Calcination
To produce the required magnesia products, QMAG converts the magnesium carbonate (magnesite) feedstock from Kunwarara to magnesium oxide (MgO) or magnesia.
This is undertaken at QMAG's Parkhurst plant on the northern outskirts of Rockhampton. Magnesite trucks discharge into a hopper and the magnesite is stockpiled using a travelling chevron stacker. The magnesite is carefully blended into the initial calcination process stage to meet quality requirements and maximise yields.
Calcining operations are conducted in two 17-hearth Multiple Hearth furnaces (MHF's), which operate at 200,000 tonnes annual product capacity. The raw magnesite is fed into the furnaces, where it is heated by natural gas to 1,050°C to produce caustic calcined magnesium oxide or magnesia (MgO).
While a considerable amount of upgrading has been achieved with the raw magnesite at Kunwarara, further upgrading of the calcined magnesia is completed prior to the production of QMAG's high-grade deadburned (DBM), electrofused (EFM) and calcined (CCM) products.
The objective of the upgrading process is to separate the calcined magnesite by crushing and screening into discrete streams based on chemistry and size. The sorted calcined magnesia is stored in bins with the contents of each bin separately analysed to allow blending to form a homogenous material of known composition suitable for the product specification in DBM, EFM and CCM products.
The various product grades are stored for blending prior to transfer to DBM or EFM plants. This allows very precise quality parameters to be set.