Reduced water requirements, tangible water savings and environmental advantages lead the list of benefits for the tailings management system at Karara Mining Limited’s Karara Iron Ore project.
With a site-wide emphasis on water management, Bis Industries, which holds the contract for operation and management of the Karara tailings facility, has commissioned an advanced dry tailings management system for the site.
The material handling system will be designed and engineered by FLSmidth.
Dry tailings in Australia
The technology behind the mobile stacking conveyor is well proven and there are more than 25 such FLSmidth® RAHCO® systems throughout the world, operating at more than 12,000 tph. The system at Karara will be the first of its type in dry tailings in Australia.
Dry stack tailings systems are considered ideal for dry climate mining operations. Along with reduced water requirements (achieved through process water recycling and the virtual elimination of water losses through evaporation and/or seepage), other direct benefits of dry tailings systems include substantially smaller tailings storage footprint and improved site rehabilitation potential.
A pressure filter, supplied by Karara, will reduce the retained moisture content of the tailings to around 15 percent, giving the tailings a consistency of wet sand. They will then be delivered to the designated storage area by conveyor and dispersed from the mobile stacking conveyor.
An area 2 km x 2 km (4 km2) has been allocated for tailings storage. By comparison, should a more traditional pond storage system be utilised, an area of around 52 km2 would be required to store the tailings the Karara project will generate. (The area required for such a pond storage system is based on a 3 metre deep pond. For a fully-lined 6 metre deep pond, the space requirement would be halved. However, even at 6 metres deep, the total area required is significantly more than that allocated for the dry storage system tailings).
Mobile stacking conveyor
Designed to suit the site's stacking plan, Bis Industries' GPS-controlled mobile stacking conveyor will be 371 metres long. Constructed of space frame truss sections, it is mounted on crawler tracks that level and move individually to maintain the required levelling and alignment as material is continuously stacked.
The conveyor has been designed to climb or descend a 10 percent slope while operating and handling material, and a 20 percent slope when travelling with an empty, non-running belt.
Initially operating at 14.6 tpa, the system has been designed to meet the increased output from the processing plant as Stage 2 of the Karara project comes on line. When fully operational, the mobile conveyor system will stack the tailings up to 90 m high (in three stages) over a 20-plus year period.
Bis Industries’ director Jim Ahearn, who led the team investigating storage methodology, said a mobile stacking conveyor system offered a number of benefits for the project and would go a long way toward Karara meeting its water reduction target of 30 percent.
“We examined multiple options,” he said, “finally arriving at the mobile stacking conveyor solution as more environmentally appealing, much less water dependent and ultimately lower cost for our customer.”
With that decision made, the question then became one of who would provide the system.
“There were multiple criteria,” said Jim Ahearn, “but key for Bis Industries were system performance and reliability, deliverability within Karara’s timelines, strong system safety under operational conditions, robust global support from the supplier, the supplier's willingness to form a close and transparent working relationship, a cost structure that delivered a commercially attractive result for Karara Mining, and evidence that the system had robust long term mechanical availability.”
“The FLSmidth® RAHCO® system met all our criteria,” Ahearn said.
The geo-technically stable dry tailings – composed predominately of silica – will also provide a secure and workable base for the mine’s reclamation and revegetation programmes. The dry condition of the tailings will also make them easier to work and, because there is no water to remove – as would be the case with traditional tailings dams rehab programs – efficiency of the programmes will be enhanced.
“This tailing strategy will cement our environmental credentials by simultaneously delivering several significant environmental benefits,” said Tim Netscher, managing director of Karara Mining and ASX-listed Gindalbie Metals that is a joint venture partner, along with Chinese iron and steel company Ansteel, in the Karara Iron Ore Project.
CONTACT: Christian Trulsson