Iron oxides aquifers

Bunn, R. A., Magelky, R.D., Ryan, J.N. Elrm-ech, M. (2002) Mobilization of natural colloids from an iron oxide sand aquifer. Effect of pH and ionic strength. Envir. Sci. Techn. 

Hence, these Qc values are a quantitative measure for the relative affinities of the various NACs to the reactive sites. Figs. 14.10e and/show plots of log Qc versus h(AtN02)/0.059 V of the 10 monosubstituted benzenes. A virtually identical picture was obtained for the log Qc values derived from an aquifer solid column and from a column containing FeOOH-coated sand and a culture of the iron-reducing bacterium, Geobacter metallireducens (GS15). Furthermore, a similar pattern (Fig. 14.10c) was found when correlating relative initial pseudo-first-order rate constants determined for NAC reduction by Fe(II) species adsorbed to iron oxide surfaces (Fig. 14.12) or pseudo-first-order reaction constants for reaction with an iron porphyrin (data not shown see Schwarzenbach et al., 1990). Fig. 14.12 shows that Fe(II) species adsorbed to iron oxide surfaces are very potent reductants, at least for NACs tv2 of a few minutes in the experimental system considered). 

Ryan, J.N. and Gschwend, P.M., Effect of solution chemistry on clay colloid release from an iron oxide coated aquifer sand, Environ. Sci. Technol., 28, 1717, 1994. 

Organic matter dominates the reduction capacity of typical leachates (Christensen et al., 2001). Ammonium and methane may also contribute significantly, showing that the fate of these inorganic compounds in the aquifer may also affect the formation of redox environments. The aquifer OXC may be dominated by iron oxides, when calculated for an aquifer volume including aquifer material and groundwater (Table 4). This is caused by the low aqueous solubility of oxygen, and the relatively low nitrate... 

There are two schools of thought about the time of the initial As mobilization either (i) it is recent and has been induced by man s activities [there are proponents of this who support both the pyrite oxidation hypothesis and the iron oxide reduction hypothesis (Acharyya et al., 2000)], or (ii) it occurred much earlier and is therefore dominantly a natural process. While we believe that an early release date, (ii) above, is the more likely, this is not to imply that man s recent activities have not had, or will not have, any impact on the extent of the groundwater arsenic problem. For example, recent changes in land use such as irrigation will not only alter the groundwater flow patterns but could also affect the boundary conditions for oxygen diffusion into the aquifer and so could also affect its redox status (Bhattacharya et al., 1997). 

A cross-flow experiment increased the iron oxide content of the basalt aquifer followed by pH adjustment. Two cycles of iron addition, pH adjustment, and recovery (Fig. 7) consisted of 1.) Addition of 1 kg of FeCls (2 kg total) with a pumping rate of about 100 L/min, 2.) HCl addition to lower the pH of the recovered ground water to < 7.0, and 3.) Pumping to waste at a rate of about 200 to 230 L/min with no injection. About one-half... 

The cross-flow and laboratory experiments demonstrate that decreasing the pH combined with increasing the iron oxide content in the basalt aquifer reduces arsenic concentrations in produced ground water. Arsenic removal... 

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