Lead-contaminated soils, washing

T0879 Western Environmental Science and Technology (WEST), Soil Washing of Lead-Contaminated Soil... 

Western Environmental Science and Technology (WEST) had developed an ex situ soil washing technology designed for the treatment of lead-contaminated soil. This technology was particularly developed for use at shooting ranges. 

WEST specializes in the development and application of soil washing technology for onsite remediation of contaminated soil. They have been remediating lead-contaminated soil since 1990. Their soil washing technology for lead-contaminated soils is commercially available. 

Van Benschoten, J.E., Matsumoto, M.R. and Young, WH. (1997) Evaluation and analysis of soil washing for seven lead-contaminated soils. J. Environ. Eng. -ASCE, 123, 217-224. 

In situ metal immobilization employing phosphate is a cost-effective and environmental friendly technique of less disruptive nature [24, 28, 47, 76] than other remediation techniques such as soil removal, washing or leaching. This technique was suggested by the United States Environmental Protection Agency in 1996 as an alternative to soil removal for the amendment of urban lead-contaminated soils [27]. The treatment of waters with calcium oxide or hydroxide can precipitate dissolved arsenate. To attain a total dissolved arsenic level lower than the maximum permissible concentration for total arsenic in potable water (0.010 mg/L arsenic) it is necessary to have a pH higher than 12.5, which poses other environmental problems. Under these conditions calcium carbonate wiU be the thermodynamically stable solid phase under ambient surface conditions. Transformation of calcium arsenates into calcium carbonate wiU re-release arsenic into the environment. For pH > 12... 

The BenCHEM soil washing system successfully treats inorganic mining ores and ore processing tailing wastes. The technology has also been successfully applied to petroleum-contaminated soils containing tetraethyl lead. 

The BESCORP Soil Washing System (BSWS) is a water-based unit for the volume reduction of coarse/sandy soils contaminated with lead or other heavy metals. It uses a combination of trommel agitation, attrition scrubbing, high-pressure washing, and separation by particle size and density to remove heavy metals and heavy-metal compounds from soil. 

As an alternative to acid washing, soils can also be flushed with chelating agents. Examples of effective chelating agents include ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA), both of which readily bind and solubilize metals. Using this approach, Peters Shem (1992) have recently reported on the removal of lead from a contaminated soil. In this study, 0.1M EDTA removed 60% of the lead in a soil containing 10 000 mg lead/kg. 

The contribution from deposition of airborne lead on soil and crops to lead in diets is estimated to be between 13% and 31% for children. For individual plants a high percentage of lead may derive from aerial deposition (40-100%). Where crops are contaminated by lead from the air and soil, much of this may be removed by washing and other normal culinary practices. 

Davis, A. P., and Hotha, B. V. (1998). Washing of various lead compounds from a contaminated soil column. J. Environ. Eng. 124(11), 1066-1075. 

Neilson, J. W., Artiola, J. F., and Maier, R. M. (2003). Characterization of lead removal from contaminated soils by nontoxic soil-washing agents. J. Environ. Qual. 32(3), 899-908. 

Mechanical recovery equipment, such as bulldozers, scrapers, and front-end loaders, can cause severe and long-lasting damage to sensitive environments. It can be used in a limited capacity to clean oil from urban areas, roadsides, and possibly on agricultural land. The unselective removal of a large amount of soil leads to the problem of disposing of the contaminated material. Contaminated soil must be treated, washed, or contained before it can safely be disposed of in a landfill site. This can cost thousands of dollars per ton. 

Rhamnolipids were applied to a soil in the presence of oil contamination [15] and from sediments to remove heavy metals [63]. Although 80-100% of cadmium and lead can be removed from artificially contaminated soil, in field samples the results were more in the range of 20-80% [64], Clay and iron oxide contents affected the efficiency of the biosurfactants but this has not been researched. Biosurfactant could be added as a soil washing process for excavated soil. Due to the foaming property of the biosurfactant, metal-biosurfactant complexes can be removed by addition of air to cause foaming and then the biosurfactant can be recycled through precipitation by reducing the pH to 2. 

Cline, S. R., Reed, B. E., and Matsumoto, M. R. (1993). Efficiencies of Soil Washing Solutions (with CaCl2) for the Remediation of Lead and Organically Contaminated Soils. Proceed. Ind. Waste Conf., Jan. 24, Vol. 48, pp. 169-177, Ann Arbor Sci. Publ. 

A distinct advantage of plastic pyrolysis into fuels as a means of recycling is its ability to handle mixed and unwashed plastics. Post-consumer plastics are often commingled and contaminated with extraneous materials such as soil, dirt, aluminium foils, paper labels and food remnants. While soil, dirt and glue can be removed from post-consumer plastics by washing, this is a fairly expensive operation and it leads to secondary waste streams... 

Unfortunately, although a lot has been done to keep lead out of soil, the soil we will be living with for the foreseeable future still bears the contamination from years and years of accumulation. Lead does not degrade. Unless it is covered by new silt deposits or washed away by erosion, the lead deposited in our soil presents a permanent health hazard to those who may come in contact with it. So we had better learn to protect ourselves from it. 

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