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MEI Online: Plant Operation News: Australasia: June 30th 2003


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:: Century Milestone Due

Since commissioning on March 1, 2000, Pasminco's Century mine has achieved a number of major milestones through ramp up and is now in the final stage of reaching the concentrator's full recovery design capacity. Mining zinc, lead and silver, the open cut operation is expected to operate until 2018

Century comprises two sites - the mine 250 kilometres north north west of Mount Isa and the port site in Karumba, which is on the coast of the Gulf of Carpentaria in Queensland.

Century is one of the largest zinc mines in the world producing more than 30% of Australia's zinc concentrate and five percent of the western world's zinc production.

This equates to 880,000 dry metric tonnes of zinc concentrate or 500,000t of zinc in metal per year. The mine produces 70,000 tonnes of lead concentrate per year.

Century's manager external affairs Kent Quiqley said that at 6am on August 29, Century declared it had reached full production after the concentrator acheived the 500,000t mark continuously for three months.

"The concentrator's next goal is acheiving full zinc recovery at 82.5%," he said.

"To achieve this three major capital projects have been undertaken at a cost of $8 million".

"These projects include the installation of a flotation feed screen, upgrade of the zinc regrind circuit and installation of a new mechanical cell".

The new flotation feed screen has been installed between the primary grinding circuit and the flotation circuit.

The purpose of the screen is to remove oversize rock from the flotation feed stream, which results from cyclone blockages, thus reducing the wear failure of all components in the primary flotation circuit, such as flotation cell floor, rotors, stator, pumps and pipelines.

Kent said the 2.4 metres wide and 6.1m long screen had improved plant availability, which improved zinc recovery due to less shutdown and start up events thus also reducing maintenance costs.

To upgrade the zinc regrind circuit, three new regrind mills were installed.

The new mills are designed to improve the separation between zinc and silica and improve the concentrate grade produced in the primary zinc circuit, which allows higher zinc recoveries to be achieved in the ultra fine cleaning circuit.

Kent said the last project saw the installation of the world's largest mechanical flotation cell.

"The cell has a capacity of 200-ct metres and was added to the zinc scavenger circuit, which comprises a series of 100 cubic metre flotation cells."

"One of the benefits of having a cell this size is space savings through having a smaller footprint overall than the combined footprint of two tanks."

"Savings are also found in the and operating costs when one large rather than two smaller ones are employed."

The cell increases the capacity of zinc scavenger circuit to allow the density to be reduced without an associated loss of residence time. Lower pulp densities in the flotation cells improve the rejection of silica in the primary zinc circuit. Kent said with these major works completed, the concentrator had achieved the full recovery rate of 82.5% of varying occasions.

"However, to officially declare full recovery, the concentrator needs to achieve this three months in a row."

"This concentrator team is working towards putting processes in place to ensure full recovery can consistently be achieved," he said.




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