Chemical oxidation with Permanganate - in situ

Description

Permanganate (MnO4-) oxidation is the most common and most used of all chemical oxidation techniques. Compared with other oxidants such as ozone or hydrogen peroxide, permanganate has a lower oxidation potential but it is more stable and more persistent in soils. As a result, it can migrate by diffusive and advective processes (FRTR, 2002), giving it a greater zone of influence. Oxidant delivery systems often employ vertical or horizontal injection wells using pressure to force the oxidant into the subsurface.

Permanganate is available in liquid (e.g. NaMnO4) or crystalline form. Permanganate salt is generally potassium permanganate (KMnO4), but calcium or magnesium salts are also available. The injection solution is denser than water, which facilitates the vertical movement of the oxidant through the contaminated matrix, and improves contact between the oxidant and the contaminant. Permanganate oxidation is effective over a pH range of 3.5 to 12, but specific oxidation reactions are pH dependent. The oxidation reactions can lower the pH if the system is not adequately buffered. Degradation rates with permanganate also depend on temperature, organic matter content and reduced mineral species.

Permanganate oxidation is suitable for all substances that can be oxidized, such as organic compounds. Compared to the ex situ permanganate chemical reaction, the in situ technique does not generate large volumes of waste material, and is effective over a shorter period of time.

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Recommended Analyses for Detailed Characterization

Chemical Analysis

  • Contaminant concentrations   Footnotes1
  • pH 
  • Organic matter content  
  • Concentration of oxidant-consuming substances   Footnotes2
  • Reaction parameters   Footnotes3

Physical Analysis

  • Soil granulometry  
  • Presence of non-aqueous phase liquids (NAPLs)  

Recommended Trials for Detailed Characterization

Chemical Trials

  • Evaluation of the matrix oxidant demand  

Physical Trials

  • Vapour survey 
  • Evaluation of the radius of influence 
  • Evaluation of operating pressure/vacuum 

Hydrogeological Trials

  • Tracer tests 

Other Information Recommended for Detailed Characterization

Phase II

  • Contaminant delineation (area and depth)  
  • Presence of environmental receptors   Footnotes4

Phase III

  • Soil stratigraphy  
  • Characterization of the hydrogeological system   Footnotes5
  • Identification of preferential pathways  
  • Volume of contaminated material to treat  
  • Conceptual site model with hydrogeological and geochemical inputs  

Notes:

Pilot scale field tests are recommended for selecting the type and position of injection wells, establishing the radius of influence of the injection wells and to calculate optimal permanganate injection rates


Applications

  • Overall effective pH range of 3.5 to 12, narrower ranges for specific oxidation reactions
  • Specific for the degradation of polycyclic aromatic hydrocarbons (PAHs), chlorinated aliphatics such as perchloroethylene (PCE), trichloroethylene (TCE), dichloroethylene (DCE), and vinyl chloride (VC) and other organic contaminants
  • Soil permeability must be sufficient to allow oxidant migration. The optimum permeability ranges from 0.25 to 0.5 pore volume/day.

Treatment Type

  • Applies In situ
  • Does not apply Ex situ
  • Does not apply Biological
  • Applies Chemical
  • Does not apply Control
  • Applies Dissolved contamination
  • Does not apply Free Phase
  • Does not apply Physical
  • Applies Residual contamination
  • Applies Resorption
  • Does not apply Thermal

State of Technology

  • Does not applyTesting
  • AppliesCommercialization

Target Contaminants

With restrictions Aliphatic chlorinated hydrocarbons

Does not apply Chlorobenzenes

With restrictions Explosives

Does not apply Metals

With restrictions Monocyclic aromatic hydrocarbons

         Does not apply Non metalic inorganic compounds

Does not apply PCBs

With restrictions Pesticides

Applies Petroleum hydrocarbons

Applies Phenolic compounds

Applies Policyclic aromatic hydrocarbons

Applies   Applies    With restrictions   With restrictions    Does not apply   Does not apply

Treatment Time

  • Applies< 1 year
  • Applies1 to 3 years
  • Does not apply3 to 5 years
  • Does not apply> 5 years


Secondary By-products and/or Metabolites

Chemical oxidation with permanganate produces carbon dioxide (CO2), water (H2O), and inorganic chloride during the oxidation of chlorinated organics. Degradation of contaminants by permanganate oxidation may produce toxic secondary by-products, depending on the nature of the contaminants. Volatile compounds may also be released. Oxidation with permanganate can also create manganese oxide deposits (MnO2) which can reduce the permeability of the aquifer.



Limitations of the Technology

  • Permanganate oxidation technology is temperature and pH dependent
  • Soil permeability and matrix heterogeneity limit the application of the technology
  • Potential for the oxidant to only move through preferential pathways
  • Potential for mobilization of redox-sensitive compounds, such as metals
  • Reduction in soil permeability during treatment due to CO2 entrapment, precipitation of KMnO4, etc.
  • Mobilisation of certain metals
  • Presence of oxidant consumers in the soil matrix that could reduce oxidant efficiency
  • Costs can quickly increase if large quantities of permanganate are required due to high concentrations of non-target oxidant consuming compounds
  • Handling of a hazardous oxidant and controlling of hazardous permanganate dust
  • The permanganate oxidation reactions may disrupt other remediation techniques, such as natural reductive dehalogenation


Complementary Technologies that Improve Treatment Effectiveness

  • Non aqueous phase liquids (NAPLs) present in the contaminated matrix must be removed prior to applying this technique
  • Radio-frequency heating, resistive heating, or surfactant technologies enhance the in situ permanganate oxidation process


Required Secondary Treatments

Controlling fugitive vapours that may be produced from the heat of reaction.



Application Examples

Application examples of chemical oxidation with permanganate are available in the following document:



Performance

According to the FRTR (2002), in situ chemical oxidation techniques can achieve high treatment efficiencies (e.g. > 90 percent) for unsaturated chlorinated aliphatics (e.g. trichloroethylene [TCE]) with very fast reaction rates (90 percent destruction in minutes).



References


Composed by:

Josée Thibodeau, M.Sc
National Research Council


External Verifier:

David Morin, Ph.D
TechnoRem Inc.


Latest update provided by:

Karine Drouin, M.Sc.
National Research Council


Updated Date:

3/1/2009



Footnotes

Return to footnote1 Contaminant concentrations: Identification and concentration of all contaminants (sorbed, dissolved, and free phase).

Return to footnote2 Oxidant-consuming substances include natural organic matter and reduced minerals, as well as carbonate and other free radical scavengers.

Return to footnote3 Reaction parameters includes : kinetic, stoichiometry, and thermodynamic parameters.

Return to footnote4 Presence of potential environmental receptors, above and below ground infrastructure, and the risk of off-site migration.

Return to footnote5 Complete characterization of the hydrogeological system includes: the depth and thickness of the aquifer, the direction and speed of the groundwater flow, etc.