Lead sulfides

The different forms of lead have different bioavailabiUty and this ultimately impacts cleanup levels. Mine tailings, slag, and other such residues have limited impact on blood lead levels because these materials contain lead in the form of lead sulfide, which has limited biological reactivity and uptake. 

In general, the chemistry of inorganic lead compounds is similar to that of the alkaline-earth elements. Thus the carbonate, nitrate, and sulfate of lead are isomorphous with the corresponding compounds of calcium, barium, and strontium. In addition, many inorganic lead compounds possess two or more crystalline forms having different properties. For example, the oxides and the sulfide of bivalent lead are frequendy colored as a result of their state of crystallisation. Pure, tetragonal a-PbO is red pure, orthorhombic P PbO is yeUow and crystals of lead sulfide, PbS, have a black, metallic luster. 

Lead sulfide is used in photoconductive cells, infrared detectors, transistors, humidity sensors in rockets, catalysts for removing mercaptans from petroleum distillates, mirror coatings to limit reflectivity, high temperature solid-film lubricants, and in blue lead pigments (82). 

Two processes, developed for the direct processing of lead sulfide concentrates to metallic lead (qv), have reached commercial scale. The Kivcet process combines flash smelting features and carbon reduction. The QSL process is a bath-smelting reactor having an oxidation 2one and a reduction 2one. Both processes use industrial oxygen. The chemistry can be shown as follows ... 

Detector elements are prepared either by sublimation in the presence of a small partial pressure of O2 or by chemical deposition from alkaline solution containing a lead salt and thiourea or selenourea (63). Lead sulfide and lead selenide deposit from solutions as mirror-like coatings made up of cubic crystallites 0.2—1 p.m on a side. The reaction may nominally be represented by the following ... 

Sulfur Polymer Cement. SPC has been proven effective in reducing leach rates of reactive heavy metals to the extent that some wastes can be managed solely as low level waste (LLW). When SPC is combined with mercury and lead oxides (both toxic metals), it interacts chemically to form mercury sulfide, HgS, and lead sulfide, PbS, both of which are insoluble in water. A dried sulfur residue from petroleum refining that contained 600-ppm vanadium (a carcinogen) was chemically modified using dicyclopentadiene and oligomer of cyclopentadiene and used to make SC (58). This material was examined by the California Department of Health Services (Cal EPA) and the leachable level of vanadium had been reduced to 8.3 ppm, well below the soluble threshold limit concentration of 24 ppm (59). 

Precipitation is affected by pH, solubiUty product of the precipitant, ionic strength and temperature of the aqueous stream, and the presence of metal complexes. For each metal precipitant, there is an optimum pH where its solubiUty is lowest and hence, the highest removals may be achieved. When an aqueous stream contains various metals, the precipitation process caimot be optimized for each metal, sometimes making it difficult to achieve effluent targets for each. SolubiUty products depend on the form of the metal compound and ate lowest for metal sulfides, reflecting the relative insolubiUty of these compounds. For example, the solubiUty product for lead sulfide [1314-87-0] is on the order of compared to 10 for lead carbonate. Metal... 

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. 

Leaded Zinc Oxide. Oxides containing more than 5 wt % basic lead sulfate are classified as leaded and are made ia the American process from high lead materials, usually lead sulfide mineral, or by blending ziac oxide and basic lead sulfate. There is only one manufacturer ia the United States and the product contains 20—28 wt % basic lead sulfate. Leaded oxides are used only ia mbber ia the United States. 

Several compounds such as BaZrS [12026-44-7], SrZrS [12143-75-8], and CaZrS [59087-48-8], have been made by reacting carbon disulfide with the corresponding zirconate at high temperature (141), whereas PbZrS [12510-11-1] was produced from the elements zirconium and sulfur plus lead sulfide sealed in a platinum capsule which was then pressurized and heated (142). Lithium zirconium disulfide [55964-34-6], LiZrS2, was also synthesized. Zirconium disulfide forms organometaUic intercalations with a series of low ionization (<6.2 eV)-sandwich compounds with parallel rings (143). 

Preparation of the Media Various sohd materials have been used to prepare the media. In the initial development of the process, a suspension of sand and also mixtures of barite and clay were used for separating coal from slate. Galena (lead sulfide mineral) was also used... 

The salt is dissolved in 800 cc. of water (Note 3) and transferred to a 5-I. round-bottom flask. To the solution is added with constant stirring a solution of 200 g. of lead nitrate (0.6 mole) in 400 cc. of water. Lead sulfide separates as a heavy brown precipitate which soon turns black. The mixture is then distilled with steam into a receiver containing 5-10 cc. of. i N sulfuric acid as long as any oil comes over (Note 4). About 2-3 1. of distillate is collected. The product is separated from the water and weighs 63-66 g. 

Aqueous hydrofluoric acid can be freed from lead by adding ImL of 10% strontium chloride per KXhnL of acid, lead being co-precipitated as lead fluoride with the strontium fluoride. If the hydrofluoric acid is decanted from the precipitate and the process repeated, the final lead content in the acid is less than 0.003 ppm. Similarly, lead can be precipitated from a nearly saturated sodium carbonate solution by adding 10% strontium chloride dropwise (l-2mL per lOOmL) followed by filtration. (If the sodium carbonate is required as a solid, the solution can be evaporated to dryness in a platinum dish.) Removal of lead from potassium chloride uses precipitation as lead sulfide by bubbling H2S, followed, after filtration, by evaporation and recrystallisation of the potassium chloride. 

The alkaline filtrate and washings are combined and partially neutralized by the addition of 150-175 ml. of concentrated hydrochloric acid. Sufficient sodium sulfide solution is added to precipitate all the lead ion present (Note 6). The suspension is brought to a gentle boil to coagulate the lead sulfide, allowed to cool somewhat, and filtered with suction. The filtrate is placed in a 2-1. beaker set in an ice bath and acidified Caution in the hood) with about 150 ml. of concentrated hydrochloric acid to precipitate crude 2-hydroxyisophthalic acid monohydrate (Note 7). The suspension is cooled to 0-5° and filtered to separate the crude acid, which weighs 35-49 g. after being dried in a vacuum oven at 110°/50-150 mm. for 5 hours (Note 8). 

The zinc. salts of these acids are extensively used as additives to lubricating oils to improve their extreme-pressure properties. The compounds also act as antioxidants, corrosion inhibitors and detergents. Short-chain dialkyl dithiophosphates and their sodium and ammonium salts are used as flotation agents for zinc and lead sulfide ores. The methyl and ethyl derivatives (RO)2P(S)SH and (RO)2P(S)CI are of particular interest in the large-scale manufacture of pesticides such as parathion, malathion, dimethylparathion, etc. For example parathion. which first went into production as an insecticide in Germany in 1947. is made by the following reaction sequence ... 

Schwefel-. of sulfur, sulfur, sulfuric, sulfide of, thio-. siilfo-. -abdruck, m. sulfiir print, -alkali, n. alkali siilfide. -alkohol, m. siilfur alcohol, thiol carbon disulfide (old name), -ammonium, -ammon, n. ammonium sulfide, -antlmon, n. antimony sulfide, -antimonblei, n, antimony lead sulfide (Min.) boulanger-ite. 

A 7-chloro-5-phenyl-l//-l,3,4-benzotriazepine-2(3//)-thione24 (2.5 mmol) in dioxane (l 5 mL) was treated with powdered Pb(OAc)2 (1.63 g. 5 mmol) and an amine was passed for 30 min into the suspension. The mixture was left for a specified time. H,S was passed through the mixture and the precipitated lead sulfide was filtered off. The filtrate was evaporated in a stream of air to leave the product, which was recrystallized (cyclohexane). 

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