Karara’s dry tailings system uses mobile conveyor
Karara Mining’s tailings facility contractor, Bis Industries, has commissioned FLSmidth to design and engineer a dry tailings system for the iron ore project.
Central to the system will be an FLSmidth RAHCO mobile stacking conveyor. Bis says FLSmidth’s system will be a first in dry tailings in Australia, adding there are 25 in operations globally.
The system uses a single conveyor supported on a series of truss frames and crawler tracks. The trusses are connected by a specially developed joint that allows the machine to follow uneven ground conditions.
The belt flight runs along the top chord of the trusses traversing the length of the conveyor. The belt drive is typically located at the end of the machine, where it is closest to the electrical power.
The mobile conveyor tripper travels along the top chords of the mobile stacking conveyor. The tripper trips ore onto the cross conveyor belt and discharges the material onto the stack.
Bis said dry stack tailings systems are ideal for dry climates, reducing water requirements and tailings storage footprint while offering improved site rehabilitation potential.
At Karara, a vacuum belt filter will reduce the retained moisture content of the tailings to around 15%, giving the tailings a consistency of wet sand, according to Bis. Tailings will then be delivered to the storage area by conveyor and dispersed from the mobile stacking conveyor.
The conveyor has been designed to climb or descend a 10% slope while operating and a 20% slope when traveling with an empty, non-running belt.
Initially operating at 14.6Mtpa, 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 tailings up to 90m high (in three stages) over a 20-plus year period.
Bis Industries’ director, Jim Ahearn, 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%.
Bis said an area of 4km² has been allocated for tailings storage. By comparison, for a traditional pond storage system an area of 52km² would likely be required. The area required for such a pond storage system is based on a 3m deep pond.
For a fully-lined 6m deep pond, the space requirement would be halved. However, even at 6m deep, the total area required is significantly more than that allocated for the dry storage system tailings, according to Bis.
Bis said the dry tailings are geotechnically stable and composed predominately of silica and will also provide a secure and workable base for the mine’s reclamation and revegetation program.
The dry condition of the tailings will also make them easier to work. Because there is no water to remove, as would be the case with traditional tailings dams rehab programs, efficiency of the program will be enhanced, Bis said.