What is an Interstage Screen?
What we call an Interstage screen is a filter solution for gold processing. This process is used during the concentration stage, after the leaching process.
Can Interstage Screens Be used for Both Carbon-in-Leach
(CIL) and Carbon-in-Pulp (CIP)?
Did you know that there are two countercurrent methods employed in the industry to adsorb leached gold from a pulp stream onto activated carbon? These methods are Carbon-in-Leach (CIL) and Carbon-in-Pulp (CIP).
CIL and CIP operations involve several adsorption tanks placed in a series. Pulp flows continuously from the first tank to the last, while carbon is pumped countercurrent from the last tank to the first.
The main difference between CIL and CIP lies in the extent to which gold is leached prior to carbon adsorption. In CIL operations, carbon is added to the leaching tanks, therefore the leaching reaction and adsorption occur simultaneously.
During the CIP process, most of the leachable gold has been leached prior to the first adsorption stage.
For both CIL and CIP operations, the adsorption tanks can be arranged in the conventional cascading configuration or the tanks may be positioned on the same horizontal elevation.
Mineral Processing Separating (MPS) and Mineral Processing Separating Pumping (MPS(P)) Interstage Screen technology was designed for use in both CIL and CIP operations. However, during the innovative Kemix way to use the pump cell/carousel mode, the carbon stays in the same tank and only the leached solution moves from one tank to the other.
When the carbon is loaded with gold, the tank is isolated, and the carbon is collected to move to the elution stage process. The isolated cell is then reloaded with fresh carbon and put back into service in the carousel arrangement.
How Does Interstage Screen Work?
MPS and MPS(P) Interstage screens are semi-submerged top exit type screens. The wedge wire screen is submerged under the pulp operating level. Pulp flows through the wedge wire screen apertures while carbon is retained. The pulp flows upwards through the inside of the screen and exits via a launder interface above the wedge wire screen and volute interface.
MPS Interstage screens are typically utilized in circuits where the tanks have been installed with a predetermined height differential i.e. cascade arrangement. This height differential compensates for the pressure drop around the wedge wire screen which in turn introduces pulp flow through the plant. The MPS Interstage screen operates with a higher pulp level in the tank relative to the pulp at the screen’s exit launder.
MPS(P) Interstage screens are installed in circuits where the tanks and operating pulp levels are at the same horizontal elevation. The pressure drop around the wedge wire screen is compensated by an up-pumping impeller which is incorporated into the MPS(P) Interstage screen.
The pumping action of the impeller induces sufficient head and pulp velocity to transport the pulp to the next adsorption tank in the circuit.
The MPS(P) Interstage screen operates with the pulp in the tank at a lower level relative to the pulp level at the screen’s exit launder. The advantage of using MPS(P) type Interstage screens on circuits having the same horizontal elevation is that civil construction requirements are notably reduced when compared to a conventional cascade circuit.
In the case of both MPS and MPS(P) Interstage screens, the drive and screen form an integrated unit that can easily be removed for cleaning and routine maintenance procedures.
How to Choose the Right Interstage Screen Size
To calculate the open area of a screen, use this simplified formula:
Open area (%) = Slot size * 100 Slot size + Wire width
The aperture size of the screen is dictated by the carbon or resin size range. All standard aperture sizes are available and the cylindrical welding machine can manufacture any intermediate aperture size. Advanced measurement and control instrumentation ensure close tolerances on apertures. Cylinders can be manufactured using different profiles.
The specially developed CIP profile is designed for the gold mining industry. The CIP profile has a high release angle to reduce blinding and an improved open area to increase throughput. The 28 sb profile, also used in the gold mining industry, can provide even longer life. 304 Stainless steel is used for applications subject to corrosion, while 430 stainless steel is used in areas that require abrasion resistance properties only.
- No air required to clean screening surface during operation;
- 13 different Kemix wedge wire profiles available;
- It can be manufactured using different profiles specifically designed for the carbon recovery process.
Cylinders are custom made for specific applications taking the aperture size, wedge wire profile, diameter, height and flange details into account.
Multotec Canada is an official agent for Kemix in North America.