zinc concentrate is the product obtained after the zinc ore has been mined and milled. It contains between 80% and 85% zinc and some other elements like iron, sulphur, silica and manganese at much lower concentrations.
Zink is found everywhere on earth and is a natural mineral. The metal is very versatile and has a huge variety of applications, from construction, to transportation, industrial machinery, communications and consumer goods. Zinc is a very strong metal, and it’s also used to protect steel from corrosion.
The major steps in the production of Zinc are smelting, purification and electrolysis. Smelting is the process of melting the metal in a furnace at high temperature, converting the metal into pure zinc and leaving behind impurities such as carbon, iron, aluminium and lead. Several processes are used to smelt Zinc, the most common being the blast furnace and ISP processes. Zinc is also produced by electrolytic and electrothermic reduction. In addition, the vertical retort, developed by the New Jersey Zinc Company, can be used (see diagram in Fig. 3.7).
The raw materials, such as ores and recycled zinc oxides are transported to Nyrstar sites by train. They are then fed into a fluid bed roaster and burned with air to turn them into a brown powder called calcine. During the roasting process, the iron and manganese minerals are removed by water washing and filtration. The calcine is leached using H2SO4, to produce a solution containing Zn and iron (Zn-Ir) sulphides. The solution is filtered to separate the zinc and the impurities. The optimum conditions for the leaching, solvent extraction and stripping of the zinc-Ir sulphide have been studied using Design Expert 7.0 software.