# Evaluation and Current State of Primary and Secondary Zinc Production--A Review
## 3 Zinc Production from Primary Resources
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**Process** & **Characteristics** \\ \hline Roasting–Leading–Electrowinning (RLE) & Conventional zinc hydrometallurgical technology, which consists of five main stages, i.e., roasting, leaching, solution purification, electrospinning and casting; \\ Roasting–Leading–Electrowinning (RLE) & the ore after enrichment becomes zinc concentrate, which is then converted into zinc oxide in the following roasting process: \\  & ZnS + 0.5O\({}_{2}\) = ZnO + SO\({}_{2}\) (1) \\  & In the leaching process, the oxidized concentrate ores are treated in a sulfuric acid solution to release zinc ions from the concentrate as follows: \\  & ZnO + H\({}_{2}\)SO\({}_{4}\) = ZnSO\({}_{4}\) + H\({}_{2}\)O (2) \\  & Due to the contamination and heterogeneity of the concentrate, other metal ions that are harmful to the electrolytic process also pass into the leaching solution, therefore, the solution is purified before the following process of electrolytic separation of zinc from the electrolyte: \\  & ZnSSO\({}_{4}\) + H\({}_{2}\)O = Zn + 0.5O\({}_{2}\) + H\({}_{2}\)SO\({}_{4}\) (3) \\ Atmospheric Direct & A typical hydrometallurgical process, which differs from the RLE process by the elimination of the roasting process (the zinc sulphide concentrate is crushed into fine particles and fed directly to the leaching process), oxygen is blown into the leaching process to oxidize the zinc sulphide (the leaching reaction takes place at high temperature and using iron ions as a catalyst), sulfur is recovered from the leach residue by flotation. \\ Engitec & EZINEX is a hydrometallurgical process, based on the electrolyte NH\({}_{4}\)Cl, capable of producing zinc \\ Zinc & metal directly from raw ZnO, the first industrial scale EZINEX plant was designed to produce zinc \\ Extraction (EZINEX) & directly from electric arc furnace (EAF) dust by Engitec in Italy in 1993; the basis of the process is a unique hydrometallurgical zinc recovery system, insensitive to typical impurities affecting traditional Zn production. \\ Zinc & Direct pressure leaching of zinc sulphide concentrates to produce zinc sulphate solutions suitable for zinc recovery by electrolytic leaching while oxidizing sulphide sulfur to its elemental form only, as follows: \\  & Laaching (ZPL) & ZnS + H\({}_{2}\)SO\({}_{4}\) + \({}_{2}^{1}\)O\({}_{2}\) = ZnSO\({}_{4}\) + H\({}_{2}\)O + S\({}^{0}\) (4) \\  & Developed by Sherritt over 40 years ago and used on an industrial scale since 1981, the Zinc Pressure Leaching (ZPL) process can be easily integrated into existing zinc refineries using RLE technology, allowing these plants to increase zinc production or replace old or obsolete equipment. \\ Direct Zinc & In the late 1990s, Outotec (formerly Ausmelt Ltd.) conducted research for BUKA Minerals Ltd. On the direct smelting of zinc sulphide concentrates using the Ausmelt TSL technology, this work led to the development of a two-stage smelting process; it is particularly well suited to the processing of low-grade concentrates containing significant amounts of iron and other gangue impurities such as MnO, SiO\({}_{2}\) and MgO. \\  & Developed by the VINITSVETMET Institute in Ust-Kamenogorsk, Kazakhstan, in 1985, consists of the following two stages: in the first stage, lead sulphide concentrate, zinc smelter waste, recycled dust, silica, limestone, fine coal and coke are introduced from the top of the reactor into reaction shaft; together with oxygen, lead, zinc and other metal sulphides are converted into metal oxides during heating; oxides, silica and limestone form half-molten slag, and the gas reaches up to 15\% sulfur \\ Thermal Process (KIVCET) & dioxide; the following reactions take place at this stage: \\  & PbS + 3/2O\({}_{2}\)(g) = PbO + SO\({}_{2}\)(g) (5) \\  & ZnS + 3/2O\({}_{2}\)(g) = ZnO + SO\({}_{2}\)(g) (6) \\  & PbS + 2 PPO = NbP + SO\({}_{2}\)(g) (7) \\  & In the second step, PbO and ZnO are reduced by adding coke; gaseous zinc can be recovered as metal in the condenser. \\  & ISP is one of the most widely used smelting technologies that simultaneously smell zinc and lead, consists of two sub-processes, lead-zinc sintering and metal smelting; unrefined lead is tapped from the bottom of the shaft furnace, while gaseous zinc is introduced into the condenser, where mixers with specifically shaped rotors spread the liquid lead over the condenser space; as a result of the contact of the shaft furnace gas stream with liquid lead intensive heat exchange and dissolving of zinc vapor in the lead takes place; the technology was developed in the middle of the last century in the UK to create a pyrometallurgical process for the continuous extraction of zinc, in addition to traditional raw materials such as lead zinc sulfide, secondary materials such as dust and sludge from metallurgical processes, for this reason, the simultaneous production of metallic lead is an advantage of the process, because the marking of most recycling materials shows, apart from zinc, also lead. \\ \end{tabular}
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