# CIP Carbon Screen Blinding: Causes, Cleaning and Maintenance

> Source: https://www.yelicarbon.com/blog-cip-carbon-screen-blinding-maintenance.html

The interstage screen is the only thing keeping carbon in its tank. When it blinds, the first symptoms appear somewhere else entirely. Here are the five causes, how to tell them apart, and the maintenance schedule that stops it coming back every three weeks.

**By the YELI Technical Team - Updated October 2026 - 8 min read**

> **Short answer:** Carbon screen blinding is pulp flow being restricted by material packed into the interstage screen apertures - mineral fibre, wood chips, flotation reagents and oils, calcium carbonate scale from lime dosing, or migrated carbon fines. It shows up as uneven tank levels, falling flow through the screen, and carbon reporting to the wrong stage or to tails. Fix the causes (harder carbon, gentler transfer, upstream wood and trash removal, acid washing where scale is present) on a fixed inspection schedule, or the same screen blinds again three weeks later.

In a CIP or CIL circuit the interstage screen is the only thing keeping carbon in the tank where it belongs. When it blinds, the plant usually notices something else first: a tank level that will not hold, an adsorption profile that stops making sense, or a rising gold grade on the tailings screen oversize. By then the screen has been restricting flow for days.

## 1. What blinding actually is

The screen is a barrier with apertures sized to retain carbon particles while letting pulp pass. Blinding is a partial or complete blockage of those apertures. It is progressive, not sudden: flow falls, the pump works harder or the tank level rises, and the operator compensates - often by transferring carbon more frequently, which accelerates the very attrition that produces the fines causing the blockage.

## 2. Aperture selection: match the screen to the carbon cut

Screen aperture follows from the carbon cut. 6x12 mesh carbon (1.70-3.35 mm) is normally run against screens in the 0.8-1.0 mm aperture range, which retains whole granules with margin while passing pulp. <em>(Industry-typical.)</em> 8x16 mesh carbon needs a correspondingly smaller aperture.

Two errors are common:

- **Aperture too large** for the carbon cut: whole particles pass and are lost to the next stage.
- **Aperture too small**: retention is safe, but the screen blinds quickly because the open area is smaller and fine material bridges more easily.

## 3. The five causes of blinding

| Cause | Where it comes from | How to recognise it |
|---|---|---|
| Mineral fibre and wood | Vegetation, wood chips and rubbish in the ore feed | Fibrous material visible in the screen during inspection |
| Flotation reagents and oils | Upstream flotation, lubricants, process oils | Slimy coating; flow drops after reagent changes |
| Calcium carbonate scale | Lime dosing for pH control, hard process water | Whitish, hard deposit; responds to acid wash |
| Carbon fines | Attrition from pumps, eductors and transfer | Fine carbon packing apertures; tailings oversize shows fines |
| Biofilm and manganese | Warm circuits, long residence, certain ores | Brown or black slime; limited response to acid alone |

## 4. Diagnosis: read the symptoms before you open the tank

- **Tank level behaviour.** A blinded screen makes one tank run high and the next run low, because transfer is restricted.
- **Adsorption profile.** Sample gold on solution across the train. If one stage stops performing while its neighbours work overtime, look at that screen first.
- **Tailings oversize.** Screen undersize or oversize samples show whether carbon is being carried out, and whether the material is whole granules (aperture problem) or fines (attrition problem).
- **Pressure and pump duty.** Transfer pumps running hotter or slower than their commissioning values indicate restriction.

## 5. Cleaning methods that work

- **Mechanical:** brush or scrape the screen in place, and clean the tank floor. Fast, but temporary if the cause is untouched.
- **High-pressure water:** effective on fibrous material and loose fines; do it with the screen out of service so debris is not pushed back into the circuit.
- **Acid wash:** dilute hydrochloric acid dissolves calcium carbonate scale. Where scale is the cause, this is the only method that removes it; where scale is not the cause, it does nothing.
- **Replace, do not repair:** screens are consumables. Keep a spare set so a blinded screen can be swapped out and cleaned off-line instead of costing production hours.

## 6. Prevention: the part that actually saves money

- **Harder carbon.** Fines generation starts with attrition. Carbon at 98% or better ball-pan hardness (ASTM D3802) sheds materially less fines than 92-95% material.
- **Gentler transfer.** Lower pump speed, correct eductor sizing, and avoiding unnecessary carbon movement all reduce fines.
- **Upstream trash removal.** Trash screens and correctly sized grizzly openings on the mill feed remove the fibre and wood that blind screens.
- **Acid washing on a trigger.** When scale is present, acid washing loaded carbon addresses the deposit before it consolidates.
- **Scheduled inspection.** Inspect on a fixed interval - weekly at first, then monthly once the circuit is stable - rather than when production drops.

## 7. A maintenance schedule you can adopt

| Frequency | Action |
|---|---|
| Daily | Record tank levels, transfer volumes and pump duty; note any drift |
| Weekly | Inspect one screen on rotation; check tailings oversize for fines |
| Monthly | Fines balance: fines generated vs fines removed; review carbon hardness on the current lot |
| Quarterly | Acid wash assessment; screen wear check; review aperture against carbon cut |
| On every lot | Record COA hardness and sieve distribution, and compare with fines generation |

## Frequently asked questions

**What causes carbon screens to blind in a CIP circuit?**
The five common causes are mineral fibre and wood from the ore, flotation reagents and oils, calcium carbonate scale from lime dosing, migrated carbon fines from attrition, and biofilm or manganese deposits. Each is fixed differently, so identify the cause before cleaning.

**What aperture should a CIP interstage screen be?**
Screens are normally sized just below the carbon cut: around 0.8-1.0 mm for 6x12 mesh carbon, smaller for 8x16 mesh. Confirm against your actual sieve distribution rather than the nominal mesh alone.

**Does carbon hardness affect screen blinding?**
Yes. Softer carbon generates more fines, and fines are one of the main causes of aperture blockage. Specifying hardness at 98% or better (ASTM D3802) reduces fines generation at the source.

**How do I clean a blinded carbon screen?**
Mechanical cleaning and high-pressure water remove fibre and loose fines; dilute hydrochloric acid removes calcium carbonate scale. Keep a spare screen set so cleaning happens off-line instead of during production.

**Will acid washing stop screens blinding?**
Only if scale is the cause. Acid washing dissolves calcium carbonate, so it helps significantly in hard-water and high-lime circuits, and does very little where the blockage is fibrous material or carbon fines.

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