Setting traps for arsenic

Sandia National Laboratories researchers have used supercomputers to design new chemicals with arsenic-trapping properties.

Successful trials of the inexpensive new materials may have nationwide implications as hundreds of American communities count the costs of reducing arsenic concentrations in water supplies. Regulations now being negotiated by the US Environmental Protection Agency (EPA) are expected to sharply reduce the maximum allowed amount of arsenic in drinking water.

The Sandia developers hope to test the new materials, called Specific Anion Nanoengineered Sorbents (SANS), at a planned city water-purification demonstration plant in Albuquerque, as well as in several smaller water systems in rural New Mexico communities.

Inorganic arsenic occurs naturally in some groundwater, seeping out of rock and soils that neighbour the aquifer. The EPA is reviewing its current arsenic limit of 50 parts per billion and plans to establish a new limit that is at least 60 percent lower.

Depending on the new limit that results, the national price tag for complying with a new EPA standard could be in the billions to tens of billions of dollars

Most mineral ”getters’ have negatively charged surfaces, so they repel anions. The SANS selectively attract dissolved anions such as arsenate to positively charged sites on the SANS surfaces and grab hold.

To create the materials, the researchers selected mineral families with known affinities for anions, then used supercomputer modelling to rapidly simulate the arsenic-trapping aptitudes of thousands of combinations and variations of the minerals.

Because there are nearly infinite variations of chemical species, phases, and surface chemistries, the researchers let the computer sort out the very best performers.

They ruled out those minerals that are difficult or expensive to obtain or produce, that would become saturated too quickly, or that would result in a hazardous by-product.

They now are verifying the computers’ results in a lab, pumping arsenic-contaminated water through the powdered materials, then measuring the arsenic content of the outflow.

For proprietary reasons, the researchers can’t yet divulge what materials the team designed, but are said to be nontoxic mixed metal oxides with high molecular surface areas.

At water treatment plants, groundwater could be pumped through columns containing the powdered materials. Arsenic content in the outflow would be reduced to undetectable levels. After perhaps years of use, the non-hazardous arsenic-saturated getters could be safely disposed of in landfills.

The SANS could be easily adapted for use with smaller water systems, even down to the individual well or household scale, said Sandia researcher David Teter.

In addition, the same research methodology used to identify the SANS for arsenic removal could be used to design getters for removing other micropollutants from drinking water, or purify industrial waste water, process streams, and other effluents, added Teter.