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Most mining legislation states that cyanide-rich plant tailings must be oxidized before being deposited into tailing ponds. An operational flowsheet using a proven treatment technology is required by most financial institutions prior to investment.


SGS is a world leader in technology relating to all aspects of cyanide use in gold recovery, including the SO2 (sulfur dioxide) air process for cyanide destruction.

SGS offers a number of cyanide destruction processes. The SO2 air process is relatively simple and invariably cost-effective. During the process, sulfite ions react with atmospheric oxygen and a copper catalyst as follows:

2CN-  +  Na2S2O5  +  2O2  +  2OH-  -->  2CNO-  + Na2SO4  +  SO42- +  H2O

The SO2 process offers a number of advantages over other cyanide destruction methods including:

  • Low reagent cost
  • Efficient oxidization of CN WAD  (weak-acid dissociable cyanide)
  • The possibility of using sulfite salts and zinc sulfate during the process

SGS can review your flowsheet at both the batch and pilot scale and assess if the SO2 air process is appropriate for your project or mine. The batch test allows our metallurgists to carefully monitor the CNWAD concentrations and establish the target conditions (catalyst, oxygen, redox potential) for continuous pilot testing. Data from these is used to design a flowsheet and set parameters resulting in compliant cyanide concentrations in your tailings at the lowest possible cost. Our pilot testing will demonstrate this for all stakeholders.

SGS has the robust technology and technical expertise to provide you with bankable and effective cyanide management at every stage of your gold recovery operation. Contact us early in the planning stages of your project to learn if the SO2 air process is the best solution for destroying the cyanide used in your operations.