Cleaning Carbon Tanks In Carbon in Leach And Carbon in Pulp Processes

Christian LindBlog, Service Adventurer, Tech TalkLeave a Comment

The two gold extraction processes CIL (Carbon in Leach) and CIP (Carbon in Pulp) are quite similar, both using granulated activated carbon to extract the gold from the solution. For the extraction processes to function efficiently a specific carbon granule size must be maintained.  It is therefore critical to handle the fragile carbon particles in a manner that does not damage or degrade the granules.

Granule size of activated carbon commonly used in CIL or CIP are: 8/16 # ASTM (1.19 mm to 2.38 mm), 6/16 # ASTM (1.19 mm to 3.36 mm), 6/12 # ASTM (1.68 mm to 3.36 mm)

As such the movement of the carbon slurry within the process is well defined using agitators and airlifts to gently move the carbon granules through the circuit.  A problem does however arise should the process be interrupted or a cleanout is required for maintenance.

In the mining industry, a tank or thickener cleanout is normally best handled by an agitator pump employing a closed or semi-open impeller. Sometimes a jet ring or water monitor is used to help suspend or direct solids toward the pump.

Agitator pumps use a “cutter fan” or “agitator” just in front of the pump inlet to aid in the re-suspension of settled solids.  ( item 6 in red)  The agitator redirects suspended solids back into the unsuspended products to help loosen additional solids and thereby increase slurry density. Unfortunately, the impact of the steel agitator on the carbon, and the suspended carbon on the unsuspended solids, causes carbon derogation. This renders the carbon unfit for use. Agitators are therefore avoided in carbon applications.

Similarly, both closed and semi-open impellers tend to degrade the carbon. In this case, the acceleration down the  “tunnel” formed by the impeller vanes is the problem. This acceleration and the change in direction are quite violent and cause the carbon to impact the steel vanes and the pump casing. In short, the problem of carbon degradation makes closed or semi-open impellers poor selections for carbon tank cleanout applications.

On the other hand, an impeller design commonly used in the pulp and paper industry has attributes that make it ideal for CIL and CIP applications.

Recessed impellers, sometimes referred to as torque flow impellers have vanes recessed out of the normal flow pattern.

The torque flow name stems from the unique way that the rotating impeller creates a fluid coupling. This coupling spins the product within the casing thereby creating the centrifugal force required to create discharge pressure.

The centrifugal force within the coupled fluid acts on the solids as they first enter the casing, transitioning the direction of the solid long before it can come into contact with the rotation impeller. With the majority of the solid, in this case, carbon, never impacting the impeller, particle degradation is minimized.  Furthermore, the acceleration of the product and its transition into the discharge pipe is smooth and gentle, again minimizing degradation.

In summary, the best selection for a CIL/ CIP tank clean-out would be a heavy-duty non-agitator, recessed impeller submersible.  If additional agitation is required add a “Jet Ring” and or a water monitor.  Be sure your motor HP is sufficient to cover run out and the high slurry density inherent to this type of application.  Our application engineers are well versed in carbon handling and are just a phone call away.

Cheers,

RJ

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