The Science behind the Technology

Elemental iron (Fe⁰) has been shown to remove the highly mobile Cr(VI) from ground water and to transform it to the immobile Cr(III), which precipitates on materials in reactive zone of the PRB.  Fe⁰ donates electrons to Cr(VI).  In the process, Fe⁰ is oxidized to Fe(III) and the Cr(VI) gains electrons and is reduced to Cr(III).  The net chemical reaction is:

Fe⁰ + CrO₄^-2 + 4H₂O → Fe(OH)₃ + Cr(OH)₃ + 2OH^-1

The permeable reactive zone of the PRB shown below typically consists of elemental iron (Fe⁰) as granules or granules embedded in ceramic foam in the shape of a block or mixed with quartz sand.

As the dissolved Cr(VI) passes through the permeable reactive zone, it reacts with the Fe⁰ to form ferric hydroxide [Fe(OH)₃], which is deposited in the matrix of the reactive zone.

For more information review the EPA report and the EPA fact sheet on this technology.