Myles, Philip (15 Greystone Drive, Reigate, Surrey RH2 0HA, GB)
Kalin, Robert M. (5 Beverly Avenue, Newtownards BT23 7UE, GB)
Myles, Philip (15 Greystone Drive, Reigate, Surrey RH2 0HA, GB)
| 1. | A method of remediating a substance contaminated with carbon disulfide, wherein'the substance is contacted with iron. |
| 2. | A method as claimed in Claim 1 wherein the substance is contacted with iron directly. |
| 3. | A method as claimed in Claim 1 wherein the substance is contacted with iron indirectly. |
| 4. | A method as claimed in any one of the preceding claims wherein the contacting includes passing the substance through a permeable body containing iron. |
| 5. | A method as claimed in any one of the preceding claims wherein the substance is one or more of the group comprising contaminated soils, liquids, gases and vapour phase contaminants. |
| 6. | A method as claimed in Claim 5 wherein the substance is either soil or groundwater or both. |
| 7. | A method as claimed in any one of the preceding claims wherein the iron is in granular form. |
| 8. | A method as claimed in Claim 7 where the iron has a granular diameter of about 15mm, generally 34mm. |
| 9. | A method as claimed in any one of the preceding claims wherein the iron is zerovalent iron. |
| 10. | A method as claimed in any one of the preceding claims further comprising the addition of one or more supplementary agents to enhance the ironcarbon disulfide reaction. |
| 11. | A method as claimed in Claim 10 wherein the one or more supplementary agents are selected from the group comprising bicarbonates, peroxides and sodium hydroxide. |
| 12. | A method as claimed in any one of the preceding claims wherein the contacting of the iron and contaminated substance is carried out insitu. |
| 13. | A method as claimed in Claim 12 which includes mechanical agitation of the iron and the contaminated substance. |
| 14. | A method as claimed in Claim 12 or claim 13 wherein the iron is added in the form of injection. |
| 15. | A method as claimed in any one of Claims 12 to 14 wherein the remediation is carried out in a reactive zone. |
| 16. | A method as claimed in Claim 15 wherein the reactive zone is a permeable reactive barrier. |
| 17. | A method as claimed in any one of Claims 1 to 12 wherein the contacting of the iron and contaminated substance is carried out exsitu. |
| 18. | A method as claimed in Claim 17 wherein the remediation is carried out using surface treatment cells. |
| 19. | A method as claimed in Claim 17 or Claim 18 wherein the contaminated substance and iron are admixed with water. |
| 20. | A method as claimed in Claim 19 wherein any water leaching from the treatment is circulated or recirculated through an iron reactive zone. |
| 21. | A method as claimed in any one of the preceding claims further comprising the addition of one or more materialhardening substances. |
| 22. | A method as claimed in Claim 21 wherein the material hardening substance is bentonite or cement or both. |
| 23. | A permeable reactive barrier adapted to carry out a method as claimed in any one of Claim 1 to 17 wherein the barrier has a reactive material which includes iron. |
Carbon disulfide is a toxic, highly flammable volatile liquid. It affects the nervous system, liver and heart as well as causing birth defects.
Carbon disulfide evaporates at room temperature ; the vapour easily explodes in air and burns to produce hydrogen sulfide, a poisonous gas.
Carbon disulfide is used in many applications, such as agricultural fumigants, the production of rubber chemicals and as the feedstock for carbon tetrachloride production. However the most important industrial use has been in the manufacture of viscose rayon and cellophane. The large-scale use and production of carbon disulfide combined with a lack of awareness of the environmental and health implications, has left a legacy of sites with carbon disulfide contaminated soil and groundwater. The US
Environmental Protection Agency's (EPA)"National oPriorities List" (NPL) of the most serious hazardous waste sites in the USA has identified carbon disulfide as the contaminant of concern in at least 200 of the 1430 current or former NPL sites.
To date there have been a number of methods developed to remediate carbon disulfide contaminated soil, these include excavation and in-situ chemical oxidation.
However, excavation of carbon disulfide contaminated soil can cause the carbon disulfide to ignite or explode when exposed to air. Excavation of soil to remediate carbon disulfide contaminated soil causes hazards associated with exposing carbon disulfide to air. A process of remediating carbon disulfide contaminated soil without exposing carbon disulfide to air is therefore desirable.
US Pat. 6, 283, 675 describes the in-situ chemical oxidation of carbon disulfide contaminated soil to produce sulfates. The reference does not address remediation of carbon disulfide contaminated soil by chemical reduction or the addition of iron. The reference relates to carbon disulfide contaminated soil and not groundwater.
US Pat 5,536, 898 describes the immobilisation of organic compounds in hazardous wastes by the mixing of such wastes with particulate rubber and biogenic amorphous silica. The tests conducted include waste
containing carbon disulfide, however the method does not destroy the carbon disulfide, only fixing it onto the additives.
US Pat 6,287, 472 describes the treatment of groundwater contaminated with chlorinated organics by passing it through a permeable body of iron particles. However, it only relates to the treatment of groundwater and not contaminated soil.
Also, it does not include carbon disulfide ; it only claims to treat"organic compounds".
According to the present invention, there is provided a method of remediating a substance contaminated with carbon disulfide, wherein the substance is contacted with iron.
The substance can be contacted with the iron either directly or indirectly. Such contacting includes passing the substance through a permeable body of iron.
Iron, generally zero-valent iron, destroys carbon disulfide by a chemical redox reaction.
The present invention is suitable for use with any substance contaminated with carbon disulfide. This includes contaminated solids such as soil, liquids such as groundwater, and gases or vapour phase contaminants.
The iron may be in any suitable form e. g. iron filings or granules such as granular iron'which is a well known product generally having a granular diameter of about 1-5mm, generally 3-4mm. Generally, it is preferred to provide the iron in a form having a large surface area.
One embodiment of the present invention includes the addition of one or more supplementary agents to enhance the iron-carbon disulfide reaction such as bicarbonate, peroxide or sodium hydroxide.
The contacting of the iron and contaminated substance can be carried out either in-situ or ex- situ. In-situ methods include mechanical agitation of the substance, such as soil, whilst adding, e. g. in the form of injecting, iron additives such as granular iron, e. g. soil mixing or jet grouting. In- situ methods also include the use of reactive zones such as Permeable Reactive Barriers (PRBs).
Some examples of PRBs include an in-situ barrier of reactive material which allows groundwater to pass through it. The reactive material in the barrier traps harmful chemicals in the groundwater or changes such chemicals to less harmful substances. A common method to construct a PRB is by digging a trench in the path of the polluted groundwater. The trench is filled with reactive material; often sand is mixed with the reactive material to increase the permeability of the reactive barrier compared to the
surrounding soil and thus allow the groundwater to flow through the barrier rather than around it.
Another method of PRB construction involves the construction of an impermeable funnel made of bentonite or sheet piling to direct the polluted groundwater flow to a permeable reactive zone. PRBs and permeable treatment zones are well known in the art.
Ex-situ methods include surface treatment cells into which the contaminated substance such as soil can be placed or groundwater can be pumped and'treated, and mechanical mixing of the iron and the contaminated substance e. g. soil, together with the addition of water so as to bring the pollutant into contact with the iron. Leached water from treatment cells could be recirculated through an iron reactive zone.
According to another embodiment of the present invention, a material-hardening substance such as bentonite and/or cement could be admixed with the other reactants so as to increase the geotechnical properties of the contaminated substance. Materials such as bentonite increase the impenetrability of an admixed substance such as soil, thereby decreasing the rate of flow of any fluid therethrough, and so increasing the contact time of the fluid with the iron.
Example 1 Batch tests combining carbon disulfide contaminated water with granular zero valent iron were conducted at 24°C over a period of 100 hours in 40ml glass vials with PTFE septa. The headspace to aqueous phase ratio was 3: 1 to allow the sampling of the headspace. The batch experiment consisted of reaction vials containing 10ml of a carbon disulfide solution of the following concentration: 50ppm and 250ppm, and 5g iron.
The results of the batch experiments are summarised in Table 1. ADDITIVE Initial carbon % carbon disulfide disulfide remaining after 4 concentration (ppm) days Iron 50 0.3 250 0.2 Control 1 50 100 Control 2 250 100 Water 0 N/a ppm = part per million Table 1. Percentage carbon disulfide in solution after treatment with iron.
Example 2 This test was conducted using the same apparatus as Example 1 and under the same conditions. However the headspace to aqueous phase ratio was 8: 1. The batch experiment consisted of reaction vials containing 5ml of a carbon disulfide solution of the following concentration: 100ppm and 400ppm. ADDITIVE Initial carbon % carbon disulfide disulfide remaining after 4 concentration (ppm) days Iron 100 0.01 400 4 Control 1 100 100 Control 2 400 100 ppm = part per million Table 2. Percentage carbon disulfide in solution after treatment with iron.
Example 3 Aerobic degradation Closed batch testing was carried out by reacting carbon disulfide solution with the following zero valent iron under aerobic conditions: The testing was carried out at room temperature 23°C and the duration of the testing was 4 days (100 hours). 40 ml glass vials with PTFE septa were used
as the reaction vessel. The headspace to aqueous phase ratio was 3: 1 to allow the sampling of the headspace. The batch experiment vials were filled with 5g zero valent iron and 10 ml of carbon disulfide solution. The zero-valent iron fillings were obtained from the University of Tuebingen, Germany.
Attached Figures 1 and 2 show the concentration (actual and log) of carbon disulfide plotted versus time. The carbon disulfide and iron mixture degrades within the first 90 hours with a half-life of 11 hours. Time (hours) Carbon disulfide Concentration (ppm) 0. 6 272. 4 0. 87 254. 4 1 245. 6 3. 47 251. 3 3. 6 254. 2 3. 73 224. 6 5. 95 202. 5 6. 22 177. 7 6. 35 197. 8 7. 07 186. 6 7. 2 193. 4 7. 33 171. 6 10. 4 136. 9 10. 53 132. 5 10. 63 145. 1 16. 78 80 16. 92 77 17. 03 70. 4 23. 4 81. 7 23. 52 83. 1 23. 65 79. 7 25. 83_ 63. 9 25. zu 4 26. 162. 5 29. 48 49. 4 29. 62 49. 1 29. 73 44. 2 31. 95 39. 9 32. 07 38. 8 32. 2 37. 1 35. 3236. 3 35. 42 31. 7 42. 03 17. 6 42. 6312. 5 59 7 90 Example 4 Anaerobic tests The test consisted of 60 samples prepared in 20ml glass vials. The simulated groundwater consisted of organic free water spiked with 100 mg/L of Carbon disulfide (CS2). Three types of samples were prepared: blank vials, containing only simulated groundwater and two sets of reaction vials, each containing 5 grams of commercially available sources of zero valent iron and simulated groundwater. The mass of iron to volume solution ratio was lg : 3. 7mL.
The simulated groundwater was prepared in a 5L gas tight Teflon lined plastic bag with Lurelock fittings. Carbon disulfide was first dissolved in methanol and then injected into the water filled bag leaving no headspace. The bag was shaken for 1 hour before the filling of the vials. The vials were filled using Teflon tubing and a peristaltic pump, leaving no headspace, then sealed immediately with Teflon septa and aluminium crimp caps. During the
sequential filling of the vials, sample vials with no iron were filled at regular intervals to determine the initial value of carbon disulfide. The test vials were then placed on a rotating disc operated at eight complete revolutions per hour.
Sampling was carried out at pre-determined intervals with more frequency within the first two days, the vials were removed from the rotating disc in batches and samples were extracted for GC-MS headspace analysis. All tests were conducted at room temperature (23°C).
Carbon disulfide analysis was performed using headspace extraction with a gas chromatograph mass spectrometer (GC-MS). The method detection limit for carbon disulfide was 10 pg/L.
Attached Figure 3 shows the concentration in parts per million (ppm) of carbon disulfide versus time in hours. The decline in the control concentrations of the experiment is due to sorption of carbon disulfide onto the Teflon septa, after about two days this stabilises at a concentration approximately 70ppm. The vials containing iron show a gradual decline with a half life estimated to be between 18 to 30 hours) within 80 hours.
Anaerobic Degradation Time Iron 1 CS2 Iron 2 CS2 Control CS2 (hou concentration concentration Concentration rs) (ppm) (ppm) (ppm) 0 95. 52 95. 52 95. 52 481. 4183. 087. 39 8 7'5. 06 81. 59 96. 14 12 63. 49 65. 78 90. 82 1. 6 55. 14 62. 77 84. 31 20 49. 45 54. 85 80. 16 24 39. 14 38. 21 80. 06 32 28. 99 37. 22 79. 19 40 23. 87 30. 09 74. 62 48 11. 35 18. 40 64. 12 60 8. 44 12. 03 65. 36 72-5. 65 67. 06 96--69. 08 120 67. 09 144 - - 76. 08 The results of the tests show that iron reacts with carbon disulfide disulfide in both aerobic and anaerobic conditions.
The. present invention provides a simple but effective method of treatment to remediate substances such as soil and groundwater contaminated with carbon disulfide.
The degradation of carbon disulfide by iron occurs due to a redox reaction. The end products of the carbon disulfide and iron reaction are iron sulfates and sulfides. Iron sulfide is a precipitate, and is in fact a naturally occurring compound, which is safe'compared with carbon disulfide.
Next Patent: METHOD OF CLEANING CONTAMINATED SOIL