# Elution Efficiency Low? Diagnose Why Gold Stays on Carbon

> Source: https://www.yelicarbon.com/blog-gold-elution-efficiency.html

Your eluate is down and bullion is short, yet the loaded carbon going into the strip still assays where you expect it. Meanwhile the stripped carbon comes out carrying a measurable gold grade, and your elution cycle keeps stretching. That combination means gold is staying on the carbon — and low elution efficiency is almost always diagnosable in an afternoon.

[Diagnosing low elution efficiency in a gold recovery plant]

**By the YELI Technical Team** · Updated September 2026 · 8 min read

## Read the Symptoms First

Low elution efficiency rarely announces itself with one number. It shows up as three symptoms at once, and once you've seen the pattern you won't misread it again.

When all three line up, stop looking at the feed. The problem is inside the strip. It's easy to blame the ore or the carbon — do neither until you've confirmed the elution circuit is actually doing its job.

- Eluate and bullion are down while loaded carbon grade looks normal. Pregnant solution grades drop and the gold room is short, but the carbon entering the strip still assays where you expect it. The gold is reaching the column fine — it just isn't leaving.

- Stripped carbon still carries gold. Your "barren" carbon comes out with a noticeable grade — enough to show on fire assay.

- Cycle times stretch. You hold the strip longer and longer chasing a barren target that never quite arrives, and elution throughput slips.

## Measure Strip Efficiency the Simple Way

Before you change anything, measure. The field method takes two samples and one comparison.

The math is rough but honest. Strip efficiency is the gold removed during elution divided by the gold that was loaded, expressed as a percentage. If your loaded carbon carries a certain grade and your stripped carbon still carries a meaningful share of it, that share is gold you are not collecting. In a well-run circuit, typical strip efficiency is high — mid-to-high 90s percent — meaning only a small fraction of the loaded gold stays behind. If your numbers sit well below that, work the checklist below.

Two cautions. First, sample several consecutive cycles and average the results — loaded grade varies batch to batch, and a single comparison can mislead you. Second, keep the sampling routine identical: same point in the cycle, same wash state, same moisture handling. Inconsistent sampling produces phantom efficiency swings that send you chasing problems that don't exist. For a fuller walkthrough of the strip itself, see our elution guide.

- Loaded carbon: take a representative sample right before the carbon enters the elution column.

- Stripped carbon: take a representative sample right after elution, at the same point in the wash every time.

- Assay both and compare the grades.

## The 6-Point Checklist — In Order of Likelihood

Work through these in order. Each item is cheaper and faster to check than the one after it, and together they cover most low-efficiency problems.

1. Eluant chemistry drifted. Caustic and cyanide strength drop as solutions are reused and topped up. Verify NaOH and NaCN concentration against target — and check the water you are using. Hard water brings in calcium that fights the strip. 2. Temperature below target. Elution is a temperature-driven process. On an atmospheric Zadra circuit (roughly 90–95 °C), confirm the eluant is actually at temperature at the column, not just at the heater. On a pressurized AARL circuit, check the strong-caustic pre-soak and the strip temperature too. 3. Carbon fouling — acid wash skipped. Calcium carbonate scale and organic buildup block the pores the gold must travel through. If the acid wash has been skipped or shortened, this is your most likely culprit. 4. Column channeling. Fines settle and compact, and poor packing leaves fast paths where eluant channels through while parts of the bed sit stagnant. Watch pressure drop and the bed surface during stripping. 5. Regenerated carbon with activity loss. Carbon that is hammered by thermal regeneration loses activity and hardness cycle by cycle, and gold gets harder to strip. See our guide on regeneration cycles. 6. Elution time and flow too short. The strip may simply not run long enough or fast enough. Compare actual time and flow against the design basis before suspecting anything exotic.

## What to Fix First — Cheapest First

Don't replace carbon or rebuild the column yet. Fix in this order.

1. Restore eluant strength and temperature. Top up caustic and cyanide to spec, confirm real temperature at the column, and switch to softer water if hard water is drifting your chemistry. This costs almost nothing and fixes a large share of cases. 2. Run an acid wash. A dilute hydrochloric acid wash dissolves calcium carbonate scale and opens the pore structure back up. If it's been weeks since your last proper wash, do this before you spend money anywhere else — many plants see the strip recover in one wash. 3. Screen the carbon and remove fines. Check fines before blaming the column. Fines plug the bed, cause channeling, and carry gold that is effectively unrecoverable once they leave the circuit. 4. Only then look at the column and the carbon itself. Packing, flow distribution, and carbon quality are the last suspects, not the first.

Most low-efficiency problems are chemistry, temperature, and fouling. The column is usually innocent.

## Why Carbon Quality Shows Up Here Too

Carbon quality shows up at elution, not just at adsorption. Consistent high-hardness carbon generates fewer fines, so the bed stays packed evenly and strips predictably cycle after cycle. Soft or substituted carbon — palm kernel shell and other fruit shells are cheaper but generally softer and less consistent, and some suppliers blend them in — breaks down faster, feeds fines into the column, and makes every strip a little different.

At our factory in Longyan, Fujian, we make coconut shell gold-grade carbon at ≥98% hardness (ball-pan, ASTM D3802), iodine 1000–1300 mg/g, with a COA issued with every batch. When fines, channeling, and unpredictable stripping keep recurring, carbon quality deserves a hard look. See our gold-grade product range.

## The Bottom Line

Diagnose low elution efficiency the way an experienced plant consultant would: measure before you change, work the checklist from cheapest to most expensive, and treat chemistry, temperature, and fouling as the prime suspects. In most plants, gold not eluting comes down to a starved strip — weak eluant, cold solution, or a scaled-up bed — not bad carbon. Fix those first, and the stripped carbon grade comes back down where it belongs.

### Gold Staying on Carbon? Let Us Check It With You

YELI Carbon is a coconut shell activated carbon manufacturer in Longyan, Fujian — 20+ years, gold-grade lines, hardness ≥98%, COA with every batch. If your stripped carbon still carries gold, send us a sample and we will run a side-by-side test: iodine, hardness, gold adsorption. Then compare against a known-good reference before you change anything.

Request a Sample Test (https://www.yelicarbon.com/contact.html#quote-form)

## FAQ: Elution Efficiency Problems

What is normal elution efficiency? +
In a well-run circuit, typical strip efficiency is high — mid-to-high 90s percent — meaning only a small fraction of the loaded gold stays on the stripped carbon. If you're consistently well below that range, work the checklist in order: eluant strength, temperature, fouling, packing, then carbon quality.

My eluted carbon still has gold — what do I check first? +
Check the cheapest things first: eluant caustic and cyanide strength, real temperature at the column, and whether an acid wash has been skipped. Those three cause most cases of gold staying on carbon. Only after that look at column channeling, fines, and regenerated carbon activity — and confirm your samples are representative before you chase anything.

Does hard vs soft carbon matter for elution? +
Yes. Hard carbon survives transport, screening, and regeneration with fewer fines, so the bed packs evenly and strips predictably. Softer carbon — often palm kernel or other fruit shells — breaks down faster, and the fines show up as low elution efficiency and climbing carbon consumption. See why carbon consumption climbs in CIL circuits.

How often should we acid wash? +
There's no universal interval — it depends on your water and ore. Plants on hard water or heavy organic load may wash before every strip; others run weekly or monthly. The practical rule: when stripped carbon grade creeps up or elution slows, it's time for an acid wash — and if you're not washing on any schedule at all, start there.

### Related reading

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

- Gold Carbon Regeneration Cycles (https://www.yelicarbon.com/blog-gold-carbon-regeneration-cycles.html)

- Gold Cip Cil (https://www.yelicarbon.com/product-gold-cip-cil.html)

- Why Carbon Consumption Increased Cil (https://www.yelicarbon.com/blog-why-carbon-consumption-increased-cil.html)

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