There are predominantly two counter current methods employed
in the industry to adsorb leached gold from a pulp stream onto
activated carbon. These methods are Carbon-in-Leach (CIL) and
CIL and CIP operations have a number of adsorption tanks placed in series. Pulp flows continuously from the first tank to the last, while carbon is pumped counter current from the last to the first tank.
The main difference between CIL and CIP lies in the extent to which gold is leached prior to carbon adsorption. In the CIL operation, carbon is added to the leaching tanks, therefore the leaching reaction and adsorption occur simultaneously. In 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 could be positioned on the same horizontal elevation.
Mineral Processing Separating (MPS) and Mineral Processing Separating Pumping (MPS(P)) Interstage Screen technology was designed to operate in both CIL and CIP operations.
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.
The MPS Interstage screens are typically utilised in circuits having the tanks installed with a predetermined height differential i.e. cascade arrangement. This height differential overcomes 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.
The MPS(P) Interstage screens are installed in circuits having the tanks and operating pulp levels at the same horizontal elevation.
The pressure drop around the wedge wire screen is overcome with 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 transports 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.
For both the 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.
MPS Interstage Screen - MPS 350
MPS(P) Interstage Screen - MPS(P) 2200
MPS Interstage Screen
The MPS screen incorporates a cylindrical
wedge wire basket (screen) attached to the
underside of the volute.
The volute also houses the driving unit and includes a discharge launder.
Rotating around the periphery of the screen is a cage with pulse blades attached and designed to keep the screen surface clear of carbon and pulp.
The rotating cage sets up a pulse and sweeping action around the periphery of the screen. This reduces the possibility of carbon and near size material pegging in the screen’s apertures which in turn ensures that pulp flowrate through the screen is maintained.
The drive shaft of the cage is surrounded by a stationary pipe, which extends up beyond the slurry operating level. This pipe is referred to as the hydraulic seal, which ensures that pulp and carbon can not by-pass the screen, thus providing an effective seal having no moving parts.
The hydraulic seal is attached to the bottom of the screen by means of hydraulic seal base.
Around the stationary hydraulic seal is a hollow (outer) shaft, which is attached to the drive shaft above the top of the hydraulic seal. This hollow shaft rotates along with the main drive shaft and has a pitch blade turbine (PBT) attached which provides the agitation inside the screen basket.
The PBT blades in turn cause an upwards movement of the pulp inside the screen thus maintaining the pulp in a suspended state. This also aids in keeping the internal wedge wire area clean.
A single gearbox and electric motor drive the entire mechanism.
The MPS screen is attached to the internal launder of the adsorption tank by means of a hook-on arrangement such that the complete mechanism can be removed from the tank without having to loosen bolts or drain the tank.
MPS(P) Interstage Screen
The MPS(P) screen is similar to the MPS
screen and has all the features of the MPS
screen except for one important feature,
the MPS(P) screen has an up-pumping
impeller as part of its internal mechanism.
The volute is also different to that of the
MPS type screen.
The hollow (outer) shaft of the MPS(P) screen houses the up-pumping impeller.
The pumping impeller is a mixflo type, specially designed to handle high flowrates at low tip speeds.
The up-pumping impeller elevates the pulp from inside the screen and deposits it higher than the level of the pulp in the adsorption contactor in which the screen is operating. Thus, the MPS(P) screen is able to generate pulp height sufficient to overcome the pressure drop around the screen, thus overcoming the need to have a series of staggered adsorption contactors.
The benefit of the MPS(P) screen is that the working platform on top of the adsorption circuit is level resulting in improved ergonomics.
A service Kemix offers to clients is the
generation of launder layout General
Arrangement (GA) drawings.
The launder layout GA indicates the positioning of the Interstage screen relative to the Agitator and launder interface. Furthermore, this GA will provide details of Interstage screen port and launder interface.
Launder Gate Valve
The Kemix launder gate valves are
designed for open launder circuits primarily
in gold adsorption circuits such as CIL, CIP
and Pumpcell plants.
These gate valves are custom designed and manufactured to suit the launder dimensions pertaining to the specific application. These gate valves can be supplied as either manual or automated units.
Hook Mounting Bracket and Hold Down Clamp
In Kemix’s experience unsecured Interstage
Screens will become dislodged from their
mounting points, which results in the following:
- A gap between the Interstage screen’s
outlet and interfacing launder which
results in carbon passing to the
- The screen could be damaged as a
result of the dislodgment. Furthermore,
this could result in the screen sinking
into the tank
Hook Mounting Brackets and Hold Down Clamps are the recommended Kemix Interstage screen mounting mechanisms for CIL and CIP applications. These Hook Mounting Brackets and Hold Down Clamps keep the Interstage screens in position which allows it to operate as per design.
These components are fabricated from stainless steel to avoid corrosion and ensure component durability.
Hook Mounting Brackets and Hold Down Clamps are supplied as a unit and perform the following functions :
- Avoids Interstage screen floating or
dislodgment through the use of the
- Ensures the Interstage screen is
secured to the tank top structure.
- Ensures appropriate sealing between
the Interstage screen’s outlet and
Additionally Hook Mounting Brackets and
Hold Down Clamps performs the following
- Hook Mounting Brackets - Hooks and aligns the front end (outlet
side) of the Interstage screen.
- Hold Down Clamps - Locks down the rear end of the