Extraction inorganic substances, soil

Con 4 Total phenolic acid content in soils was overestimated by the Folin Ciocalteu s phenol reagent because a number of other organic and inorganic substances also reduce the phenol reagent. In fact, some of these other organic compounds may have been important, if not more important, in the inhibition observed for soil extracts. 

Piccolo, A. (1988). Characteristics of soil humic substances extracted with some organic and inorganic solvents and purified by HC1-HF treatment. Soil Sci. 146,418 126. 

Extraction of humic substances has been a useful way of characterizing NOM properties by NEXAFS. In those cases where the element studied also has significant inorganic fractions such as sulfur in submerged soils and sediments, or phosphorus in most mineral soils and sediments, an extract appears to be the only approach to obtain meaningful information about NOM. Often, it was found that the spectra have a lower background and can be more easily analyzed quantitatively... 

The best extractants in the above list of salts form complexes with the polyvalent metals that neutralize charges on the humic substances and link them to the inorganic soil colloids. These polyvalent ions are replaced by sodium ions from the salts. The efficiency of each solvent system will depend on the extent to which the resident cations are exchanged and removed from humic structures. Diffusion of the salts to the interior of solid humic substances is slow. Some channeling can take place, but extensive penetration would probably require the opening up from the outside of the macro-molecular structures. It would be necessary for these structures to remain open to allow exchange from the interior to take place. 

Humins - the fraction of humic substances that is not soluble in water at any pH value. On this basis, humins include any humic-type material that is dissolved in non-aqueous solvents after the soil has been exhaustively extracted with basic aqueous solvents. Humins are often considered to consist mainly of humic materials strongly associated with the soil inorganic colloids. 

In contrast to the S forms identified in isolated humic materials, S NEXAFS spectroscopy studies of pristine soil samples showed distinctly different ratios for the oxidized to reduced sulfiir species (Fig. 38 Myneni and Martinez 1999). A detailed examination of the pine Ultisol from Puerto Rico showed that the percentage of oxidized S forms is higher than that of reduced forms. The NEXAFS spectroscopy studies indicated that the oxidized forms of sulfur (sulfonate, organo-sulfate, inorganic sulfates) are preferentially lost and the reduced-sulfur forms are retained during humic substance extraction. 

Many insoluble compounds of the metals are found in the earth s crust. Solids that contain these compounds are the ores from which metals are extracted. Ores contain minerals, which are naturally occurring inorganic solid substances having definite chemical compositions and characteristic crystalline structures. These minerals occur in mixtures with relatively large amounts of gangue—sand, soil, rock, and other material. Soluble compounds are found dissolved in the sea or in salt beds in areas where large bodies of water have evaporated. Metal ores can be classified by the anions with which the metal ions are combined (Table 26-1 and Figure 26-1). 

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