Cleansing Power of Iron

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Cleansing Power of Iron

AN ultrafine, nanoscale powder made from iron, one of the most

abundant metals on Earth, is turning out to be a remarkably effective

tool for cleaning up contaminated soil and groundwater - a trillion-

dollar problem that encompasses more than 1,000 still-untreated

Superfund sites in the United States, some 150,000 underground

storage tank releases, and a staggering number of landfills,

abandoned mines, and industrial sites.The case for nanoscale iron is

laid out in the September 3 issue of the Journal of Nanoparticle

Research, where Lehigh University environmental engineer, Mr Wei-xian

Zhang reviews his eight years of pioneering work with the material.

Much of Mr Zhang's research has been funded by the National Science

Foundation as a part of the federal government's 16-agency National

Nanotechnology Initiative (NNI).

 

The cleansing power of iron stems from the simple fact that it rusts,

or oxidises, explains Mr Zhang. Ordinarily, of course, the only

result is the familiar patina of brick-red iron oxide. But when

metallic iron oxidises in the presence of contaminants such as

trichloroethene, carbon tetrachloride, dioxins, or PCBs, he says,

these organic molecules get caught up in the reactions and break down

into simple carbon compounds that are far less toxic.

 

Likewise with dangerous heavy metals such as lead, nickel mercury, or

even uranium, says Zhang. The oxidising iron will reduce these metals

to an insoluble form that tends to stay locked in the soil, rather

than spreading through the food chain. And, iron itself has no known

toxic effect -just as well, considering the element is abundant in

rocks, soil, water, and just about everything else on the planet.

 

Not only are nanoscale iron particles some 10 to 1000 times more

reactive than conventional iron powders, because their smaller size

collectively gives them a much larger surface area, but they can be

suspended in a slurry and pumped straight into the heart of a

contaminated site like an industrial-scale hypodermic injection. Once

there, the particles will flow along with the groundwater to work

their decontamination magic in place - a vastly cheaper proposition

than digging out the soil and treating it shovelful by shovelful

which is how the worst of the Superfund sites are typically handled

today.

 

In that sense, says Mr Zhang, nanoscale iron is similar to in situ

biological treatments that use specialised bacteria to metabolise the

toxins. But unlike bacteria, he says, the iron particles are not

affected by soil acidity, temperature, or nutrient levels. – USIA