Risdon smelter

The Risdon smelter in Hobart, Tasmania, is a large zinc smelter situated on the western shore of the Derwent River. It uses the roast, leach and electrolysis (RLE) process for producing zinc and works closely with the Nyrstar multu-metals smelter at Port Pirie in South Australia. The Port Pirie smelter further processes the by-product paragoethite and other leach by-products that result from the smelting of zinc at the Risdon smelter. The Risdon Smelter is regarded as being one of the world's most efficient and largest zinc producers having a capacity to produce 280,000 tonnes of market quality zinc annually.

Work on building the Risdon smelter in Hobart began in 1916 when a 10 tonne a day demonstration plant was constructed.†In 1920 the Electrolytic Zinc Company (EZ) was formed to operate the Rosebery mine on the West Coast of Tasmania, as well as to operate the Risdon smelter. In 1971 the EZ Company introduced the jarosite process of smelting zinc and the plant became a world leader in zinc technology. North Broken Hill Peko acquired the smelter in 1984 when it took over the EZ company and in 1988 North Broken Hill and CRA merged their smelting, lead and zinc mining interests to form a new company, Pasminco. The jarosite process was replaced by paragoethite in 1997. the next major event took place in 2004 when Pasminco went into voluntary administration which resulted in a new company Zinifex being formed to operate the smelter. In 2007 Zinifex merged with Umicore to form Nyrstar. At its height the Risdon smelter employed up to 3,000 workers. Today it employs 499 who produce 272,000 tonnes of zinc metal a year.

Risdon smelter's current owner, Nyrstar, is a world leading zinc smelting company and among the top five zinc mining company's .†It produces zinc from concentrates sent to it from various mines, the main two being the Rosebery mine in Tasmania and the Century mine in Queensland. The smelter produces special high grade (SHG) zinc galvanising alloys as well as zinc die casting alloys.

The Risdon smelter converts zinc concentrate into zinc metal for use in a wide variety of applications as zinc gives iron and steel excellent corrosion resistance.† It is also a reasonably hard metal in its own right and it has a low melting point. This makes it suitable for die casting but still malleable enough to be extruded, rolled and formed.

Around 500,000 tonnes of zinc concentrate is received at the Risdon smelter wharf every year. †The concentrate is unloaded into covered stockpiles before being transported 800 metres by conveyor belts to be fed into one of two roasting furnaces. Here the concentrate is roasted to a temperature of between 930 and 960 degrees Celsius. This turns the concentrate into calcine that will dissolve. The steam produced in this process is captured and used to heat acid in the later leaching stage of the process. The calcine is then taken along conveyor belts to undertake leaching. Leaching dissolves the zinc out of the calcine concentrate as well as removing other impurities such as iron leaving a zinc rich, yet still impure, solution.

This impure solution requires purification which is obtained by adding pure zinc dust, this zinc dust is collected during casting. †This allows the remaining impurities to be removed as solids, a result of the zinc dissolving. The final stage is reached when the zinc solution is placed onto aluminium cathodes by having an electric current pass through the cathodes as well as lead anodes. This is known as electrowining. The cathodes are then removed from the cells to allow the zinc sheets to be stripped from them for sending off to be cast.