CIL and CIP Interstage Screen Baskets: How They Work, Why They Wear and How to Order a Replacement

How a CIL/CIP interstage screen basket works, why it wears, slot and material choice, and the dimensions we need to make a replacement wedge wire basket.

By Serkan İnkaya, Mert Aytünür, Ümit Can Özer, ADEN Wedge Wire · 29 October 2026 · 15 min read

CIL and CIP interstage screen baskets: the short answer

An interstage screen basket is the cylindrical wedge wire screen that lets pulp leave a CIL or CIP adsorption tank while the activated carbon stays inside. Pulp flows outside to inside. The slot is usually 0.6-0.8 mm (industry sources quote 0.5 to 1.0 mm). Abrasive pulp wears the wire and widens the slot; the basket is a wear part.

We get inquiries for these baskets regularly, nearly always for a replacement: sometimes with a drawing, sometimes only with an OEM part number. Below we go through how the basket works inside a mechanically swept interstage screen, why it wears, how we choose slot, wire and material, and which dimensions we need so that a replacement fits the first time.

How carbon is kept in each tank

CIL (carbon-in-leach) and CIP (carbon-in-pulp) plants use a row of agitated tanks. The pulp, ground ore with water and cyanide, flows from the first tank to the last. Activated carbon is pumped the other way, from the last tank back to the first, and picks up gold as it goes. In CIL the leaching and the adsorption happen in the same tanks at the same time; in CIP most of the gold is leached before the carbon sees the pulp.

For this counter-current flow to work, each tank has to pass its pulp forward and keep its carbon. The interstage screen does that separation at the outlet of every tank. The leach pulp is alkaline, pH approx. 9.5 to 11, and it is abrasive. Stange (1999) gives 0.6-0.8 mm as the screen aperture for retaining the carbon in each reactor and notes that leakage comes from holed, poorly maintained screens or from off-size carbon, a point of "particular importance for slotted inter-stage screens such as those based on wedge-wire".

How a mechanically swept interstage screen works

The most common design we are asked to supply baskets for is the semi-submerged, top exit type. Our baskets are made as replacements compatible with this kind of unit; we do not supply the drive or the mechanism.

1. The cylindrical wedge wire basket is bolted to the underside of the volute with its top flange and sits below the pulp level.
2. Pulp passes through the slots from outside to inside. Carbon cannot pass and stays in the tank.
3. Inside the basket the pulp rises and leaves through a launder above the volute to the next tank.
4. A cage with pulse blades rotates around the outside of the basket. It sweeps the surface and keeps carbon and near-size particles from pegging in the slots, so the outer face has to be smooth and free of lugs or welds standing proud.
5. A stationary pipe, the hydraulic seal, surrounds the drive shaft and stops pulp and carbon from bypassing the screen. Its base is fixed to the bottom of the basket. This is why the bottom of the basket is an open ring with a bolt circle and not a closed cap.
6. A pitch blade turbine on a hollow shaft turns inside the basket and keeps the pulp moving upward and the inner surface clean.

The MPS version is used where the tanks are in cascade, so the level difference between tanks overcomes the pressure drop across the screen. The MPS(P) version has an up-pumping impeller inside the basket and is used where all tanks sit at the same elevation. For the basket itself, both versions have something rotating inside, so the inner diameter matters. The whole unit hooks onto the tank launder and can be lifted out without draining the tank, so changing a basket is routine maintenance and plants keep spares.

Why wedge wire is used for carbon retention

A wedge wire basket is made by winding a V-shaped profile wire around a ring of longitudinal support rods and welding every crossing point. On an interstage basket the flat face of the V-wire is on the outside and the rods are inside.

The slot widens toward the inside of the basket. A particle that passes the outer face does not get stuck further in, which is the main reason wedge wire resists pegging better than woven mesh or punched plate. More on the mechanism in our article on screen blinding prevention.

The outer surface is smooth and continuous, so the rotating cage can sweep it without catching an edge. The slot itself is a measured gap between two turns of wire, held by a weld at every rod. It does not stretch or shift like mesh, so the cut point stays where it was set until the wire wears.

Slot against carbon size, with mesh openings taken as the standard sieve sizes (6 mesh is 3.35 mm, 12 mesh is 1.70 mm):

At the typical slot, a new 6 x 12 carbon particle is more than twice the slot width. The margin is there on purpose: carbon breaks down by attrition in the agitated tanks, and the screen should keep holding the smaller pieces as long as possible. A wider slot passes more pulp, a narrower one holds more broken carbon. The plant sets the slot and we make the basket to it.

Slot, wire width and open area

Open area of a wedge wire screen is slot / (slot + wire width) x 100. The wire width is the top width of the V-wire. For the two wire widths we use most on interstage baskets:

A heavier wire gives a stronger, longer-lasting surface and costs approx. 6 to 7 percentage points of open area at the same slot. On an existing unit the basket size is fixed, so this trade-off has to be accepted knowingly. You can try other combinations in the open area calculator; the background is in open area explained.

Support rods on these baskets are placed close together because the wall takes the pulse of the rotating cage as well as the pressure drop. On one recent basket of approx. 430 mm diameter the drawing called for 80 rods around the circumference, about 17 mm apart. We count rods from the drawing or the old basket and do not reduce them to save welding time.

Why interstage baskets wear out

In our experience these baskets are replaced for wear far more often than for corrosion. The pulp is abrasive, the cage sweeps the surface continuously, and the pulp is driven through the slots under agitation. The top of each V-wire wears down and its edges round off, so the slot opens up. Once the slot is wider than the smaller carbon pieces, or a wire breaks and leaves a hole, carbon starts to pass to the next tank. Stange (1999) names holed screens as a cause of carbon leakage.

What decides how long a basket lasts:

• wire width and height (more steel on the surface, more to wear away before the slot opens);
• material strength and hardness of the wire;
• support rod spacing and size, which keeps the wall from flexing under the cage pulse;
• weld quality at every wire-rod crossing, since a failed weld lets the wire lift;
• a consistent slot along the whole basket, so that the slot does not start out at the wide end of its tolerance.

Carbon quality matters too. Off-size or flaky carbon passes slotted screens more easily, which is the other cause of leakage named in the SAIMM paper.

Material and wire: what we recommend

The replacement baskets we have quoted so far were in AISI 304 stainless, with surface wires of approx. 1.5 to 1.6 mm width. 304 is widely used for interstage screens; screen literature lists it for the corrosive part of the duty, and alkaline cyanide pulp with fresh process water is generally mild on stainless steel. We make baskets to this specification when the customer asks for it.

Our own recommendation is different, and we say so in every offer. From what we have seen in the field, 304 with a 1.6 mm wire wears quickly in this duty and has to be changed often. We recommend Super Duplex 2507 with a 2.2 mm wide wire. Super Duplex is a much stronger alloy than 304, and together with the heavier wire it wears considerably slower. It costs more per basket, and the 2.2 mm wire lowers the open area as shown above. We usually quote both, the customer's specification and our recommendation, so that the plant can compare the price against its own change-out interval. We do not quote a service life figure, because it depends on ore, grind, pulp density and cage speed at each plant.

Where the plant runs on saline or brackish process water, chloride pitting becomes the concern, and the grade is chosen by corrosion resistance as well:

More on grades in our material grade comparison.

What we need to make a replacement basket

The basket has to fit an existing volute, hydraulic seal and rotating cage, so the interfaces are copied exactly and the screen surface is designed around them. With a drawing of the old basket we can quote straight away. Without one, a photo of the old basket plus the following dimensions is enough:

Some notes from the inquiries we have handled:

• The diameter in an email is not always the tube diameter. In one case the 437 mm in the email was the outer diameter of the bottom ring, and the tube itself was 432 mm. We always take dimensions from the drawing, not from the text.
• If an inquiry gives only an OEM part number, we cannot read dimensions from it. We ask for the drawing or the photo and the dimensions above.
• A heavier wire or rod makes the wall thicker. With the outer diameter fixed, the inner diameter becomes smaller, for example from approx. 419 mm to approx. 415 mm on a 432 mm basket. We state this in the offer and confirm it on the approval drawing before production, because of the turbine inside.
• Gaskets, bolts and the parts that connect to the flange and ring are outside our scope unless agreed separately.

How we make interstage baskets

ADEN Wedge Wire is a wedge wire screen manufacturer based in Istanbul, Turkey, with a European office in Sindelfingen, Germany. Our baskets are spiral wound, with every wire-to-rod crossing joined by automated resistance welding. Slot width and weld penetration are checked during production. The flange and bottom ring are laser cut and welded to the screen tube, and the outer face is kept free of anything that would touch the rotating cage. Before production the customer receives an approval drawing with all interfaces and the resulting inner diameter. Each basket ships with a material certificate to EN 10204 3.1 with heat numbers and a final dimensional inspection.

Interstage baskets from our production are in operation in gold plants, in sizes up to 1,050 mm diameter x 1,600 mm length. Smaller baskets, such as the approx. 430 mm size found on some existing units, are made the same way. For carbon-in-column (CIC) plants we make the flat retention screens and bed-support screens for the columns; that duty is gentler because the solution entering the columns is clear.

Common mistakes we see in inquiries

• Assuming the flow is inside to outside. On a top exit interstage screen the flow is outside to inside, and a basket built the other way round has its rods outside, where the cage hits them.
• Drawing a closed bottom cap. The bottom is an open ring for the hydraulic seal base, and the inner diameter has to clear the turbine.
• Specifying the same light wire again after short basket life without looking at a heavier wire or another grade.

Send us your drawing or your old basket's dimensions

Send the drawing of your interstage basket, or a photo of the old basket with the dimensions listed above, together with slot, material and quantity. We reply within 24 hours and follow up with a technical proposal and, where it makes sense, a second option with a heavier wire or a higher grade. Contact: info@adenwedgewire.com or the RFQ form.

Frequently asked questions

References

1. The process design of gold leaching and carbon-in-pulp circuits (Stange, 1999), Journal of the South African Institute of Mining and Metallurgy
2. ASTM E11, Standard Specification for Woven Wire Test Sieve Cloth and Test Sieves, ASTM International
3. EN 10204, Metallic products, Types of inspection documents, CEN