Kaolinite organic complexes

The presence of soil complicates metal removal because soils sorb metals strongly and can also affect microbial—metal complexation. Walkeretal. (1989) showed that purified preparations of cell walls from Bacillus subtilis and Escherichia coli (423 to 973 mmol metal/g cell wall) were more effective than either of two clays, kaolinite (0.46 to 37 mmol metal/g clay), or smectite (1 to 197 nmol metal/g clay), in the binding of seven different metals. However, in the presence of cell-wall/clay mixtures, binding was reduced. In summary, there are several parameters that affect metal complexation. These include specific surface properties of the organism, cell metabolism, metal type, and the physicochemical parameters of the environment. 

Buffered (pH 7) 0.1 M ammonium acetate and 0.43 M acetic acid have also been adopted to extract soil plant-available PTMs (Burridge and Berrow, 1984 Ellis and Alloway, 1983 Haq etal, 1980 John etal, 1972 Merkel, 1996 Obrador et al, 2007 Sastre et al, 2004 Soon and Bates, 1982 Sterckeman et al, 1996). For both extractants, acetate complexation ability may contribute to increase the amounts of PTMs released (Adamo et al, 1996 McLaren and Crawford, 1973). Only for acetic acid, in addition to readily exchangeable, also specifically adsorbed and carbonate-bound metals are likely displaced by hydrogen ions (Berrow and Mitchell, 1980). Acetic acid could partially extract metals bound to organic matter (Paya-Perez et al, 1993) and associated with minerals (kaolinite, K-feldspars and ferrihdrite) (Whalley and Grant, 1994). 

The features of the adsorbed complex of the Cambrian argillites were intensely transformed by diagenetic reactions, making them unsuitable for any interpretations. The complex composition of the clays which consist of kaolinite, illite, chlorite and mixed-layer minerals, together with the absence of organic matter leads to the conclusion that the areas of denudation must have been of a local nature. At the same time, we may reconstruct a temperate to humid climate interrupted at times by periods of relative aridity. This explains the lack of laterites on the eruptive and metamorphic rocks. 

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