Tailings disposal system for fast track contract

In less than a year Demotech Engineering designed and supervised the construction and commissioning of a materials handling system for Liqhobong Diamond Mine in Lesotho.

The contract was awarded to Demcotech by Turnkey Civil Lesotho, on behalf of diamond-producer, Firestone Diamonds. The brief called for a system to dispose of between three and four million tons per year of dry tailings, which also had to be capable of withstanding the extreme weather and rugged mountainous conditions in Lesotho. At the same time, it had to be completely re-routable or extendable.
The first route comprised of a downhill conveyor, transfer house and mobile slewable stacker, which became operational in November 2016 – just eight months after the contract was awarded. The second, main route was operational by February 2017. These tight contract deadlines were met despite the challenges posed by access to, and working in, the high altitude location of Liqhobong (2 600 m above sea level), which required special engineering solutions.

Advanced features
Advanced features were designed into the operation, including a belt storage system, enabling the entire arrangement to be extended by 60m within a 24-hour time period. The tailings disposal system consists of a fixed downhill conveyor rated at 700tph, which is equipped with a regenerative electric-hydraulic braking system to prevent the conveyor from running away.
In addition, a 20m mobile slewable emergency boom is part of the standby route, while other components of the system include a 120m-long retractable conveyor, a 450m-long extendable conveyor inclusive of the belt storage system, and a slewable 15m mobile stacker that is 4-wheel driven. This allows the machine to be self-propelled.The 450m-long extendable storage system’s ability to extend the conveyor by 60m increments reduces the number of belt splices, thereby reducing the standing time when the head station, also mounted on a pontoon, is pulled for repositioning using mobile equipment, such as a front end loader. The head of the conveyor feeds onto a mobile, self-propelling slewable stacker, mounted on rubber tyres and equipped with hydraulic drives, which can be repositioned by remote control.

Proven track record
Demcotech has a well-established track record in Southern Africa, working in similarly challenging, high altitude environments such as Letšeng Diamond Mine, also in Lesotho. First contracted in 2008 for the taillings disposal system at the mine, the company has continued to service the mine’s expansion initiatives, with its most recent work focused on upgrading part of the mine tailings materials handling capability. While it is a South African based operation, the company has also seen considerable success internationally. It was recently awarded the contract for a sulphur handling system in Malaysia, following the successful completion of other offshore work, which included the detailed design for an import terminal at Port of Ploce in Croatia, handling both iron ore and coal, through to the contract for the multimillion-dollar iron-ore import/export facility in Lumut, Malaysia.
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