By the YELI Technical Team · Updated August 2026 · 7 min read
Short answer: To detect blended or adulterated activated carbon, test four things on the delivered lot (not the sample): 1) hardness — palm shell and other feedstock are softer than pure coconut shell, so an abrasion test exposes blending; 2) iodine vs. performance gap — a high iodine number with poor actual loading suggests a different pore structure; 3) ash and density — different feedstocks carry different ash profiles; 4) visual and sieve inspection — mixed lots often show inconsistent particle color and mesh distribution. The definitive check is a side-by-side lab test of the delivered lot against the approved sample.
The oldest trick in the activated carbon trade: send a perfect sample, then ship a cheaper blended lot. Coconut shell carbon is the premium feedstock, so some suppliers cut it with palm shell, apricot shell or coal-based material to lower cost — while keeping the paperwork identical. If the carbon in your circuit suddenly produces more fines, or recovery drifts, blended feedstock should be on your checklist. Here is how to catch it.
Why Blending Is Hard to Catch on Paper
A supplier can label the lot "coconut shell, iodine 1050" and the COA may even be technically true for the blended average. The problem is performance: palm shell and other feedstocks are softer, so they generate more fines in your circuit — and fines carry gold out. The COA won't tell you this; only testing the actual lot will.
Check 1: Hardness (The Most Telling Test)
Pure coconut shell carbon typically tests 95%+ hardness. Palm shell, apricot shell and wood-based material are softer. Run an abrasion test on a sample from the delivered lot. If hardness comes back below the COA, or significantly below 95%, you have strong evidence of blending — because hardness is the first thing blending degrades.
Hardness is measured by the ball-pan method (ASTM D3802): a 100 g sample is tumbled with steel balls for a fixed time, and the fraction retained on the reference sieve is reported as percent hardness. The numbers separate feedstocks cleanly. Coconut-shell gold-grade carbon typically tests 96–99%, while palm-shell blends typically sit at 90–94%. On a lot labeled pure coconut shell, a result below 95% is strong evidence of blending — and hardness is the first test to flag it.
Check 2: Iodine vs. Actual Performance
Blended carbon can still show a decent iodine number — iodine measures surface area, which some blends preserve. But real gold loading depends on pore structure and hardness. If the delivered lot has a good iodine number yet loads gold poorly or produces fines, the pore structure is wrong for the job, which points to non-coconut feedstock.
Check 3: Ash and Apparent Density
Different feedstocks carry different ash profiles. Coconut shell is naturally low-ash; coal-based carbon is higher; palm shell sits between. Compare the delivered lot's ash and density against the COA and against a known coconut shell reference. A jump in ash is a red flag.
Check 4: Visual and Sieve Inspection
Blended lots often show visible differences: inconsistent particle color, shape or gloss, and a wider mesh distribution than a single feedstock would give. Spread a sample on a white tray — pure coconut shell looks relatively uniform; a blend shows mixed particle types. Run a sieve analysis to check the distribution matches the certified cut.
The Definitive Check: Side-by-Side Lab Test
If you suspect blending, do not argue on paper. Take a sample from the delivered lot and a reference sample of known pure coconut shell carbon, and run them together through the full battery:
| Test | Method | What it catches |
|---|---|---|
| Sieve analysis | ASTM D2862 | Mesh cut matches the certified 6×12 distribution |
| Moisture | ASTM D2867 (dried at 110–115 °C) | Removes the variable that skews every other result |
| Iodine number | ASTM D4607 (mg/g) | Surface area — blends can still score high here |
| Hardness | ASTM D3802 (ball-pan) | The feedstock fingerprint — coconut vs. palm band |
| Ash & apparent density | ASTM D2866 (ash at 650 °C) | Feedstock fingerprints that blending shifts |
Then the definitive gold test: a bottle-roll on your own ore and solution — same pulp density, same contact time — fire-assay both carbons and compare gold loading side by side. The numbers side by side tell the truth quickly. One rule: a COA must state the test method — a number without a method cannot be compared. Any confident supplier welcomes this test — and we do.
Verify Your Carbon Against Ours
YELI Carbon produces pure coconut shell activated carbon in Longyan, Fujian — Philippine and Indonesian coconut shell feedstock, hardness 98%+ (98% available), iodine 1000-1300, COA with every batch. Send us a sample of what you are using now and we will run iodine, hardness and ash against ours, side by side.
Run a Comparison Test →The Bottom Line
Blended carbon is hard to catch on a COA but easy to catch in a lab. Test hardness, ash and sieve distribution on the delivered lot, and run a side-by-side comparison when in doubt. It takes a day and saves months of hidden gold loss. For the full supplier verification process, see our verification guide.
FAQ: Detecting Adulterated Activated Carbon
Test the delivered lot, not the sample. Hardness is the most telling: pure coconut shell tests 95%+, while palm shell and other feedstocks are softer, so an abrasion test exposes blending. Also check ash (different feedstocks carry different ash profiles) and sieve distribution, plus visual inspection for inconsistent particle types.
Palm shell and other non-coconut feedstocks are softer, so they generate more fines in your CIP/CIL circuit — and fines carry adsorbed gold out of the circuit. A blended lot can still show a decent iodine number while performing poorly, because pore structure and hardness are wrong for gold duty.
A COA describes what the supplier claims. The definitive check is testing the actual delivered lot: hardness, ash, sieve distribution, and a side-by-side comparison against a known pure coconut shell reference. A confident supplier welcomes this.
Order a small trial lot, test it independently (iodine, hardness, ash), and run a side-by-side comparison with a reference. Also verify the factory with a live video tour or visit. These three checks catch most quality and blending issues before you commit to a container.
Start with hardness (ASTM D3802): coconut-shell gold-grade carbon typically tests 96–99%, while palm-shell blends typically sit at 90–94%. Then check ash and apparent density, which shift when a second feedstock is blended in. The definitive check is a side-by-side gold loading test on your own ore and solution, with both carbons fire-assayed after the same contact time.