Hydraulic and earth engineering – Soil remediation – In situ contaminant removal or stabilization
Patent
1996-07-01
1998-02-24
Suchfield, George A.
Hydraulic and earth engineering
Soil remediation
In situ contaminant removal or stabilization
210721, 210762, 210912, 588224, A62D 300, B09C 108
Patent
active
057205787
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a process for the treatment of contaminated mud or suspended soil. One of the most commonly and successfully used processes for treating contaminated soils is washing. One such process is described, for example, by E. Hilmer and E. Schramm in the journal "Altlasten" 1/92, pages 32 to 34. In this process, the material to be treated, generally earth mixed with sand or gravel, is subjected to intensive multistage washing with high-pressure water jets. Irrespective of the washing process itself, the waste-water contains co-called "fine silt" in addition to the soil contaminants dissolved in the water. Fine silt is understood to be the fine-particle component of the soil with a particle size of less than 0.5 mm. However, experience has shown that this fine component contains most of the organic soil contaminants (hydrocarbons, polycyclic aromatic hydrocarbons (PAHC's) or chlorinated hydrocarbons (CHC's), etc.,) which are not destroyed by the soil washing process.
Another serious problem is the decontamination or treatment of contaminated dredger muds. Ports in particular are confronted by the problem of disposing of dredger muds which are often contaminated with organic contaminants and also with heavy metals. The solids are separated according to particle size on board the dredger itself by means of hydrocyclones. In this case, too, most of the contaminants are to be found in the fine component with a particle size below 0.5 mm.
The problem addressed by the present invention was to provide a process for eliminating the contaminants in contaminated soils or muds. More particularly, the invention set out to decontaminate soils or muds contaminated with mineral oil, PAHC's, PCB's and residues of plant protection agents.
SUMMARY OF THE INVENTION
According to the invention, the solution to this problem is characterized in that the contaminated mud or the suspended earth emanating from the soil to be decontaminated with a concentration of 3% to 25% dry matter and preferably 10% to 15% dry matter is wet-oxidized by addition of pure oxygen or an oxygen-containing gas at a temperature of 80.degree. C. to 330.degree. C. and preferably at a temperature of 120.degree. C. to 220.degree. C., under a pressure of 1 bar to 200 bar and preferably under a pressure of 3 bar to 50 bar and at a pH value below 7, iron ions alone or in combination with quinones or quinone-forming substances being added to the mud or to the suspended earth to accelerate the oxidation reaction.
It has also been found that, instead of quinones, surplus sludge or digested sludge from a biological sewage treatment plant may be added to the quinones as co-catalyst to accelerate the reaction.
If the soil or mud to be treated contains coarse particles, it is best wet-ground to particle sizes below 500 .mu.m and preferably to particles below 100 .mu.m.
In a further development of the process according to the invention, the heavy metals which may have passed into solution in an acidic oxidation reaction are precipitated as hydroxides by addition of alkali after separation of the oxidatively treated solids and are subsequently filtered off.
The invention affords the following advantages: the oxidation reaction can be carried out under relatively mild conditions at temperatures below 220.degree. C. and under pressures below 50 bar. This reduces the strain on materials, lowers costs and increases the safety of the process.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE is a flowchart showing the process of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is described in more detail in the following with reference to a flow chart and is illustrated by Examples.
In the application of the process according to the invention for the oxidative treatment of contaminated soils or muds on an industrial scale, the suspended soil or the mud with a solids content of around 10% to 15% dry matter is first homogenized to particle sizes below 0.2 mm in a wet grinding unit 1. Thereafter the mud can
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Holzer Klaus
Horak Otto
Melin Thomas
Bayer Aktiengesellschaft
Suchfield George A.
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