Mineral phase, soil

Kaiser, K. Zech,W. (1997) Competitive sorption of dissolved organic matter fractions to soils and related mineral phases. Soil Sci. 

Other studies use soil or sediment samples for a more accurate indication of microbial activity in natural environments. In these samples, organic matter and clay particles play a role in metal toxicity.76112113 Both organic material and clay particles in soil can bind metals and reduce their bioavailability. For example, Pardue et al.87 demonstrated that much less solution-phase cadmium was required to inhibit trichloroaniline (TCA) dechlorination in a mineral-based soil than in a soil containing a higher concentration of organic matter. Other studies have shown that adding clay minerals to a medium mitigates toxicity. Clay minerals, such as kaolinite, montmorillonite, bentonite, and vermiculite, can bind to metals to decrease the amount that is bioavailable.112 115... 

Introduction and setting The purpose of this study was to identify and quantify the sources of heavy metals, especially lead, in soils and plants of the Lower Guadiana River basin and thereby model the potential mobility of lead. Other than direct pollution from mining, the main sources of heavy metal pollution in the environment are by diffuse pollution (Callender, 2004). In agricultural areas this can include lead from the use of pesticides, fertilizers and municipal sludge (Alloway, 1985). Metals can be attached or associated with different mineral phases in the soil, this along with environmental parameters determinesthe availability to plants. 

The geochemical fate of most reactive substances (trace metals, pollutants) is controlled by the reaction of solutes with solid surfaces. Simple chemical models for the residence time of reactive elements in oceans, lakes, sediment, and soil systems are based on the partitioning of chemical species between the aqueous solution and the particle surface. The rates of processes involved in precipitation (heterogeneous nucleation, crystal growth) and dissolution of mineral phases, of importance in the weathering of rocks, in the formation of soils, and sediment diagenesis, are critically dependent on surface species and their structural identity. 

The fast reactions of ions between aqueous and mineral phases have been studied extensively in a variety of fields including colloidal chemistry, geochemistry, environmental engineering, soil science, and catalysis (1-6). Various experimental approaches and techniques have been utilized to address the questions of interest in any given field as this volume exemplifies. Recently, chemical relaxation techniques have been applied to study the kinetics of interaction of ions with minerals in aqueous suspension (2). These methods allow mechanistic information to be obtained for elementary processes which occur rapidly, e.g., for processes which occur within seconds to as fast as nanoseconds (j0. Many important phenomena can be studied including adsorption/desorption reactions of ions at electri fied interfaces and intercalation/deintercalation of ions with minerals having unique interlayer structure. 

Table 4.3 Some possible mineral phases in reduced soils and their equilibrium constants...

Figure 4.7 Calculated changes in pe, pH, [O2] and [Fe +] in an idealized soil during reduction. Mineral phases Fe(OH)3 and Fe3(OH)g. Parameters for pH buffering and cation exchange differ between (a)-(d) as indicated. Units of fees (soil pH buffer power), mmolkg pH CEC (initial cation exchange capacity), cmolc kg and [X ]l (concentration of non-carbonate anions), mM. CO2 pressure = lOkPa, 9 = 0.6, p = 1.0, initial pH = 4.5...

The discovery of the calcrete hosted surfical uranium deposits of Namibia demonstrated the presence of widespread uranium in calcrete filled palaeochannels (Hambleton-Jones 1984) and similar mineral deposits have been observed elsewhere in Southern Africa, USA and Australia (Carlisle 1978 Hambleton-Jones 1978 Mann Deutscher 1978). The host rocks are typically lenticular bodies of alluvium, soil or detritus material cemented by calcite, gypsum, palygorskite, and other mineral phases. Uranium mineralogy is dominated by the mineral Carnotite [K2(U02)2(V04)2.3(H20)] as the main mineral in these channels. However other phases such as andersonite (Na2K3U03(C03)3(H20)6), liebigite (Ca2U02(C03)3(H20)io ... 

Kaiser, K. Zech, W. (2000a) Sorption of dissolved organic nitrogen by acid subsoil horizons and individual mineral phases. Fur. J. Soil Sci. 51 403-411... 

Kleber, M., Mikutta, R., Torn, M. S., and Jahn, R. (2005). Poorly crystalline mineral phases protect organic matter in acid subsoil horizons. Eur. J. Soil Sci. 56(6), 717-725. 

Selim et al. (1976a) proposed a mathematical model for potassium reactions and transport in soils. Kinetic reactions were assumed to govern the transformation between solution, exchangeable, nonexchangeable (secondary minerals), and primary mineral phases of potassium shown in Fig. 9.3. 

Mathematical derivations of potassium transport and transformation processes may be formulated as follows. The following new terms can be defined C, concentration of potassium in solution phase Si, amount of potassium in exchangeable phase S2, amount of potassium in nonexchangeable phase S5, amount of potassium in primary mineral phase wPW, pore water velocity Dc, dispersion coefficient and d, depth or distance below soil surface. 

Sequential extraction is now a well-established tool in soil and sediment analysis. Although the approach is unlikely to provide precise information on the mineral phases to which trace metals are bound, it does provide useful information on potential mobilities of heavy metal contaminants which is not available from (pseudo)total metal determination. The adoption of standard protocols, such as that recommended by BCR, means that reliable and comparable data can be obtained by different laboratories. 

Kordel, W., Stutte, J., Kotthoff, G. (1995b) HPLC-screening method to determine the adsorption coefficient in soil-comparison of immobilized humic acid and clay mineral phases for cyanopropyl columns. Sci. Total Environ. 162, 119-125. 

Archaeological fragments of bones and teeth take up fluorine from the surrounding soil and accumulate it in their mineral phase when they are exposed to a humid environment. Geological time spans are needed for this process to reach equilibrium and for the fluorine distribution to become uniform. In cortical parts of long bone diaphysis, an initially U-shaped fluorine concentration profile can be observed, which decreases from the outer surface and the marrow cavity towards the inner parts of the bone and carries information on the exposure duration of the buried object in its shape. The time dependence of the profile slope is usually described in a simplified way by a diffusion model. The quantitative mathematical evaluation of these profiles may provide information on the exposure duration and the physical condition of the samples. Therefore, several attempts to use fluorine profiling as a dating method have been undertaken [3,39], The distribution of... 

Bioaccessibility, and therefore oral bioavailability of soil contaminants, depends on soil type and contaminant (Davis et al., 1997 Gr0n and Anderson, 2003 Hamel et al, 1998 Ruby et al., 1999). PTMs occur in soil as a complex mixture of solid-phase chemical compounds of varying particle size and morphology, characterised by variable metal bioavailability. Mineral phases that form under acidic conditions (e.g. lead sulphate, iron-lead sulphate) will tend to be more stable in the acidic conditions of the stomach and hence less bioaccessible. By contrary, mineral phases... 

The squeezing process involves the expulsion of pore water from the material being compressed. In general, the material consists of solid particles (mineral phase), and spaces (voids), which in an unsaturated environment such as a soil, contain both air and water. When a squeezing stress is applied to a water-saturated material, its volume decreases by three main mechanisms ... 

Soil organic matter can be measured with or without their separation from the mineral phases. In the case of there being no separation, the usual procedure is the oxidation of soil organic matter, for example, by potassium dichromate in acidic medium. In this way, the carbon content is determined, from which soil organic matter content is calculated using the average elementary composition of humic substances (Kononova 1972). 

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