In-situ chemical oxidation-reduction and precipitation of heavy metals in soils and groundwater

• US 6,623,646 B2
• Filed: 05/15/2001
• Issued: 09/23/2003
• Est. Priority Date: 05/16/2000
• Status: Expired due to Fees

• Current Assignee: Geo-Cleanse International Incorporated
• Original Assignee: James Daniel Bryant
• Inventors: Bryant, James Daniel, Wilson, James Thomas
• Primary Examiner(s): Hruskoci, Peter A.
• Application Number:
  US09/855,442
• Publication Number:
  US 20010042722A1
• Time in Patent Office: 861 Days
• Field of Search: 166/245, 166/52, 166/270, 166/370, 166/250.01, 210/717, 210/719, 210/720, 210/721, 210/724, 210/722, 210/739, 210/743, 210/747, 210/757, 210/759, 210/904, 210/912, 210/913, 405/128.5, 405/263, 588/246, 588/256
• US Class Current: 210/717
• CPC Class Codes: A62D 2101/43 containing heavy metals, in the bonded or free state
• CPC Class Codes: A62D 3/33 by chemical fixing the harmful substance, e.g. by chelation or complexation
• CPC Class Codes: B09C 1/08 chemically
• CPC Class Codes: B09C 2101/00 In situ
• CPC Class Codes: Y10S 210/904 -CN containing
• CPC Class Codes: Y10S 210/912 Heavy metal
• CPC Class Codes: Y10S 210/913 Chromium

Abstract

A method is taught for converting metal contaminants in the soil to less toxic forms as well as permitting their removal from groundwater. A first reactive solution comprising ferrous sulfate and an acid selected from the group consisting of sulfuric acid and phosphoric acid is injected to decomplex contaminants and precipitate them as insoluble compounds. A second reactive solution comprising hydrogen peroxide, and an acid selected from the group consisting of sulfuric acid and phosphoric acid is then injected to destroy organic liquids and enhance decomplexation. The pH of the first solution may range from 3 to 5, and the pH of the second solution range from 3 to 7, preferably 5 to 7. The process is particularly effective where chromium compounds such as hexavalent chromium are the contaminants.

Claims

1. A method for the in-situ treatment and remediation of an underground area contaminated with at least one member selected from the group consisting of hexavalent chromium and other heavy metals, semi-metals and cyanide comprising the steps of:

(a) determining an effective amount and concentration of a first reactive solution comprising ferrous sulfate and an acid selected from the group consisting of sulfuric acid and phosphoric acid required to decomplex chromium and other heavy metals, semi-metals and cyanide from mineral surfaces, initiate reduction of hexavalent chromium to trivalent chromium and reduction of heavy metals and semi-metals to their least soluble valence state and to precipitate trivalent chromium, heavy metals and semi-metals as insoluble compounds;

(b) determining an effective amount and concentration of a second reactive solution comprising hydrogen peroxide and an acid selected from the group consisting of sulfuric acid and phosphoric acid to have a pH of about 3 to about 7 required to destroy organic ligands and enhance decomplexation;

(c) injecting the first reactive solution and subsequently the second reactive solution at an effective pressure and at a flow rate in excess of a sustainable yield, the amount of said first reactive solution and second reactive solution into one or more injectors that are inserted into the ground, sealed and positioned so as to assure liquid flow and dispersion of the reactive solutions through the contaminated area; and

(d) allowing said first and second reactive solutions to flow through the contaminated area thereby reacting chemically with the contaminants contained therein, and converting said contaminants into environmentally inert substances without producing collateral contamination.

2. A method as recited by claim 1, wherein during the flow of the second reactive solution, the hydrogen peroxide concentration is repetitively pulsed.

3. A method as recited by claim 1, wherein the underground area is contaminated with hexavalent chromium.

4. A method as recited by claim 1, wherein the underground area is contaminated with hexavalent chromium and it is precipitated as insoluble compounds of trivalent chromium.

5. A method as recited by claim 1, wherein the pH of the first reactive solution is between about 3 and about 5 and the pH of the second reactive solution is also between about 5 and about 7.

6. A method as recited by claim 5, wherein the pH of the first reactive solution is between about 4 and about 5.

7. A method as recited by claim 1, wherein the contaminant is hexavalent chromium and the effective amount of ferrous ion in proportion to the amount of said contaminant is between about 133% and 333% of the theoretical stoichiometric amount.

8. A method as recited by claim 7, wherein the effective amount of ferrous ion in proportion to the amount of contaminant is between about 167% and 233% of the theoretical stoichiometric amount.

9. A method as recited by claim 1, wherein the concentration of ferrous ion in the first reactive solution is between 100 mg/L and about 6000 mg/L.

10. A method as recited by claim 1 wherein the contaminant is a non-chromium constituent and wherein the iron concentration of the first reactive solution is between 50 and 1000 mg/L and the peroxide concentration in the second solution is 1-25 wt/%.

11. A method for the in-situ treatment and remediation of an underground area contaminated with at least one member selected from the group consisting of hexavalent chromium and other heavy metals, semi-metals and cyanide comprising the steps of:

(a) determining an effective amount and concentration of a first reactive solution comprising ferrous sulfate and an acid selected from the group consisting of sulfuric acid and phosphoric acid required to decomplex chromium and other heavy metals, semi-metals and cyanide from mineral surfaces, initiate reduction of hexavalent chromium to trivalent chromium and reduction of heavy metals and semi-metals to their lowest soluble valence state and to precipitate trivalent chromium, heavy metals and semi-metals as insoluble compounds;

(b) determining an effective amount and concentration of a second reactive solution comprising hydrogen peroxide and an acid selected from the group consisting of sulfuric acid and phosphoric acid to have a pH of about 3 to about 7 required to destroy organic ligands and enhance decomplexation;

(c) injecting the first reactive solution and subsequently the second reactive solution at a flow rate in excess of a sustainable yield and with a pulsating pressure, the amount of said first reactive solution and second reactive solution into one or more injectors that are inserted into the ground, sealed and positioned so as to assure liquid flow and dispersion of the reactive solutions through the contaminated area; and

(d) allowing said first and second reactive solutions to flow through the contaminated area thereby reacting chemically with the contaminants contained therein, and converting said contaminants into environmentally inert substances without producing collateral contamination.

12. A method as recited by claim 11, where the magnitude of the pressure pulsations is at least 5% of the formation pressure in the underground area and the frequency of the pulsations is at least equal to one-fourth the reciprocal of the decay time of a pressure pulse.

13. A method as recited by claim 11, wherein the underground area is contaminated with hexavalent chromium.

14. A method as recited by claim 11, wherein the underground area is contaminated with hexavalent chromium and it is precipitated as insoluble compounds of trivalent chromium.

15. A method as recited by claim 11, wherein the pH of the first reactive solution is between about 3 and about 5 and the pH of the second reactive solution is between about 5 and about 7.

16. A method as recited by claim 11, wherein the contaminant is hexavalent chromium and wherein the effective amount of ferrous ion in proportion to the amount of contaminant is between about 133% and 333% of the theoretical stoichiometric amount.

17. A method as recited by claim 16, wherein the effective amount of ferrous ion in proportion to the amount of contaminant is between about 167% and 233% of the theoretical stoichiometric amount.

18. A method as recited by claim 11, wherein the concentration of ferrous ion in the first reactive solution is between 100 mg/L and about 6000 mg/L.