Mining Operations - Pacific Aluminium

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Mining Operations - Pacific Aluminium
Mining Operations
Gove Operations bauxite mine and alumina refinery is located on the Gove Peninsula in the east Arnhem Land region of
Australia’s Northern Territory. From this remote location Gove operations supplies alumina for the international
aluminium industry.
1. Tree Clearing
Timber clearing is carried out two to five years prior to mining. This
allows all the understorey plant species to propagate within the
topsoil. It also helps the various bacteria in the topsoil to flourish
creating a healthy and viable topsoil. The redistribution of the topsoil
on mined areas is a key part of our rehabilitation process
3. Rehabilitation
As part of the rehabilitation program, seeds and plant species from
the area to be mined are collected, with the assistance of local
indigenous people, carefully catalogued and stored. The topsoil is relaid over the prepared areas and area is ‘deep-ripped’ to promote
drainage, aeration and root penetration. This step, which is the
nucleus of the regeneration program, preserves the soil biota and
encourages plant regeneration. The area is then planted and
fertilised immediately before the commencement of the wet season.
5. Crushing and Screening
The haul trucks dump the bauxite into a hopper at the crusher. It then
passes through a primary crusher, screening plant and secondary
crusher to produce material that is less than 25mm in size. The ore is
held in 1700 tonne surge bins before being transported to the refinery
on the 18.7 kilometre overland conveyor.
2. Overburden
The bauxite deposit is overlain by less than one metre of overburden
and topsoil. The overburden and topsoil is returned directly to mined
areas as part of the rehabilitation process. A twin engine scraper
removes approximately 50 per cent of the overburden. The remaining
overburden is removed by the truck and loader fleet.
4. Mining
The bauxite ore is mined using track bulldozers which rip the bauxite
and push it into stockpiles. Front-end loaders then load the ore into
trucks which transport the ore to the crusher. Prior to mining, grade
control drilling is undertaken to establish the grade of ore in each
area of the mine. The mined ore from various areas of the mine is
blended to ensure the ore meets the specifications required in the
refinery.
6. Bauxite Stockpiles
The crushed bauxite is stacked at the refinery on stockpiles. It is
laid down on the stockpiles by a stacker that constantly passes up
and down the stack being built to ensure a uniform grade of bauxite.
There are four 100,000 tonne stockpiles and crushed bauxite is
reclaimed from the stockpiles by either a barrel reclaimer or a
bucket reclaimer.
Refinery
Operations
Gove Operations uses the Bayer alumina
production process developed by Austrian
chemist Karl Joseph Bayer in 1888. The
main stages in the refining process are as
follows:
1. Grinding
4. Security Filtration
5. Mud Washing
Liquor is pumped to security filtration where Kelly and Gaudfrin filters
remove fine bauxite residue particles from the turbid liquor that is not
settled in ferrosilt.
8. Precipitation
With the sand and mud removed, the solution is filtered and cooled
before being ‘seeded’ with crystals of alumina tri-hydrate, causing the
alumina trihydrate in the solution to deposit in solid form around the
seed crystals.
12. Silos
The alumina is stored in concrete silos until it is conveyed via the
export conveyor to waiting bulk carriers.
Bauxite ore is ground to a fine powder in three grinding mills before
being mixed with caustic soda to form a slurry.
Bauxite residue is washed to recover as much caustic as possible
prior to the mud being pumped to the Residue Disposal Area. The
caustic is washed from the bauxite residue using recycled
condensate in a counter-current washing process. Recovered caustic
is recycled from mud washing.
9. Hydrate Classification
Hydro-cyclones in classification separate the slurry into three sizes;
product, fine seed and coarse seed.
13. Port
Situated in Melville Bay, the port facility is connected to the refinery
by a 3 kilometre conveyor loading up to 2,000 tonnes of alumina per
hour. The port has two tugs named Baru and Guya, which in Yolgnu
Matha, the local language, mean crocodile and fish.
2. Digestion
The slurry is heated to 145°C in low temperature digestion and 220°C
in high temperature digestion. The combination of caustic soda and
heat dissolves the aluminium oxide out of the bauxite. Following
digestion, the slurry passes though a series of flash vessels which
reduce the pressure and allow the steam to flash off.
6. Geho Pumps
Large positive displacement Geho pumps are used to deliver high
density bauxite residue waste to the Residue Disposal Area.
10. Hydrate Filtration
The slurry is filtered through disc filters to remove liquor which is then
returned to evaporation. The product from the pan filters is conveyed
to calcination, and the hydrate from the disc filters is recycled back to
precipitation as a seed.
14. Lime Kiln
The lime kiln is heated by fuel oil. The limestone is burnt in the kiln,
transformed into burnt lime and then slaked with water to produce
milk of lime which is pumped to Redside (used for filter aid
preparation and impurities control).
3. Ferrosilt
After cooling, the slurry is pumped into large tanks where bauxite
residue is separated, washed and pumped to a residue disposal
area. Bauxite residue is separated from alumina rich caustic slurry in
large tanks called high rate decanters. Polymer is added to assist in
the settling of bauxite residue.
7. Evaporation
The evaporation plant removes water from spent caustic liquor to
enable the liquor to be recycled to the digestion area. The water
evaporated from the liquor is condensed and recycled in the mud
washing process.
11. Calcination
After being washed and filtered, the alumina trihydrate is heated to
1,100°C in large kilns to dry it and drive off the chemically bound
water molecules, transforming it from alumina tri-hydrate to alumina,
a fine white powder. Gove has four rotary kilns and three fluid bed
calciners.
15. Residue Disposal
Bauxite residue from the refining process is drystacked at the
Residue Disposal Area. Dry stacking is an efficient disposal method
which provides environmental benefits including the need for less
area and improved rehabilitation.
Refinery Process Flow
www.pacificaluminium.com.au

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