Clay nanopillars for removing groundwater arsenic
doi:10.1038/nindia.2016.32 Published online 3 March 2016
Researchers have synthesized clays that can remove arsenic from potable groundwater1. The clays, which contain nanopillars of iron oxide and manganese oxide, remove arsenic by binding to arsenic ions through adsorption. Similar to molecular sieves, the clays have a uniform pore distribution with a high surface area.
The researchers tested the clays’ efficiencies to adsorb arsenic ions from solutions that mimic arsenic-contaminated groundwater. The clays’ ability to adsorb arsenic increased with time up to 2 hours after which it remained relatively constant. Arsenic uptake was also found to increase with increasing temperature, indicating that heat is absorbed when arsenic binds to the clays.
The clay containing manganese oxide nanopillars adsorbed arsenic more efficiently than that containing iron oxide nanopillars.
Since contaminated groundwater contains both trivalent and pentavalent arsenic ions, the clay adsorption efficiencies for the two ions were tested by exposing them to solutions containing both arsenic ions. Manganese oxide nanopillars showed a higher affinity for trivalent arsenic than the iron oxide nanopillars. After being oxidized, trivalent arsenic ions adsorbed onto the oxide pillars rather than the clay surface.
The clay adsorbents also reduced the arsenic levels of a natural groundwater sample from 156 parts per billion (ppb) to 6 ppb after ten cycles of adsorption, indicating their potential for field use.
Arsenic adsorbed onto the clays did not leach. In addition, the arsenic-bound clays behaved much like natural arsenic-containing soil, suggesting that they could be safely disposed as waste material, the researchers say.