ASTM Testing Standards for Gold Recovery Carbon: Iodine, Ash, Hardness and Abrasion

By the YELI Technical Team - Updated October 2026 - 8 min read

Short answer: A gold recovery carbon certificate of analysis should report six numbers with their test methods attached: iodine number (ASTM D4607 / GB/T 12496.8), ball-pan hardness or abrasion resistance (ASTM D3802 / GB/T 12496.6), ash (ASTM D2866 / GB/T 12496.3), moisture (ASTM D2867 / GB/T 12496.4), apparent density (ASTM D2854 / GB/T 12496.1) and particle size distribution (ASTM D2862 / GB/T 12496.2), plus gold-specific K-value and R-value where offered (GB/T 32992-2016). The method name matters as much as the number: the same parameter tested to a different standard can look better without being better.

Buyers who compare activated carbon quotations quickly discover that the numbers are not always comparable. One supplier reports hardness to ASTM D3802, another quotes an "abrasion number" from an in-house method, a third quotes attrition after a tumbling test developed for catalysts. All three can be true and still describe very different material. This guide lists the tests that matter for gold recovery carbon, what each one actually measures, and how to read them on a real lot certificate.

1. The test list for gold recovery carbon

<em>Ranges above are the specification YELI Carbon ships for gold CIP/CIL grade 6x12 mesh coconut shell carbon; industry values for other grades differ.</em>

2. Why the method name on the COA matters as much as the number

Three practical traps:

• Hardness versus abrasion. ASTM D3802 is the ball-pan method: a weighed sample is tumbled with steel balls, then screened, and the retained mass is reported as a percentage. Some data sheets quote an "abrasion number" from a different tumbling or attrition procedure, sometimes developed for catalyst carriers rather than carbon. The two are not interchangeable. Ask which method was used before comparing two suppliers.
• Iodine versus methylene blue. Iodine number reflects micropore capacity, which is what suits the small, linear gold cyanide complex. Methylene blue reflects mesopore capacity and is a legitimate test for colour and odour removal, but it says very little about gold adsorption. A high methylene blue number is not a gold benefit.
• "Typical" versus "this lot". A data sheet range describes a product family. A certificate describes the material in the bags on the pallet in the container. Only the second one can support an acceptance decision.

3. The three numbers buyers compare first, and what they miss

Most purchase decisions turn on iodine, hardness and mesh. That leaves two gaps:

• Ash. Ash does not adsorb gold. Above roughly 5% it also contributes to elution circuit fouling and to scale formation. Low-ash grades are acid-washed; if ash matters to your circuit, put a maximum on the purchase order rather than accepting whatever the lot carries.
• Adsorption kinetics and gold capacity. Iodine is an equilibrium measurement. It does not tell you how fast the carbon loads gold in your last adsorption tank, nor how much gold it holds at equilibrium in your liquor. Those are the K-value (equilibrium gold loading, commonly expressed in kg Au per tonne of carbon) and the R-value (adsorption rate), testable per GB/T 32992-2016 by an independent laboratory using your own liquor.

For a plant choosing between two acceptable carbons, K-value and R-value on the actual production lot are more informative than a 50 mg/g difference in iodine number.

4. Sampling before you send a sample to a laboratory

Most disputes about test results are sampling disputes. A practical field method:

1. Take increments from across the lot - multiple bags, top, middle and bottom of the pallet, not one convenient bag.
2. Combine the increments, mix thoroughly on a clean tarpaulin, and quarter down to a composite sample of 1-2 kg.
3. Split the composite into three sealed portions: one for the supplier's record, one for your laboratory, one held in reserve for a third party if the first two disagree.
4. Record the lot number, the date and the bag numbers sampled, and keep the record with the sample.

Carbon is hygroscopic. Sealed, moisture-proof packaging matters as much as the sampling itself, because moisture content is one of the parameters you are paying for.

5. Third-party verification: when it is worth the cost

An independent test report is worth commissioning when the order is large enough that a rejection would be expensive, when it is your first order from a supplier, or when the terms require it. Standard practice is to nominate the laboratory and the method in the purchase order, and to sample at the load port or on arrival rather than at the factory.

For most routine reorders, a lot-specific COA from the manufacturer plus a periodic spot check at your own laboratory is sufficient and far cheaper.

6. What a certificate of analysis must not be

• A promotional specification sheet.
• A range copied from a product brochure.
• A certificate issued for a different lot, or without a lot number.
• A document with no method column.

Anything in that list cannot support acceptance, rejection or a claim.

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