Metal-contaminated soils remediation

Biological activity can be used in two ways for the bioremediation of metal-contaminated soils to immobilize the contaminants in situ or to remove them permanently from the soil matrix, depending on the properties of the reduced elements. Chromium and uranium are typical candidates for in situ immobilization processes. The bioreduction of Cr(VI) and Ur(VI) transforms highly soluble ions such as CrO and UO + to insoluble solid compounds, such as Cr(OH)3 and U02. The selenate anions SeO are also reduced to insoluble elemental selenium Se°. Bioprecipitation of heavy metals, such as Pb, Cd, and Zn, in the form of sulfides, is another in situ immobilization option that exploits the metabolic activity of sulfate-reducing bacteria without altering the valence state of metals. The removal of contaminants from the soil matrix is the most appropriate remediation strategy when bioreduction results in species that are more soluble compared to the initial oxidized element. This is the case for As(V) and Pu(IV), which are transformed to the more soluble As(III) and Pu(III) forms. This treatment option presupposes an installation for the efficient recovery and treatment of the aqueous phase containing the solubilized contaminants. 

Mench M.J., Didier V.L., Loftier M., Gomez A., Masson P. A mimicked in-situ remediation study of metal-contaminated soils with emphasis on cadmium and lead. J Environ Qual 1994 23 58-63. 

Role of Bacteria and Bacteria-Soil Composites in Metal Biosorption and Remediating Toxic Metal-Contaminated Soil Systems... 

Bacteria and their composites with soil minerals or organic matter are capable of taking up a wide range and variety of toxic metals in soil environments. Research done over the last decade or so has greatly improved our understanding of the mechanisms on biosorption of metals and bacte-ria-metal-soil component interactions. However, more studies from molecular level are needed in order to enhance the ability of bacteria and their association with soil components to remediate toxic metals-contaminated soils. The focus of future investigations should be on the mechanisms by which metals are sorbed and bound by bacterial cell surfaces and bacteria-soil/mineral composites. In this connection, X-ray absorption spectroscopy (XAS) is a promising technique because it can provide information about... 

Kelly JJ, Tate RL (1998) Effects of heavy metal contamination and remediation on soil microbial communities in the vicinity of a zinc smelter. J Environ Qual 27 609-617... 

Chaney R. L., Angle J. S., Wang A. S., McIntosh M.S., Broadhurst L., and Reeves R. D., 2005, Phytoextraction of soil Cd, Ni and Zn using hyperaccumulator plants to alleviate risks of metal contaminated soils requiring remediation. International Workshop Current developments in remediation of contaminated lands p. 39, 27-29 October 2005. Pulawy, Poland. 

The MRU technology is not applicable to heavy-metal-contaminated soils nor to radioactive waste contamination. The one exception to heavy-metals remediation is mercury. The vaporization temperature for mercury is well within the operating range of the MRU, and because of closed chamber construction, it is ideally suited for the removal and reclamation of mercury from contaminated soil. 

Cost estimates for phytoremediation vary widely. One estimate for phytoextraction included 10,000 per acre for planting, with total remediation costs estimated at 60,000 to 100,000 per acre. Total costs included expenses associated with maintenance, monitoring, and verification testing. Another estimate placed phytoremediation costs at 80/yd of contaminated soil (D131431). Cleanup costs for an acre of metal-contaminated soil were estimated to range from 60,000 to 100,000. This estimate assumes remediation to a depth of 50 cm. In contrast, excavation and disposal storage without treatment for a comparable site would cost at least 400,000 (D16482T). 

Hodson, M. E., Valsami-Jones, E. Cotter-Howells, J. D. 2000. Bonemeal additions as a remediation treatment for metal contaminated soil. Environmental Science Technology, 34, 3501-3507. 

Miller, R.M. (1995a). Biosurfactant-facilitated remediation of metal-contaminated soils. 

Otte, M. L. (1991). Contamination of coastal wetlands with heavy metals factors affecting uptake of heavy metals by salt marsh plants. In Ecological Responses to Environmental Stresses, ed. J. Rozema J. A. C. Verkleij, pp. 126-33. London Kluwer Academic. Peters, R. W. Shem, L. (1992). Use of chelating agents for remediation of heavy metal contaminated soil. In Environmental Remediation, ed. American Chemical Society, pp. 70-84. Washington, D.C. American Chemical Society. 

Mulligan, C.N., Yong, R.N. and Gibbs, B.F. (2001) Remediation technologies for metal-contaminated soils and ground-water an evaluation. Engineering Geology, 60(1-4), 193-207. 

Chaudhry, T.M., Hayes, W.J., Khan, A.G., and Khoo, C.S. 1998. Phytoremediation—focusing on accumulator plants that remediate metal-contaminated soils. Australasian Journal of Ecotoxicology, 4 37-51. 

M. Hodson, E. Valsami-Jones, and J. Cotter-HoweUs, Bonemeal additions as a remediation treatment of metal contaminated soil, Environ. Sci Technol, 34 (2000) 3501-3507. 

While electrokinetic treatment of soils looks promising, most of the work performed was bench-scale, under carefully controlled laboratory conditions. For electrokinetic remediation to be a viable alternative for in-situ cleanup of waste sites, a number of factors will have to be investigated. All of the work to date has dealt with uniformly contaminated soil samples. Studies performed on partially saturated soils will yield different results. Further studies on the removal of mixed metal contaminated soils, using different soil types, are needed. The presence of organic compounds in the soil will also influence successful treatment of real contaminated soils. The use of reagents which could increase desorption and/or solubilization (without further contaminating the soil matrix) may also be areas of future investigation. Finally, field tests need to be performed to substantiate studies accomplished on the bench scale. 

C.N. Mulligan, R.N. Yong, and B.E Gibbs, Remediation Technologies for Metal-contaminated Soils and Groundwater An Evaluation, Engin. Geol. 60(1 ), 193-207, June (2001). 

Use of Chelating Agents for Remediation of Heavy Metal Contaminated Soil... 

Tmovsky, M. Oxer, J.P. Rudy, R.J. Hanchak, M.J. Hartsfield, B. Site Remediation of Heavy Metals Contaminated Soils and Groundwater at a Form Battery Reclamation Site in Florida, In Hazardous Waste, Detection, Control, Treatmeru Abbou, R., Ed. Elsevier Science Publishers, B.V. Amsterdam, The Netherlands, 1988 pp 1581-1590. 

Adriano, D. C., Albright, J., Whicker, F. W., and Iskandar, I. K. (1997). Remediation of metal- and radionuclide-contaminated soil. In Remediation of Metal-Contaminated Soils, ed. Iskandar, I. K., and Adriano, D. C., Science Reviews, Northwood, Middlesex, England, 27-45. 

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