Geochemical transport mechanisms

In a more descriptive sense, speciation relates to the characterization of geochemical transport mechanisms, like advection, diffusion, and dispersion leading to the accumulation or deprivation of metals. It also describes transformation phenomena, like adsorption-desorption, precipitation-dissolution, complexation, and alkylation, by which operationally defined metal species may mobilize or bind to various environmental media (Reuther 1987). 

Measurements made in the Type I pile and the Type III pile show no depletion in oxygen or increase in carbon dioxide concentrations, indicating gas transport mechanisms are fast relative to the rate of the oxygen consumption and carbon dioxide production due to geochemical reactions. In the Covered pile, significant depletions in oxygen and increases in carbon dioxide concentration have been observed at some locations, suggesting gas transport rates are limited by the till... 

Interest in trace element speciation studies in natural waters has increased considerably during the last decade. It has become apparent that data on total concentrations of any element rather than on individual well defined chemical entities, are often inadequate to identify transport mechanisms, ultimate fate and toxicity of particular elements to organisms. A study of the different trace metal species and their relative distribution will assist in understanding the chemical processes that take place in the highly reactive estuarine zone and in the open sea. These processes include the rate at which chemical processes take place, the participation in geochemical processes (precipitation/dissolution, adsorption/desorption). 

Torgersen, T., Clarke, W. B. (1992) Geochemical constraints on formation fluid ages, hydrothermal heat flux, and crustal mass transport mechanisms at Cajon Pass. J. Geophys. 

Eyles N., Sasseville D. R., Slatt R. M., and Rogerson R. J. (1982) Geochemical denudation rates and solute transport mechanisms in a maritime temperate glacier basin. Can. J. Earth Sci. 19, 1570-1581. 

During the weathering process, elements can disperse from source mineralisation by a variety of chemical processes. For reasons discussed below, electrochemical processes are increasingly thought to be the primary transport mechanism in environments of thick, young, exotic (i.e., transported) overburden. They are also likely to operate in other environments but their dominance as a transport mechanism is less certain. This chapter presents the principles behind electrochemical masj transport and discusses the role of natural geoelectrochemical processes in the formation of selective leach and conventional geochemical soil anomalies. 

Milltown Supefund Site supplemental data interpretation of geochemical release mechanisms and arsenic fate and transport Helena, Montana, USEPA. 

There are different patterns of distribution of the inventories of pollutants in the basins of the central and southwestern Baltic Sea, probably caused by the differences in the transport mechanisms and geochemical behavior of the components. However, most of the components show arelatively uniform distribution of the inventories (e.g., PCBs, Fig. 14.21). It means that the anthropogenic amount of these contaminants deposited in the basins varies only in narrow ranges. Independent of the location of possible sources, these contaminants were widespread and distributed over the whole area before deposition. 

Barth, T. Bjorlykke, K. (1993) Organic acids from source rock maturation generation potentials, transport mechanisms and relevance for mineral diagenesis. Appl. Geochem., 8, 325-337. 

This paper has presented a summary of a coupled formulation that combines an existing THM formulation with reactive transport equations in a fully coupled way. The reactive transport formulation takes into account some of the most relevant geochemical processes (acid/base, redox, dissolution/precipitation and complex formations). The transport mechanisms included are advection, molecular diffusion and mechanical dispersion. 

Electrokinetic remediation involves the installation of electrodes into multiple wells within a contaminated zone, followed by the application of a low electric potential. Ideally, the contaminants migrate toward the electrodes due to different transport mechanisms, and, upon reaching the wells, contaminant-laden liquids are extracted and treated. Although implementation is simple, the geochemical processes that occur within soils during electrokinetic remediation are complex and dependent on system variables such as soil type, pollutant type, treatment time, electrolyte solution, and applied voltage. 

Ear from being just the processing of water on Earth, this cycle is the basis for a wide range of meteorologic, geochemical, and biological systems. Water is the transport medium for all nutrients in the biosphere. Water vapor condensed into clouds is the chief control on planetary albedo. The cycling of water is also one of the major mechanisms for the transportation of sensible heat (e.g. in oceanic circulation) and latent heat that is released when water falls from the air. 

Salts with the [Au(CO)2]+ cation have been proposed to be important intermediates in the transport of gold in hydrothermal fluids. Gold deposits may accumulate through formation and decomposition of (carbonyl)gold salts under geochemically relevant conditions, similar to the mechanism advanced with salts based on the [Au(SH)2]- anion.303... 

From a geochemical perspective, sinking POM is an important mechanism by which carbon and other elements are transferred from the sea surfece into the deep sea and onto the sediments. This transport is termed the biological pump and includes the sinking of inorganic particles that are of biogenic origin, namely calcium carbonate and silicate shells. 

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