Our site purchased a second hand CIL pilot plant to do testwork on different plant conditions. 

The plant consists of 6 leach tanks, each of around 65L in volume. We plan to feed the plant concentrate at around 33% solids and a flowrate of 70ml/min, with gravity fed cascading flow between tanks. 

The plant came with a removable basket in each tank with 1mmx1mm steel mesh around the outside. The baskets are designed to prevent carbon (p80 = 4mm) flowing out of the tank and to allow carbon to be moved up the circuit by transferring each basket to the previous tank. 

The problem is that the mesh creates an abrasive surface against which the activated carbon is ground fine enough to pass through it in a matter of days. Additionally, solids accumulate on the mesh and eventually cover almost the entirety of the mesh, preventing slurry from passing through. 

The baskets aren't going to work, so we have removed them and intend to capture carbon using a strainer and manually transfer it to the previous tank, which is fine. But now we don't have a way of preventing carbon leaving the tanks.

We have tried covering the tank discharge in 1mm and 2mm aperture steel mesh, but in both cases the screens block with slurry in a matter of hours. As a test we installed the end of a tea strainer to increase the surface area, but it too blocked up.

Does anyone have experience with CIL pilot plants? What was used to prevent carbon leaving the tanks? Or if you don't have experience, do you have any ideas we can try? 

Thanks