Abiotic organic reactions at mineral

Voudrias, E. A. Reinhard, M. (1986). Abiotic organic reactions at mineral surfaces. In Geochemical Processes at Mineral Surfaces, ed. J.A. Davis K. F. Hayes, pp. 462-86. Washington, DC American Chemical Society. 

Voudrias, E.A., and M. Reinhard. 1986. Abiotic organic reactions at surfaces of minerals, p. 462-486. In J.A. Davis and K.F. Hayes (ed.) Geochemical processes at mineral surfaces. ACS Symposium Series 323. ACS, Washington, DC. 

Abiotic organic reactions that may be influenced by mineral surfaces include hydrolysis, elimination, substitution, redox, and polymerization. The effect of the surface may be either to promote (increase the rate of) or to inhibit (decrease the rate of) reactions that may occur in homogeneous solution. In addition, mineral surfaces may promote reactions that do not occur in homogenous solution by selectively concentrating molecules at the mineral surface... 

DOC transport through the soil and its concentration leaving a soil profile depends on abiotic sorption and desorption reactions with mineral surfaces. The tendency for organics to be strongly sorbed to soil particles through a variety of bonds can explain the order of magnitude drop in DOC fluxes in subsurface horizons (Neff and Asner, 2001 Ugolini et aL, 1977). For example, at the Harvard Forest, Massachusetts, Currie et al. 

Let us now take a brief look at some important redox reactions of organic pollutants that may occur abiotically in the environment. We first note that only a few functional groups are oxidized or reduced abiotically. This contrasts with biologically mediated redox processes by which organic pollutants may be completely mineralized to C02, HzO and so on. Table 14.1 gives some examples of functional groups that may be involved in chemical redox reactions. We discuss some of these reactions in detail later. In Table 14.1 only overall reactions are indicated, and the species that act as a sink or source of the electrons (i.e., the oxidants or reductants, respectively) are not specified. Hence, Table 14.1 gives no information about the actual reaction mechanism that may consist of several reaction steps. 

Other reactions which may generate CAA in the subsurface are the mineral oxidation of dissolved organic material to CAA by such inorganic species as ferric iron (released during clay diagenesis) (24), as well as abiotic sulfate reduction/hydrocarbon oxidation (25) which may take place at temperatures as low as KX>>C (59). 

As the sandstone/shale system exits the zone of intermediate burial and enters the zone of deep burial (>130°C), the organic acids have been decarboxylated and the alkalinity of the pore waters is again dominated by HCOi . Siebert (1985) has suggested that the thermal (or abiotic) reduction of sulfate by hydrocarbons begins at approximately 140 °C and ends at 210 °C, and that the chemical evolution of many deeply buried and relatively exotic reservoir fluids can be explained by the reduction of sulfate by hydrocarbons and the reaction of the resulting hydrogen sulfide with other minerals. This mechanism is outlined in the seven equations in Table 4. Reactions (l)-(5) in Table 4 show that the reduction of sulfate to H2S and the oxidation of hydrocarbons to CO2 in the presence of iron can be an important source of protons in deeply buried diagenetic systems. 

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