Cyanide Compounds
Real destruction process setpoints, safety hazards, and the surprising truth about material compatibility.
Cyanide salts are comparatively easy on standard equipment materials — broadly resistant across PVC, CPVC, HDPE, PP, PVDF, PTFE, FKM, EPDM, FEP, and PFA. The real engineering challenge isn't material compatibility, it's the destruction process chemistry: precise pH/ORP setpoints, correct staging, and a real toxic-gas release hazard if the process is run incorrectly. This is used in plating, chemical milling, and several other named industrial processes and requires vendor-published process control, not general chemical handling caution.
Real Process Control Setpoints
Stage 1 — Cyanide to Cyanate: pH raised to 11.5 using sodium hydroxide, then chlorine added until ORP reaches +450mV.
Stage 2 — Cyanate to Carbonate: the same tank neutralized with acid plus a small amount of chlorine.
Both stages are monitored to a 9.5 pH / 450mV oxidation target. This two-stage method is the nationally preferred treatment approach; some jurisdictions accept single-stage (batch) treatment instead.
Where This Goes Wrong
Batch method: acid injection must be manually locked out to prevent pH from dropping below pH 11 during the destruct stage — below roughly pH 11, oxidation cannot properly break down cyanide to cyanate.
Two-step method: pH must be adjusted rapidly in Stage 1 specifically to avoid releasing extremely toxic cyanogen chloride gas. This is a real, named gas-release hazard, not general chemical caution.
Named Cyanide-Generating Processes
The Same Destruction Chemistry, a Different Source
Gold and silver heap leaching uses a cyanide solution to dissolve the target metal from ore — a different source than plating/finishing wastewater, but the barren cyanide solution leaving the circuit requires the same two-stage pH/ORP-controlled destruction process described above before discharge. Real, confirmed equipment for the full leach circuit — irrigation, collection, and destruction — is covered on the Hydrometallurgy Equipment page.
Frequently Asked Questions
Is cyanide itself hard on equipment materials?
No — this is a genuinely counterintuitive finding. Cyanide salts (potassium cyanide, zinc cyanide) are comparatively easy chemicals for standard plastic and elastomer piping/valve materials to handle — real data shows PVC, CPVC, HDPE, PP, PVDF, PTFE, FKM, EPDM, FEP, and PFA all resistant through 140-176°F for saturated potassium cyanide. The real engineering challenge in cyanide systems is the destruction process chemistry, not simple storage/transport material compatibility.
What is the two-stage cyanide destruction process?
Stage 1 converts cyanide to cyanate: pH raised to 11.5 using sodium hydroxide, then chlorine added until ORP reaches +450mV. Stage 2 converts cyanate to carbonate: the same tank is neutralized with acid plus a small amount of chlorine. Both stages are monitored to a 9.5 pH / 450mV oxidation target. This two-stage method is the nationally preferred treatment approach; some jurisdictions accept single-stage batch treatment instead.
What is the real safety hazard in cyanide destruction systems?
Two distinct hazards by method. Batch method: acid injection must be manually locked out to prevent pH from dropping below 11 during the destruct stage — below roughly pH 11, oxidation cannot properly break down cyanide to cyanate. Two-step method: pH must be adjusted rapidly in Stage 1 specifically to avoid releasing extremely toxic cyanogen chloride gas. These are real, vendor-published process control hazards, not general caution.
What industrial processes generate cyanide-bearing wastewater?
Plating of copper, brass, gold, and zinc; conversion coatings; chemical milling; barrel finishing; burnishing; heat treating; and electrochemical machining — all named real processes that generate cyanide-bearing wastewater requiring a destruction system before discharge.
Does gold/silver heap leach mining use the same cyanide destruction process as plating wastewater?
Yes — the barren cyanide solution leaving a gold or silver heap leach circuit requires the same two-stage pH/ORP-controlled destruction process (pH to 11.5, chlorine to +450mV ORP, then neutralization) described above. The cyanide source differs — ore leaching vs. plating/finishing wastewater — but the destruction chemistry and the cyanogen chloride gas hazard during pH adjustment are the same.
Designing or auditing a cyanide destruction system?
Send LibertyCES your process flow, loading rate, and current control setup — instrumentation and control design matter more than material selection here.
Ready to buy or need a fast answer? Call, text, or email James directly — (559) 395-5500 · james@libertyces.com.