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

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.

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.

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.

Mining Operations

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 re-laid 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.

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:

Refinery Operations

12. Silos The alumina is stored in concrete silos until it is conveyed via the export conveyor to waiting bulk carriers.

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.

4. Security Filtration

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.

9. Hydrate Classification Hydro-cyclones in classification separate the slurry into three sizes; product, fine seed and coarse seed.

1. Grinding Bauxite ore is ground to a fine powder in three grinding mills before being mixed with caustic soda to form a slurry.

5. Mud Washing 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.

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.

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.

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.

6. Geho Pumps Large positive displacement Geho pumps are used to deliver high density bauxite residue waste to the Residue Disposal Area.

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.

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.

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.

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).

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

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