Smectites decomposition

An actual contribution of humic substances to metal oxide reduction in natural systems has not been demonstrated, and there are processes such as adsorption or decomposition that could limit their effectiveness. Kostka et al. (2002a) observed that AQDS additions elicited a larger increase in Fe(III) reduction by S. oneidensis growing on ferrihydrite than smectite clay minerals. This suggests that the influence of humic substances may depend on soil or sediment mineralogy. Nevertheless, there is ample evidence to suggest that a portion of the anaerobic metabolism that was previously attributed to direct enzymatic Fe(III) and Mn(IV) reduction was actually none-nzymatic reduction by microbially reduced humic substances. 

Significant replacement of monovalent metal cations on layer silicate clay surfaces by protons can occur if the electrolyte concentration is very low. The long-term result, beyond hydrolytic exchange, is acidic decomposition of the clay structure in part, and release of structural AP or Mg + to solution. These multivalent cations may then readsorb onto exchange sites, influencing the rheological properties of clays in very dilute salts. Some of the anomalous behavior of Na -smectites suspended in... 

Lanson B, Besson G(1992) Characterization of the end of smectite-to-illite transformation Decomposition of X-ray patterns. Clays Clay Minerals 40 40-52... 

Aluminosilicate smectite clays have been ion-exchanged with water-soluble, cationic porphyrins and metalloporphyrins. Characteristics of their thermal stability were measured by thermal gravimetric analysis in an inert atmosphere, which yielded approximately 60% weight loss of organics. Detailed structural information about the decomposition products was obtained by performing pyrolysis-gas chromatography-mass spectrometry on the clay-organic complexes. 

Specific lithological classification permits placing constraints on the final petrophysical solution. In the case of feldspathic sand, for example, one might wish to predict the presence of illite/smectite, chlorite and kaolinite based on various feldspar decomposition models. Similarly, it might be predicted that calcic dolomite, one of the specific lithologies for carbonate, is composed mainly of dolomite with small amounts of calcite and possibly anhydrite (Pemper et al., 2006). 

In attempting the procedure of intercalation different authors usually follow one of two possible routes The first one is by introducing the metallic cations into a complex, which is often polynuclear (ref.15), and which is then intercalated into the smectite layers. It then leaves behind the oxidic pillars after thermal decomposition of its ligand. The second route is by attempting intercalation of the hydroxy-species of the metal, which results from a gradual addition of NaOH into the suspension of rnontmori1 Ionite and the metal salt, often a chloride. 

---