelectric point, arsenate precipitated with calcium ion to form the low solubility compound calcium arsenate, while steric hindrance was the main mechanism of arsenate removal. In contrast, below the isoelectric point, the nanofiltration membrane with positive charges rejected calcium ion by electrostatic repulsion. The high electrostatic shielding of calcium ion prevented arsenate from coming close to the NF membrane. Either high feed arsenate concentration or high calcium oxide dose improved the removal amount of arsenate during the nanofiltration membrane separation process. In addition, the arsenate removal efficiency approached the highest value at 200 μg/L of feed arsenate concentration. The optimal transmembrane pressure was in a range of 0.5-0.7 MPa to restrict the formation of fouling cake on the nanofiltration membrane surface.
采用沉淀法和纳滤膜组合处理去除水中的砷酸盐。所选择的纳滤膜是一种两性荷电膜，这一点可从 ATR-FTIR 光谱和 ζ 电位的结果得到证实。砷酸盐和钙的去除效率在纳滤膜的等电点处达到最低值，这归因于最宽松的空间位阻和最弱的静电排斥。在等电点以上，砷酸盐与钙离子形成低溶解度的砷酸钙化合物沉淀，而空间位阻是去除砷酸盐的主要机制。相比之下，在等电点以下，带正电荷的纳滤膜通过静电排斥作用排斥钙离子。钙离子的高静电屏蔽作用阻止了砷酸盐靠近纳滤膜。无论是高进料砷酸盐浓度还是高氧化钙剂量，都可以在纳滤膜分离过程中提高砷酸盐的去除量。此外，在进料砷酸盐浓度为 200μg/L 时，砷酸盐的去除效率接近最高值。最佳跨膜压力范围为 0.5-0.7MPa，以限制纳滤膜表面结垢层的形成。
