Technology
To the right is a brief description of the nickel production process utilised at Murrin Murrin. Click the image to download the complete flowchart.
At nameplate capacity, the Murrin Murrin plant has the potential to produce 40,000 tonnes of nickel and 5,000 tonnes of cobalt per annum, making Minara one of the world's largest producers of LME grade nickel and cobalt metal.
After mining from nearby open pits, ore is dumped on the run of mine (ROM) pad, where it is sorted according to grade and blended to ensure consistent feed to the feed preparation circuit.
The pressure acid leach circuit consists of four giant titanium lined autoclaves, each the size of a small submarine.
The nickel and cobalt is leached out of the ore slurry, grading approximately 1.35% nickel and 0.09% cobalt, and into solution, by raising the pressure up to 44 atmospheres and spraying it with highly concentrated sulphuric acid at a temperature of 255 degrees celsius. This generates substantial quantities of heat and acid which are later recycled throughout the plant.
The ore is leached, with the valuable nickel and cobalt in a soluble form which must be separated from the residue waste material. This solution is then "washed" to remove waste materials and is recycled back into the slurry ore preparation before eventually being pumped out to the tailings dam as neutralised and inert waste.
Leached ore solution now passes into the neutralisation circuit where calcrete is added to neutralise the acid. The solution is then passed into the mixed sulphides precipitation circuit, where hydrogen sulphide gas is added to convert the solution into a mixed nickel cobalt sulphide.
The mixed nickel cobalt sulphide enters another autoclave where pure oxygen converts the solution from a mixed sulphide into a metal sulphate. At this point the nickel and cobalt molecules remain attached to each other. Impurities such as iron and zinc are removed, before the cobalt is separated using an organic reagent.
The nickel sulphate solution then enters five parallel autoclaves, known as the hydrogen reduction circuit, where the hydrogen is added, liquids are separated and the remaining solids are converted into a dry powder of pure nickel.
The powder is formed into a pillow-shaped briquette, sintered in a furnace and then packaged for transportation. The entire process from beginning to end takes approximately 14 days. Murrin Murrin produces nickel and cobalt briquettes that easily meet the highest A Grade standards of the London Metals Exchange and are highly regarded and in strong demand from consumers around the world.
Heap Leach
Since the Murrin Murrin plant commenced operation the company has been stockpiling low grade ore and scats (reject material from the ore processed for HPAL).
Following a thorough research and development program that commenced in 2004 Minara has successfully demonstrated commercial scale heap leaching of laterite ores and scats to recover nickel and cobalt. The demonstration plant included purpose built stacking equipment and heap leach pads. The stacking of ore and scats commenced in the first quarter of 2007. During the demonstration phase the key technical and economic objectives for both ore and scats were achieved.
The heap leach facility is fully integrated with the existing processing plant allowing for additional production of both nickel and cobalt metal direct from heap leach. Operating costs for heap leach are below that of the existing HPAL circuit.
As at July 2009, over 680,000t of ore and scats had been stacked on the heap leach pads. Operating costs for heap leach are below that of the existing HPAL circuit. It is anticipated that additional process refinements and adjustment to input costs will reduce cost further by the end of 2009.
The heap leach operation provides a second low risk processing stream independent from HPAL delivering an on-going source of revenue not previously available to Minara. It also delivers increased recovery of nickel and cobalt from our mineral resources, reduces CO2 emissions by neutralising excess acid, reduces overall consumption of water per tonne of metal product and provides additional improvements in process efficiency of our operations.