Sulfidic metal associations

ALABANDITE. Manganese sulfide. MnS. Associated with pyrite, sphalerite. and galena in metallic sulfide vein deposits. 

Silver is a rare element, which occurs naturally in its pure form as a white, ductile metal, and in ores. It has an average abundance of about 0.1 ppm in the earth s crust and about 0.3 ppm in soils. There are four oxidation states (0, 1 +, 2+, and 3+) the 0 and 1 + forms are much more common than the 2+ and 3+ forms. Silver occurs primarily as sulfides, in association with iron (pyrite), lead (galena), and tellurides, and with gold. Silver is found in surface waters in various forms (1) as the monovalent ion (e.g., sulphide, bicarbonate, or sulfate salts) (2) as part of more complex ions with chlorides and sulfates and (3) adsorbed onto particulate matter. 

In operationally defined speciation the physical or chemical fractionation procedure applied to the sample defines the fraction isolated for measurement. For example, selective sequential extraction procedures are used to isolate metals associated with the water/acid soluble , exchangeable , reducible , oxidisable and residual fractions in a sediment. The reducible, oxidisable and residual fractions, for example, are often equated with the metals associated, bound or adsorbed in the iron/manganese oxyhydroxide, organic matter/sulfide and silicate phases, respectively. While this is often a convenient concept it must be emphasised that these associations are nominal and can be misleading. It is, therefore, sounder to regard the isolated fractions as defined by the operational procedure. Physical procedures such as the division of a solid sample into particle-size fractions or the isolation of a soil solution by filtration, centrifugation or dialysis are also examples of operational speciation. Indeed even the distinction between soluble and insoluble species in aquatic systems can be considered as operational speciation as it is based on the somewhat arbitrary definition of soluble as the ability to pass a 0.45/Am filter. 

The sulfide minerals are at present the major source of the base metals. Associated with most of the sulfide ores are the minerals pyrite and pyrrhotite. If the hydrometallurgical processing of ores becomes the predominant method of metal extraction, the recovery of elemental sulfur as a by-product is a very promising possibility. The formation of elemental sulfur has been observed by many investigators as a reaction product of sulfide minerals under certain experimental conditions. 

In anaerobic soils, the individual chemistry of the ions is more distinctive. The transition metal ions in the middle of each period of the periodic table—chromium, manganese, iron, nickel, cobalt, and copper—can reduce to lower oxidation states, while the end members—scandium, titanium, and zinc—have only one oxidation state. The lower oxidation states are more water soluble but still tend to precipitate as carbonates and sulfides, or associate with organic matter, thus reducing their movement but increasing then plant availability. 

Huerta-Diaz, M.A., Carignan, R., Tessier, A., 1993. Measurement of trace metals associated with acid volatile sulfides and pyrite in organic freshwater sediments. Environ. Sci. Technol. 27, 2367-2372. 

Toxic metals associated with wetland soils are present in various forms dissolved, adsorbed, bound to carbonates, to Fe and Mn oxides, to sulfides, and insoluble organic matter forms, and within the crystalline structure of primary minerals (Shannon and White, 1991). The amount of organic matter and clay minerals, the soil acidity (pH), and the sediment oxidation-reduction status (Eh) of soils are very important physicochemical properties influencing the mobility of toxic metals. 

Surface heterogeneity may be inferred from emission studies such as those studies by de Schrijver and co-workers on P and on R adsorbed on clay minerals [197,198]. In the case of adsorbed pyrene and its derivatives, there is considerable evidence for surface mobility (on clays, metal oxides, sulfides), as from the work of Thomas [199], de Mayo and co-workers [200], Singer [201] and Stahlberg et al. [202]. There has also been evidence for ground-state bimolecular association of adsorbed pyrene [66,203]. The sensitivity of pyrene to the polarity of its environment allows its use as a probe of surface polarity [204,205]. Pyrene or ofter emitters may be used as probes to study the structure of an adsorbate film, as in the case of Triton X-100 on silica [206], sodium dodecyl sulfate at the alumina surface [207] and hexadecyltrimethylammonium chloride adsorbed onto silver electrodes from water and dimethylformamide [208]. In all cases progressive structural changes were concluded to occur with increasing surfactant adsorption. 

The abundance of indium in the earth s cmst is probably about 0.1 ppm, similat to that of silver. It is found in trace amounts in many minerals, particulady in the sulfide ores of zinc and to a lesser extent in association with sulfides of copper, tin, and lead. Indium follows zinc through flotation concentration, and commercial recovery of the metal is achieved by treating residues, flue dusts, slags, and metallic intermediates in zinc smelting and associated lead (qv) and copper (qv) smelting (see Metallurgy, EXTRACTIVE Zinc and zinc alloys). 

AEROPHINE 3418A promoter is widely used ia North and South America, AustraHa, Europe, and Asia for the recovery of copper, lead, and ziac sulfide minerals (see Elotatton). Advantages ia comparison to other collectors (15) are said to be improved selectivity and recoveries ia the treatment of complex ores, higher recoveries of associated precious metals, and a stable grade—recovery relationship which is particularly important to the efficient operation of automated circuits. Additionally, AEROPHINE 3418A is stable and, unlike xanthates (qv), does not form hazardous decomposition products such as carbon disulfide. It is also available blended with other collectors to enhance performance characteristics. 

Sulfide Stress Cracking Resistant Metallic Materialfor OilField Equipment, NACE Standard MR-01-75, 1980 rev.. Technical Practices Committee, National Association of Corrosion Engineers, Houston, Tex., 1980. 

Cadmium occurs primarily as sulfide minerals ia ziac, lead—ziac, and copper—lead—ziac ores. Beneftciation of these minerals, usually by flotation (qv) or heavy-media separation, yields concentrates which are then processed for the recovery of the contained metal values. Cadmium follows the ziac with which it is so closely associated (see Zinc and zinc alloys see also Copper Lead). 

More than 200 ores are known to contain cobalt but only a few are of commercial value. The more important are arsenides and sulfides such as smaltite, C0AS2, cobaltite (or cobalt glance), CoAsS, and linnaeite, C03S4. These are invariably associated with nickel, and often also with copper and lead, and it is usually obtained as a byproduct or coproduct in the recovery of these metals. The world s major sources of cobalt are the African continent and Canada with smaller reserves in Australia and the former USSR. All the platinum metals are generally associated with each other and rhodium and iridium therefore occur wherever the other platinum metals are found. However, the relative proportions of the individual metals are by no means constant and the more important sources of rhodium are the nickel-copper-sulfide ores found in South Africa and in Sudbury, Canada, which contain about 0.1% Rh. Iridium is usually obtained from native osmiridium (Ir 50%) or iridiosmium (Ir 70%) found chiefiy in Alaska as well as South Africa. 

Sulfides such as pentlandite, (Ni,Fe)9Ss, associated with copper, cobalt and precious metals so that the ores typically contain about lt% Ni. These are found in more temperate regions such as Canada, the former Soviet Union and South Africa. 

Although estimates of their abundances vary considerably, Pd and Pt (approximately 0.015 and 0.01 ppm respectively) are much rarer than Ni. They are generally associated with the other platinum metals and occur either native in placer (i.e. alluvial) deposits or as sulfides or arsenides in Ni, Cu and Fe sulfide ores. Until the 1820s all platinum metals came from South America, but in 1819 the first of a series of rich placer deposits which were to make Russia the chief source of the metals for the next century, was discovered in the Urals. More recently however, the copper-nickel ores in South Africa and Russia (where the Noril sk-Talnakh deposits are well inside the Arctic Circle) have become the major sources, supplemented by supplies from Sudbury. 

Silver is widely distributed in sulfide ores of which silver glance (argentite), Ag2S, is the most important. Native silver is sometimes associated with these ores as a result of their chemical reduction, while the action of salt water is probably responsible for their conversion into hom silver , AgCl, which is found in Chile and New South Wales. The Spanish Americas provided most of the world s silver for the three centuries after about 1520, to be succeeded in the nineteenth century by Russia. Appreciable quantities are now obtained as a byproduct in the production of other metals such as copper. 

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