Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Patent
1996-10-03
1999-04-20
Straub, Gary P.
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
405263, 4352625, 588236, 423DIG17, A62D 300, B09B 300
Patent
active
058958320
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for the treatment of contaminated material, in particular a process for the removal of metal, especially heavy metal, contaminants from bulk particulate material such as land or soil using biochemical processes.
BACKGROUND OF THE INVENTION
World-wide, substantial amounts of land have become metal contaminated as a result of industrial, waste disposal and other activities. Examples of such contaminants include: mercury, cadmium, barium, chromium, manganese and lead, radionuclides such as actinides and fission products. Such contaminants can pose a significant threat to ground water and therefore drinking water supplies and in many cases either limit, or prevent land re-use. Additionally, as a result of recent legislation in the United States of America and likely similar legislation within the European Community and elsewhere, waste producers are becoming increasingly liable to prosecution and to meet the costs of recovery and clean up if they do not act responsibly towards their wastes. Consequently there is a growing need for technologies which can help solve the problems caused by contaminated land.
To date, a number of techniques have been developed to remediate contaminated land. Examples include: soil stabilization, electromigration, vitrification, volatilization, incineration, soil washing, pump and treat systems, land farming, slurry phase bioremediation, etc. Many of these known techniques possess several limitations including: material to a toxic landfill, or entrapment within matrixes possessing a limited life; contaminated land in the case of currently used biological processes; e.g. soil stabilization and incineration; particular site, e.g. as in the case of incineration and soil washing; when applied to metals.
The present invention seeks to address these problems by enabling biological systems to remediate metal contaminated land non-specifically.
SUMMARY OF THE PRESENT INVENTION
According to the present invention a process for the decontamination of a medium comprising a particulate material contaminated with one or more metal species comprises the steps of treating a body of the said medium with microbially produced sulfuric acid so as to solubilize and leach the metal species as a metal sulfate; treating the leached metal sulfate by a bioprecipitation process which converts the said sulfate to an insoluble sulfide; separating hydrogen sulfide produced during bioprecipitation from the insoluble metal sulfide; and oxidizing the separated hydrogen sulfide to form a reusable source of a sulfur-containing ingredient.
The medium to be decontaminated may comprise a particulate material such as soil, rock particles, dredgings, sediments, sludges, process residues, slags from pyrolytic processes, furnace dusts and the like. The contaminants may be contained on the surface of the particulate material or may be bound inside the particles thereof.
Several metal species may be present in the said medium and these may be converted to various metal sulfates and subsequently bioprecipitated as various metal sulfides. The term "metal species" as used herein includes metals, alloys, metal salts, metalloids and metal containing compounds and complexes.
The said metal species contaminants may include:
Actinides are elements having periodic numbers in the inclusive range 89 to 104.
The term `fission product` as used herein refers to those elements formed as direct products (or so-called `fission fragments`) in the fission of nuclear fuel and products formed from such direct products by beta decay or internal transitions. Fission products include elements in the range from selenium to cerium.
Non-radioactive heavy metals desired to be separated by the process of the present invention include toxic metals such as nickel, zinc, cadmium, copper and cobalt and other common contaminants. These are commonly found as earth contaminants or in aquatic sediments near industrial plants in which chemicals containing those elements have been employed,
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British Nuclear Fuels plc.
Straub Gary P.
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