Organic matter iron oxidation

Jozefaciuk, G. and Sokolowska, Z. (2003). The effect of removal of organic matter, iron oxides and aluminium oxides on the micropore characteristics of the soil clay fraction. Pol. J. Soil Set 36, 111-118. 

Many experiments oti electrokinetic remediation are carried out on a laboratory or pilot plant scale, with artificially polluted clay media like kaolin. This is because clay soils usually contain a variety of other substances that are present in smaller or trace amounts, such as organic matter, iron oxides, quartz, feldspars, aluminum and manganese hydroxides, titanium oxides, carbonates, and calcite, which could affect electrokinetic response by decreasing the resistance to the flow of water through the sediment [10]. 

If the product is to be used in the manufacture of nitrous oxide, an anesthetic gas, a purity of not less than 99.5% is required. The salt must be almost completely free of contaminating organic matter, iron, sulfate, and chloride. 

The major raw materials used at present for the production of alumina are bauxites, which are found in the following mineral forms gibbsite (Al(OH)3), boehmite (AlO OH), and diaspore (AlO OH). The major impurities are the oxides of iron, silicon, and titanium, and organic compounds, all of which must be removed before alumina is suitable for aluminum production. The process objectives are, therefore, separation of impurities and compound production in the present case. Bauxite is first dried to facilitate grinding, destroy organic matter, and oxidize the associated ferrous minerals to the ferric state. The temperature of drying is not allowed to exceed 150 °C, because at higher temperature a part of the combined water is expelled and the solubility is affected adversely. 

Sedimentary rocks with the highest arsenic concentrations largely consist of materials that readily sorb or contain arsenic, such as organic matter, iron (oxy)(hydr)oxides, clay minerals, and sulfide compounds. Arsenian pyrite and arsenic-sorbing organic matter are especially common in coals and shales. Ironstones and iron formations are mainly composed of hematite and other iron (oxy)(hydr)oxides that readily sorb or coprecipitate arsenic. Iron compounds also occur as cements in some sandstones. Although almost any type of sedimentary rock could contain arsenic-rich minerals precipitated by subsurface fluids (Section 3.6.4), many sandstones and carbonates consist almost entirely of minerals that by themselves retain very little arsenic namely, quartz in sandstones and dolomite and calcite in limestones. 

A wide range of research publications has identified various soil properties and their potential influence on substance behavior. Soil properties such as organic matter, iron, manganese, and aluminum (hydro)oxide concentrations, cation exchange capacity, and pH can all affect the bioavailability, form, and toxicity of substances. 

The multireaction approach, often referred to as the multisite model, acknowledges that the soil solid phase is made up of different constituents (clay minerals, organic matter, iron, and aluminum oxides). Moreover, a heavy metal species is likely to react with various constituents (sites) via different mechanisms (Amacher et al 1988). As reported by Hinz et al. (1994), heavy metals are assumed to react at different rates with different sites on matrix surfaces. Therefore, a multireaction kinetic approach is used to describe heavy metal retention kinetics in soils. The multireaction model used here considers several interactions of one reactive solute species with soil matrix surfaces. Specifically, the model assumes that a fraction of the total sites reacts rapidly or instantaneously with solute in the soil solution, whereas the remaining fraction reacts more slowly with the solute. As shown in Figure 12.1, the model includes reversible as well as irreversible retention reactions that occur concurrently and consecutively. We assumed that a heavy metal species is present in the soil solution phase, C (mg/L), and in several phases representing metal species retained by the soil matrix designated as Se, S, S2, Ss, and Sirr (mg/kg of soil). We further considered that the sorbed phases Se, S, and S2 are in direct contact with the solution phase (C) and are governed by concurrent reactions. Specifically, C is assumed to react rapidly and reversibly with the equilibrium phase (Se) such that... 

Organic matter is oxidized in the suboxic zone through iron or manganese reduction. This may be a direct oxidation by metal reducing bacteria or an indirect oxidation via sulfate reduction and sulfide oxidation. Does it matter for the end products which pathway dominates ... 

Letunova et al. (1987) calculated that the microorganism biomass contains from 0.012 to 3.24% of the iodine present in surface soil layers, though some fungi that occur in soils are known to accumulate much higher amounts of iodine. Soil acids favor iodine sorption by soil components such as organic matter, hydrous oxides of iron and aluminum. However, liming is known to reduce the solubility of iodides, iodates and iodine in soils and thus also to reduce iodine bioavailability. 

There are several causes of the generally poor correlation between the extractable quantity of a heavy metal and soil pH or availability to plants. Varying amounts of carbonates, organic matter, hydrous oxides of manganese and iron, as well as soil Eh values all affect the amounts of these metals which are extractable. Much better correlations than those obtained would be expected if the heavy metals were located on clay mineral exchange sites or were complexed by organic matter. 

Biooxidation is decomposition of organic matter with oxidizing of its carbon. Organic matter in these reactions is donor of electrons, and the acceptors are elements or compounds outside it O, NO3. NO T Fe, iron hydroxide Fe(OH)3>, CO, some chlorinated solvents, etc. There may be aerobic and anaerobic oxidizing. In the former case acceptor of electrons is directly molecular oxygen O, in the latter oxidized forms of nitrogen (NOj", NO3 ), manganese (Mn ), iron (Fe +), sulphur (SO ), etc. 

The amount of herbicide sorbed by a given soil is influenced by properties of both the soil and the herbicide. Important properties related to the soil s retention abiHty include clay mineralogy, organic matter content, soil pH, and iron and aluminum oxide content. These properties, in turn, affect the... 

Impurities. Impurities usually found in manganese ore may be classified into metal oxides, eg, iron, 2inc, and copper gangue volatile matter such as water, carbon dioxide, and organic matter and other nonmetaUics. 

In this work ion-exchange and gel-permeation chromatography coupled with membrane filtration, photochemical oxidation of organic metal complexes and CL detection were applied to the study of the speciation of cobalt, copper, iron and vanadium in water from the Dnieper reservoirs and some rivers of Ukraine. The role of various groups of organic matters in the complexation of metals is established. 

In catalytic incineration, there are limitations concerning the effluent streams to be treated. Waste gases with organic compound contents higher than 20% of LET (lower explosion limit) are not suitable, as the heat content released in the oxidation process increases the catalyst bed temperature above 650 °C. This is normally the maximum permissible temperature to which a catalyst bed can be continuously exposed. The problem is solved by dilution-, this method increases the furnace volume and hence the investment and operation costs. Concentrations between 2% and 20% of LET are optimal, The catalytic incinerator is not recommended without prefiltration for waste gases containing particulate matter or liquids which cannot be vaporized. The waste gas must not contain catalyst poisons, such as phosphorus, arsenic, antimony, lead, zinc, mercury, tin, sulfur, or iron oxide.(see Table 1.3.111... 

An excess of a standard solution of iron(II) must therefore be added and the excess back-titrated with standard cerium(IV) sulphate solution. Erratic results are obtained, depending upon the exact experimental conditions, because of induced reactions leading to oxidation by air of iron(II) ion or to decomposition of the persulphate these induced reactions are inhibited by bromide ion in concentrations not exceeding 1M and, under these conditions, the determination may be carried out in the presence of organic matter. 

We cover each of these types of examples in separate chapters of this book, but there is a clear connection as well. In all of these examples, the main factor that maintains thermodynamic disequilibrium is the living biosphere. Without the biosphere, some abiotic photochemical reactions would proceed, as would reactions associated with volcanism. But without the continuous production of oxygen in photosynthesis, various oxidation processes (e.g., with reduced organic matter at the Earth s surface, reduced sulfur or iron compounds in rocks and sediments) would consume free O2 and move the atmosphere towards thermodynamic equilibrium. The present-day chemical functioning of the planet is thus intimately tied to the biosphere. 

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