# Gold Carbon 101: Iodine, Hardness & Moisture Explained

> Source: https://www.yelicarbon.com/blog-gold-carbon-specs.html

What an activated carbon COA really tells you — and the spec ranges to buy for a gold CIP/CIL circuit.

[Laboratory testing of gold carbon with a certificate of analysis]

**By the YELI Technical Team** · Updated August 2026 · 5 min read

A datasheet for gold recovery activated carbon lists maybe a dozen numbers, and most buyers read one of them — the iodine value — before deciding. It is a good instinct, but it is only half the story. Hardness, moisture, ash and mesh size decide whether that iodine value actually shows up in your recovery. Here is a plain-language walkthrough of the numbers on a gold carbon COA, and the ranges we recommend for a CIP/CIL circuit.

## 1. Iodine Value: The Number Everyone Quotes

Iodine value measures how much iodine the carbon adsorbs, reported in mg/g. It is a proxy for the micro-pore surface area available for adsorption — not a direct measure of gold loading, but a reliable cousin of it. For gold recovery, the practical working range is about 1000–1300 mg/g. Above that, you are usually paying for numbers that do not change your recovery. Below it, loading slows and the circuit needs more carbon inventory to hold the same gold. The important thing is consistency: a batch at 1250 followed by a batch at 1050 will wreck an elution schedule built around the first one.

## 2. Hardness: The Number That Pays

Gold carbon is screened, pumped, stripped and roasted, day after day. Every mechanical step grinds it, and what grinds off becomes fines that leave the circuit carrying gold with them. Hardness, tested by attrition, tells you how much of that loss to expect. Coconut shell GAC normally delivers 95% or better; we target 98%+ on gold-grade lots. Below 95%, watch your monthly make-up volume creep up — and your gold room losses with it. Over a year, a few points of hardness are worth more than a few dollars per ton on the invoice.

## 3. Moisture and Ash: Small Numbers, Real Money

Moisture is the easy one: wet carbon is heavy carbon. At 10% moisture you are paying freight for 100 kg of water on every tonne. Gold-grade carbon should ship at 5% or less, and it should be packaged so it stays that way — PE-lined bags and pallet wrapping are not decoration. Ash is the inert residue left after activation. Low ash, under 5%, means less dead weight in your charge and fewer impurities bleeding into the pregnant solution. Neither number is glamorous; both hit your cost per ounce.

## 4. Mesh Size: Match the Carbon to Your Circuit

Gold carbon is normally supplied in 6×12 or 3×6 mesh. The right cut depends on your interstage screens, elution column and regeneration kiln. Change the carbon size without checking the screens and you will lose carbon through the panels or blind them with fines. This is a spec to discuss, not to guess: tell your supplier your screen apertures and they should tell you which cut fits. If a supplier sells "one size fits all" gold carbon, ask how they sized it for your plant.

## 5. How to Compare Two COAs Properly

When you put two supplier COAs side by side, do not compare the best line — compare the spread across batches. A supplier who ships 1180–1230 mg/g iodine every month is more valuable than one who ships 950 one month and 1300 the next, even if the average is the same. The same logic applies to hardness and moisture. Ask for COAs from the last three or four batches, not just the sample batch. That is the closest thing to a crystal ball this industry has.

### Need Gold-Grade Carbon You Can Trust?

We produce coconut shell GAC for CIP/CIL at our own plant in Longyan, Fujian — 1000–1300 iodine, ≥98% hardness (98%+ typical on gold-grade), COA with every batch. Tell us your circuit size and we will help you spec the right cut.

See Gold Carbon Specs → (https://www.yelicarbon.com/product-gac.html)

## The Bottom Line

Iodine value gets the carbon through the door; hardness, moisture, ash and sizing decide whether it stays in the circuit. Buy on the full picture, and buy on consistency. If a spec sheet looks too good to be true, ask for the last three batches' COAs — that usually sorts things out quickly.

New to gold carbon? Start with why coconut shell carbon dominates CIP/CIL plants (https://www.yelicarbon.com/blog-gold-cip-cil.html), then read the coconut shell vs coal comparison (https://www.yelicarbon.com/blog-coconut-vs-coal-gold.html).

### Related reading

- Coconut Shell vs Coal-Based Activated Carbon for Gold Recovery (https://www.yelicarbon.com/blog-coconut-vs-coal-gold.html)

- Why Coconut Shell Carbon Dominates Gold CIP/CIL Plants (https://www.yelicarbon.com/blog-gold-cip-cil.html)

- Gold Carbon Elution: The Complete Guide (https://www.yelicarbon.com/blog-gold-carbon-elution-guide.html)

- Coconut Shell vs Palm Shell Carbon: Spotting Substitution (https://www.yelicarbon.com/blog-coconut-vs-palm-shell-gold.html)

Browse all activated carbon products & request a quote → (https://www.yelicarbon.com/products.html)