The process of ore mining involves several steps to extract valuable minerals from the ore. Initially, the ore is fed into a jaw crusher, which breaks it down into smaller pieces. The broken ore is then transported to a ball mill, where it is ground to a fine powder. After this, the ore fines are classified using a spiral classifier, which separates solid particles of different densities in the liquid based on their precipitation speeds. The mineral mixture is washed and graded according to the proportion of solid particles.
The next step is the flotation process, which separates the mineral particles from other substances based on their characteristics. Different drugs are added to the mixture depending on the mineral characteristics, which cause the minerals to separate. This process upgrades the ore, which may initially contain a low percentage of zinc, to a concentrate that contains more than 50% zinc. The concentrate is then dried, and up to 90% of the zinc in the ore can be recovered.
There are two processes used to produce zinc metal in Australia: electrolysis and smelting. The electrolytic process is used at the Risdon zinc refinery in Tasmania, where zinc concentrate from various Australian mines is roasted to eliminate most of the sulphur and make impure zinc oxide. The roasted concentrate is then leached with sulphuric acid to form a zinc sulphate solution, which is purified by adding a small amount of zinc powder to precipitate and remove traces of copper, cadmium, cobalt, and nickel. The solution is piped to electrolytic cells, where the zinc is electrochemically deposited on aluminium cathodes. The zinc is then removed from the cathodes, melted in a furnace, and cast into slabs.
The smelting process is used at Cockle Creek near Newcastle in New South Wales to produce zinc and lead metal simultaneously in a blast furnace. Zinc and lead concentrates from various mines are blended and sintered or partly melted to combine the fine particles into lumps and remove some sulphur as sulphur dioxide. The sintered product is mixed with coke and smelted in a blast furnace to produce zinc vapour, which is condensed by cooling with a spray of molten lead to form impure molten zinc metal. To remove the small amount of lead and cadmium impurities, the liquid zinc is twice boiled to zinc vapour and recondensed to produce high purity zinc metal.
Zinc oxide and zinc dust are produced from primary and scrap zinc at West Footscray in Melbourne, Victoria, and in minor amounts in Brisbane, Queensland. Risdon is Australia’s largest zinc refinery and one of the largest in the world. Overall zinc recovery from concentrates is about 95%, and less than half of Australia’s zinc concentrates are processed domestically.