Trace elements reactions clay minerals

REACTIONS OF TRACE ELEMENTS WITH CLAY MINERALS... 

Four billion years ago, the Earth s thin crust consisted of geochemicals (i.e., compounds containing the elements Si, O, Al, Fe, Mg, Ca, K and Na, as well as traces of other elements). Thus, some biogenesis researchers believed that the first replicating material consisted of geochemical material rather than substances containing carbon and other bioelements. Clay minerals in particular were included in experimental and theoretical studies. The most important are kaolinite and montmorillonite the latter was, and still is, used in many experiments carried out to simulate prebiotic reactions. 

Chemical Synthesis. If cholesterol is heated with elemental sulfur at 150°C for several days, a mixture of PCAH results (J2), the detailed composition of which is not known. Other dehydrogenation reagents, such as selenium, catalyze the production of alkyl naphthalenes and phenanthrenes from naturally occurring terpenes (J3). Thus, in principle, it is possible that the PCAH in an anoxic sediment could result from the chemical dehydrogenation of various naturally occurring compounds. These reactions may take place slowly over the years and may be catalyzed by trace elements, elemental sulfur, and clay minerals. 

The non-equilibrium condition of most groundwater systems with respect to many primary minerals, or similarly the metastability which exists with respect to many semi-crystalline or amorphous phases are common problems, especially for silicates. Some clear identification is needed for system reaction time, or the rate at which equilibrium is approached, and similarly identification is needed for metastable plateaus of pseudo-equilibrium, especially for compounds such as amorphous silica, cristobalite, quartz, clay minerals, etc. The likely magnitude of saturation indices which could apply to a given mineral could be specified for a variety of conditions. In this volume, Glynn, and elsewhere others, have recently shown that some error occurs in the calculated saturation values for trace elements when pure end member minerals are assumed to be present, when actually the phases are solid solutions. The consensus among modelers appears to be that error is present and significant the challenge is to develop procedures that quantify the error, so models become tools that provide realistic and interpretable results. 

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