An Electrochemical Investigation into the Origin of the Enhanced Reactivity of Clays in Contact with Iron Metal
EMSL Project ID
2335
Abstract
While clays and iron metal are each independently capable of reducing a range of contaminants in aqueous solutions, there is a synergistic effect on the rate of reduction when clays are in contact with iron metal. In our current research, we are using clay-modified iron electrodes to examine the mechanism whereby clays interact with iron metal to produce a reductant stronger than either clay or iron alone. Specifically, we have the following questions: (i) is Fe(II) from the electrochemical corrosion of iron metal responsible for the increased reactivity of clays in contact with iron metal?; (ii) what is the mobility of the Fe(II) in the clay?; and (iii) does the clay accelerate the corrosion of iron or serve only as an Fe(II) adsorber?. Electrochemical techniques enable us to address these questions as they allow us to bias the electrode in an electrochemically active region and to quantify the amount of Fe(II) generated during the iron corrosion. Preliminary results show that the presence of the clay film alters the electrochemical response of the iron electrode. Specifically, the peak associated with the oxidation of Fe(0) to Fe(II) and the growth of the Fe(OH)2 pre-passive film is enhanced. With continued electrochemical cycling of the clay-coated iron electrode this peak is reduced; if the electrode is allowed to sit at open circuit potential, the peak is restored in the subsequent electrochemical cycle. These observations suggest that the clay film next to the iron electrode can become saturated with Fe(II) but that the Fe(II) adsorbed to the clay can diffuse away from the iron-clay interface, permitting more Fe(II) to adsorb to the clay. More experiments need to be done before we can give a detailed account of the clay-iron interaction. For example, we need to examine the effect of scan rate, biasing in the active region, clay type, and ionic strength on the Fe(0) to Fe(II) oxidation peak. We propose to borrow EMSL's EG&G PAR Model 273 potentiostat, which I used during my sabbatical at EMSL, to collect data at Lewis & Clark College. This potentiostat has data analysis and acquisition capabilities superior to those of the potentiostat available at Lewis & Clark College (most notably, it is able to determine peak areas and provide electronic filtering) and would give us unlimited access to a potentiostat. We also propose to collaborate with John Daschbach; John has experience using and access to coupled kinetic reaction diffusion codes that will help us in our interpretation of our electrochemical data. Ideally, the combination of the potentiostat and John's expertise will enable us to determine how much of the oxidized iron is adsorbed into the clay versus how much goes towards pre-passive film formation, as well as the time scale of diffusion of the Fe(II) in the clay film.
Project Details
Project type
Exploratory Research
Start Date
2001-09-01
End Date
2004-09-02
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members