24/09/2026
Specific Effects of Zinc-Bearing Minerals on Cyanidation Gold Extraction
1. Significant consumption of cyanide reagents (the primary impact)
- **Zinc sulfide minerals (Sphalerite, ZnS)**: These react in the cyanide solution to form zinc-cyanide complexes (e.g., $\boldsymbol{Na_2[Zn(CN)_4]}$) while releasing sulfide ions. These sulfide ions undergo further oxidation to form intermediate products such as thiosulfates and sulfates, continuously consuming free cyanide ions and dissolved oxygen in the pulp.
Reaction: $\boldsymbol{ZnS + 4NaCN = Na_2[Zn(CN)_4]+Na_2S}$
- **Zinc oxide minerals (Smithsonite, $\boldsymbol{ZnCO_3}$; Zincite, $\boldsymbol{ZnO}$)**: These react more rapidly with cyanide, also forming zinc-cyanide complexes. They directly consume sodium cyanide, significantly driving up reagent costs.
Reaction: $\boldsymbol{ZnCO_3+4NaCN=Na_2[Zn(CN)_4]+Na_2CO_3}$
Once zinc binds with cyanide ions, that portion of cyanide converts into complexed zinc-cyanide species and **is no longer effective free cyanide capable of leaching gold**. Even if titration indicates "residual cyanide," the actual gold-leaching capacity is reduced, which can easily lead to misinterpretation of the process status.
2. Consumption of dissolved oxygen in the pulp, inhibiting gold dissolution
Oxygen is essential for the cyanidation leaching of gold. Sulfides released during the dissolution of sphalerite undergo continuous oxidation in the pulp (S²⁻ → thiosulfate → sulfate); this process rapidly depletes the oxygen available in the pulp, creating an oxygen-deficient environment. Insufficient oxygen directly slows the dissolution rate of gold particles and reduces the gold leaching efficiency. 3. Deterioration of the solution system and interference with subsequent cementation/carbon adsorption stages
- Zinc-cyanide complex ions accumulate in the solution, leading to increased pulp viscosity and ionic strength;
- Zinc ions interfere with gold recovery via zinc dust cementation, increasing zinc consumption and compromising gold sludge quality; in carbon-in-leach (CIL) processes, zinc complexes compete for adsorption sites on activated carbon, thereby reducing the gold-loading capacity of the carbon.
4. Overall production consequences
1. Specific consumption of sodium cyanide rises significantly, increasing production costs;
2. At the same cyanide dosage, the **gold leaching rate decreases**;
3. Zinc salts accumulate in the solution, causing the quality of recycled barren cyanide solution to deteriorate; prolonged recycling leads to a continuous decline in leaching performance.
Production response strategies (integrated approach)
When dealing with zinc-bearing gold ore, direct cyanidation should not be employed; **beneficiation testing is mandatory**:
Prioritize flotation to pre-separate and remove zinc minerals (such as sphalerite), thereby reducing the zinc content of the ore fed to the leaching circuit; subsequently, proceed with cyanidation to eliminate zinc-related interference.
