Arsenate removal by Donnan dialysis: Effects of the accompanying components

Donnan dialysis has been proven to be effective in removing ionic contaminants from water. In this paper, the effects of nitrate, sulfate, phosphate, bicarbonate, and silicate on the arsenate (As(V)) removal by Donnan dialysis have been systematically studied compared to that of chloride. In order to interpret the different interaction phenomena and identify potential underlying mechanisms, both the simultaneous transfer of these accompanying components and their influence on the ion exchange reaction between the arsenate ions and the anion exchange membrane have also been investigated. In the presence of nitrate, sulfate, or phosphate, their competition with As(V) for the functional groups in the membrane dominated the average flux of As(V) through the membrane within the first 2 h of the batch dialytic process. However, the overall removal of As(V) mainly depended on the dialytic kinetics of these accompanying anions when the batch dialysis lasted as long as 24 h. The presence of bicarbonate increased the solution pH and the fraction of HAsO42− ions; as a result, the transfer of As(V) was accelerated. At neutral pH, the undissociated silicate exhibited negligible inhibition on the As(V) removal. The arsenic concentration remaining in feed solutions at 24 h was less than 50 μg L−1 in all tests except in the presence of phosphate. The current results indicate that Donnan dialysis successfully removes the arsenate ions from groundwater containing various accompanying components. This feature makes it an attractive alternative for the As(V) removal point-of-use (POU) technologies in rural areas.