Iron uptake behavior

In contrast to ferritin, very little work has been done on the reconstitution of BFR cores, other than the experiments mentioned above that showed that, in the absence of phosphate, crystalline ferrihydrite formed inside the protein shell. The intermediate stages in this process are unknown, but the sigmoid iron uptake behavior (25) suggests there could be a similar succession of events oxidation and nucleation on the protein shell followed by direct oxidation on the core. The influence of the heme, if any, on BFR iron core formation also awaits investigation. As mentioned above, the presence of the iron core influences the heme redox potential, but it is not known whether the presence of heme influences the redox potential of the nonheme iron. 

This approach successfully described the experimental results of several adsorption studies with various metal ions and oxide substrates ( 2). In addition, one can make predictive calculations of metal ion uptake, if the surface parameters of an oxide/elec-trolyte can be estimated. For example. Figure 4 shows predicted and experimental adsorption behavior of Cd(II) on amorphous iron oxyhydroxide. Surface stability constants for Cd(II) were estimated ( ) from an experimental study of Cd(II) uptake by a-FeOOH (21, %). 

A study of iron, cadmium and lead mobility in remote mountain streams of California by Erel et al. (1990) showed that the excess of atmospheric pollution-derived lead and cadmium is rapidly removed downstream. The comparison of truly dissolved, colloidal, and surface particle concentrations measured in the stream with the results of a model of equilibrium adsorption indicates that the mechanism of removal in this organic-poor environment is essentially by uptake onto hydrous iron oxides. The experimentally determined partition coefficients (Dzomback and Morel, 1990) explain the behavior of lead however, they fail to explain the cadmium removal. It is proposed by the authors that cadmium is taken up by surfaces other than hydrous iron oxides. 

Finally, in the group of acids whose 0 < pKai < 4, sigmoidal uptake curves and uptake curves with a maximum are reported in different sources, and there is no apparent correlation between the type of uptake curve, and the nature of the adsorbent (actually most available data on anion adsorption are for aluminum and iron III oxides and hydroxides as adsorbents) or the experimental conditions (e.g. the initial concentration of the adsorbate). Arsenate V, chromate VI, phosphate, and molybdate are typical examples of such behavior. For three former anions the number of publications reporting sigmoidal uptake curves on the one hand and uptake curves with a maximum on the other are approximately equal, but for molybdate the sigmoidal curves are more abundant. Comparison of molybdate with other anions in terms of pKa, is difficult in view of tendency to form polyacids (condensation). 

Even when considered on a long term basis, there is considerable doubt that the presence of land filled battery metals such as lead, zinc, and cadmium would have the catastrophic environmental effects which some have predicted. Studies on 2000-year old Roman artifacts in the United Kingdom (Thornton 1995) have shown that zinc, lead and cadmium diffuse only very short distances in soils, depending on soil type, soil pH and other site-specific factors, even after burial for periods up to 1900 years. Another study in Japan (Oda 1990) examined nickel-cadmium batteries buried in Japanese soils to detect any diffusion of nickel or cadmium from the battery. None has been detected after almost 20 years exposure. Further, it is unclear given the chemical complexation behavior of the metallie ions of many battery metals exactly how they would behave even if metallic ions were released. Some studies have suggested, for example, that both lead and cadmium exhibit a marked tendency to complex in sediments and be unavailable for plant or animal uptake. In addition, plant and animal uptake of metals such as zinc, lead and cadmium has been found to depend very much on the presence of other elements such as iron and on dissolved organic matter (Cook and Morrow 1995). Until these behavior are better understood, it is unjustified to equate the mere presence of a hazardous material in a battery with the true risk associated with that battery. Unfortunately, this is exactly the method which has been too often adopted in comparison of battery systems, so that the true risks remain largely obscured. 

The zeolite-encapsulated iron phthalocyanine catalyst exhibited a similar behavior. When the oxygen uptake in the first run had ceased, 1-decene was injected into the reactor (second run), and the oxygen uptake was measured again. A similar rate was measured in the second run as in the first one, i.e. the catalytic activity did not decrease during the oxidation reaction, in spite of the presence of the strong acid HCIO4 in the reaction mixture. 

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