How to Read a Gold Recovery Activated Carbon COA Before Purchase

A practical pre-purchase review of batch identity, test method, units, reporting basis, particle size, hardness / attrition, adsorption indicators and contract compliance

Author: YICARB Technical Expert (15+ years experience in activated carbon industry)

Introduction

A gold recovery activated carbon COA should be read as a batch-specific quality document, not as a marketing sheet. Before purchase, the buyer should confirm that the COA belongs to the actual grade and production lot, that each result uses an agreed test method and unit, that the reporting basis is clear, and that the particle-size, mechanical and adsorption indicators match the contract specification. A complete COA helps verify consistency, but it does not replace gold-specific testing where the mining operation requires it.

1. Start With Batch Identity and Traceability

The first section of a gold recovery activated carbon COA should identify what was actually tested. At minimum, check the product or grade name, batch or lot number, production or test date, and the manufacturing or laboratory reference used by the supplier.

· Does the COA grade match the purchase order and approved sample?

· Is the batch / lot number unique and traceable?

· Is the COA recent enough to represent the shipment being purchased?

· If the supplier uses multiple factories, is the production location clear where this matters contractually?

If the document cannot be tied to the material being shipped, even technically correct laboratory results provide weak purchase control.

2. Check Test Method, Unit and Reporting Basis Together

A value has limited meaning without the method and unit that produced it. For example, iodine number is commonly reported in mg/g under ASTM D4607-14(2021), while CTC activity is reported as a percentage under ASTM D3467-04(2020). [1][2] Results from different methods should not be compared as if they were directly interchangeable.

Reporting basis also matters. ASTM D2867-23 notes that moisture content is often required to define and express activated-carbon properties in relation to the net weight of carbon. [3] For purchasing, the COA and contract should therefore state whether relevant values are on an as-received basis, dry basis, or another defined basis. Do not assume every percentage on a COA uses the same basis.

A pre-purchase COA audit should verify traceability, method, unit, basis and contract compliance.

Figure 1: A pre-purchase COA audit should verify traceability, method, unit, basis and contract compliance.

3. Review Particle Size Beyond the Mesh Label

ASTM D2862-16(2022) measures the particle-size distribution of granular activated carbon and notes that PSD influences both pressure drop and adsorption rate. [4] A COA should therefore show more than a nominal label such as 6×12 mesh.

· On-size percentage within the contracted mesh range.

· Oversize percentage above the upper sieve.

· Undersize or fines below the lower sieve.

· The sieve or test method used for the calculation.

For a gold-recovery circuit, particle-size results should be checked against the plant's interstage or carbon-retention screens. A product can meet a general '6×12 mesh' description yet still have too much near-size or undersize material for a particular screening system.

4. Interpret Hardness and Attrition Correctly

ASTM D3802-23 provides the ball-pan hardness number for granular activated carbon. ASTM explicitly states that this test is useful for comparing lots of nominally the same grade, but it does not actually measure in-service resistance to degradation. [5]

ASTM D5159-21 addresses dusting attrition and notes that abrasion is a common cause of dust formation in actual service. It also cautions that conventional hardness results do not generally correlate directly with field experience. [6] For gold recovery, a strong COA review therefore considers hardness together with attrition / fines data, particle-size distribution, and the plant's handling and regeneration conditions.

5. Read Adsorption Indicators as Indicators

Iodine number is a relative indicator of porosity. ASTM D4607 states that it does not necessarily measure the carbon's ability to adsorb other species and that its relationship with surface area cannot be generalized across raw materials and pore structures. [1]

CTC activity is a gas-phase pore-volume / activation indicator. ASTM D3467 states that the value does not necessarily provide an absolute or relative measure of effectiveness for other adsorbates or other operating conditions. [2]

For gold-recovery purchasing, iodine and CTC can support batch consistency and product characterization, but they should not be used alone to predict gold adsorption rate, equilibrium gold loading, carbon loss, or plant recovery. Where required, compare them with a direct gold-specific adsorption test under stated solution and particle-size conditions.

Common COA parameters answer different questions and have different limits.

Figure 2: Common COA parameters answer different questions and have different limits.

6. Check Moisture, Ash and Apparent Density in Context

ASTM D2867-23 covers moisture determination; ASTM D2866-11(2025) covers total ash; and ASTM D2854-09(2025) covers apparent density of granular activated carbon. [3][7][8]

These values are useful for quality control and purchasing, but each answers a different question. Moisture affects the net carbon basis and shipping weight; ash describes mineral residue that may influence certain end uses; apparent density is important for estimating packed-bed volume and material quantity. None of these should be treated as a stand-alone measure of gold adsorption performance.

7. Match Every Result to the Contract Specification

The final COA review is a line-by-line comparison with the purchase specification. The buyer should not accept 'typical values' when the contract requires a guaranteed minimum, maximum or range.

COA check	Buyer question	Action before approval
Batch / grade	Does this COA belong to the actual shipment?	Request shipment-linked COA if traceability is incomplete
Method + unit	Is each result measured and reported as agreed?	Resolve method or unit mismatch before comparison
Basis	Is the result dry basis, as-received or otherwise defined?	Require the basis to be stated where it affects compliance
Particle size	Are on-size, oversize and undersize within contract limits?	Compare with plant screen requirements
Hardness / attrition	Does the mechanical-quality package meet the contract?	Review hardness together with fines / attrition data
Adsorption indicators	Do iodine / CTC meet the agreed specification?	Use direct gold test too when contract or qualification requires it

8. Application Example

Illustrative example - not a customer case study: A buyer receives a COA showing acceptable iodine, CTC and hardness values, but the particle-size section lists only '6×12 mesh' without on-size, oversize or undersize percentages. The test-method column is also blank for hardness. The buyer does not reject the product immediately; instead, the supplier is asked to provide the actual sieve distribution and the hardness method so the shipment can be compared fairly with the contract.

YICARB Perspective

YICARB recommends treating the COA as one part of supplier qualification. The strongest purchase control combines batch-specific COA data, clearly stated methods and units, contract limits, particle-size and mechanical data, and gold-specific application testing where the mine requires it.

Conclusion

A gold recovery activated carbon COA should be checked item by item before purchase: batch identity, method, unit, reporting basis, particle-size distribution, hardness / attrition, adsorption indicators and the contract specification. A technically complete COA improves batch consistency and purchasing control, but the final decision should still reflect the mine's screens, process conditions and any required direct gold-adsorption qualification.