From: Public Services and Procurement Canada
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.
Potassium permanganate (KMnO4) and sodium permanganate (NaMnO4) are the most commonly used. Permanganate is available in liquid or crystalline form. 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 is highly selective and is typically applied to degrade chlorinated ethenes but is not usually effective at oxidizing benzene, chlorinated benzenes, MTBE, carbon tetrachloride, or chlorinated ethanes. In some instances, permanganate has been used to degrade petroleum hydrocarbon compounds. The fact that it is available in a solid form makes it advantageous for transportation to remote sites. It has the major disadvantage of producing a purple colour which can be problematic if dilute permanganate solution can reach water bodies or sewers. Since it also produces a by-product of oxidized manganese, build up of manganese in soils can be an issue in some jurisdictions. Also, as any chemical oxidation process, it is not applicable in the presence of free phase.
In situ chemical oxidation (ISCO) with permanganate consists of injecting a solution of permanganate in the soils and/or groundwater using direct injection equipment on direct push rigs, trenches, infiltration galleries, well recirculation, deep soil mixing rigs, hydraulic fracturing equipment and other equipment may also be used. The objective is to bring the oxidant in contact with contaminants, mineralizing the contaminant, in the case of a complete oxidation, into carbon dioxide and water. For halogenated compounds intermediate compounds may be formed. Multiple injection events (usually two or three) are often required. The primary issue in chemical oxidation is the distribution of treatment media in the subsurface.
Implementation of permanganate oxidation projects may include:
Permanganate oxidation treatment doesn’t require activator, stabilizer or additive for pH adjustment.
Solid or liquid forms of permanganate must be stored safely in a suitable and capped container, at ambient temperature and away from heat or incompatible materials.
Permanganate dust, which can be a health hazard, must be controlled during handling.
In some instances, oxidant reactivity with subsurface contaminants, including unexploded munitions and explosives, may be sufficient to result in combustion.
Complete mineralization of organic compounds leaves carbon dioxide, water, and inorganic ions (like chloride). In some instances, complete mineralization doesn’t occur.
Sodium or potassium permanganate leaves elevated sodium or potassium levels and precipitated manganese dioxide (because of oxidation state, dissolved manganese is typically not an issue, but this may be confirmed through monitoring).
System installation typically requires drilling or excavating in contaminated areas, resulting in the handling and disposal of contaminated soils, typically containerized and disposed of off-site.
There is potential for contaminated or oxidant rich groundwater to flow out of the treatment zone. Properly designed injections do not result in uncontrolled flow of oxidants or contaminated groundwater along preferential pathways.
Notes:
On-site treatment trials will establish the efficiency of the technology and the parameters that influence the treatment time and cost (e.g. residence time, pump flow rate, requirements for pre-treatment, etc.).
Tests examining the effect of temperature change on hydraulic conductivity and establishing the zone of freezing with a pilot scale tubing system are recommended to properly design the full-scale containment system.
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
In situ chemical oxidation (ISCO), for example, using campaign-based injection or the in situ mixing of solids is potentially applicable to remote northern sites, however, significant impediments to material transport and injection equipment mobilization must be overcome. Given the high cost of mobilizing reagents and equipment, ISCO may be pursued on a one-time basis with the objective of reducing concentrations to levels amendable to monitor natural attenuation or another alternative. Northern systems require climate-appropriate design, including consideration of permafrost and of seasonal changes in ground conditions.
Long-term consideration associated with the implementation of permanganate oxidation includes:
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.
By-product formation can be a concern if complete reaction cannot be obtained; bench top and/or pilot testing, as well as strict quality control for injected materials, is typically required. Oxidation products are usually (but not always) less toxic, more mobile and more biodegradable than parent compounds. For example, MTBE may degrade into acetone or tert butyl formate. Petroleum hydrocarbons may generate acetone or alcohols. Explosives (RDX and HMX) may create elevated levels of nitrate.
High levels of manganese oxides residue (MnO2) in soils can be an issue in some jurisdictions where manganese generic criteria for soils exist.
Application examples of chemical oxidation with permanganate are available in the following documents:
In situ permanganate oxidation is a well-proven technology that allows relatively quick treatment (from one to three years).
The long persistence of permanganate in the subsurface allows a better distribution of the oxidant, as compared to less persistent oxidants, especially in low-permeability soil.
According to the FRTR (2002), in situ chemical oxidation techniques can achieve high treatment efficiency (for example >90 percent) for unsaturated chlorinated aliphatic (such as trichloroethylene [TCE]) with very fast reaction rates (90 percent destruction in minutes).
Measures to improve sustainability of the technology
Unavailable for this fact sheet
Composed by : Josée Thibodeau, M.Sc, National Research Council
Updated by : Karine Drouin, M.Sc., National Research Council
Updated Date : March 1, 2009
Latest update provided by : Marianne Brien, P.Eng., Christian Gosselin, P.Eng., M.Eng., Golder Associés Ltée
Updated Date : March 22, 2019
