Basic soil extractants

Salts, in addition to causing the soil to be basic, can have deleterious effects on analytical procedures. For example, significant error can occur if a potassium-selective electrode is used to determine potassium in a high-sodium soil (see Chapter 9). As discussed in Chapter 14, other salts could cause inaccurate results when atomic absorption analysis of a soil extract is carried out. 

Polycarbonyl and polyamino compounds include chelates, which are manmade compounds, and siderophores, which are biologically derived and more specialized. They can help dissolve inorganic ions, keep ions in one specific ionic state, and maintain them in biologically available forms. Because of their ability to bring ions into solution, they are often used to extract specific ions in specific forms from soil. Cationic micronutrients, particularly iron and zinc, are often applied in chelated form as a foliar spray to alleviate nutrient deficiencies. This is particularly true of plants growing in basic soil and is done even when plants do not show micronutrient deficiencies. Typically, both foliar and soil applications are effective in this regard. 

Basic soils present a unique analytical challenge. Most of these soils contain calcium carbonate (CaC03) as the primary base. Basic soils also contain magnesium and, to a lesser extent, sodium carbonate. Although soils containing lithium and potassium carbonate are known, they are uncommon. These compounds produce a basic solution when dissolved in water. This means that adding either water as an extractant or water containing small amounts of salt is not effective because the soil already contains salts and solutions immediately become basic when added to these soils. 

Adding acidic extractants to basic soils is ineffective for a number of reasons. First, the acid in acid extractants will be neutralized as illustrated in Equation... 

For these reasons, basic soils are extracted using a basic solution. The most common is the Olson extractant, which is 0.5 M sodium bicarbonate (NaHC03). 

Procedure 11.7. Extraction of Basic Soils (Olson Extraction)... 

There are only a few extractions other than the Olson extraction for basic soils [8,9], A typical basic environmental extraction of soil is given in Procedure 11.8. Note that in this procedure, the components of interest are first extracted with basic solutions. Thus, the components present in the final analysis will only be those extracted by base. However, acid is used to adjust the pH before final analysis, although the solution is still basic (pH 7.5), at the end of the procedure [15],... 

What is the danger associated with extracting basic soils with acid (Hint something is rapidly released.)... 

Q Basic soil measurement techniques and extraction procedures... 

Soxhlet extraction is used as the benchmark against which any new extraction technique is compared. The basic Soxhlet extraction apparatus consists of a solvent reservoir, an extraction body, a heat source (e.g. an isomantle) and a water-cooled reflux condenser (Figure 7.2). A Soxhlet uses a range of organic solvents to remove organic compounds, primarily from solid matrices. The solid sample (ca. 10 g if a soil) and a similar mass of anhydrous sodium sulfate are placed in the porous thimble (cellulose), which in turn is located in the inner tube of the Soxhlet apparatus. The apparatus is then fitted to a round-bottomed flask... 

Iron-deficiency in fruit trees (citrus and pomes) causes poor crops. A soil may be rich in iron, and yet so basic that the iron is not available to the rootlets. Ethylenediaminetetracetic acid (EDTA), sprayed on such soil, extracts iron by forming the EDTA-ferric complex, which is absorbed by the rootlets. Experiments with tomato plants, grown in an iron-EDTA medium labelled with Fe, and with in the 2-position of the acetate-group, showed that the plant absorbs the intact complex, which is translocated. Later, the organic part is broken down by metabolism which leaves the inorganic iron (Hill-Cottingham and Lloyd-Jones, 1961). When soil is poor in iron, ferric EDTA is sprayed on the ground with the same result. 

Economic feasibility studies suggest that even at the present state of the art photocatalytic technology indeed can be competitive with the traditional carbon adsorption or incineration technologies in treatment of contaminated soil vapor extraction vents and small scale VOC-containing vents [28]. Rapid progress in basic and applied research in photocatalysis suggests... 

Residue analytical methods for neonicotinoids in crops, soil and water samples have been developed. The basic principle of these methods consists of the following steps extraction of the crop and/or soil samples with acetone or the other organic solvent, cleanup by liquid-liquid partition or column chromatography, and quantitative analysis by high-performance liquid chromatography with ultraviolet detection (HPLC/UV). Simple column cleanup procedures are used to improve the accuracy and sensitivity of these methods. 

The movement of air in the subsurface during the application of SVE is caused by the pressure gradient that is applied in the extraction wells. The lower pressure inside the well, generated by a vacuum blower or pump, causes the soil air to move toward the well. Three basic equations are required to describe this airflow the mass balance of soil air, the flow equation due to the pressure gradient, and the Ideal Gas Law. 

Integrated vapor extraction and steam vacuum stripping can simultaneously treat groundwater and soil contaminated with VOCs. The system developed by AWD Technologies consists of two basic processes a vacuum stripping tower that uses low-pressure steam to treat contaminated ground-water and a soil gas vapor extraction/reinjection process to treat contaminated soil. The two processes form a closed-loop system that provides simultaneous in situ remediation of contaminated groundwater and soil with no air emission. 

When considering CEC or AEC, the pH of the soil solution is extremely important. There will be competition for binding sites between H30+ and other cations in the soil solution. Therefore, the observed CEC will be lower at high proton concentrations, that is, at low or acid pH levels, and higher at basic pH levels. For analytical measurements, the CEC of soil at the pH being used for extraction is the important value, not a CEC determined at a higher or lower pH. 

Figure 4.12. A basic extract of an organic soil is shown on the left a sample of the sodium salt of humic acid is seen on the right. 

Inorganic components in soil are extracted with water, acidic solutions containing highly soluble ligands and chelates, and basic solutions. Acidic solutions are typically used for extraction of metals and metal ions in both exchangeable and nonexchangeable forms. Basic solutions are used much less commonly, although they are important for oxyanions, particularly phosphate. 

Inorganic species in soil are generally extracted with either water or an acid solution typically containing hydrochloric acid. Various other components that aid either in the solubilization, extraction, or stabilization of extracted inorganics, such as chelates, are also often added during the extraction process. Basic extractions are not as commonly used as are acid extractions with a few notable exceptions. The use of ion exchange resins to extract ions from soil is well established. 

Karasek et al. [1] determined hydrocarbons in benzene water extracts (pH7) of soil and in incinerator or fly ash by a variety of techniques including gas chromatography with flame ionization, electron capture and mass spectrometric detectors. Benzene water extractants were adjusted to pH4, 7 and 10 before the extraction in order to selectively extract various types of acidic and basic organic compounds in addition to hydrocarbons. 

Neutral and basic herbicides were extracted from water made alkaline with sodium hydroxide or from soil, with chloroform extracts of soil were cleaned up on basic alumina containing 15% of water. Acidic herbicides were extracted with ethyl ether from water acidified with hydrochloric acid or from an aqueous extract of soil prepared by treatment with 10% aqueous potassium chloride that was 0.05M in... 

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