Decontamination of polluted soils

• US 5,405,579 A
• Filed: 07/22/1992
• Issued: 04/11/1995
• Est. Priority Date: 07/22/1991
• Status: Expired due to Fees

• Current Assignee: Linde AG (Linde Plc)
• Original Assignee: Linde AG (Linde Plc)
• Inventors: Melzer, Reiner, Mikulla, Klaus
• Primary Examiner(s): Jones, W. Gary
• Assistant Examiner(s): EDWARDS, LAURA ESTELLE
• Application Number:
  US07/916,788
• Time in Patent Office: 993 Days
• Field of Search: 422/1, 422/26, 422/38, 34/135, 34/136, 210/634, 210/774, 210/747, 110/236, 110/246, 110/226, 405/128, 55/222, 55/223, 55/228, 55/259
• US Class Current: 422/26
• CPC Class Codes: B09B 3/45 Steam treatment, e.g. supercritical water gasification or oxidation
• CPC Class Codes: B09C 1/06 thermally

Abstract

For the thermal treatment of contaminated soils, excavated soil is heated by indirect heat exchange up to 650° C. in a rotary drum in the absence of oxygen. Pollutants are separated from the soil by a desorption medium. Moisture in the soil vaporized to steam can serve as the desorption medium. The resultant gaseous pollutant stream is condensed, and the pollutants are separated.

Claims

1. A process for the decontamination of an excavated soil containing soil pollutants and water moisture, comprising the steps of:

passing the excavated soil to a thermal treatment zone, heating the soil in the absence of oxygen and under superatmospheric pressure by indirect heat exchange to a temperature not higher than 650°

C. under sufficient time-temperature conditions, such that the water moisture in the soil is vaporized to form steam, contacting a desorption medium comprising said steam with said soil in the absence of oxygen, and under sufficient time-temperature conditions to desorb the soil pollutants from the soil, cooling the desorption medium containing the soil pollutants in a scrubbing step, separating the cooled and scrubbed desorption medium into individual phases at least one phase being a gaseous phase, dissolving any precipitating solids in the gaseous phase in a solvent and cooling the gaseous phase.

2. A process according to claim 1, wherein the desorption medium acts on the soil for a time period of about 0.5-1 hour.

3. A process according to claim 1, wherein during said heating or desorbing step, an inert gas is further added to the desorption medium.

4. A process according to claim 1, further comprising injecting supplemental water or steam into the thermal treatment.

5. A process according to claim 1, wherein an aqueous phase is obtained after phase separation, and said aqueous phase is filtered through a filter containing filter media.

6. A process according to claim 5, wherein resultant decontaminated soil is utilized as filter media.

7. A process according to claim 5, wherein resultant laden filter media is thermally treated together with the contaminated soil.

8. A process according to claim 1, wherein said excavated soil is purged with a gas to remove oxygen prior to the heating step.

9. A process according to claim 1, wherein the temperature in the thermal treatment zone is 200°

-650°

C.

10. A process according to claim 1, wherein the temperature in the thermal treatment zone is 350°

-550°

C., and the superatmospheric pressure is not more than 2 bars absolute.

11. A process for the decontamination of an excavated soil containing soil pollutants and water moisture comprising the steps of:

passing the excavated soil to a thermal treatment zone having at least two stages, in a first stage, heating the soil in the absence of oxygen and under superatmospheric pressure by indirect heat exchange to a temperature not higher than 650°

C. under sufficient time-temperature conditions such that the water moisture in the soil is vaporized to form steam, in a second stage, desorbing the soil pollutants from the soil by passing a desorption medium comprising the steam formed in the first stage through the soil, in the absence of oxygen, wherein the desorption medium is present in the second stage for a time period of 0.5-1 hour, and under sufficient time-temperature conditions to desorb the soil pollutants from the excavated soil, cooling the desorption medium containing the soil pollutants in a scrubbing step, separating the cooled and scrubbed desorption medium into individual phases at least one phase being a gaseous phase, dissolving any precipitating solids in the gaseous in a solvent and cooling the gaseous phase.