Zinc sulfide minerals

WURTZITE. A mineral zinc sulfide, (Zn, Fe),S. similar to sphalerite. Crystallizes in the hexagonal system. Hardness, 3.5-4 specific gravity, 3.98 color, brownish-black with resinous luster. Named after Adolphe Wiirtz. Fiance. 

Depressants are reagents that selectively prevent the reaction between a coUector and a mineral, thus preventing its flotation. For example, sodium cyanide [143-33-9] depresses sphalerite [12169-28-7] (zinc sulfide) and pyrite [1309-36-0] (iron sulfide) but not galena. It thus enhances selective flotation of the galena. 

Finally, selective separation and dewatering of one suspended substance in a slurry containing different minerals or precipitates is possible by selectively adsorbing a magnetic material (usually hydrophobic) onto a soHd that is also naturally or chemically conditioned to a hydrophobic state. This process (Murex) was used on both sulfide ores and some oxides (145). More recently, hydrocarbon-based ferrofluids were tested and shown to selectively adsorb on coal from slurries of coal and mineral matter, allowing magnetic recovery (147). Copper and zinc sulfides were similarly recoverable as a dewatered product from waste-rock slurries (148). 

It is found that the dissolution of zinc sulfides occurs more rapidly when they are in contact with copper sulfide or iron sulfide than when the sulfides of these types are absent. This enhancement is brought about by the formation of a galvanic cell. When two sulfide minerals are in contact, the condition for dissolution in acidic medium of one of the sulfides is that it should be anodic to the other sulfide in contact. This is illustrated schematically in Figure 5.3 (A). Thus, pyrite behaves cathodically towards several other sulfide minerals such as zinc sulfide, lead sulfide and copper sulfide. Consequently, pyrite enhances the dissolution of the other sulfide minerals while these minerals themselves understandably retard the dissolution of pyrite. This explains generally the different leaching behavior of an ore from different locations. The ore may have different mineralogical composition. A particle of sphalerite (ZnS) in contact with a pyrite particle in an aerated acid solution is the right system combination for the sphalerite to dissolve anodically. The situation is presented below ... 

Rao SR, Finch JA, Zhou ZA, Xu Z (1998) Relative flotation response of zinc sulfide mineral and precipitate. Sep Sci Tech 33 819-833... 

Several reviews on ore processing by flotation are available.17-21 In addition to providing details of the chemistry of collectors they describe the use of activators and depressants. The former usually convert the surfaces of an ore particle which does not bind strongly to conventional collectors to one that does. The addition of Cu2+ ions to enhance the flotability of minerals such as sphalerite, a zinc sulfide, has been exploited for some time.4 Formation of a surface layer of CuS has been assumed to account for this, but the mechanisms and selectivities of such processes continue to be investigated.18,22,23... 

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. 

Yu and Bailey (1992) studied the reaction of nitrobenzene with four sulfide minerals under anaerobic conditions. Observed half-lives of nitrobenzene were 7.5, 40, 105, and 360 h for the reaction with sodium sulfide, alabandite (manganese sulfide), sphalerite (zinc sulfide), and molybdenite (molybdenum sulfide), respectively. Aniline and elemental sulfur were found as reduction products of nitrobenzene-manganese sulfide reaction. Aniline was also a reduction product in the nitrobenzene-molybdenum sulfide and nitrobenzene-sodium sulfide reactions. Several unidentified products formed in the reaction of nitrobenzene and sphalerite (Yu and Bailey, 1992). 

Its compounds have many practical uses. For example, when the mineral barite is ground up into a fine powder, it can be used as a filler and brightener for writing and computer paper. It is also used (along with zinc sulfide) as a pigment, called lithopone, for white paint. Barium compounds are also used in the manufacture of plastics, rubber, resins, ceramics, rocket fuel, fireworks, insecticides, and fungicides and to refine vegetable oils. 

It is not found in its pure metallic form in nature but is refined from the mineral (compound) zinc sulfide (ZnSO ) known as the ores sphalerite and zincblende. It is also recovered from minerals and ores known as willemite, hydrozincite, smithsonite, wurtzite, zincite, and Franklinite. Zinc ores are found in Canada, Mexico, Australia, and Belgium, as well as in the United States. Valuable grades of zinc ores are mined in Colorado and New Jersey. 

The zinc that is produced today starts as the zinc sulfide (ZnS) minerals zinc blende or sphalerite or from zinc carbonate (ZnCO ) known as smithsonite or calamine. In the electrolytic process, these minerals are dissolved in water to form the electrolyte in the cell where the zinc cations are attracted and collected at the cathode and deposited as a dull, brittle type of zinc. 

Minerals as found in nature are always mixed together (e.g., zinc sulfide and feldspar minerals). In order to separate zinc sulfide, the mixture is suspended in water, and air bubbles are made to achieve separation. This process is called flotation, where an ore heavier than water is floated by bubbles. 

Zinc sulfide occurs in nature in two crystalline forms, the minerals, wurtzite, and sphalerite. Sulfide ore is the principal zinc mineral. 

Zinc sulfide is white to gray-white or pale yellow powder. It exists in two crystalline forms, an alpha (wurtzite) and a beta (sphalerite). The wurtzite form has hexagonal crystal structure refractive index 2.356 density 3.98 g/cm3 melts at 1,700°C practically insoluble in water, about 6.9 mg/L insoluble in alkalis soluble in mineral acids. The sphalerite form arranges in cubic crystalline state refractive index 2.368 density 4.102 g/cm changes to alpha form at 1,020°C practically insoluble in water, 6.5 mg/L soluble in mineral... 

Unit cells of these two structures are shown in Figure 1.37 and Figure 1.38, respectively. They are named after two different naturally occurring mineral forms of zinc sulfide. Zinc blende is often contaminated by iron, making it very dark in colour and thus lending it the name of Black Jack . Structures of the same element or compound that differ only in their atomic arrangements are termed polymorphs. 

Sphalerite and wurtzite, the two common forms of zinc sulfide,68 have the tetrahedral structures shown in Figures 7-5 and 7-6. Pure zinc sulfide is colorless. The minerals are usually yellow, brown, or black, the color probably being due to imperfections and impurities. The luster is not metallic, but resinous or adamantine. 

Production. The raw material for the production of cadmium yellow pigments is high-purity cadmium metal (99.99 %), cadmium oxide, or cadmium carbonate. If the metal is used it is first dissolved in mineral acid. A zinc salt is then added to the solution the amount added depends on the desired shade. The zinc salt is followed by addition of sodium sulfide solution. An extremely finely divided cadmium sulfide or cadmium zinc sulfide precipitate is formed, which does not possess any pigment properties. This intermediate product can also be obtained by mixing the cadmium or cadmium-zinc salt solution with sodium carbonate solution. An alkaline cadmium carbonate or cadmium zinc carbonate precipitate is formed which reacts in suspension with added sodium sulfide solution. 

These zinc sulfides are sufficiently resistant to all media except strong mineral acids. A disadvantage is that they become grey through the action of high intensity... 

SPHALERITE BLENDE. Also known as zinc blende, this mineral is zinc sulfide, tZn, Fc)S, practically always containing some iron, crystallizing in the isometric system frequently as tetrahedrons, sometimes as cubes or dodecahedrons, but usually massive with easy cleavage, which is dodecahedral. It is a brittle mineral with a conchoidal fracture hardness, 2.5-4 specific gravity, 3.9-4.1 luster, adamantine to resinous, commonly the latter. It is usually some shade of yellow brown or brownish-black, less often red, green, whitish, or colorless streak, yellowish or brownish, sometimes white transparent to translucent. Certain varieties... 

The most widely applied activation procedure is that involving the use of copper(II) ions to enhance the floatability of some sulfide minerals, notably the common zinc sulfide mineral sphalerite.2 Sphalerite does not react readily with the common thiol collectors, but after being treated with small amounts of copper it floats readily owing to the formation of a surface layer of CuS." A similar procedure is often adopted in the flotation of pyrrhotite (FeS), pyrite (FeS2), galena (PbS) and stibnite (Sb2S3). In the context of coordination chemistry, the major contribution has been to the understanding of the chemistry involved in the deactivation of these minerals, a procedure often adopted in the sequential flotation of several minerals from a complex ore. 

Depressants (or deactivators) are chemicals that ensure that undesired particles remain hydrophilic and therefore do not get floated. Conversely to the activation of zinc sulfide by copper ions above, zinc ions from zinc sulfate act as a depressant for zinc sulfide. Another example is the use of cyanide to complex with copper and prevent adsorption of collectors in the flotation of base-metal sulfides with xanthates. There are many other depressants but they tend to be quite specific to one of a few types of minerals. In some cases, such as some uses of cyanide as a depressant, the mechanism of depressant action remains unclear. 

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... 

Some non-enzymatic antioxidants play a key role in these defense mechanisms. These are often vitamins (A, C, E, K), minerals (zinc, selenium), caretenoids, organosulfur compounds, allyl sulfide, indoles, antioxidant cofactors (coenzyme Qio)> and polyphenols (flavonoids and phenolic acids) [1,37]. Further, there is good evidence that bilirubin and uric acid can act as antioxidants to help neutralize certain free radicals [38]. Alpha-carotene, lycopene, lutein, and zeaxanthine [39] can be considered subgroups of carotenoids [40] that are effective antioxidant compounds. 

Berzelius went further in his attempt to simplify the science. He joined the symbols of the elements to represent the simplest parts of compounds. Thus copper oxide was written CuO, and zinc sulfide ZnS. He had, at first, denoted the number of oxygen atoms by dots and the number of sulfur atoms by commas thus carbon dioxide was C and carbon disulfide was C. But he soon discarded these dots and commas, although for decades after, mineralogists utilized this method of writing the formulas of minerals. 

According to the foregoing interpretation, chrysocolla of ancient times is neither malachite nor a blue copper silicate (the mineral now called chrysocolla) but is a yellow substance, possibly the yellow mineral cadmium sulfide, which appears as a coating on other minerals, chiefly zinc sulfide. This description fits Pliny s text, which describes gold solder (chrysocolla) as a liquid that flows from several mines to give a solid deposit. ... 

Keys, J. D., J. L. Horwood, T. M. Baleshta, L. J. Cabri, and D. C. Harris (1968). Iron-iron interaction in iron-containing zinc sulfide. Canad. Mineral. 9, 453-67. 

More and more minerals are being found amenable to bacteriological leaching. The copper sulfide minerals, such as chalcopyrite (B31-B33, D22, D24), chalcocite (B35), and tetrahedrite (B32, D21) are among the best studied. The iron sulfide (pyrite) (B31, B33, C22, L4) and sulfur (B33, B34, C22, L4) oxidation processes are the best understood. Investigations on the leaching of nickel sulfides (D21, D24, T17), lead sulfide (E4), molybdenum sulfide (molybdenite) (B17, B31, D24), cobalt sulfide (D9), zinc sulfide (D24), and uranium oxide (D24, F2, H13, H14, Ml) have been reported in the literature. 

Weisener C. G. (2002) The reactivity of iron and zinc sulfide mineral surfaces adsorption and dissolution mechanisms. PhD Thesis, University of South Austraha. 

Figure 15.12. Schematic diagram showing inorganic chemical processes occurring at warm- and hot-water vent sites. Deeply circulating seawater is heated to 350°-400°C and reacts with crustal basalts, leaching various species into solution. The hot water rises, reaching the sea floor directly in some places and mixing first with cold, down-welling seawater in others. On mixing, iron-copper-zinc sulfide minerals and anhydrite precipitate. (From Jannasch and Mottl, 1985.)...

Sulfur also occurs in a number of important minerals. Some examples are barite, or barium sulfate (BaS04) celestite, or strontium sulfate (SrS04) cinnabar, or mercury sulfide (HgS) galena, or lead sulfide (PbS) pyrites, or iron sulfide (FeS2) sphalerite, or zinc sulfide (ZnS) and stibnite, or antimony sulfide (Sb2S3). 

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. 

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