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Clay-humus and oxide-humus complexes : Extensive studies have been done on complexes of montmorillonite, illite, kaolinite, hematite, goethite, gibbsite and boehmite with humic and fulvic acids. New concepts have been proposed to understand the mechanism of bonding, the influence of crystal edges, layer charge, cations, etc. in clay-humus bonding. These concepts have been developed based on an in-depth study of crystal structures, chemical reactions and high precision analytical data. Details of sites and modes of interaction and the reasons for behavioural differences between the minerals have been deduced. It was shown how (a) charges are distributed at various surfaces of crystals, (b) coordinate bonding with a crystal surface is possible and (c) strengths of cation-bridged bonds vary with the crystal structure. |
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Weathering of silicates by organics : Reaction of olivine, epidote, hornblende, tourmaline, biotite and microcline by organic acids were studied. It was observed that the position of an ion within the crystal, its polymeric nature, steric factors and ligand strength, together influence dissolution of ions from the minerals; surface etching, fragmentation, layer opening and new crystal growth was demonstrated. Dissolution of oxide coatings from clay minerals : The short-comings of the Mehra-Jackson (DCB) method have been investigated. An improved method has been proposed. |
References : |
1. Varadachari C and Ghosh K (2006) Development of computer generated structural models : Teaching aids in soil mineralogy. Clay Research 25 45-53.
2. Varadachari C, Goswami, G and Ghosh K (2006) Dissolution of iron oxides. Clay Research 25 1-22
3. Soil clay-humus complexes. I. Alkali dissolution, TEM and XRD studies : N. Ahmed, C Varadachari & K. Ghosh : Australian Journal of Soil Research (Australia) 40 : 691-703 (2002).
4. Soil clay-humus complexes. II. Bridging cations and DTA studies : N. Ahmed, C Varadachari & K. Ghosh : Australian Journal of Soil Research (Australia) 40 : 705-713 (2002).
5. The crystallo-chemistry of oxide–humus complexes : C. Varadachari, T. Chattopadhyay & K. Ghosh : Australian Journal of Soil Research (Australia) 38 : 789-806 (2000).
6. Organic solvent separation of iron oxides from layer lattice silicates : G.Goswami, C. Varadachari & K. Ghosh : Journal of the Indian Society of Soil Science 46 : 135-137 (1998).
7. Complexation of humic substances with oxides of iron and aluminum : C.Varadachari, T. Chattopadhyay & K. Ghosh : Soil Science (USA) 162 : 28-34 (1997).
8. Dissolution of iron oxides by a dithionite-oxalate-carbonate method : G.Goswami, C. Varadachari & K. Ghosh : “Clays Controlling the Environment” (Eds. G.J. Churchman, R. Fitzpatrick & T. Eggleton) CSIRO Publishing, Collingwood, Victoria, Australia (1995).
9. The influence, of crystal edges on clay-humus complexation : C. Varadachari, A.H. Mondal & K. Ghosh : Soil Science (USA) 159 : 185-190 (1995).
10. Clay-humus complexation : Effect of pH and the nature of bonding : C.Varadachari, A. H. Mondal, D.C. Nayak & K. Ghosh : Soil Biology & Biochemistry (UK) 26 : 1145-1149 (1994).
11. Weathering of silicate minerals by organic acids. II. Nature of residual products : C. Varadachari, A.K. Barman & K. Ghosh : Geoderma (Netherlands) 61 : 251-268 (1994).
12. A novel method for the determination of total acidity of humic substances : C.Varadachari, D.C. Nayak & K. Ghosh : Journal of the Indian Society of Soil Science 40 : 682-687 (1992).
13. Weathering of silicate minerals by organic acids : I. Nature of cation solubilisation : A.K. Barman, C. Varadachari & K. Ghosh : Geoderma (Netherlands) 53 : 45-63 (1992).
14. Some aspects of clay-humus complexation : Effect of exchangeable cations and lattice charge : C. Varadachari, A.H. Mondal & K. Ghosh : Soil Science (USA) 151 : 220-227 (1991).
15. Influence of organic acidic functional groups of humic substances in complexation with clay minerals : D.C. Nayak, C. Varadachari & K. Ghosh : Soil Science (USA) 149 : 268-271 (1990).
16. Synthesis and characterisation of crystalline aluminum compounds : M. Datta & C. Varadachari : Clay Science (Japan) 7 : 337-342 (1990).
17. Studies on decomposition of humus in clay-humus complexes : C. Varadachari, N.K. Biswas & K. Ghosh : Plant & Soil (Netherlands) 78 : 295-300 (1984).
18. On humus formation : C. Varadachari & K. Ghosh : Plant & Soil (Netherlands) 77 : 305-313 (1984).
