Direct zinc smelting

DIRECT ZINC SMELTING IN AN IRON OXYSULHOE BATH... 

Figure 1 illustrates the main features of the direct zinc smelting process. The bath smelting process can be described as follows ... 

Figure 1 - Schematics of the Noranda Direct Zinc Smelting Flowsheet...

The main reaction of the direct zinc smelting process may be written as Femme + Zn >n-m. = Zn(g) + FeSnmie Femme + ZnOmme = Zn(g) + FeOmrne... 

Fortunately, unlike the Cu-S system, molten Fe and FeS are completely miscible and the sulfur potential decreases with increasing iron content in the Fe-S matte. Thus, the sulfur potential can be controlled to any desired low value by varying the Fe/S ratio in the Fe-S matte. Basically, the iron required for fixation of the sulfur can be in any form, such as scrap iron, iron ore, steel plant dust and even zinc plant leach residues. When iron oxides are used, reductants such as coal or coke are required to produce reduced iron. The overall reaction of direct zinc smelting is ... 

Under direct zinc smelting conditions, if the CO/COz is controlled above 3 at temperatures above 1300 C, the Fe-S-0 matte as shown in Table 1 can be approximately considered as a FeO-FeS binary system. Consequently, the composition of slag can be estimated from Figure 3 and is presented in Table n. 

Table II - Estimated Slag Compositions in Equilibrium with FeS-FeO Matte Under Direct Zinc Smelting Conditions, Pzn=0.1 atm and 1350"C...

Flicker A process for producing zinc oxide by direct oxidation of zinc vapor. Operated by the Fricker s Metal Company at Luton and Burry Port, UK, in the 1920s and 30s, subsequently acquired by the Imperial Smelting Corporation. Also operated by the Anglo American Corporation, South Africa, after World War II. 

The principal direct raw materials used to make sulfuric acid are elemental sulfur, spent (contaminated and diluted) sulfuric acid, and hydrogen sulfide. Elemental sulfur is by far the most widely used. In the past, iron pyrites or related compounds were often used but as of the mid-1990s this type of raw material is not common except in southern Africa, China, Kazakhstan, Spain, Russia, and Ukraine (96). A large amount of sulfuric acid is also produced as a by-product of nonferrous metal smelting, ie, roasting sulfide ores of copper, lead, molybdenum, nickel, zinc, or others. 

Roasting. Copper and lead sulfides are directly smelted but not zinc sulfide. However, theoretical calculations are encouraging (20) and, if an efficient means of condensing zinc rapidly from 1600 K in the presence of carbon dioxide, sulfur dioxide, and steam can be devised, the process may be feasible. The reaction of zinc vapor to yield zinc oxide or zinc sulfide presents the main difficulty. 

A pyrometallurgical process for the direct recovery of zinc from zinc concentrates and zinc/iron residues has been proposed and tested extensively by Noranda. The process consists of smelting bone-dry zinc containing materials (sulfide concentrates and secondary zinc/iron materials) in a molten iron oxysulfide bath to volatilize metallic zinc into a SOz-fiee ofTgas. Sulfiir contained in the feed materials is fixed as an iron oxysulfide matte for di sal. Thus, this process not only is capable of treating zinc sulfide concentrates and secondary zinc materials simultaneously, but also eliminates the need of sulfuric acid production. Detailed thermodynamic analysis and experimental test work are described in this paper. 

R. Li, J. G. Peacey and P. J. Hancock, Direct Smelting of Zinc Concentrate and Residues , The Howard Womer International Symposium on Injection in Pvrometallurgv. M. Nihnani and T. Lehner, Eds., The Minerals, Metals and Materials Society, Warrendale, PA, U.S.A., 1996,107-121. 

N.A. Warner, Direct Smelting of Zinc-Lead Ore , Trans. Institution of Minina and Metallurgy, 1983, Sect C, C147-152. 

R.K. Hanna and N.A.Warner, Process Requirements for the Direct Condensation of Both Zinc and Lead as Metals in Polymetallic Smelting of Zn-Pb-Cu Sulphides , Proc. Non-Ferrous Smelting Symposium 100 Years of Lead Smelting and Refining in Port Pine, The Australasian Institute of Mining and Metallurgy, Melbourne, Australia, 1989, 227-236. 

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