Application of calcined iowaite in arsenic removal from aqueous solution

Abstract

Unlike the other family members of anion clay, iowaite, a Mg-Fe based layered double hydroxide, was seldom used in removing undesirable constituents from natural or contaminated waters. In this study, iowaite as well as its calcination product were employed to treat arsenic-spiked solutions, taking into account that anion clays exhibited great capacity to incorporate anionic pollutants as a result of their relatively weak interlayer bonding, and Fe-bearing minerals had high affinity to both arsenate and arsenite. The thermal decomposition process and structural memory effect of synthetic iowaite were investigated over a wide temperature range of 300–1000°C for the first time, based on which the calcination product obtained at 450°C was finally selected to be used in solution dearsenication experiments. The experimental results showed that the content of Fe in pristine iowaite significantly affected its arsenite sorption behavior, whereas the calcination process weakened the effect of Fe content on arsenite uptake. The calcined iowaite was generally characterized with higher arsenic uptake capacity as compared to some other sorbents commonly used for arsenic removal from solution in recent years as well as the pristine iowaite synthesized in this study. A contrast experiment suggested that magnoferrite in the calcination products of iowaite made no contribution to the enhanced arsenic uptake capacity of calcined iowaite. Hence, calcined iowaite performed better in arsenic removal because of the high availability of arsenic oxyanions to the interlayer regions during its structural restoration. The arsenic oxyanions did not need to diffuse into the interlayers to replace the original chloride ions as they did for pristine iowaite.