Cyanides
What are Cyanides ?
Cyanides are chemical compounds containing the cyano group (-C≡N), consisting of a carbon atom triple-bonded to a nitrogen atom. They occur in several forms, including free cyanide (HCN, CN⁻), simple cyanide salts (NaCN, KCN), and metal-cyanide complexes such as ferrocyanides and ferricyanides.
Cyanide contamination is commonly associated with:
- Mining and metallurgical operations
- Electroplating facilities
- Chemical manufacturing
- Manufactured Gas Plants (MGPs)
- Coke oven operations
- Former industrial waste disposal sites
Because of their acute toxicity and mobility under certain environmental conditions, cyanides can pose significant risks to human health, groundwater resources, and ecological receptors.
Why are cyanides a concern?
Cyanides are among the most acutely toxic contaminants found in industrial soils.
Potential impacts include:
💨 Toxicity through inhalation of hydrogen cyanide (HCN)
💧 Groundwater contamination
🌱 Toxicity to plants and microorganisms
⚠️ Risks to human health and ecosystems
🏭 Long-term industrial site liabilities
The behavior of cyanides depends strongly on pH, temperature and the presence of metals such as iron, copper and zinc. Under certain conditions, stable cyanide complexes can release free cyanide and hydrogen cyanide gas.
Remediation Strategies - State of the Art
Several technologies have been developed to treat cyanide-contaminated soils.
| Technology | Cyanide Removal | Speed | Long-Term Liability | Main Limitations |
| Excavation & Disposal | 🟠 Partial | 🟢 Fast | 🔴 High | Transfers contamination elsewhere |
| Chemical Oxidation | 🟠 Partial | 🟠 Medium | 🟠 Medium | Often ineffective on complex cyanides |
| Bioremediation | 🟠 Partial | 🔴 Slow | 🟠 Medium | Limited for stable complexes |
| Soil Washing | 🟠 Partial | 🟠 Medium | 🟠 Medium | Generates secondary waste streams |
| Containment | 🔴 No | 🟢 Fast | 🔴 High | Contamination remains on site |
| Thermal Desorption | 🟢 Yes | 🟢 Fast | 🟢 Low | Requires vapor treatment systems |
Research has shown that thermal treatment is one of the most effective technologies for destroying both free cyanides and stable iron-cyanide complexes. Complete cyanide removal was observed at temperatures above 300–450°C depending on cyanide speciation.
Thermal Desorption with Haemers Technologies
Thermal desorption is particularly effective for industrial source zones contaminated with stable cyanide complexes.
The effectiveness of thermal remediation relies on the unique properties of cyanide compounds.
Typical removal efficiencies often exceed 95–99%, depending on contaminant type and treatment conditions.
Soil targeted temperature at cold point is fixed between 100°C to 400°C in function of the product.
🔥 1. Controlled Heating
The soil is heated uniformly through thermal conduction.
Treatment temperatures are adapted to the cyanide species present on site.
🌡️ 2. Hydrocarbons Becomes Volatile
As temperature increases, cyanide compounds dissociate and convert into volatile forms, primarily hydrogen cyanide (HCN).
The volatility of HCN allows efficient recovery through vacuum extraction systems.
💨 3. Vapor Extraction Under Vacuum
A dedicated vacuum extraction network continuously captures:
✓ Hydrogen cyanide (HCN)
✓ Volatile contaminants
✓ Process vapors
This ensures full containment throughout the treatment process.
🧪 4. Reburn Technologie
For sites containing cyanides and hydrocarbons, Haemers can use its proprietary Re-Burn Technology.
Extracted vapors are reinjected into the heating system and destroyed at temperatures exceeding 800°C, while simultaneously generating useful thermal energy.
For more complex sites containing mercury, chlorinated compounds or mixed contaminants, a dedicated Vapor Treatment Unit (VTU) is installed.
Key Benefits
🎯 Permanent Source Removal
Cyanides are removed from the soil rather than contained or transferred.
📈 Effective on Complex Cyanides
Treats both free cyanides and stable ferrocyanide/ferricyanide compounds.
⚡ Fast Remediation
Treatment is completed within weeks rather than years of monitoring or biological treatment.
🛡️ Reduced Long-Term Liability
Eliminates persistent contamination sources and minimizes future risks.
🏭 Ideal for Industrial Brownfields
Applicable to MGP sites, metallurgical facilities, electroplating plants and mining operations.