Processes Affecting the Remediation of Chromium-Contaminated Sites

Abstract

The remediation of chromium-contaminated sites requires knowledge of the processes that control the migration and transformation of chromium. Advection, dispersion, and diffusion are physical processes affecting the rate at which contaminants can migrate in the subsurface. Heterogeneity is an important factor that affects the contribution of each of these mechanisms to the migration of chromium-laden waters. Redox reactions, chemical speciation, adsorption! desorption phenomena, and precipitation/dissolution reactions control the transformation and mobility of chromium. The reduction of CrvI to Crl' can occur in the presence of ferrous iron in solution or in mineral phases, reduced sulfur compounds, or soil organic matter. At neutral to alkaline pH, the Cr"' precipitates as amorphous hydroxides or forms complexes with organic matter. Cr"'' is oxidized by manganese dioxide, a common mineral found in many soils. Solidphase precipitates of hexavalent chromium such as barium chromate can serve either as sources or sinks for Cr'v'. Adsorption of Crv' in soils increases with decreasing chromium concentration, making it more difficult to remove the chromium as the concentration decreases during pumpand-treat remediation. Knowledge of these chemical and physical processes is important in developing and selecting effective, cost-efficient remediation designs for chromium-contaminated sites.

Soil humic acids may favour the persistence of hexavalent chromium in soil

“…More than three decades ago Bartlett and Kimble (1976) and recently also several other scientists (Banks et al, 2006;Jardine et al, 1999), recognised that Cr(VI) can be rapidly reduced to Cr(III) by soil organic matter. In fact, Cr(VI), being a strong oxidant, can be readily reduced to Cr(III) in the presence of various electron donors (Nakayasu et al, 1999;Palmer and Wittbrodt, 1991). However, even when dealing with propitious soil composition (i.e.…”

“…However, even when dealing with propitious soil composition (i.e. electron donor chemical domains, competing ions and soil texture) and favourable physical conditions, Cr(VI) may persist, especially in organic soils, for prolonged periods of time, even years (Palmer and Wittbrodt, 1991). Humic acids (HAs) are natural carbon-rich biopolymers ubiquitous in terrestrial and aquatic environments, whose multiple properties seem to be purpose-built for many life-sustaining functions, from agriculture to industry, environment and biomedicine (Peñ a-Mé ndez et al, 2005).…”

Stabilization of Cr(VI) from fine ferrochrome dust using exfoliated vermiculite

“…were evaluated by means of the linear forms of the Lagergren equations (4) and (6). The values for these parameters, along with their correlation coefficients, are presented in Table 2.…”

Remoción de Cromo (VI) por una Cepa de Paecilomyces sp Resistente a Cromato

“…al., 2010). Además, el Cr(VI) puede ser reducido a Cr(III) en el suelo por reacciones redox con especies inorgánicas acuosas, transferencia de electrones en superficies minerales, reacción con substancias orgánicas no húmicas, (carbohidratos y proteínas), ó reducción por substancias húmicas del suelo (Palmer y Wittbrodt, 1991). También, la actividad microbiana puede contribuir a su reducción en estos ambientes contaminados, a través de la liberación del ión ferroso, sulfuros o intermediarios orgánicos reactivos (Buerge y Hug, 1998).…”