SMBS for Gold Cyanide Destruction: Dosage, Handling & Export Specs

Sodium metabisulphite (SMBS, Na₂S₂O₅) is one of the most widely used reagents for cyanide destruction in gold and silver processing. As leached tailings move to the detox circuit, residual free and WAD (weak-acid-dissociable) cyanide must be reduced to environmentally compliant levels before discharge - and SMBS, often paired with a copper catalyst and air, is the workhorse chemistry for the SO₂/air (Inco) process.

Why SMBS over liquid SO₂

For most African mine sites, importing and storing liquid SO₂ is impractical. SMBS is a stable, free-flowing powder that releases SO₂ in solution on demand, making it far easier to ship in 25 kg bags or jumbo bags, store in a warehouse, and dose with standard equipment. This logistical simplicity is why SMBS dominates demand across Tanzania, Zambia, DRC, and Ghana.

Typical dosage

Dosage depends on the cyanide load, but a common starting point is roughly 2.5–5 kg of SMBS per kg of cyanide to be destroyed, optimised on site through bench testing. The reaction is catalysed by copper (often added as copper sulphate) and requires controlled aeration and pH (around 8–9) for efficient oxidation of cyanide to cyanate.

What to specify when importing

For metallurgical use, specify technical-grade SMBS at 96.5% min purity with an SO₂ content of 64% min. Always request a manufacturer Certificate of Analysis (COA) per batch, plus MSDS and IMDG documentation for ocean freight. Jaydev Multicomm supplies GACL/Kutch-origin SMBS with full export documentation, CIF to Mombasa, Dar es Salaam, and Beira.