The year 1917 was a watershed for Australian copper mining and particularly for copper smelting.
Prior to this time many copper mines were equipped with an on-site smelter, into which high-grade copper ore or a gravity copper concentrate were fed to produce a copper matte (with 40 per cent copper) for subsequent converting to blister copper (99 per cent copper) and refining at centralised copper refineries in Australia or overseas. During the early 1900s several on-site smelters were also equipped with converters.
During World War I (WWI), copper was in demand and the price was abnormally high. The average annual copper spot price (nominal) on the London Metal Exchange peaked in 1917 at £126 and by 1922 had dropped to £63, and reserves of higher grade ore were running out at some mines. The change in copper price is shown in Figure 1.
This article was inspired by a two-part paper, The evolution of early copper smelting technology in Australia, by Peter Bell and Justin McCarthy published in the Journal of Australasian Mining History Association in 2010 and 2011. The paper included descriptions and comparisons of reverberatory furnaces and waterjacket blast furnaces, and converters, and identified 156 copper smelters built in Australia between 1847 and 1918.
Copper smelting is typically a two-stage process, with a feed of copper ore or concentrate to a roaster or sinter plant to agglomerate the concentrate and remove some sulfur. This material, along with fluxing minerals and a fuel such as coal or oil, is then fed to a furnace where a copper matte is produced. The slag from the furnace is essentially an iron-calcium silicate and some oxides. The copper matte is transferred to a converter where iron sulfide is removed as a copper-rich slag, and finally the copper sulfide (‘white metal’) is blown with air or air and oxygen to produce blister copper for subsequent fire and electrolytic refining.
Bell and McCarthy describe the period up to 1918 as being characterised by an early use of reverberatory furnaces and later by adoption of waterjacket blast furnaces. A reverberatory furnace is a horizontal structure built of refractory bricks in which feed is introduced at one end and copper matte and slag removed at the other. A waterjacket blast furnace is a water cooled vertical steel structure lined with refractory bricks. The feed is introduced from the top and a blast of air blown up through the furnace, with copper matte and slag removed at the base. The waterjacket blast furnace was relatively easy to move from mine to mine, but required a reliable water supply for the water jacket. Converters used included the horizontal barrel type such as the Pierce-Smith and the older vertical cylindrical type such as the Hartmann.
The large copper mines of the early 1900s in Queensland, New South Wales, South Australia and Tasmania each had a smelter close to the mine. This was also a period when concentration of ore using gravity methods such as jigs and tables and froth flotation were increasingly used to reduce the amount of material fed to smelters. Mount Morgan in Queensland experimented with and then commissioned a flotation plant in 1914. The Mount Lyell mine in Tasmania had started smelting concentrates from a small geologically different orebody and concentrator in 1916. Many copper mines and smelters closed in the period from 1917-1920.
The Hampden smelter at Kuridala, south of Cloncurry, consisting of two waterjacket blast furnaces and a converter section, produced blister copper from 1911 until the drop of the copper price in 1918, and again for a period in 1920. Various waterjacket blast furnaces were used at the nearby Mount Elliott mine site from 1909, but the smelter closed in 1919 following falling copper prices.
The Mount Cuthbert smelter north-west of Cloncurry was commissioned in early 1917 and comprised a single waterjacket blast furnace and two converters, smelting ore from local mines, which was previously transported by rail to the smelter at Mount Elliott. The mines and smelter closed in 1920.
The Corella Copper Company commissioned a 60 t/d waterjacket blast furnace adjacent to the Rosebud mine west of Cloncurry in 1915, but falling ore reserves and copper grade prompted the closure of the Rosebud and satellite mines, and the smelter, in 1917.
The Great Cobar operation was one of several copper mines in the Cobar district of New South Wales and had three waterjacket blast furnaces, and three converters commissioned in 1907. The mine and smelter were closed in 1914, and smelting recommenced in 1916, continuing until 1919. There was a small waterjacket blast furnace commissioned at the Cornish, Scottish and Australian (CSA) mine in the Cobar district in 1917 and this was superseded by a larger waterjacket blast furnace in 1918. The CSA mine closed in 1920 following an underground fire.
The small State Smelting Works at Phillips River west of Esperance on the south coast of Western Australia was commissioned in 1904. There was a waterjacket blast furnace, and a later concentrating plant and converter added to produce blister copper. The smelter closed in 1918 due to the fall in the price of copper.
The copper smelters and furnace types operating in Australia in 1917 and since that time are shown in Figure 2.
From 1912 the Mount Morgan gold and copper mine in central Queensland used concentration and smelting with the gold being won in subsequent copper refining operations. By 1918 approximately 35 per cent of the gold-copper ore was fed directly to a single waterjacket blast furnace with the remainder of the gold-copper ore being processed in the gravity and flotation concentrator and sintered before smelting. The waterjacket blast furnaces at Mount Morgan are shown in Figure 3. The operation closed in 1925 but was reopened in the early 1930s, and the copper and gold concentrate shipped to custom copper smelters in the USA.
The Wallaroo smelter on the west coast of South Australia’s Yorke Peninsula was supplied with copper concentrates from mines at Wallaroo and Moonta. A single waterjacket blast furnace was fed from a desulferising section and the matte held in a reverberatory furnace before converting to blister. This property lasted longer than some other copper mines and smelters following WWI. The company went into liquidation in 1923, with the smelter operating until 1926, treating precipitates and ore stockpiles.
The only smelters remaining in operation after this period were those at Chillagoe in Queensland, Port Kembla in New South Wales and Mount Lyell in Tasmania. The smelter at Port Kembla was part of an integrated custom smelter and refinery complex commissioned in 1908. It was originally equipped with two reverberatory furnaces and two blowing stands for converters. It survived the period after WWI and the reverberatory furnaces had been replaced by two waterjacket blast furnaces by 1915.
The Mount Lyell mine in Tasmania was producing blister copper from two waterjacket blast furnaces in 1918, together with a new converter section adjacent to the blast furnaces. The majority of the feed was crushed ore, with a minor amount of gravity and flotation concentrates that were sintered before being fed to the blast furnaces.
During the next ten years the Mount Lyell concentrator was expanded and in 1928 the direct feed of ore to the blast furnace was only 12 per cent of the total, consisting mainly of high grade siliceous ore as flux. A sinter plant was installed to treat the concentrate feed, but was later shut down, and the concentrate fed directly to the blast furnace, a rare practice in the smelting industry. The Mount Lyell smelter closed in 1969.
The Queensland state government purchased lead and copper smelters at Chillagoe in 1918. The smelters were renovated and copper smelting of ores from the Chillagoe district and as far away as the Cloncurry district proceeded under government management. There were five waterjacket blast furnaces and converters at the site.
The lead smelting ceased in 1933, while the copper smelting continued until 1943, when copper smelting commenced at Mount Isa.
The reconstituted Mount Morgan company commissioned a new reverberatory furnace in 1939, with higher grade concentrates being fed directly to the furnace and lower grade concentrates being roasted in four Edwards roasters before feeding to the furnace.
The wartime government required a greater production of copper in Australia and, rather than using the run-down Queensland government Chillagoe smelter, saw a better opportunity by directing the Mount Isa mine to mine known copper deposits and to smelt the ore. One of the existing lead smelter waterjacket blast furnaces was modified and the converter section with the enclosing building purchased from the abandoned Kuridala mine site. After much preparation a changeover of only three days was required to change from lead to blister copper production in 1943. The end of World War II (WWII) signalled the change back to lead smelting and the implementation of a long-term plan for both lead and copper smelting at Mount Isa.
A permanent copper smelter at Mount Isa, equipped with a reverberatory furnace, was commissioned in 1953. The smelter was rebuilt and commissioned in 1962, with an increased capacity of 100 000 t/a of blister copper. The feed to the furnaces was from five roasters. A fluid bed roaster replaced the multiple bed roasters in 1973.
In the 1960s the Port Kembla smelter and refinery were upgraded, including a new larger waterjacket blast furnace to receive concentrates from the newly commissioned CSA mine at Cobar in New South Wales. In the late 1960s a pilot plant for the WORCRA process, which integrated the furnace and converter in a continuous process, was constructed at the Port Kembla site but was not replicated at commercial scale.
A flash furnace consists of a vertical reaction shaft and a horizontal settler, and smelting is performed with dried concentrates that provide a portion of the fuel. The Edwards roasters and reverberatory furnace at Mount Morgan were replaced by a concentrate dryer, Outukumpu flash furnace, and two converters in 1972. Smelting at Mount Morgan is shown in Figure 4.
A smelter using a flash furnace was commissioned in 1973 near the new Warrego copper mine in the Tennant Creek district of the Northern Territory. The smelting operation was shut down in 1975 due to the falling copper price and technical problems in the converting section, and there was a brief recommencement of smelting at the Warrego smelter in 1980.
A major change to copper smelting came with the commissioning of a flash furnace at the Olympic Dam mine in 1988. The flash furnace incorporated oxygen-enriched air to produce blister copper directly, without separate converters. A new larger flash furnace was commissioned in 1999 as part of an expansion project.
Top submerged lance furnaces
The Commonwealth Scientific and Industrial Research Organisation (CSIRO) developed a top submerged lance furnace technology in the 1960s known as SiroSmelt, which has been licensed and developed as Ausmelt and IsaSmelt furnace technology. It consists of a refractory lined cylinder with a lance introduced from the top to blow air or oxygen-enriched air into the bath of molten copper matte and slag.
A 15 t/h demonstration IsaSmelt furnace was operated at Mount Isa from 1987 until 1992, when it was replaced with a 104 t/h unit. The 104 t/h unit replaced the older of the two reverberatory furnaces. The smelter was upgraded between 1995 and 1998, an acid plant commissioned, and the remaining reverberatory furnace shut down. An IsaSmelt furnace operated briefly at the Radio Hill nickel-copper mine in Western Australia from 1991.
By the late 1980s the Port Kembla smelter was drawing concentrates from the Woodlawn and CSA mines in New South Wales, and the Moonta mine on the Yorke Peninsula in South Australia, and required either modernisation or potential closure. Studies identified the Noranda reactor as a replacement furnace for the existing waterjacket blast furnace. An acid plant was installed to manufacture sulfuric acid from the sulfur dioxide produced in the Noranda reactor. The smelter shut down in 1995 due to environmental and market difficulties.
The ownership at Port Kembla changed again in the late 1990s. The smelter was modified and reopened in 1999 with the Pierce-Smith converters replaced with a holding furnace and a Mitsubishi converter. The smelter closed in 2003 due to ongoing breaches of its environmental operating licence including discharges of sulfur dioxide. The site was eventually cleared and the remaining smelter stack demolished in a highly publicised blasting operation in 2014.
The period in review ended with only the Mount Isa and Olympic Dam copper smelters in operation, and the planned closure of the Mount Isa smelter in 2016 deferred until 2022.
Thanks are due to Peter Bell, Geoff Kelly and Dr Ray Boyle for copies of papers, suggestions and photographs.