Oxidation of zinc sulfide

In another example, Beveridge studied the oxidation of zinc sulfide spheres and reported that the global rate was, in turn, controlled by the surface chemical reaction at low temperatures, diffusion through the zinc oxide product layer at intermediate temperatures, and external mass transfer resistance at higher temperatures. 

The thermodynamics of zinc sulfide roasting have been studied by numerous investigators. The classical work on this subject is the paper by Ingraham and Kellogg [36]. Since iron tends to be present in the vast majority of naturally occurring zinc sulfide ores, the zinc-iron-oxygen-sulfur system is of considerable practical interest. This problem has been discussed extensively in Gray et al. [35] and some useful papers on this subject have been written by Kubaschewski [37] and Benner and Kenworthy [38]. Numerous kinetic studies have been made of oxidation of zinc sulfide the results of some... 

E. Mendoza, R. E. Cunningham, and J. J. Ronco, Oxidation of zinc sulfide pellets. Application of a model of diffusion with simultaneous reaction under effective dif-fusivity and surface area profiles, J. Catal. 17, 277-286 (1970). 

Zinc is also used extensively to galvanize other metals such as iron to prevent corrosion. Zinc oxide is a unique and very useful material for modern civilization. It is widely used in the manufacture of paints, rubber products, cosmetics, pharmaceuticals, floor coverings, plastics, printing inks, soap, storage batteries, textiles, electrical equipment, and other products. Lithopone, a mixture of zinc sulfide and barium sulfate, is an important pigment. 

Roasting. Copper and lead sulfides are direcdy 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. 

Geon and Seo [47] also determined the effect of vulcanization time on the adhesion of natural rubber to brass-plated steel. For relatively short times, there was a peak at the end of the copper profile that corresponded well with a peak in the sulfur profile. Similarly, peaks in the zinc and oxygen profiles corresponded well. These results showed that copper sulfide and zinc oxide mostly formed at short times but some evidence for formation of zinc sulfide was also obtained. For long times, the peak in the sulfur profile no longer corresponded with that in the copper profile. Instead, the peak in the sulfur profile corresponded to the peak in the zinc profile. It was concluded that the formation of zinc sulfide increased substantially at long times. An increase in vulcanization time correlated well with a decrease in the force required to pull brass-plated steel wires out of rubber blocks. 

Raw Materials. The source of zinc can be zinc oxide from a smelter, zinc dross or sweepings, ammonium chloride slag from hot dip galvanizing, or liquid waste such as pickle liquors from galvanizing plants. Variations in the price of zinc have a large effect on the economics of zinc sulfide pigments. 

The most common white pigments are titanium dioxide, zinc oxide, leaded zinc oxide, zinc sulfide [1314-98-3], and lithopone, a mixture of zinc sulfide and barium sulfate [7727-43-7]. The use of lead whites and antimony oxides has been decreasing steadily for environmental reasons. 

The principal source of zinc is zinc sulfide or zinc blende. This ore occurs mainly in Australia, Canada and the US. The zinc ore is first concentrated by a process called froth flotation. The crushed ore is fed into tanks of water containing a chemical frothing agent. Air is blown through so that the whole mixture froths up. The rock particles become soaked with water and sink to the bottom of the tank. However, the zinc sulfide particles, into which the water cannot soak, are carried to the top of the tank by the air bubbles and are skimmed off and dried. This ore now contains 55-75% of zinc sulfide. The zinc sulfide is then heated very strongly in a current of air in a furnace (Figure 10.16) to convert it to the oxide ... 

Zinc oxide (ZnO), which is produced by burning zinc vapor in atmospheric oxygen, is by far the most important compound of zinc. Under the name of zinc white, the oxide is used as a paint pigment. It is also used as a base in the manufacture of enamels and glass, and as a ruler in the fabrication of automobile tires and other kinds of rubber goods. Zinc sulfide (ZnS) is also an important white paint pigment which is used either as such or in the form of lithopone, which is a mixture of zinc sulfide and barium sulfate. This widely used pigment is prepared by the metathetical reaction between zinc sulfate and barium sulfide, a reaction in which both of the products are insoluble ... 

The second step (eq. 4.5) is a thermal oxidative process. This initiates the reaction of ZDDP with oxygen, and enhances the decomposition. Since oxygen and/or hydroperoxide is present in the oil, decomposition is not a pure thermal degradation. The main products on the surface are zinc polyphosphates with minor amounts of zinc sulfides. As the rubbing continues, the polyphosphate layer comes into closer contact with water in oil and is hydrolyzed to give short-chain polyphosphates (eq. 4.6). 

X-ray Diffraction Analysis. The inorganic components of paper are the most suitable ones for quantitative X-ray diffraction analysis. Most of these compounds are minerals and are present as fillers, coatings and pigments (often whiteners) which are added to improve the properties of the paper. Examples of compounds commonly added to paper are alumina, aluminum silicate, barium sulfate, calcium carbonate, calcium sulfate, calcium sul-foaluminate, iron oxide, magnesium silicate, silica, titanium dioxide, zinc oxide, and zinc sulfide (28). Some of these, e.g., calcium carbonate and titanium dioxide, may be present in any of... 

It should not be supposed that crystal defects enter into the picture only as nuisances which the chemist seeks to avoid or eliminate. Actually, certain optical and electrical properties of oxides, sulfides, and halides have been found to depend strongly on the nature and extent of crystal defects. Indeed, semiconductivity, fluorescence (absorption of radiation and emission of less energetic radiation), and phosphorescence (delayed fluorescence) of some salts may be spectacularly increased, not only by a small stoichiometric excess of one of the constituents, but also by addition of very tiny quantities of a foreign ion. Perhaps the best known example is the case of zinc sulfide which, when precipitated from aqueous solution and dried at low temperatures, shows negligible fluorescence upon exposure to ultraviolet light. When the sulfide is heated to... 

Regulated Colorants That Are FDA Approved. It often seems a contradiction that many of the colorants that are suitable for use in food contact applications must also appear on an MSDS as a reportable or hazardous material. Examples include zinc oxide and zinc sulfide, both zinc compounds chromium oxide green (pigment green 17), a chromium compound carbon black and cobalt aluminate blue (pigment blue 28), which is not only reportable because of its cobalt content but is also a suspected carcinogen. 

The pre-1991 research involving microbial oxidation of 29 sulfide minerals of iron, copper, arsenic, antimony, gallium, zinc, lead, nickel, and mercury was compiled by Nordstrom and Southam (1997). The importance of microbially mediated sulfide oxidation has been recognized for several decades (Nordstrom and Southam, 1997). Bacteria catalyze the oxidative dissolution of sulfide minerals, increasing the production of acidity in mine wastes. In the absence of bacteria, the rate of sulfide oxidation stabilizes as the pH decreases below 3.5 (Singer and Stumm, 1970). 

Activators Activators selectively react with particles to cause the collector to surface. The classic example, as mentioned above, is the use of copper sulfate for the activation of zinc sulfide so that it can be collected by standard sulfide mineral collectors. Another example is the surfacing of lead carbonate, copper carbonate, and copper oxide with the use of sodium sulfide so that collection is also possible by the sulfide collectors. 

Beveridge, G. The oxidation rates of zinc sulfide spheres. In Agglomeration Knepper, W., Ed. Interscience Publishers New York, 1962 303-349. 

Zinc sulfide has the next highest refractive index to titanium dioxide and zirconium oxide making it a very efficient pigment. The spectrum of absorption of zinc sulfide resembles more closely anatase than rutile. Because it does not absorb certain UV wavelength, zinc sulfide is useful as a pigment for UV curable materials. 

Persson, P, Parks, G.A., and Brown, G.E., Adsorption and structural environment of Co(II) at the zinc oxide-and zinc sulfide-aqueous solution interfaces, Langmuir, 11, 3782, 1995. 

Reduction of halides. Chromous chloride (prepared by reduction of chromic chloride with zinc powder) has been used to reduce the exo chlorine atom of (1), prepared by Diels-Alder reaction between cyclopentadiene and thiophosgene followed by oxidation of the sulfide group to the sulfone.2... 

Alumina catalysts activated by additions of dehydrogenating catalysts, e.g., nickel oxide, copper oxide or sulfide, zinc oxide or sulfide, cobalt selenide, zinc phosphate, cadmium tungstate, mixtures of the oxides of zinc and tungsten, of cadmium and molybdenum, etc., are claimed to be superior in the formation of acetaldehyde from mixtures of steam and acetylene at 350° to 400° C.l-la Zinc oxide catalysts may be activated in a similar way by the addition of small amounts of molybdates or molybdic acid, and are effective at 300° to 350° C.121b... 

Lithopone, C.I. Pigment White 5 Griffith s zinc white. A white pigment consisting of a mixture of zinc sulfide. barium sulfate and some zinc oxide. Several grades of lithopone are commercially available. The zinc sulfide content varies from 26 to 60%. The commercial importance of lithopone has decreased since the introduction of titanium pigments. 

Ruhr-Zinc GmbH (the first zinc smelter in Europe) defined a concept, which eliminated these two problems (Veltman and Weitz 1982). It used sulfuric acid, oxidizing pressure-leaching of zinc sulfide, with which Fe(III) ions take over a catalytic role by constant oxidation with oxygen. The resulting elementary sulfur can be produced in either liquid or solid form by further pressure-leaching of the residues. Pyrite (FeS) can also be used for meeting the sulfuric... 

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