Roasting leaching

Fig. 6. Roast-Leach electrowinning process for the production of zinc metal from a sulfide concentrate.

For direct precipitation of vanadium from the salt-roast leach Hquor, acidulation to ca pH 1 without the addition of ammonia salts yields an impure vanadic acid when ammonium salts are added, ammonium polyvanadate precipitates. The impure vanadic acid ordinarily is redissolved in sodium carbonate solution, and ammonium metavanadate precipitates upon addition of ammonium salts. Fusion of the directly precipitated ammonium salts can yield high purity V20 for the chemical industry. Amine solvent extraction is sometimes used to recover 1—3 g/L of residual V20 from the directly precipitated tail Hquors. 

For operations producing 30,000 tons or less of copper annuaHy, hydrometaHurgy offers an alternative to smelting that avoids problems associated with sulfur dioxide recovery and environmental controls. Techniques include the Anaconda oxygen—ammonia leaching process, the Lake Shore roast-leach-electrowin process, and ferric chloride leaching processes for the treatment of copper sulfides. AH the facHities that use these techniques encountered serious technical problems and were shut down within a few years of start-up. 

Includes electrowon copper from concentrates roast-leached. 

RLE [roasting, leaching, electrowinning] A process for extracting copper from sulfide ores, using the three named processes. Developed by Hecla Mining Company, AZ, in 1969. 

In 2003, the world zinc production was 9 880000 tons [55]. The most important zinc production process is the electrolytic or roast-leach-electrowinning (RLE) process. This was first used in 1916 by Anaconda and Cominco. The industrial processes of zinc production use zinc oxides as raw materials. The most important natural raw material is zinc sulfide, and, therefore, it needs to be roasted and converted to oxide. The main problem in leaching and liquor purification is separation of zinc and iron. As dissolution of iron cannot be avoided, it must be precipitated from the zinc sulfate solution. Impurities still present after the iron precipitation stage can lead to lower current efficiency and impurities in the zinc cathode. Therefore, the solution is further purified by cementation with zinc powder. 

Today, hydrometaUurgy is well established as the principal method for extraction of many important industrml metals. Hydrometallurgy for the direct treatment of base metal sulfide concentrates, as a widely used technology, must yet prove itself. The roast-leach electrowinning of zinc is a noteworthy exception and is evolving as standard practice hi the zinc industiy worldwide. Relatively recent developments by way of jarosite and iron oxide hydrolysis and precipitation processes have improved recovery and helped secure zinc hydromemllurgy as standard in the industiy.w... 

Parker developed the energy and capital-cost-saving roast-leach-disproportionation process for sulfide concentrates of Cu and Ag. The process makes use of the different solvating powers of AN and HjO, respectively. The equilibria... 

Zinc melts at a relatively low temperature (907°C) and is removed from its zinc oxide ores pyrometallurgically by being distilled and condensed, or by being roasted, leached, then electrodeposited. Zinc residues and zinc drosses can be generated from these, as well as remelting processes. 

Ruhr-Zink is the name of a German zinc plant located in the Ruhr area. This plant has an annual production of 105,000 tonnes of zinc. About 30 different concentrates are treated in this plant via the RLE process (roasting, leaching and electrowinning) to produce 6-t zinc ingots. 

The Zincor process is based on the roast-leach-electrowinning process. The zinc sulphide concentrate is roasted in four Lurgi fiuo-solids roasters to produce zinc oxide and sulphur dioxide gas. The SO2 gas is fed to two Monsanto double absorption acid plants. 

The existing facilities need to be upgraded from the current consumption levels of 138 M Wh (the equivalent to the consumption rate of a city with 400,000 inhabitants) to a consumption of 191 M Wh afer the expansion. In order to comply with this requirement, the modification of the existing network, the expansion of the current SF6, and the creation of new substations in the roasting, leaching, purification and cellhouse areas is foreseen. 

The main process for recovering zinc fiom sulphide concentrates is, of course, the hydrometallurgical roast-leach-electrowin or pressure leach-electrowin approach. This process is not readily ade )table to increasing amounts of non-zinc elements in the feed. In the 1980 s the Low Contaminant Jarosite Process (2) was developed at the Electrolytic Zinc Co. of Australasia in Tasmania and this might have been developed further to enable plants to be fed with less pme sulphide concentrates. Faced with the rising social pressure to improve the disposal of iron residues, however, the company had to pursue other routes to meet those pressing requirements. 

Lower temperature and atmospheric pressure direct leaching of zinc sulphide concentrates has also been investigated in considerable detail (6), and there are two commercial facilities in operation, integrated with roast-leach-electrowin operations. The first is located at the Korea Zinc refinery in Onsan, Korea, and the second, at Outokumpu s zinc refinery in Kokkola, Finland (7). Similar to the pressure leach plant installations described above, both of these facilities were installed to expand zinc production. Table II summarizes the commercial zinc atmospheric pressure leach facilities. 

For the zinc concentrates tested by Dynalcc an expansion of an existing roast-leach-electrowin plant using pressure leaching offers economics that arc favourable in comparison to those of an atmospheric leach. 

The policy of TR is continuously to explore all new possibilities to apply the MZP to any zinc material different than oxidized or carbonated zinc ores, and zinc secondaries. An example would be the treatment of zinc sulfides that are difficult to process via conventional roast-leach-electrowinning technology. 

Most of the world s zinc production is obtained via the roast/leach/electrowinning (RLE) process. Starting from sulphidic concentrates, this hydrometallurgical process allows the production of special high-grade zinc. During this process, an iron rich residue (goethite or jarosite) is produced. This residue has to be stockpiled, and this is clearly an environmental issue for the future. 

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