Black metal sulphide

Patches of conductive lead sulphide can be formed on lead in the presence of sewage. This can result in the flow of a large corrosion current . Sulphate-reducing bacteria in soils can produce metal sulphides and H2S, which results in the formation of deep pits containing a black mass of lead sulphide . Other micro-organisms may also be involved in the corrosion of lead in soil . 

Metals tarnish when their surface atoms react with gaseous substances in the air. Oxygen is a highly reactive element, as we saw in the previous chapter, and it combines with iron to form the ruddy oxide compound we recognize as rust. Copper reacts with oxygen and carbon dioxide to form a greenish patina of copper carbonate. Silver resists the advances of oxygen but will slowly combine with sulphur compounds in the air to form black silver sulphide. 

Antidotes.—Two classes of agents axe known, which lessen or destroy the poisonous effects of lead thess are sulphide of hydrogen and the soluble metallic sulphides, snd sulphuric aeid and the soluble sulphates. With the first class, black sulphide of lead is immediately formed, and as this body is almost inert, if not imm cuoue, the further deleterious action of the lead salt is... 

Other forms of amorphous sulphur, which have been described at various tunes in chemical literature, are the so-called blue sulphur and black sulphur our present state of knowledge of these is far from satisfactory, and their existence as definite modifications of pure sulphur is questionable, especially in the case of the latter variety, the colour of which appears to be due to small quantities of carbon or of metallic sulphides.1... 

Ionic Displacement. Electromotive Series. When a strip of zinc is placed in a solution of copper sulphate, it is noticed that a spongy deposit of copper metal soon appears on the surface of the zinc, and that the solution loses its blue color. Then if the solution is tested for the presence of copper and zinc ions by adding ammonium sulphide, it is found that this reagent gives a white precipitate. This test shows that copper ions are now absent and that zinc ions are present because we know ammonium sulphide will precipitate black copper sulphide from a solution of copper ions, and white zinc sulphide from a solution of zinc ions. Since ordinary pieces of metal are not charged, it is obvious that the reaction consists in a transfer of the positive charges of the copper ions to the zinc atoms, or, more strictly, of negative electrons from the zinc atoms to the copper ions ... 

The characteristic colours and solubilities of many metallic sulphides have already been discussed in connection with the reactions of the cations in Chapter III. The sulphides of iron, manganese, zinc, and the alkali metals are decomposed by dilute hydrochloric acid with the evolution of hydrogen sulphide those of lead, cadmium, nickel, cobalt, antimony, and tin(IV) require concentrated hydrochloric acid for decomposition others, such as mercury(II) sulphide, are insoluble in concentrated hydrochloric acid, but dissolve in aqua regia with the separation of sulphur. The presence of sulphide in insoluble sulphides may be detected by reduction with nascent hydrogen (derived from zinc or tin and hydrochloric acid) to the metal and hydrogen sulphide, the latter being identified with lead acetate paper (see reaction 1 below). An alternative method is to fuse the sulphide with anhydrous sodium carbonate, extract the mass with water, and to treat the filtered solution with freshly prepared sodium nitroprusside solution, when a purple colour will be obtained the sodium carbonate solution may also be treated with lead nitrate solution when black lead sulphide is precipitated. 

Gold monosulphide, AuS.—Hydrogen sulphide or an alkali-metal sulphide precipitates the monosulphide from solutions of auric chloride,8 and it is also produced by the action of hydrogen sulphide on sodium aurothiosulphate. It is a black substance, insoluble in acids except aqua regia, but soluble in alkali-metal sulphides.8... 

Auric selenide.—Although gold and selenium do not combine directly,1 hydrogen selenide precipitates auric selenide from solutions of auric chloride in absence of light.2 It is an amorphous, black substance, of density 4-65 at 22° C., and is decomposed by heat with separation of selenium. It dissolves in aqua regia and in solutions of alkali-metal sulphides. 

On account of the readiness with which both the sulphur dyes and the alkali sulphides liberate hydrogen sulphide, the use of rnetal dye vessels, other than stainless steel, can be dangerous. Machines composed of copper or containing this metal in the form of fittings should never be used. Most metallic sulphides are insoluble and black or dark in colour and will stain the goods and flatten the shade. 

Molten lead passed as drops through a card or colander perforated with numerous holes— 1448 for the smallest shot — and fell into water which usually contained a little sodium sulphide. This coated the shot with a thin layer of sulphide of a lustrous black metallic colour which remained permanent in moist air. The size of the shot depended not only on the diameter of the holes in the colander, but also on the initial temperature and composition of the molten metal. The shot was sorted by sieves and by rolling down an inclined plane, the imperfectly shaped pellets remaining behind. Finally the shot was polished by rolling with plumbago in a barrel or rumble. 

In principle, the chemical stability of harbour sludge deposits, such as at Rotterdam and Hamburg (Fig. 10.10), is based on the low solubility of metal sulphides as well. The major difference is less mechanical stability of these structures compared with the deep anoxic marine basins, such as the Black Sea (many fjords provide similar conditions). Compaction and erosion are the problems at the man-made disposal sites. 

Preliminary studies of the interaction of leachate with natural clay mineral liners, has revealed the development of a black sludge material. The formation of a sulphide sludge at the leachate clay interface is well documented and has been acknowledged to be a significant factor in the blinding of pores and the consequent reduction in the permeability of clay mineral liners (Bisdom et al. 1983 Brune et al. 1991). It is postulated that this material may act as a sink for metals and other contaminants in leachate, by microbially controlled precipitation. Specific micro-organisms exist that are able to reduce sulphates and initiate the precipitation of metal sulphides, in this way (Brune et al. 1991 Watson et al. 1995). 

Addition of an alkali metal hydroxide solution to an aqueous solution of a nickel(II) salt precipitates a finely-divided green powder. nickel(II) hydroxide NilOHfj on heating this gives the black oxide. NiO. which is also obtained by heating nickel(II) carbonate or the hydrated nitrate. Black nickel(II) sulphide, NiS, is obtained by passing hydrogen sulphide into a solution of a nickel(II) salt. 

Traces of many metals interfere in the determination of calcium and magnesium using solochrome black indicator, e.g. Co, Ni, Cu, Zn, Hg, and Mn. Their interference can be overcome by the addition of a little hydroxylammonium chloride (which reduces some of the metals to their lower oxidation states), or also of sodium cyanide or potassium cyanide which form very stable cyanide complexes ( masking ). Iron may be rendered harmless by the addition of a little sodium sulphide. 

Fig. 1.2 Crystal structures of the major sulfides (metal atoms are shown as smaller or black spheres) (A) galena (PbS) structure (rock salt) (B) sphalerite (ZnS) structure (zinc blende) (C) wurtzite (ZnS) strucmre (D) pyrite structure and the linkage of metal-sulfur octahedra along the c-axis direction in (/) pyrite (FeSa) and (//) marcasite (FeSa) (E) niccolite (NiAs) structure (F) coveUite (CuS) structure (layered). (Adapted from Vaughan DJ (2005) Sulphides. In Selley RC, Robin L, Cocks M, Plimer IR (eds.) Encyclopedia of Geology, MINERALS, Elsevier p 574 (doi 10.1016/B0-12-369396-9/00276-8))...

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