Activated carbon: Characteristics
Iodine numbers and hardness: grading a sponge
What this tab covers The physical and chemical properties that set its grade, price and uses, with the commercial grades and the standards that define them.Buyers specify adsorption capacity, hardness, particle size and ash. Iodine number measures micropores for small molecules; molasses number measures larger pores for colour; hardness matters where carbon is reused or abraded, as in gold circuits. Food and drinking water grades need certified low leachables.
Properties that matter commercially
| Property | Value / specification | Why it matters | Source |
|---|---|---|---|
| Iodine number | about 900-1,200 mg/g for coconut grades (indicative) | Main price determinant for micropore carbons | IMARC (test list); indicative |
| Surface area | about 500-1,500 m2/g (indicative) | Adsorption capacity | Indicative |
| Hardness | coconut grades about 95-99% ball-pan hardness (indicative) | Survives reactivation and gold circuits | Indicative |
| Ash | coconut under about 3-5%; coal about 8-15% (indicative) | Purity and leachables | Indicative |
| CTC activity | about 50-70% for gas-phase grades (indicative) | Gas and vapour adsorption | IMARC (test list); indicative |
Commercial grades
- Granular (GAC) for water and gas beds
- Powdered (PAC) for water and mercury injection
- Extruded pellets for gas and canisters
- Impregnated grades (sulphur, KOH) for mercury and acid gases
- Gold recovery grades
- Food and pharma grades
- Supercapacitor grades