Comparing Potassium and Sodium Permanganate for In Situ Chemical Oxidation

In situ chemical oxidation (ISCO) is a popular remediation technique for cleaning up contaminated groundwater and soil. The process involves introducing oxidizing agents directly into the subsurface to destroy organic contaminants such as solvents, fuels, and pesticides. Two common ISCO oxidants are potassium permanganate (KMnO4) and sodium permanganate (NaMnO4). Both effectively oxidize a wide range of contaminants, but they have some key differences that impact their suitability for specific remediation projects.

Overview of Potassium and Sodium Permanganate

Potassium permanganate (KMnO4) and sodium permanganate (NaMnO4) are inorganic compounds that serve as strong oxidizing agents. When dissolved in water, they produce permanganate ions (MnO4-), which drive the chemical oxidation reactions that break down contaminants.

Potassium permanganate is commercially available as a crystalline solid, while sodium permanganate is available as a liquid solution. Both forms contain permanganate as the active ingredient. The key advantages and disadvantages of each oxidant are summarized below:

Potassium Permanganate

Advantages:

  • Safer to handle and apply
  • Lower costs compared to sodium permanganate
  • Can be used at 6% concentration when heated above 65 degrees in proper conditions

Disadvantages:

  • Listed on DHS’s Chemical Facility Anti-Terrorism Standards (CFATS) program
  • Limited to maximum 5% solution concentration under normal circumstances

Sodium Permanganate

Advantages:

  • Provides a ready-to-use liquid product
  • Available in concentrations up to 40%
  • Avoids DHS CFATS restrictions

Disadvantages:

  • Higher material costs compared to potassium permanganate
  • Potential sodium issues in environment (e.g. sodium adsorption ratio concerns)
  • Greater health and safety risks 

Comparing Performance for ISCO

Both potassium and sodium permanganate are versatile and effective oxidants for a wide range of common groundwater and soil contaminants. These include:

  • Chlorinated solvents – PCE, TCE, DCE, VC
  • polyaromatic hydrocarbons
  • 1,4-dioxane
  • phenolic compounds
  • Various other organic contaminants

The oxidizing power, reactivity, and treatment mechanisms are similar between both permanganate forms when applied under comparable conditions. Key advantages of permanganate ISCO generally include:

  • Rapid degradation of contaminants
  • Active over a wide pH range
  • Persistence in the subsurface
  • Easy to monitor and trace
  • No activation required
  • Approved for potable water treatment

Sodium permanganate holds an advantage in that it can be purchased ready for injection at concentrations up to 40%. Potassium permanganate is limited to a 5% concentration before precipitation issues occur. However, a 5% potassium permanganate solution still provides sufficient oxidizing power for most sites. Potassium permanganate can be used at a 6% solution in careful conditions where the water is kept above 65% after blending. This is not widely feasible for most on-site injections, however it may be useful for certain applications. 

Higher concentrations may provide faster treatment, but potassium permanganate can achieve similar treatment results with proper application techniques. One advantage of the lower concentrations is that potassium permanganate produces less heat when reacting with contaminants.

Considerations for Remediation Project Design

Several factors should be evaluated when selecting between potassium and sodium permanganate for an ISCO project:

Site Contaminant Characteristics

  • Type of contaminants present
  • Concentrations of contaminants
  • Presence of co-contaminants that may interfere with oxidation

Site Geochemical Conditions

  • Soil types – fine-grained vs coarse-grained
  • Presence of natural organic matter
  • Groundwater pH, alkalinity, hardness

Delivery Logistics

  • Injection approach 
  • Volume of oxidant required
  • Site access limitations

Regulatory Requirements

  • Meeting cleanup standards for site
  • Avoiding secondary water quality impacts
  • Handling any security-related requirements

Cost Considerations

  • Chemical purchase costs
  • Shipping and handling costs
  • Injection equipment and staffing
  • Long-term monitoring requirements

Potassium permanganate may be preferred for smaller sites where container shipping and handling is easier. Sodium permanganate can be ideal for larger scale projects where the liquid bulk is more easily transported and injected, as well as limiting the amount of on-site mixing of potassium permanganate. 

Safety and regulatory requirements should also be reviewed. Consultation with an environmental consultant is recommended when evaluating the site conditions and selection of the optimal oxidant.

Conclusion

Both potassium and sodium permanganate are viable choices as chemical oxidants for in situ remediation of contaminated groundwater and soil. While sodium permanganate offers higher solution concentrations, potassium permanganate can also achieve effective treatment results through proper design and application.

Site-specific conditions should be evaluated to determine whether there are distinct advantages or disadvantages for using one permanganate form over the other. Safety, cost, ease of delivery, and regulatory factors should all play into the decision. With the right design and execution, both oxidants can successfully clean up challenging contaminated sites.