Allophanes soils

Robertson, R.H.S., 1963. Allophanic soil from Trail Bridge, Oregon, with notes on mosaic growth in clay minerals. Clay Miner., 5 237-247. 

Boron adsorption takes place independently of concomitant adsorption of other anions. For example, adsorption studies with allophanic soils from central Mexico 22) and southern Chile 18) revealed no effect from the simultaneous adsorption of sulfate or phosphate on boron adsorption. 

Chlordecone is a pesticide very resistant to degradation, that is, with a long lifetime [8] it was used mainly for the protection of banana plantations. Now, chlordecone is becoming a new source of contaminatiOTi for cultivated roots as it is still polluting agricultural soils. In the literature [9], it is shown that allophanic soils retain and trap more pesticides than other kinds of soils. Therefore, allophanic soils could be highly polluted but less contaminated for crops and water, and the clay microstructure should be an important physico-chemical characteristic governing the fate of the pesticide in the environment. 

This investigation of the pore structure details allows one to propose a possible mechanism for the C and N sequestration and pesticides retention in allophanic soils. The large specific surface area is the signature of small pore sizes. Associated to the fractal... 

Buuiman P, Peterse F and Almendros Martin G (2007) Soil organic matter chemistry in allophanic soils a pyrolysis-GC/MS study of a Costa Rican Andosol catena. European Journal of Soil Science 58 1330 1347... 

The TLM model has been applied not only to inorganic anions but also to organic species. In a study of 2,4-dichlorophenol, 2,4,6-trichlorophenol, andpentachlorophe-nol sorption in an allophanic soil (Cea et al. 2010), the isotherm experiments were well described (as shown in Figure 12.4) by the TLM in which monodentate outer and inner sphere complexes were considered to form between deprotonated organic molecules and active sites on the variable-charge soil. The calculated thermodynamic parameters suggest that chlorophenol sorption is a spontaneous (AG < 0), endothermic (AH > 0), and entropy-driven reaction (AS > 0). 

FIGURE 12.4 2,4-Dichlorophenol isotherms in allophanic soil, at pH 4.5, in 0.1 mol L"i KCl background electrolyte at temperatures of 25°C, 35°C, and 45°C. (Reprinted from Chemosphere, 78, cea, M. et al.. Kinetic and thermodynamic study of chlorophenol sorption in an allophanic soil, 86-91. Copyright 2010, with permission from Elsevier.)... 

MARTIN J.P., ZUNINO H., PEIRANO P., CAIOZZI M. and HAIDER K. 1982, Decomposition of 14-C labelled lignins, model humic acid polymers and fungal pigments in allophanic soils. Soil Biology and Biochemistry, 14,289-293. 

Non-allophanic soils (Collipulli) have a low lEP value due to the presence of more stable crystalline aluminosilicates and iron oxides which are more important than their low organic matter content (Collipulli soil has 0.6% of organic carbon), and little or no change of the lEP is observed with heating (Table 1). 

Kanno [1964] described the occurrence of allophane in a humic allophane soil from the Tachikawa loam bed of a soil in Mitaka, Tokyo, derived from basaltic ash. Similarly, the amorphous clays from certain soils from basalt of northern Ireland and many other parts of the world are allophanic, and the amorphous clays in young soils derived from ultrabasic rocks such as dunite in New Zealand clearly have allophanic constituents, though these may be inseparable from gels of hydrous iron oxides, antigorites, and other secondary minerals. 

Coarse clays (0.2 to 2 nm) of allophanic soils dispersed after less severe chemical treatments seem to contain similar constituents together with undispersed allophane. It does not appear possible at this stage to decide whether the latter material should be regarded as undispersed aggregates or as gel-like particles or both. This matter is further discussed later. 

X-ray diffraction patterns of ordered structure in allophanic soil clays are evidence of the presence of crystalline impurities. It is, however, possible that finely divided particles showing some evidence of crystallinity by X-ray or electron diffraction patterns may have allophanic surface properties, and such materials (e.g., hydrous feldspars) may be conveniently regarded as special cases of allophane. 

Bolt, G. H., and B. P. Warkentin, 1956. Influence of the method of sample preparation on the negative adsorption of anions in montmorillonite suspensions. Proc, 6th Int, Congr, Soil Sci. B 33-40. Broadbent, F. E., R. H. Jackman, and J. McNicoll, 1964. Mineralization of carbon and nitrogen in some New Zealand allophanic soils. Soil ScL 98 118-128. 

Deuterium exchange of hydroxyl groups in allophane. Soil Sci, Plant Niitr, 12 176,... 

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