Zinc sulphide concentrate

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. 

Since the lead smelter owned by OAO Kazzinc has ten years of experience in smelting lead-zinc sulphide concentrates by the Kivcet technology, a method of comparing physical and chemical properties of the bulk concentrate to the characteristics of typical lead-zinc raw materials has been developed. This method was used to decide on the feed composition and process operating conditions. Two major features of the bulk concentrate that affect the results of the smelting in the Kivcet unit were examined the calorific value and the desulphurization rate. 

ATMOSPHERIC LEACHING OF ZINC SULPHIDE CONCENTRATES USING REGENERATED FERRIC SULPHATE SOLUTIONS... 

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. 

The use of various chemical reagents to either encourage floatability ( collectors ) or inhibit it ( depressants ) therefore allows the flotation process to be highly selective. It can yield up to five different concentrates from a complex, lead-zinc mixed ore. In addition to separate lead and zinc sulphide concentrates, a zinc-lead bulk concentrate may also be produced, which helps improve overall metal recovery from the ore. The efficiency of flotation operations will vary with mineral grain size (the coarser the better) and the relative dispersion of lead and other metal minerals in the ore. Prior to shipment to the metallurgical plant, moisture is removed from the concentrates. 

Staeking faults and sometimes proper polytypism are found in many inorganic compounds - to pick out just a few, zinc sulphide, zinc oxide, beryllium oxide. Interest in these faults arises from the present-day focus on electron theory of phase stability, and on eomputer simulation of lattice faults of all kinds investigators are attempting to relate staeking-fault concentration on various measurable character-isties of the compounds in question, such as ionicity , and thereby to cast light on the eleetronic strueture and phase stability of the two rival structures that give rise to the faults. 

Acids, when used as scale inhibitors, are extremely corrosive. Their effectiveness has been laboratory tested. Parameters include acid type, metallurgy, temperature, inhibitor type and concentration, duration of acid-metal contact, and the effect of other chemical additives [279]. Lead and zinc sulphide scale deposits can be removed by an acid treatment [922]. 

In the 2nd period ranging from the 1930s to the 1950s, basic research on flotation was conducted widely in order to understand the principles of the flotation process. Taggart and co-workers (1930, 1945) proposed a chemical reaction hypothesis, based on which the flotation of sulphide minerals was explained by the solubility product of the metal-collector salts involved. It was plausible at that time that the floatability of copper, lead, and zinc sulphide minerals using xanthate as a collector decreased in the order of increase of the solubility product of their metal xanthate (Karkovsky, 1957). Sutherland and Wark (1955) paid attention to the fact that this model was not always consistent with the established values of the solubility products of the species involved. They believed that the interaction of thio-collectors with sulphides should be considered as adsorption and proposed a mechanism of competitive adsorption between xanthate and hydroxide ions, which explained the Barsky empirical relationship between the upper pH limit of flotation and collector concentration. Gaudin (1957) concurred with Wark s explanation of this phenomenon. Du Rietz... 

Zinc sulphide does not precipitate from an acidified solution because the S ion concentration is repressed by the H+ ions of the strong acid, H2S 2H+ + S, and the solubility product of zinc sulphide cannot be reached. Acetate ions, however, remove H+ ions, and, the hydrogen sulphide thus being allowed to ionize to a greater extent, the solubility product of zinc sulphide is exceeded and the white precipitate appears. (See Solubility Product, page 131, and Experiment 22, page 175.)... 

Barium was present in high concentrations on the green side of all denominations and might be present as the sulphate or as lithopone, which is a mixture of barium sulphate and zinc sulphide. Barium was rubbed readily off the green but not the black side, indicating that it was definitely a part of the green ink. 

Hydrogen sulphide partial predpitation of zinc sulphide in neutral solutions when the concentration of acid produced is about 0-3m (pH about 0-6), the sulphide-ion concentration derived from the hydrogen sulphide is depressed so much by the hydrogen-ion concentration from the acid that it is too low to exceed the solubility product of ZnS, and consequently precipitation ceases. 

Thus any advantage of molybdenum disulphide in an oil in reducing friction will be limited to the boundary and mixed lubrication regions, where the reduction in friction may be considerable. One theoretical analysis suggested that the influence of the dispersed powder depends only on particle shape, size and concentration , or in other words that the dispersed powder is simply forming a physical barrier between the interacting surfaces. It would follow that the same effect could be produced by other dispersed solids, and this was confirmed by studies with zinc sulphide, zinc pyrophosphate and calcium hydroxide. 

Turkevich et u/. have used epr techniques to follow the interaction of manganous halides with zinc sulphide. Zinc sulphide shows no resonance, but on heating with manganous salts at 600° C the resonance lines appear. Measurements were made on a Varian spectrometer operating at 9.5 kMc. sec", with the magnetic field modulated to 100 kc. sec . A Varian multipurpose cavity was used with the sample extending beyond the confines of the cavity. The spin concentration was determined with an internal ruby standard. 

Cardiovascular Effects. No atypical heart sounds or blood pressure abnormalities were observed in 24 employees occupationally exposed to concentrations as high as 130 mg zinc/m of metallic zinc dust, zinc oxide dust, zinc sulfide dust, or lithophone dust (a combination of barium sulphate and -5-30% zinc sulphide) for 2-35.5 years (Batchelor et al. 1926). However, this study is limited because only selected employees were examined, and they were not compared to controls. 

Over the period 1955-1961, the electrolytic plant processed only calcined zinc oxide having a composition of 60% Zn, 3-4% Pb and 0.03% Cd. The zinc oxide was produced by calcination of the fumes from the Waelz process at temperatures from 1420 to 1470 K. Zinc carbonate ores, Zn-Fe residues and other zinc-bearing materials were used as raw materials in the Waelz process. After enhancement of the electrolytic zinc plant in 1962, the importance of roasted sulphide concentrates was continuously growing in the feed. Currently, only the calcine from fluid-bed roasters is processed. Table I shows the analysis of the raw materials processed over the period 1998-1999. 

The feed consisting of zinc and lead sulphidic concentrates, oxidic materials and fluxes is desulphurised and agglomerated. 

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. 

Dutrizac has reviewed (4) the dissolution of zinc sulphide minerals in acidified ferric sulphate solutions. The results suggested that the important parameters involved are temperature and ferric ion concentration, and that the dissolution rates are rapid, at least near the solution boiling point. The reaction involved when using ferric sulphate solutions can be... 

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. 

The quality of zinc and nickel/cobalt sulphides has been very good. Nickel/cobalt sulphide contains about 50% of nickel and 1.5% of cobalt, the moisture content is under 20%. Zinc sulphide contains about 64% of zinc and its moisture content is about 10%. The impurity levels in both sulphides are very low. Copper concentrations have just started to rise in the PLS and saleable amounts of copper sulphide production started in 2012. 

Since thiosulphate is an intermediate oxidation product of sulphide in an alkahne or neutral medium, sulphide interferes with the determination of thiosulphate and, thus, any traces of sulphide should be removed by the precipitation of zinc sulphide with zinc acetate before the iodometric determination of thiosulphate. The solubility constant for ZnS has been given by Dyrssen and KremUng (1990). After precipitation of the zinc sulphide in a stoppered bottle full to the brim, a measured amount of the supernatant seawater sample is pipetted into a known amount of iodine. The latter oxidizes the thiosulphate to tetrathionate. The surplus iodine is then titrated by adding a thiosulphate solution of known concentration. 

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