Zinc, extraction

The principal ores of zinc are sphalerite (sulfide), smithsonite (carbonate), calamine (silicate), and franklinite (zine, manganese, iron oxide). One method of zinc extraction involves roasting its ores to form the oxide and reducing the oxide with coal or carbon, with subsequent distillation of the metal. 

Harvey, T. J. Yen, W. T. Paterson, J. G. Selective zinc extraction from complex copper-zinc sulfide concentrates by pressure oxidation. Miner. Eng. 1992, 5, 975-992. 

Cupertino, D. C. Dalton, R. F. Seward, G. W. Townson, B. Harris, G. B. Tasker, P. A. Iron control in zinc circuits the role of highly selective zinc extractants. Iron Control and Disposal, Proceedings of the International Symposium on Iron Control in Hydrometallurgy, 2nd, Ottawa, Oct. 20-23, 1996, 369-379. 

Lacell A zinc extraction process in which zinc sulfide is converted to zinc chloride and molten sulfur, and the molten zinc chloride is electrolyzed. 

Zincex [Zinc extraction] A process for extracting zinc from pyrite cinder leachate, using organic solvents. The chloride leachate is first extracted with a secondary amine, and then with di(2-ethylhexyl)phosphoric acid to remove iron Developed by Tecnicas Reunidas, first commercialized in 1976, and now used in Spain and Portugal. 

Fig. 14.2 Zinc extraction plant at Enka AKZO, Netherlands. Full-scale plants have heen built and operated at Svenska Rayon AB in Sweden and at Enka AKZO in The Netherlands. 

Indium may be recovered from zinc ores by several patented processes. Usually it is recovered from residues obtained from zinc extraction. The residues, slags, fume, or dusts from zinc smelting or lead-zinc smelting are treated with a mineral acid. Other steps involved in recovery often vary, but mostly use solvent extraction and precipitation steps. In some processes, treatment with caustic soda yields indium hydroxide. The hydroxide is calcined to obtain oxide, which then is reduced with hydrogen at elevated temperatures to obtain the metal. Distillation or electrolysis are the final steps to... 

Lei et al. reported a method for the indirect determination of trace amounts of procaine in human serum by atomic absorption spectrophotometry [54], The sample was mixed with HCIO4, heated at 85°C for 30 minutes, diluted to a known volume with water, and centrifuged. 1 mL of the supernatant solution was buffered with 0.1 M sodium acetate-acetic acid to pH 3.86, and mixed with 0.2 M Zn(SCN)j reagent to a final concentration of 0.1 M. After dilution to 50 mL with water, the solution was shaken for 1 minute with 10 mL of 1,2-dichloroethane, whereupon the zinc extracted into the organic phase was determined by air-acetylene flame atomic absorption spectrometry for the indirect determination of procaine. The detection limit was found to be 0.1 pg/g, with a recovery of 89-98% and a coefficient of variation (n = 10) equal to 3.2%. 

If the ratio be unity, the concentrations of the solute in each solvent will be the same if the ratio be far removed from unity, a correspondingly large proportion of the solute will be found in the one solvent which can be utilized to extract the Soln. from the other solvent. E.g. ether will remove ferric chloride from its aq. soln., and since many other chlorides are almost insoluble in ether, the process is utilized in analysis for the separation of iron from the other elements the solubility of cobalt thiocyanate in ether is utilized for the separation of cobalt perchromic acid is similarly separated from its aq. soln. by ether molten zinc extracts silver and gold from molten lead the extraction of organic compounds from aq. soln. by shaking out with ether or other solvent is much used in organic laboratories. 

The roaster product is lcachcd with spent electrolyte 1 sulfuric acid) under near-neutral conditions to dissolve most of the zinc, copper, and cadmium, but little of the iron. The leach residue solids are releached in hot, strong add to dissolve more zinc, since it attacks the otherwise insoluble zinc femtes. The iron which is also dissolved in this second leach is then precipitated as jarosite, goethite, or hematite. The development of these iron predpitation techniques permitted the use of the hot. strong acid leach and an increase 111 zinc extraction from about 87% to greater Ilian 95%. Simultaneously, the hot acid leach frequently generates a leach residue rich enough in lead and silver to provide significant byproduct value, as well as increased recovery of cadmium and copper. 

Standing Committee of Analysts (DoE) (1979) The Analysis of Agricultural Materials -Zinc Extractable in Soil, MAFF Method 82, HMSO, London, UK. 

The macrokinetics of zinc extraction is discussed in detail in Ref. 8. It is a combination of a reaction kinetics term (55) with the Maxwell-Stefan (54) or eddy diffusion (56). The rate law is as follows ... 

The ion exchanger is known to be in dimeric form in aliphatic diluents [30], and the stoichiometry in Eq. (7) was found with classical slope analysis at low concentrations and FTIR-analysis even at high concentrations [31, 32], A compilation of all thermodynamic parameters is given in http //dechema.de/Extraktion/, as this system is a recommended test system for reactive extraction studies by the European Federation of Chemical Engineering (EFCE). The predictability of the model is quite good, as is depicted in Fig. 10.10, where zinc extraction from chloride media is predicted from sulfate media [33],... 

The molten copper is circulated back to the first furnace. The sulfur dioxide is converted to sulfuric acid for sale. Overall, the process uses much less energy than other zinc extraction processes. Developed in the 1980s by N.A. Warner at the University of Birmingham, UK, but not piloted as of 1992. 

Fig. 3. mg/g of zinc extracted by the extracting solutions versus time. Experimental conditions as reported in the text... 

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