Arsenate removal from sulphate-containing water streams by an ion-exchange membrane process

A possible limitation of applying Donnan dialysis for arsenate removal from drinking water supplies is when sulphate is present as an accompanying anion in the water to be treated, due to strong competition between arsenate and sulphate transport through standard grade anion-exchange membranes. This work aims at evaluating the feasibility of employing an ion-exchange membrane Donnan dialysis based process with a new strategy of using sulphate as the driving counter-ion for arsenate counter-transport and removal from sulphate-containing drinking water streams. The process performance with different arsenate receiving solutions (containing chloride or sulphate as driving counter-ions and with or without arsenic precipitation) was investigated and compared. Experiments were carried out to separate arsenate from contaminated water comparing the performance of three anion-exchange membranes: one with mono-valent anion permselective properties and two standard grade membranes. As selection criteria, the transport rate of arsenate and its membrane retention were investigated. The effects of pH variation and co-ion (cation) leakage on the Donnan dialysis process efficiency were also studied. Efficient arsenic removal was achieved through integrating Donnan dialytic transport of arsenate with its simultaneous precipitation in the receiving compartment with FeSO4. The process proposed is environmentally friendly and with minimal maintenance requirements, which makes it especially attractive to be applied in rural areas located far from centralized drinking water supply infrastructures.