Activated Carbon for Gold Elution & Desorption
High-hardness coconut shell carbon that survives repeated high-temperature stripping in Zadra and AARL elution circuits — low attrition, stable gold loading cycle after cycle.
The Elution Stage
Why elution decides your carbon cost
After gold-bearing carbon leaves the CIP/CIL adsorption circuit, the loaded carbon is stripped in an elution column — the gold-cyanide complex is desorbed into a hot caustic-cyanide eluate, then recovered by electrowinning. This is the harshest duty an activated carbon endures: repeated cycles of hot alkaline solution, acid washing and thermal reactivation. Soft or low-quality carbon fractures under this stress, generating fines that carry gold to tailings and drive up make-up carbon cost. Elution performance therefore depends less on adsorption capacity and more on mechanical durability — hardness, abrasion resistance and the ability to be reactivated hundreds of times without collapsing.
How Elution Works
From loaded carbon to pregnant eluate
Loaded carbon is acid-washed (dilute HCl) to dissolve carbonate scale and inorganic foulants, restoring the pore network before stripping so the eluate runs cleanly.
Carbon is contacted with a hot caustic-cyanide solution. Elevated temperature reverses the adsorption equilibrium, releasing the Au(CN)2− complex into a concentrated pregnant eluate for electrowinning.
Stripped (barren) carbon is thermally reactivated in a kiln at ~650–750°C to restore activity, screened to remove fines, and returned to the adsorption circuit.
Zadra vs AARL
Elution process comparison
The two dominant elution methods place different demands on the carbon. Both reward high hardness, but AARL's pre-soak/higher-pressure cycle is especially punishing on soft grades.
| Parameter | Zadra (atmospheric / pressure) | AARL (Anglo American) |
|---|---|---|
| Reagents | Hot caustic-cyanide, recirculated | Acid wash → pre-soak (caustic-cyanide) → hot water elution |
| Temperature | ~90–110°C atmospheric; up to ~135°C pressurised | ~110–135°C, elevated pressure |
| Cycle time | Longer (8–60 h, recirculating) | Shorter, single-pass (≈10–14 h) |
| Eluate | Combined with electrowinning loop | Clean, concentrated single-pass eluate |
| Carbon demand | High hardness to resist recirculation attrition | Very high hardness — pre-soak + pressure stress fines badly |
Carbon Selection
Choosing carbon for the elution circuit
For elution and desorption duty, prioritise mechanical durability and reactivation stability over raw iodine number. Our coconut shell grades are graded specifically for CIP/CIL/elution circuits.
| Grade | Mesh | Hardness | Best for |
|---|---|---|---|
| Coconut GC 6×12 | 6×12 | ≥98% | Standard elution / ADR columns — low pressure drop, easy screening |
| Coconut GC 8×16 | 8×16 | ≥98% | Finer circuits needing faster kinetics with strong retention |
| Reactivation grade | 6×12 | ≥98% | Operations running frequent thermal reactivation cycles |
| High-activity 1050 | 6×12 | ≥97% | High gold loading where adsorption capacity is also critical |
Not sure which hardness grade fits your circuit? Send us your elution method and batch size.
Get a Grade RecommendationCircuit Design
Elution & ADR design factors
Column sizing & flow
Elution columns are sized to the carbon batch (typically 2–8 t). Uniform 6×12 sizing keeps pressure drop predictable and prevents channelling during the hot strip.
Acid wash integration
An in-line or separate acid-wash vessel removes carbonate and iron scale before elution. Clean carbon strips faster and produces a cleaner eluate for electrowinning.
Reactivation kiln
Thermal reactivation at 650–750°C restores 90%+ of original activity. Hard carbon tolerates repeated kiln passes; soft carbon burns off as fines and inflates make-up cost.
Fines & make-up control
Screening after each cycle removes attrition fines. High-hardness carbon minimises fines generation — the single biggest driver of annual carbon spend and gold-to-tailings loss.
Field Performance
Proven in African gold operations
Case: 56-tonne coconut carbon shipment to Ethiopia gold recovery
An Ethiopian gold producer running a CIL + Zadra elution circuit sourced 56 tonnes of our 6×12 coconut shell carbon after attrition losses on their previous supplier drove up make-up carbon cost. Batch COA confirmed hardness ≥98% and iodine ≥1000 mg/g. The high-hardness carbon reduced fines generation across strip and reactivation cycles, stabilising the barren-carbon return rate. Loading, dimension and moisture checks were documented pre-shipment.
Gold Elution — Frequently Asked Questions
What is the difference between Zadra and AARL elution?
Zadra recirculates a hot caustic-cyanide solution through the carbon (often combined with the electrowinning loop) and can run atmospheric or pressurised. AARL is a single-pass sequence — acid wash, then a caustic-cyanide pre-soak, then hot-water elution at elevated pressure — giving a cleaner, more concentrated eluate in a shorter cycle. Both need high-hardness carbon; AARL's pre-soak and pressure make hardness even more critical.
Why does carbon hardness matter so much in elution?
Elution and reactivation subject carbon to repeated hot alkaline solution, acid washing and ~700°C kiln passes. Soft carbon fractures under this stress, creating fines that (1) carry adsorbed gold to tailings as loss and (2) must be replaced as make-up carbon. Ball-pan hardness ≥98% minimises attrition and is the key spec for elution-circuit carbon.
What temperature is used for elution?
Atmospheric Zadra runs around 90–110°C; pressurised Zadra and AARL run roughly 110–135°C under elevated pressure to accelerate desorption and shorten cycle time.
Can your carbon be reactivated repeatedly?
Yes. Our coconut shell grades are engineered for repeated thermal reactivation at 650–750°C, recovering 90%+ of original activity per cycle. High hardness is what allows carbon to survive many strip-reactivation cycles before it must be replaced.
Which mesh size do you recommend for elution columns?
6×12 is the standard choice for most elution and ADR columns — it balances kinetics, retention and low pressure drop, and screens cleanly after each cycle. 8×16 is available for circuits needing faster kinetics.
What is your MOQ and lead time for gold-recovery carbon?
MOQ is 1 tonne with a typical 7–15 day lead time. We ship worldwide to major gold-mining regions and provide a batch COA (hardness, iodine number, mesh, moisture) with every order.
Cut your make-up carbon cost
Send us your elution method (Zadra or AARL), batch size and current attrition rate. We'll recommend the right hardness grade and mesh, with a batch COA on every shipment.
Request a Gold Carbon Quote