How to Read an Activated Carbon Spec Sheet (COA) Before You Order
What iodine number, methylene blue, mesh size, hardness, ash and moisture on an activated carbon spec sheet or COA mean, and which ASTM method to ask for.
Two quotations for activated carbon can carry almost the same numbers and still perform very differently once the carbon is in your filter or leach tank. Most of the time the reason is on the spec sheet itself. Either the test method is missing, or the figures are "typical" rather than guaranteed, or the one parameter that matters for your process isn't listed at all.
We get asked about this a lot, so here is how we read a sheet or a certificate of analysis (COA) when a buyer sends one over for comparison.
Typical value or guaranteed limit: which one is on the sheet?
Check the column header before the numbers. A typical value is an average of past production; a limit such as "iodine ≥ X mg/g" is what every lot has to meet.
In practice this is where most disputes start. A buyer orders against a sheet that says "Iodine: 1000 typical", the container arrives, their lab measures lower, and there is nothing in the contract to claim against. Typical values are fine for shortlisting suppliers. They are not acceptance criteria.
So in the purchase order, write the two or three parameters your process depends on as limits. Then agree on the test method, who does the testing, and whether the sample is taken at loading or on arrival.
What does iodine number tell you about activated carbon?
Iodine number (mg/g) is a rough measure of micropore development, and it's the most widely quoted activity figure. It's usually tested to ASTM D4607 or a national equivalent.
Higher isn't automatically better. Small molecules like many taste-and-odour compounds sit comfortably in micropores. Bigger organics and colour bodies need larger pores, and a carbon with a very high iodine number can still do poorly on them.
That's why some buyers also ask for methylene blue adsorption, which points to the larger pore range and matters for decolourisation and some wastewater duties. Units and methods differ between standards, so don't compare two figures measured differently.
For vapour and solvent recovery, ask for CTC or butane activity instead. Iodine number isn't a good proxy for gas-phase performance.
Which physical properties affect how the carbon runs in your plant?
Mesh size, hardness and apparent density decide pressure drop, carbon losses and how much fits in your vessel.
Mesh size (8×30, 12×40, 6×12 and so on) only tells you the nominal range. Ask for the sieve analysis, for example to ASTM D2862, with the percentage of oversize and undersize. A gold CIP or CIL circuit is the classic case: fines below the screen size go out with the tailings, and any gold loaded on them goes too.
Hardness shows how well the granules survive shipping, backwashing, agitation and regeneration. Ball-pan hardness to ASTM D3802 is common. If two suppliers quote different hardness tests, ask both for the same method; the results aren't comparable.
Apparent density (ASTM D2854) converts the tonnes you buy into the cubic metres your vessel holds. If your filter is sized by volume, a lighter carbon means fewer kilograms per fill.
Ash, moisture and pH: do they matter for your application?
Moisture affects what you pay for. Ash and leachables matter most in drinking water, food and pharmaceutical work.
Ash (ASTM D2866) is the mineral residue left after burning off the carbon, and it follows the raw material. Coconut-shell carbon is generally low in ash; coal-based carbon usually runs higher.
Moisture (ASTM D2867) creeps up during storage and sea freight. You're paying for that water by weight, so put a maximum in the contract.
pH and water-soluble ash come up for potable water, food, pharma and some electronics uses. If your customer needs a specific certification or contaminant limit, name the standard in your inquiry. Don't assume a general-purpose sheet covers it.
Quick reference: spec sheet parameters and test methods
| Parameter | What it tells you | Common test method |
|---|---|---|
| Iodine number | Micropore development, general activity | ASTM D4607 |
| Methylene blue | Larger pores, colour and big molecules | Varies by standard, confirm |
| Mesh size / sieve analysis | Pressure drop, fit to screens, fines loss | ASTM D2862 |
| Hardness (ball-pan) | Resistance to breakage and attrition | ASTM D3802 |
| Apparent density | Weight per vessel volume | ASTM D2854 |
| Total ash | Mineral content, tied to raw material | ASTM D2866 |
| Moisture | Water you pay for by weight | ASTM D2867 |
Which parameters matter for water, gold, gas or COD?
Pick the three or four lines that actually decide performance in your process and negotiate those as limits. The rest can stay as typical values.
Drinking water and wastewater: iodine or methylene blue, mesh size, ash, plus any leachable or certification requirement.
For gold recovery in CIP/CIL, hardness and the undersize limit usually come before activity. More in Activated Carbon for Gold Recovery: What CIP and CIL Buyers Should Confirm.
Air and gas purification needs gas-phase activity (CTC or butane), particle size and hardness.
COD removal is about pore structure suited to larger organic molecules. See Activated Coke for COD Adsorption: What to Confirm Before Ordering.
What should you send with an activated carbon inquiry?
Send the application, your acceptance parameters with test methods, and the commercial details.
Application and what you need to remove or recover
Acceptance parameters, each with its test method
Mesh size, with undersize and oversize limits
Raw material preference, if you have one (coconut shell, coal-based or other)
Quantity, packing and destination port
Any certification your end user requires
We supply activated carbon and also build production and regeneration equipment, so we look at a spec from both the product side and the process side. You can browse our activated carbon products and send your sheet through the contact page or to Vincentlee@gblcarbon.com.
FAQ
What is a good iodine number for activated carbon?
There's no single good number. It depends on the molecule you're removing. Iodine number reflects micropores, so it suits small molecules; for large organics or colour, methylene blue and pore structure often say more.
What is the difference between a spec sheet and a COA?
A spec sheet describes the product grade, often with typical values. A COA reports test results for one specific lot. For acceptance, ask for a COA per lot, tested by the method agreed in the contract.
Why does mesh size matter so much in gold recovery?
Fine particles pass through the interstage screens and are lost with the tailings, along with the gold loaded on them. That's why gold buyers set an undersize limit and a hardness requirement.
Is coconut shell carbon always better than coal-based carbon?
No. Coconut shell carbon is usually lower in ash and rich in micropores. Coal-based carbon often has more larger pores, which can suit some wastewater and decolourisation work. Choose by the duty, not the raw material.
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