By the YELI Technical Team · Updated September 2026 · 8 min read
Short answer: For a gold mine in West Africa buying coconut shell activated carbon, the only spec evidence worth paying for is a batch COA with the test method named on every parameter — plus the right to re-test independently. Before releasing payment, demand five verifiable numbers — hardness ≥98% (ASTM D3802 / GB/T 12496.6), platelet content <1.5%, mesh 6×12 or 8×16, iodine 1000–1300 mg/g, and K-value / R-value per GB/T 32992—2016 — and build a small pre-shipment test into the contract.
The five numbers every gold carbon COA must carry — and what they should say
A useful COA for gold recovery carbon (CIP / CIL / CIC) is not a list of adjectives. It is five numbers, each with a named test method:
- Hardness ≥98% — GB/T 12496.6 / ASTM D3802 (ball-pan). Soft carbon sheds fines under flow and agitation, and fines carry adsorbed gold out of the circuit.
- Platelet content <1.5% — de-flaked, water-polished granules. Flat flakes channel a packed column and blind screens.
- Mesh 6×12 (1.70–3.35 mm) or 8×16 — GB/T 12496.2 / ASTM D2862, with the full sieve analysis, not just a nominal cut.
- Iodine value 1000–1300 mg/g — GB/T 12496.8 / ASTM D4607, consistent lot to lot.
- K-value / R-value (gold adsorption dynamics) — tested in our own QC laboratory per GB/T 32992—2016, with the result reported on the batch COA.
Moisture ≤5% and ash ≤5% complete the picture. If a supplier will not put these numbers — with methods — on the certificate of the actual lot you are buying, that is your answer before payment.
Why the COA, not the brochure, is the only number that matters
Most sourcing failures in gold carbon are verification failures, not quality failures. The brochure says "high hardness"; the delivered lot may not. The COA closes that gap — but only if it is the COA of your batch, not a sample from last year, and only if every method is stated. A number without a method cannot be compared: GB/T and ASTM variants do not always read identically, and a supplier who hides the method is hiding the comparison. Our production and testing follow the key requirements of YS/T 3038—2020 (Granular Activated Carbon for Gold Production), and every shipment carries a COA for that exact lot.
The two specs that protect you in a vat-leach CIC column: hardness and platelets
West African small- and mid-scale operations increasingly leach in vats, ponds or heaps, then recover gold from the clear pregnant solution through carbon-in-column (CIC) beds. The column changes what the carbon must survive:
- Fluid scouring. Solution flows through the packed bed at design flow for the life of the column. Soft carbon breaks down, and every fine it sheds carries adsorbed gold with it — out through the nozzle screens and into the elution tail or tailings. That is why hardness ≥98% (ASTM D3802) is the first number to check.
- Flake behaviour. Flat, platelet-shaped particles survive a sieve but behave badly in a bed: they orient across the flow, create channels where solution shortcuts past the carbon, raise pressure drop, and blind screens. Platelet content <1.5% is the quiet spec most buyers skip — and the one that shows whether the factory actually de-flakes its product.
The process that controls both is water-polishing / de-flaking: after activation the granules are de-dusted and water-rounded so they stay round in service. On a COA, ask that platelet content and fines be stated with the method, not left to a verbal "yes we de-flake".
K-value and R-value: the third-party test most buyers never ask for
Iodine value is a useful proxy for surface area, but it is not the number your circuit was built around. What decides loading and barren losses is how much gold the carbon actually takes up and how fast — measured as K-value (gold loading capacity, mg Au/g) and R-value (adsorption rate).
These are not brochure numbers. They are measured in our own QC laboratory per GB/T 32992—2016, and a factory confident in its product will supply the report alongside the batch COA. If you want proof on your own ore rather than a lab's standard solution, run a side-by-side bottle-roll test: same ore, same solution, same contact time, your carbon vs a reference carbon, then fire-assay the loaded carbon. That number — on your material — is the only one worth negotiating on.
A five-step pre-payment verification checklist
Before you release payment, run these five steps — each one is cheap compared with a bad container:
- Ask for the COA of the actual batch you are buying — not a sample COA, not a brochure range. Confirm it names the lot number and every test method.
- Check the methods. Iodine (GB/T 12496.8 / ASTM D4607), hardness (GB/T 12496.6 / ASTM D3802), sieve (GB/T 12496.2 / ASTM D2862). No method, no comparison.
- Request the test result for K-value / R-value per GB/T 32992—2016, supplied alongside the COA.
- Order a small sample pack — e.g. three grades at iodine 1000 / 1100 / 1200, each with its own COA — and run a bottle-roll or small column test on your own pregnant solution at your real flow and contact time.
- Verify the factory. A real carbon factory has kilns, a QC lab and a production address; a trading office has neither. Ask for a live video walk of the plant, and confirm the relationship between the export entity and the factory before volume orders.
If a supplier hesitates on any of the five, treat that hesitation as data.
Need Gold-Grade Carbon with a COA You Can Verify?
We produce coconut shell GAC for gold recovery at our own factory in Longyan, Fujian — 6×12/8×16 mesh, iodine 1000–1300, hardness ≥98%, platelet content <1.5%, COA with every batch, K/R results per GB/T 32992—2016 reported on the certificate. Tell us your circuit and target iodine — we will confirm a grade within 24 hours.
See Gold Carbon Specs →FAQ: Verifying Gold Recovery Carbon Before You Pay
Ask for the COA of the exact lot you are buying, with the test method named on every parameter, then re-test a retained sample at an independent laboratory (SGS, BV or an accredited lab) and compare the two reports. A genuine factory encourages re-testing; the certificate is tied to a lot number that should match your packing list.
Flat, flaky particles orient across the flow in a packed bed, creating channels where solution bypasses the carbon, raising pressure drop and blinding nozzle screens. De-flaked, water-polished granules with platelet content below 1.5% stay round, pack evenly and keep the whole bed working.
Iodine value (GB/T 12496.8 / ASTM D4607) measures surface-area proxy and is a consistency check between lots. K-value (gold loading capacity) and R-value (2-hour adsorption rate) measure how the carbon actually performs on gold: 8–12 kg Au/t (≈ 8–12 mg Au/g) equilibrium loading in high-grade circuits, and 52–58% of equilibrium loading within 2 h in a standard ~1000 ppm Au cyanide solution — measured in our own QC laboratory per GB/T 32992—2016.
Yes, for any first order. Take your ore and your plant solution, run the supplier's carbon against a reference carbon at the same pulp density and contact time, and fire-assay the loaded carbon. The result on your material beats any datasheet, and it gives you a benchmark to compare future lots against.