Capture and storage of hydrogen gas by zero-valent iron

Abstract

Granular Fe(o), used to reductively degrade a variety of contaminants in groundwater, corrodes in water to produce H2(g). A portion enters the Fe(o) lattice where it is stored in trapping sites such as lattice defects and microcracks. The balance is dissolved by the groundwater where it may exsolve as a gas if its solubility is exceeded. Gas exsolution can reduce the effectiveness of the Fe(o) treatment zone by reducing contact of the contaminant with iron surfaces or by diverting groundwater flow. It also represents a lost electron resource that otherwise could be involved in reductive degradation of contaminants. It is advantageous to select an iron for remediation purposes that captures a large proportion of the H2(g) it generates. This study examines various aspects of the H2(g) uptake process and has found 1) H2(g) does not have to be generated at the water/iron interface to enter the lattice. It can enter directly from the gas/water phases, 2) exposure of granular sponge iron to H2(g) reduces the dormant period for the onset of iron corrosion, 3) the large quantities of H2(g) generated by nano-Fe(o) injected into a reactive barrier of an appropriate granular iron can be captured in the lattice of that iron, and 4) lattice-bound hydrogen represents an additional electron resource to Fe(o) for remediation purposes and may be accessible using physical or chemical means.