Soils, oxide content

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... 

Being widespread in the lithosphere and insoluble in the usual range of soil pH, oxides and hydroxides of Al, Fe and Mn are common in soil clays. Red or yellow coloration of soils is apparent at Fe oxide contents of only 0.1 % or less, especially if the Fe is amorphous and coats other minerals. The most visible change occurring when soils are submerged is the conversion of the red and yellow compounds of Fe(III) to the bluish-grey compounds of Fe(II). 

Isomorphous substitution of iron oxides is important for several reasons. In the electronics industry, trace amounts (dopants) of elements such as Nb and Ge are incorporated in hematite to improve its semiconductor properties. Dopants are also added to assist the reduction of iron ores. In nature, iron oxides can act as sinks for potentially toxic M", M and M heavy metals. Investigation of the phenomenon of isomorphous substitution has also helped to establish a better understanding of the geochemical and environmental pathways followed by Al and various trace elements. Empirical relationships (e. g. Fe and V) are often found between the Fe oxide content of a weathered soil profile and the levels of various trace elements. Such relationships may indicate similarities in the geochemical behaviour of the elements and, particularly for Al/Fe, reflect the environment in which the oxides have formed (see chap. 16). 

The binding of cations and anions by Fe oxides through surface adsorption (see Chap. 11) and/or incorporation (see Chap. 3) makes soils important sinks for a range of compounds such as heavy metals, phosphate and sulphate. This can be derived from significant correlations between such compounds and the Fe oxide content of the soils. 

The performance of ISC units is affected by soil type and soil moisture content. Waste streams derived from ISC processing may consist of volatile off-gases formed during oxidation reactions and products of incomplete oxidation. Bench-scale studies have shown that volatile residuals can be created by ISC, but they have, as yet, not been fuUy characterized. 

Nitrous oxide is important not only as a greenhouse gas but, as discussed in Chapter 12, as the major natural source of NC/ in the stratosphere, where it is transported due to its long tropospheric lifetime (Crutzen, 1970). The major sources of N20 are nitrification and denitrification in soils and aquatic systems, with smaller amounts directly from anthropogenic processes such as sewage treatment and fossil fuel combustion (e.g., see Delwiche, 1981 Khalil and Rasmussen, 1992 Williams et al., 1992 Nevison et al., 1995, 1996 Prasad, 1994, 1997 Bouwman and Taylor, 1996 and Prasad et al., 1997). The use of fertilizers increases N20 emissions. For pastures at least, soil water content at the time of fertilization appears to be an important factor in determining emissions of N20 (and NO) (Veldkamp et al., 1998). 

Whereas several specific soil attributes are advocated as being responsible for DOC sorption in the mineral soil (Table V), it appears that the greater the clay or aluminum and iron oxide content of a soil, the greater its adsorptive capacity for DOC. For example, there is a positive correlation between m (the measure of the affinity of a substance for the sorbent or the partition coefficient) and soil clay content, dithionite extractable iron (Fej), and oxalate extractable aluminum (Al0) (Moore et al., 1992 Nelson et al., 1993 Kaiser and Zech, 1998). Direct measurements of the surface area of soil particles also correlate very well with DOC adsorption capacity (Nelson et al., 1993). Furthermore, Nelson et al. (1993) report that riverine DOC concentrations are negatively correlated to the clay content of watershed... 

The two processes involved in the transport of elemental phosphorus from soil are volatilization and leaching. When 35 mg of elemental phosphorus was added to two soils, one acid and the other calcareous, 0.004-0.6% of the applied phosphorus found at a depth of < 10 cm volatilized as elemental phosphorus (not as oxides) in 3 days (Warnock 1972). The loss of a maximum amount of 0.6% phosphates was complete in 3-7 days. The amount of phosphorus volatilized appeared to be similar from both soils. The rate of volatilization decreased by increasing the depth to which the phosphorus was applied or by increasing soil moisture content the rate did not go to zero. The transport of elemental phosphorus from soil by leaching depends on the Koc value. The estimated Koc value of 3.05 (see Table 3-2) indicates that phosphorus may moderately sorb in soil. Therefore, moderate leaching of phosphorus may occur from the anaerobic soil zone where elemental phosphorus will be stable toward chemical oxidation (EPA 1989 Richardson 1992). 

The optimum alcohol and amount of ethylene oxide is dependent upon the type of soil and the type of foam desired for for the finished product. Figure 1(4) shows the optimum ethylene oxide content in a heavy-duty powder formulation similar to that shown in the foregoing. Lines are "isodets"—lines of equal detergency ranging from a lower detergency rating of 1 to a high of 4. 

The factors that influence corrosion of steels in soils are the type of soil moisture content and the position of the water table soil resistivity and soluble ion content soil pH oxidation-reduction potential and the role of microbes present in soil. The exposure of a buried pipe to the soil environment is illustrated in Figure 4.2. The steel pipe is exposed to both meteoric water passing through ground surface and the water in the ground. The meteoric water may be acidic due to the presence of carbon dioxide and sulfur dioxide in the atmosphere. The soil water may be acidic in addition to some dissolved minerals. The steel pipe is partially above the water table with the rest below the water. The pH and the dissolved ions in the ground water provide a corrosive environment. 

The affinity of DOM with soil was very low with an average DOM sorption percentage of about 22.4 4.8% to 31.2 +5.2% only at an initial DOC concentration of 100 mg/1 and 200 mg/1, respectively, for the live selected DOMs (Table 10.3). This result was supported by the small slope m of 0.11 to 0.24 and Kd of 0.47 to 1.23 ml/g obtained from the IM isotherms. Liang et al. (1996), who worked on a variety of soils with clay contents ranging from 3 to 54%, showed that the adsorption of the DOC by soils increased as the clay, organic matter contents, and the surface areas of the soils increased. The coarse texture of the selected calcareous soil and the characteristics of the selected DOM itself can explain the lower affinity of DOM with soil observed in the present study. In addition, the acidic soil with higher Fe-oxide and Mn-oxide content exhibited much higher DOC adsorption ability than calcareous soil rich in 2 1 minerals. 

Arsenate has chemical behavior similar to that of phosphate in soils it is chemisorbed by Fe and A1 oxides, noncrystalline aluminosilicates, and, to a smaller extent, layer silicate clays. Being the anion of the strong acid, H3ASO4, with pKa values (2.24, 6.94, and 11.5) similar to those of phosphoric acid, arsenate adsorbs most effectively at low pH. Consequently, its mobility is fairly low in acid soils with high clay or oxide content. In neutral to alkaline soils, especially those that are sodic, As may be mobile in the soluble Na arsenate form. Soil microbes and Mn oxides are able to promote the oxidation of arsenite to arsenate under aerobic conditions. 

A similar detergency maximum at almost the same oxyethylene content has been observed in the removal of oily soil from metal surfaces using similar surfactants in an alkaline, built formulation (Komor, 1969). The maximum here is at 68% oxyethylene (about 11 oxyethylene units per nonylphenol) at bath temperatures from 40 to 80°C. For a series of polyoxyethylenated nonrandom linear alkylphenols with Cg-Cig alkyl chains, optimum removal of sebum soil from cotton at 49°C and 50 and 300 ppm water hardness was obtained at 63-68% oxyethylene content (Smithson, 1966). A study of the removal of oily soil from cotton and permanent press cloths, and of clay from permanent press cloths by commercial POE alcohols, showed that POE Ci2-Ci4 alcohols with 60% or greater ethylene oxide content achieved the best soil removal (Cox, 1989). 

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