Iron cations, source

C22-0082. A river contains a high concentration of iron cations, and environmental activists contend that an industrial manufacturing plant is the source. The manufacturer says that although the plant generates aqueous iron waste, it is processed on site and does not contaminate the river. How might this disagreement be resolved using radioactive tracers ... 

The zinc cation gives by far the most active catalyst. Iron, cobalt, and nickel cations also gave salts with considerable catalytic activity. Cadmium, because of its chemical similarity to zinc, and aluminum, because of its use in other epoxide polymerization catalysts, were considered as likely candidates to give active catalysts. However, complexes of the salts of these cations were only slightly catalytic. The salts used as cation sources in catalyst preparations also affected catalytic activity. Zinc salts, especially zinc chloride and zinc bromide, were retained in considerable amounts in the finished complexes, and the use of these salts gave the most active catalysts. 

EDTA is also used to remove the calcium carbonate and sulfate scales that form in hot-water boilers and heaters. Calcium carbonate precipitates out when hard water is heated because the bicarbonate present in any naturally aerated water supply decomposes under the action of heat into carbonate, water, and carbon dioxide, as shown in Equation (6.15). (This reaction is the source of some of the very small bubbles that form on the sides of a beaker before water heated in it comes to a boil.) The carbonate is then available to be precipitated by calcium, magnesium, or iron cations that are often present in a natural water supply. This precipitation reaction is shown for calcium in Equation (6.16) ... 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

In all cases, water and carbonic acid, the latter of which is the source of protons, are the main reactants. The net result of the reaction is the release of cations (Ca " ), Mg ", K", Na" ) and the production of alkalinity via HCO. When ferrous iron is present in the lattice, as in biotite, oxygen consumption may become an important factor affecting the weathering mechanism and the rate of dissolution. 

The reactions of some transition metal cluster ions have been described in a review by Parent and Anderson (201). The review covered reactions reported up to 1992 and so the reactions reported here are generally later than 1992. A recent review by Knickelbein (202) discusses the reactions of cation clusters of iron, cobalt, nickel, copper, silver, niobium, and tungsten with small molecules such as H2 and D2. Some of the reactions in Knickelbein s review are included in the following tables of reactions (Tables IV and V). Table IV gives examples of the reactions of transition metal cluster ions and includes the vaporization source, experimental apparatus, the reactants, and the observed product ions. A few examples from these tables will be selected for further discussion. 

One more source of complexity comes from the fact that the lattice generally contains cations with several degrees of oxidation. Iron is the most common example. Therefore, charge transfer may occur between adsorbed species and some lattice sites. Vacancies in the lattice may play a similar role. 

Extensive investigations on the catalytic mechanism of classical peroxidases resulted in a consensus model involving five different iron species [30, 31], These species are ferrous, ferric, Compound I, Compound II, and Compound III (Fig. 11.1). As discussed in Chap. 5, after the reaction of ground state (GS) Femporphyrin with H202, Compound I (Cl) is formed, a cationic oxob e,vpor-phyrin-based Ji-free radical. Electron paramagnetic resonance (EPR) studies established that, in peroxidases of classes I and III, the second oxidation equivalent in Cl is present as a porphyrin-based free radical [32, 33]. In peroxidases from fungal sources, electron abstraction from the protein results in the formation of a different species with the free radical based in a residue close to the porphyrin. 

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