Once the sodium cyanide molecules have done their important job of lixiviating the gold or silver from the ore, some level of residual cyanide will remain in the mine’s effluent and tailings.  At Cyanco we have developed a number of proprietary technologies to help destroy and detoxify this residual cyanide and offer these technologies to our customers to keep their operations safe and compliant.

Phase 1 Detoxification

Initial test work to assess the most suitable process based on operating and capital costs between technologies

  • Hydrogen Peroxide Based Processes
  • Caro’s Acid
  • SO2/Air
  • CombinOx®
  • Many other processes can also be considered (e.g. Cl2)

Phase 2 Detoxification

Using the data from Phase 1 work, Cyanco can also provide a Phase 2 Treatment Circuit Design Package, which includes:

  • Process design criteria
  • Capital and operating cost estimates
  • Reagent design criteria
  • General mechanical, electrical, and instrumentation specifications

Circuit Design Study also available for existing circuits, including:

  • Estimated reagent requirement & handling systems
  • Equipment list for preliminary capital estimates
  • Engineering Review
  • Review of existing cyanide destruction circuits or designs

Phase 3 Detoxification

Cyanco can also assist with the commissioning and start-up of detoxification plant with training. Our on-site start-up package includes any or all of the following:

  •  Review of circuit design
  • Review or preparation of SOP’s for circuit operation
  • Reagent mixing systems, dosing rates and addition points
  • Assistance with data collection and circuit management
  • Laboratory set-up including procurement, equipment and reagents
  • Analytical procedures
  • Process control
  • Operator training, Lab personnel training and safety training

Phase 4 Detoxification

Cyanco also provides long term servicing of the treatment circuit and related equipment. On-site service after start-up includes:

  • Review of circuit data
  • Assist with circuit optimization and management
  • Provide assistance to react to changing conditions
  • Refresher training on safety, process, equipment and laboratory
  • Assistance with emergency situations
  • Process recommendations
  • Circuit and Process upgrades

Metal/Metalloid Precipitation

Cyanco has extensive experience with the precipitation of heavy metals, such as copper, mercury and lead.  Mine effluents often contain these metals, which may need to be removed prior to discharge to the environment.

metal precip 1

After cyanide destruction, most of the metals are precipitated as metal hydroxides.  However, other metal precipitation agents, may need to be used. Cyanco will conduct a comprehensive assessment of each customer’s process and recommend an appropriate solution.


With current regulations and industrial standards, like those from the EU and ICMI, requiring industries to monitor cyanide concentration in the effluents in terms of “Weak Acid Dissociable Cyanide” (CNWAD), new methodologies must be considered beyond the standard “Free Cyanide” (CNF) titrations that are commonly used for analysis and control. In order to accomplish this, Cyanco developed the Oxitrol® on-line CNWAD analyzer to accurately measure CNWAD concentration in a treatment circuit, and allow for control of the reagents addition required for cyanide detoxification of the effluents.
The Cyanco Oxitrol® patented analytical system can measure and monitor the cyanide ion, CN- , and the cyanide complexes of Cu, Ni, Zn, Cd, Ag, among other species that collectively are referred to as Weak Acid Dissociable Cyanide (CNWAD).

Cyanco will install the Oxitrol® unit and train all personnel, with refresher training available upon request of customer. All units are designed and built based on each customer’s application.

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Benefits of the Cyanco Oxitrol® unit:

  • The Oxitrol® can precisely analyze CNWAD in the effluent samples before or after treatment.
  • Quick, accurate and repeatable analytical results are produced.
  • It is possible to use the system on slurry samples with the included filtration system.
  • This system results can be used as part of a reagent addition control strategy for cyanide detoxification, thereby reducing treatment costs by avoiding overdosing.
  • The system monitors the effluent treatment circuit to ensure compliance with treatment regulations, such as the International Cyanide Management Code and other regulations.
  • The system minimizes the need for manual sample analyses thereby reducing turn-around times. This further contributes to the potential savings by reducing manpower costs.

Caro’s Acid

Cyanco will custom design a generator using our conventional Cyanco “Hot” Caro’s acid
generator or our Cyanco High Yield “Cold” Caro’s acid generator. The “Hot” and “Cold” technologies differ by the amount of H2SO5 yielded from the reactants, and is effected by controlling the temperature during and after the reaction. The “Cold” generator produces a higher concentration H2SO5 solution than the “Hot” generator. Depending on the customer’s process, either a “Hot” or “Cold” Caro’s acid generator will be recommended by Cyanco.

Advantages of using Caro’s acid

  • Caro’s acid works extremely well for destroying cyanide in slurries.
  • Typically no additional catalyst is required
  • The reaction between cyanide and H2SO5 is very quick, in most cases, which eliminates the
    need for large costly reaction vessels.
  • Both feedstock materials, sulfuric acid and peroxide, are readily available worldwide.