Heap-Leach Cyanide Solution Storage & Tank Compatibility

Storing Heap-Leach Cyanide Solution? Start Here

Heap-leach cyanide solution is the working fluid of conventional gold and silver heap-leach operations. It is not a single compound but a dilute alkaline process stream: water carrying roughly 500–1,000 ppm of sodium cyanide (NaCN), with lime (CaO) or caustic soda (NaOH) added to hold the pH at 10–11. Solution sprayed onto the ore heap (barren solution) percolates through, dissolves precious metals as cyanide complexes, and drains off the pad as gold-bearing “pregnant” solution for recovery, after which it is recycled.

Because the fluid is mostly water at high pH, its material-of-construction behavior is mild — standard polyethylene and FRP tanks are the industry norm. The governing design concerns are therefore toxicity and containment rather than chemical attack: the solution must never contact acid (which liberates hydrogen cyanide gas), and copper or aluminum must be excluded from wetted paths. Composition, pH and toxicity all vary by site, so always defer to the project SDS.

Is Polyethylene (HDPE / XLPE) Suitable for Heap-Leach Cyanide Solution?

Yes — polyethylene is a suitable and widely used material for storing dilute alkaline cyanide leach solution. Sodium cyanide solutions rate as satisfactory/resistant on HDPE and XLPE at both ambient and elevated service temperatures, and the alkaline, water-based matrix (pH 10–11) poses no chemical challenge to polyethylene. Crosslinked polyethylene (XLPE) and HDPE tanks are routinely deployed for barren and pregnant solution storage, process water, and lime/caustic make-up around heap-leach pads.

The cautions are operational, not chemical: PE tanks must be fitted with sealed, vented containment to manage cyanide toxicity; the solution must be kept alkaline and isolated from any acidic stream (an acid mix-up generates lethal HCN gas); and fittings/gaskets should avoid copper-bearing alloys. Confirm specific gravity, temperature, and concentration against the SDS when sizing the tank.

Material compatibility at a glance

Heap-leach cyanide solution is a dilute, alkaline (pH 10–11) aqueous stream, so the dominant compatibility driver is the water/alkaline matrix — not an aggressive solvent or oxidizer. Polyethylene (HDPE/XLPE), polypropylene, FRP and 316 stainless all serve well. The real engineering constraints are toxicity containment (no acid contact, no HCN release) and keeping copper/aluminum out of wetted paths. Carbon steel works only while alkalinity is maintained.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

• Acutely toxic by all routes — cyanide is fatal if swallowed, inhaled, or absorbed through skin; treat even dilute solution as life-threatening (H300/H310/H330).
• Never mix with acid — contact with any acid liberates hydrogen cyanide gas (EUH032); keep acidic chemicals physically segregated from all cyanide service.
• Maintain alkalinity (pH ≥10.5) — pH drift toward neutral/acidic releases HCN; monitor and dose lime/caustic continuously.
• Severe aquatic hazard — very toxic to aquatic life (H410); secondary containment, lined pads, and spill control are mandatory.
• Cyanide antidote and gas detection — provide HCN monitoring, emergency response procedures, and trained personnel; do not enter confined spaces without testing.
• PPE — chemical-resistant gloves, splash goggles/face shield, and respiratory protection where mist or HCN evolution is possible.

Common questions

What is heap-leach cyanide solution made of?

It is mostly water carrying a low concentration of sodium cyanide (typically ~500–1,000 ppm), with lime or caustic soda added to hold the pH at 10–11. ‘Pregnant’ solution also contains dissolved gold/silver cyanide complexes; ‘barren’ solution is the recycled, metal-depleted stream.

Can I store heap-leach cyanide solution in a polyethylene tank?

Yes. Sodium cyanide solutions are rated satisfactory/resistant on HDPE and XLPE, and the alkaline aqueous matrix is benign to polyethylene. PE and FRP tanks are the industry standard. The critical requirements are toxicity containment, sealed/vented design, and keeping the solution away from acids.

Why must the solution be kept alkaline?

Cyanide stays as the relatively stable cyanide ion only at high pH. If the pH drops toward neutral or acidic, it converts to and releases hydrogen cyanide (HCN) — a rapidly lethal gas. Operations hold pH at or above about 10.5 specifically to suppress HCN evolution.

What materials should be avoided for cyanide leach service?

Avoid copper and copper alloys (cyanide dissolves copper) and aluminum (attacked by the alkaline solution). Carbon steel is acceptable only while alkalinity is maintained and is often lined. Above all, never allow acid contact, which generates toxic HCN gas.