Palmer C D, Wittbrodt P R
Environmental Science and Engineering, Oregon Institute, Beaverton 97006-1999.
Environ Health Perspect. 1991 May;92:25-40. doi: 10.1289/ehp.919225.
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 CrIII 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 CrIII precipitates as amorphous hydroxides or forms complexes with organic matter. CrIII is oxidized by manganese dioxide, a common mineral found in many soils. Solid-phase precipitates of hexavalent chromium such as barium chromate can serve either as sources or sinks for CrVI. Adsorption of CrVI in soils increases with decreasing chromium concentration, making it more difficult to remove the chromium as the concentration decreases during pump-and-treat remediation. Knowledge of these chemical and physical processes is important in developing and selecting effective, cost-efficient remediation designs for chromium-contaminated sites.
铬污染场地的修复需要了解控制铬迁移和转化的过程。平流、弥散和扩散是影响污染物在地下迁移速率的物理过程。非均质性是影响这些机制中每一种对含铬水体迁移贡献的重要因素。氧化还原反应、化学形态、吸附/解吸现象以及沉淀/溶解反应控制着铬的转化和迁移性。在溶液中或矿物相、还原态硫化合物或土壤有机质中存在亚铁离子的情况下，CrVI可还原为CrIII。在中性至碱性pH条件下，CrIII以无定形氢氧化物形式沉淀或与有机质形成络合物。CrIII被二氧化锰氧化，二氧化锰是许多土壤中常见的矿物。六价铬的固相沉淀物如铬酸钡既可以作为CrVI的源，也可以作为汇。土壤中CrVI的吸附随铬浓度降低而增加，这使得在抽提处理修复过程中，随着浓度降低，去除铬变得更加困难。了解这些化学和物理过程对于开发和选择针对铬污染场地的有效、经济高效的修复设计非常重要。
