On the move heap leach stacking system

World-class heap leach stacking system supplied to the mineral-rich Zambian copper belt

World-class heap leach stacking system supplied to the mineral-rich Zambian copper belt

FLSmidth’s Johannesburg team, in collaboration with the company’s Spokane team, supplied a world-class heap leach stacking system to the mineral-rich Zambian copper belt. The system serves as a key step toward FLSmidth’s future leach stacking offerings, both in this region and around the world.

The main benefit is that this is the first system delivered by FLSmidth in Southern Africa, and thus will act as a reference for future heap leaching and waste handling opportunities in the Southern Africa market
— Lorrie Dicks FLSmidth Business Development Manager – Material Handling

The portable heap leach stacking system was provided to CNMC Luanshya Copper Mines PLC—located in Luanshya, Zambia—for the conveying of 1,071 t/hr (design) of copper agglomerate onto its heap leach pads.

FLSmidth's Material Handling office in Johannesburg signed the supply contract in 2011, and commissioning was completed in the first quarter of 2013.

The order included an overland (OL) conveyer, a mobile overland tripper (MOT), 20 grasshopper conveyors, a mobile transfer and bridge conveyor and an automated radial stacking conveyor. FLSmidth's Spokane team designed and detailed the leach pad stacking conveyors, while FLSmidth's Johannesburg team designed and detailed the OL conveyor and MOT. All conveyor structures were fabricated in South Africa.

“The main benefit is that this is the first system delivered by FLSmidth in Southern Africa, and thus will act as a reference for future heap leaching and waste handling opportunities in the Southern Africa market,” said Lorrie Dicks, FLSmidth Business Development Manager – Material Handling.

Fabrication and factory acceptance testing (FAT)

The contract required that trial assembly and FAT testing of the MOT, bridge and radial stacker be executed in South Africa before the equipment was transported to Zambia via road.

FAT tests were successfully witnessed by the client in Johannesburg, and video footage of the results was also provided to Luanshya Copper Mines. The video illustrated the mobile equipment’s travel, relocation and control capabilities.

Operations and integration

The MOT, which straddles the OL conveyor, was supplied with two driving stations so it could be driven to the required stacking location along the OL conveyor. The MOT has intelligent anti-collision instrumentation to assist the operator in keeping it located on the overland centerline while being driven, thus preventing a potential collision that would damage the OL conveyor stringers.

The transfer conveyor feeding the bridge conveyor was provided with variable luffing.

The bridge conveyor was supplied with hydraulically driven tracks that could be manually or remotely driven via an operator-controlled radio pendent. The bridge had a separate onboard generator used to power the bridge track drives whilst towing the radial stacker over long distances.

The radial stacker has an elevated operator control cabin that includes an HMI and manual operator controls. Retractable gull wing wheels slew the radial stacker and are powered by hydraulic motors in the wheels. Fixed in-line wheels are used for moving or towing the radial stacker using the bridge conveyor. Once the radial stacker is set in the operating position, the gull wing wheels are lowered for service, lifting the in-line wheels off the ground and out of service. The radial stacker angle encoder measures the slew angle offset of the radial stacker relative to the bridge conveyor.

Control and instrumentation

An auto-stacking solution was developed to provide the radial stacker with full operational capabilities in automatic mode. To do this, a mathematical auto-stacking solution was developed in-house on a conceptual level and refined through numerous design iterations. The final auto-stacking algorithms required specialized programmable logic controller coding and included processes for cone stacking at low tonnages, continuous stacking and manual stacking.

No central control room was available to provide indication of the run status or fault conditions of the conveyors and instruments, so two human machine interfaces (HMIs) were supplied—one being in the field at the head end of the OL conveyor and the other located in the operator control room on the radial stacker.

FLSmidth provided a wireless network for the transfer of all instrument signals from each mobile conveyor to both HMIs, which allows one operator to efficiently pinpoint a technical problem. The wireless network is used for indication only, while all controls were hardwired on each mobile conveyor.

A group-start facility in AUTO was provided from the radial stacker’s HMI operator interface. Maintenance mode can be selected from dedicated conveyor local control system panels so that each piece of equipment can be started individually.

Stockpile height and slew speed are determined by two radar ultrasonic level sensors located on the mobile slinger. The control algorithm of the radial stacker was programmed to suit the design requirements in stockpiling height (trough to peak).

Intelligent pullkeys were used on the overland conveyor with feedback to the HMIs where status could be monitored in defined zones. Thermistors were supplied on the 250 kW overland conveyor drive motor to monitor winding temperatures. All gearboxes have PT100s to monitor gearbox oil temperature, and fluid couplings were supplied with thermo switches. All process and control instruments were hardwired back to their respective mobile conveyors.

Commissioning

The Muliashi Project was commissioned by CNMC Luanshya Copper Mines PLC under the technical supervision of FLSmidth's Johannesburg team during the first quarter of 2013. 600,000 tons of copper agglomerate has subsequently been stacked onto the leach pads.

CONTACT: Lorrie Dicks