Ranger Mine Rehabilitation, Pit 3 Tailings Dewatering

- Stephen Bourhill, Ventia Australia Pty Ltd

It is a strategic priority for Energy Resources of Australia (ERA) to comprehensively rehabilitate the Ranger Project Area.

Rehabilitation and closure planning began soon after the Ranger mine began producing uranium oxide in 1981. Mining finished in 2012 and with the completion of ore processing in 2021 the mine transitioned to its final rehabilitation and closure stage. ERA’s focus is to create a positive legacy and achieve world class, sustainable rehabilitation and closure of its former mine assets.

An essential early stage to the successful rehabilitation of the site involved the enhanced consolidation of a 20-90m deep layer of tailings that had been transferred to the former mine pit, Pit 3. To achieve this, the design required over 41,000 Prefabricated Vertical Drains (PVDs) to be installed into the tailings to depths of up to 40 metres. Once installed the PVD would provide a preferential flow path (using capillary action) for water trapped within the tailings, allowing the water to be expressed upward and the tailings to rapidly consolidate. Due to a covering layer of water up to 5 metres in depth over the tailings, a specialised delivery method would be required to achieve the projects aims.

The approach

Ventia was engaged to design, construct and operate a unique barge system to allow the installation of the PVDs from the water’s surface. Working closely with ERA and Ventia’s subcontractors, Ventia designed a barge system that could:

• be easily transported to the remote site,
• be quickly and safely assembled,
• manage the extensive forces applied to it by the two 100 tonne mobile PVD installation rigs,
• included integrated moon pools to allow wicks to be installed from within the barge footprint
• provide all necessary support functions for the works and workforce,
• could be positioned using a highly accurate computer controlled winching system, and;
• anchor the winch wires to specifically installed rock anchors in the pit wall

Safety to the workforce was of paramount importance. The challenging site conditions required a workforce to operate in close quarters to operating plant in a hot, humid tropical environment on an acidic water body. Systems were designed and implemented prior to the commencement of works to allow the workforce to operate safely in the environment and Ventia’s drive towards continuous improvement ensured processes were updated where potential improvements were identified.

The Result

The works required an onsite workforce of over 70 personnel and over 101,000 hours worked on site to successfully deliver the project. Ventia’s Senior SHEQ Engineer, Allan Garland, said the team’s strong commitment to safety ensured the project was completed lost time injury free and demonstrated the value of early innovative design approaches for safety.

In March 2023, Ventia successfully completed the installation of 41,850 PVDs with 1,640,643LM of PVD material installed into the tailings (equating to driving the distance from the mine to Alice Springs NT). And throughout installation, the barge positioning system used 4 winches under 11t of tension each to hold the ±500t barge within an average of 89mm, which was well within the design specification, said Ventia Senior Project Engineer, Stephen Bourhill.

The successful delivery of this project leveraged the innovative skills of the Ventia team to develop a safe and reliable wick installation process. Ongoing survey of the tailings indicate the wicking process has met and exceeded the expectations of ERA’s model and will help ensure the success of future rehabilitation stages, said Ventia Project Manager, Jayson Gaul.

Figure 1: Figure 1: Barge with 2 x PVD Installation Rigs

Figure 2: Drone Photo of the Wicking Barge Operating Deck

Figure 3: A PVD Installation Rig

Figure 4: A rock anchor group, used to anchor the Barge Positioning System

Article Published on 12/12/2023

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