Gold Recovery
Gold Recovery Carbon Reactivation: Kiln Specs, Cycle Life & When to Replace
Reactivation extends carbon life 50–100 cycles — but only if your kiln is dialed in. Here's the complete spec sheet for getting it right.
Why Reactivation Is Critical to Gold Recovery Economics
Fresh gold recovery carbon costs $2,500–$3,500/ton. A typical CIP/CIL circuit holds 20–50 tons of carbon. That's $50K–$175K of carbon inventory that degrades with every adsorption-elution cycle unless you reactivate properly.
Thermal reactivation at 650–750°C burns off organic fouling, restores pore structure, and returns carbon to 90–95% of original capacity. Done right, you replace only 3–5% of your inventory per month instead of 100%.
Reactivation Kiln Specifications
| Parameter | Optimal Range | Consequence If Wrong |
|---|---|---|
| Temperature | 650–750°C | <600°C: organics not removed; >800°C: pore collapse + excess burn-off |
| Residence time | 15–30 min | Too short: incomplete reactivation; too long: mass loss |
| Atmosphere | Steam + limited O₂ | Excess O₂: uncontrolled combustion; no steam: surface oxidation |
| Kiln type | Rotary or vertical tube | Rotary preferred for uniform heat; vertical for smaller operations |
| Feed moisture | <5% (pre-dried) | Wet carbon causes thermal shock and cracking |
| Cooling | Quench in water or indirect | Air cooling causes re-oxidation and capacity loss |
Cycle Life: What Determines How Long Carbon Lasts
Three factors control the number of useful reactivation cycles:
- Initial hardness — 97%+ ball-pan carbon lasts 80–100 cycles; 95% carbon lasts 30–50 cycles
- Kiln temperature control — ±25°C deviation can cut cycle life by 30%
- Ore type — preg-robbing ores and high-calcium waters cause faster fouling and more aggressive reactivation needed
Typical Capacity Decay Curve
| Cycle Count | Iodine Number Retention | Gold Loading Capacity | Mass Remaining |
|---|---|---|---|
| Fresh | 100% | 100% (15–25 kg Au/ton) | 100% |
| After 10 cycles | 92–95% | 90–95% | 85–90% |
| After 25 cycles | 85–90% | 80–90% | 70–80% |
| After 50 cycles | 75–85% | 70–80% | 55–70% |
| After 75 cycles | 65–75% | 60–70% | 45–60% |
| Replace threshold | <75% (iodine <800) | <65% | <50% |
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Carbon Loss: Where Your Carbon Goes
| Loss Source | % of Total Loss | Mitigation |
|---|---|---|
| Attrition (fines through screens) | 50–60% | Higher hardness (≥97%), gentle pumping, proper screen maintenance |
| Kiln burn-off | 20–30% | Temperature control ±25°C, steam atmosphere, proper residence time |
| Screen losses (hole wear) | 10–20% | Regular screen inspection, correct aperture (0.8mm for 6×12) |
| Handling spillage | 5–10% | Enclosed transfer systems, spillage recovery |
Industry benchmark: 30–50 g/ton ore for high-quality carbon (97%+ hardness); 80–100 g/ton for standard grades. At $3,000/ton carbon cost:
- Premium carbon: $0.09–$0.15 per ton of ore
- Standard carbon: $0.24–$0.30 per ton of ore
The premium carbon costs 20% more upfront but saves 40–60% on make-up — pays back within 3 months on a 1,000 tpd operation.
When to Replace vs Continue Reactivating
Replace your carbon inventory (or a portion) when:
- Iodine number drops below 800 mg/g after reactivation
- Ball-pan hardness falls below 90%
- Gold loading rate in the plant drops >20% vs fresh carbon baseline
- Gold-in-solution tails increase despite normal circuit operation
- Carbon fines generation exceeds 5% per cycle
Pro tip: Don't replace all at once. Blend 20–30% fresh carbon with aged carbon each quarter. This maintains consistent performance while amortizing replacement cost.
Our Carbon: Built for Long Reactivation Life
| Specification | GRC Premium | Industry Standard |
|---|---|---|
| Hardness (ball-pan) | ≥97% | ≥95% |
| Iodine number | ≥1050 mg/g | ≥1000 mg/g |
| Ash content | <3% | <5% |
| Expected cycle life | 80–100 cycles | 30–50 cycles |
| Make-up rate | 30–50 g/ton | 80–100 g/ton |
Related Resources
Frequently Asked Questions
How many reactivation cycles can gold carbon withstand?
High-quality coconut shell carbon (hardness >97%) withstands 50–100+ cycles. Standard grade (95% hardness) typically lasts 30–60 cycles. Each cycle loses 3–5% mass and 1–2% iodine number. Replace when iodine drops below 800 mg/g or hardness below 90%.
What temperature is used for gold carbon reactivation?
650–750°C in a rotary kiln with 15–30 minutes residence time under steam or limited oxygen atmosphere. Below 600°C won't fully burn off organics. Above 800°C causes excessive burn-off and pore collapse. Target: 700°C ± 25°C for optimal balance.
What is the typical carbon make-up rate in gold mining?
30–100 grams of fresh carbon per ton of ore processed. Losses come from: attrition/fines (50–60%), kiln burn-off (20–30%), and screen losses (10–20%). Higher-hardness carbon (>97%) can reduce make-up to 30–50 g/ton vs 80–100 g/ton for standard grades.
Can reactivated carbon perform as well as fresh carbon?
After proper reactivation, carbon recovers 90–95% of original gold loading capacity. The remaining 5–10% loss is permanent (collapsed micropores). After 50 cycles, cumulative capacity is typically 70–80% of fresh. Still economical vs buying fresh at $2,500–3,500/ton.