Hazardous or toxic waste destruction or containment – Containment
Reexamination Certificate
1999-01-28
2001-06-26
Suchfield, George (Department: 3672)
Hazardous or toxic waste destruction or containment
Containment
C134S010000, C134S025100, C134S040000, C210S690000, C588S253000, C588S253000, C588S255000
Reexamination Certificate
active
06251058
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for the treatment of soil materials contaminated with hazardous hydrophobic organic substances or residues, and in particular to a method for removal of such hazardous hydrophobic organic substances in which the soil material is substantially comprised of clay and/or sand. Hazardous organic substances or residues are referred to herein as “organic contaminants”. As noted herein, organic contaminants may include hydrocarbon materials e.g. oil, provided such materials are present in a minor amount.
Reference is made herein to the use of adsorbent materials. However, it is to be understood that those materials might also exhibit absorbent properties with respect to the organic contaminants or combinations of the contaminants with oil or other mobilizing agents. In addition, as used herein, soil includes clays and sands.
BACKGROUND OF THE INVENTION
Owners of sites containing soils contaminated with hazardous substances may be required by governmental or other regulations to remediate these materials. Examples of known methods of doing so include application of biological, physical or chemical methods to remove or stabilize/destroy the substances, or to transfer the contaminated material to approved off-site landfills. The methods used to remediate solid materials include bioremediation, aqueous soil washing including use of surfactants, soil extraction with organic solvents, thermal desorption and incineration. Although such methods may be effective, they also tend to be expensive.
There is substantial interest in development of cost effective methods for removing or remediating organic contaminants from solid particulate materials such as soil. Because of the low solubility of these organic contaminants in water, such contaminants tend to tightly adsorb on or absorb into the solid materials and consequently are less amenable to biodegradation by microorganisms, which normally requires an aqueous phase for growth and metabolism.
It has been observed that the degree of difficulty of extracting or remediating organic contaminants from soil increases with an increased content of clay and/or humic substances or organic carbon in the soil.
More economic methods for removal of hazardous contaminants from soils are required for purposes of remediating the soil and to prevent contaminants from spreading through the soil and/or to prevent contamination of groundwater.
SUMMARY OF THE INVENTION
A method for remediating soils containing hazardous organic contaminants has now been found.
Accordingly, one aspect of the present invention provides a method for remediating soil containing organic contaminants, comprising:
a) forming an aqueous slurry of a mixture of a hydrophobic adsorbent selected from foamed synthetic materials with said soil in the presence of water, the adsorbent having a density less than water;
b) mixing said slurry for a period of time; and
c) effecting a gravity separation of the adsorbent from the aqueous admixture thus obtained.
In another aspect, the present invention provides a method for removal of organic contaminants from solid particulate soil contaminated with the organic contaminant, comprising:
a) forming an aqueous slurry of a mixture of a hydrophobic adsorbent selected from natural materials which entrap gas, and cellular or foamed materials prepared by synthesis or modification of natural fibres with said soil in the presence of water, the adsorbent having a density less than water;
b) mixing said slurry for a period of time; and
c) effecting a gravity separation of the adsorbent and sorbed organic contaminant from the aqueous admixture thus obtained.
In a preferred embodiment, the adsorbent is a natural material with entrapped gas-containing pores.
In preferred embodiments of the methods of the present invention, the slurry is subjected to a step to permit settling of soil and other particulate prior to effecting separation of the adsorbent.
In further embodiments, the admixing of the slurry effects contact between the adsorbent and the soil.
In a further embodiment, a mobilizing agent may be added to the aqueous slurry to promote better mobilization of the contaminant from the soil particles to the adsorbent and/or for better sorption.
In a still further embodiment, the hydrophobic adsorbent may be added and mixed with the soil prior to addition of water to form an aqueous slurry.
In another embodiment, a surfactant is added to the slurry to effect separation of the organic contaminant from the soil, said surfactant being selected in an amount that does not inhibit adsorption of the organic contaminant on the adsorbent.
In yet another embodiment, the water content of the aqueous slurry is at least 25% by weight of the soil, especially 25-100% by weight.
In a further embodiment, the soil is comprised of clay and/or sand.
DETAILED DESCRIPTION OF THE INVENTION
The method of the invention involves mixing the soil, water, with or without any other agents e.g. oil material, and the adsorbent, thereby forming a slurry. These components may be added and mixed with the soil in a single operation or by adding and mixing individual components in any sequence. Mixing may be accomplished using processes known in the art, including using reactors, tanks with air spargers, impellers, rakes, screw assemblies or stirrers, rotating drums e.g. similar to a cement mixer, tumblers, reactors on reciprocating or orbital shaking machines, vibration or sonication mixers and screw or other conveyor equipment.
The slurry is preferably directed to a settling step, which may be accomplished in the mixing vessel or a following conveyance, including by pouring or other transfer of the slurry to a separating vessel. The separating vessel may or may not contain additional water to promote separation of soil and adsorbent. The mixing and/or separation stages may be carried out in a batch or continuous mode.
The separated floating organic contaminant/adsorbent material is recovered and may be further processed by a variety of methods e.g. compression, heating or washing. The adsorbent binding the organic contaminant may be volume reduced by thermal or solvent treatment or by using other physical or chemical methods which melt the polymer and destroy the cellular structure or depolymerize or otherwise modify the polymer, or the adsorbed organic contaminant or the mixture.
In the method of the present invention, an aqueous slurry is formed from a mixture of a hydrophobic adsorbent and soil. The soil may be obtained from a wide variety of sources, and is soil that has been contaminated with an organic contaminant. The soil is a solid particulate, which may be in a variety of forms.
Hazardous organic contaminants that may be treated by the method of the invention include aliphatic, aromatic, polycyclic aromatic, heterocyclic and other cyclic compounds, and derivatives of such compounds, especially derivatives containing halogen, nitrogen, sulphur and/or oxygen atoms. Examples of toxic compounds include polycyclic aromatic hydrocarbons (PAHs); polychlorinated biphenyls (PCBs); phthalate esters; phenols and chlorinated phenols; pesticides and herbicides and related structures; chlorinated ethanes, ethylenes and methane; monoaromatics including BTEX compounds; dioxins and furans; nitrotoluenes and nitrobenzenes. BTEX is a mixture of benzene, toluene, ethyl benzene and xylene. The method of the invention may also be used to treat other known hazardous organic contaminants, unidentified toxic substances and mixtures of toxic organic components.
A variety of adsorbent materials may be used, which as discussed above may also exhibit absorbent properties towards the organic contaminants. Examples of adsorbents are given below. The preferred adsorbents are hydrophobic and float in water e.g. have a density of less than one, and are particularly effective in promoting flotation of the hydrophobic adsorbent with associated organic contaminant.
The adsorbent materials are foamed synthetic materials, especially polymeric foams or cellular poly
Billingsley Kate
Singh Ajay
Ward Owen P.
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
Petrozyme Technologies Inc.
Suchfield George
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