Lead sulfide, precipitation

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... 

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). 

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). 

Iron is the most abundant, useful, and important of all metals. For example, in the 70-kg human, there is approximately 4.2 g of iron. It can exist in the 0, I, II, III, and IV oxidation states, although the II and III ions are most common. Numerous complexes of the ferrous and ferric states are available. The Fe(II) and Fe(III) aquo complexes have vastly different pAa values of 9.5 and 2.2, respectively. Iron is found predominantly as Fe (92%) with smaller abundances of Fe (6%), Fe (2.2%), and Fe (0.3%). Fe is highly useful for spectroscopic studies because it has a nuclear spin of. There has been speculation that life originated at the surface of iron-sulfide precipitants such as pyrite or greigite that could have caused autocatalytic reactions leading to the first metabolic pathways (2, 3). 

A commonly held belief is that lead-containing pigments react with hydrogen sulfide in polluted air to form the black precipitate lead sulfide. On exposure to hydrogen sulfide gas, all of these pigments will darken because of the formation of the black lead sulfide, PbS ... 

No longer used as a manufacturing process, but still used as a qualitative test for mercaptans in petroleum fractions. The presence of mercaptans is indicated by a black precipitate of lead sulfide. 

In some locations, high-temperature fluids undergo considerable subsurfece mixing with relatively fresh seawater. This leads to precipitation of the less soluble iron and copper sulfides within the conduits. The fluids discharging into the ocean generally have temperatures less than 400°C and are milky white because of zinc sulfide precipitates. These white smokers also build chimneys, some of which are as much as 13 m high. Because of their lower temperatures, white smokers are typically encrusted with worm... 

Reaction with hydrogen sulfide forms black precipitate of lead sulfide, PbS. A paper soaked with lead acetate solution turns black on exposure to H2S, a test often used to detect sulfide. 

Lead sulfide occurs naturally as the mineral galena. It can be prepared in the laboratory as a black precipitate by passing hydrogen sulfide through a dilute acid solution of inorganic lead salt, such as lead nitrate or lead acetate ... 

The mother liquor from seaweed ash contains quite a large quantity of a very peculiar and curious substance it is easily extracted one merely pours sulfuric acid on the mother liquor and heats the mixture in a retort the mouth of which is connected to a delivery-tube leading to a bulb. The substance which is precipitated in the form of a black, shining powder immediately after the addition of sulfuric acid, rises, when heated, in vapor of a superb violet color. This vapor condenses in the delivery-tube and receiver in the form of very brilliant crystalline plates having a luster equal to that of crystalline lead sulfide. Upon washing these plates with a little distilled water, one obtains the substance in the pure state (45, 23). 

The -pH relations for the important iron-water system at 25 °C are summarized in Fig. 15.3 with some simplifications. First, it is assumed that no elements other than Fe, O, and H are involved in a natural water system, the presence of C02 would oblige us to include FeCC>3 (siderite), and sulfur compounds could lead to precipitation of iron sulfides in certain Eh-pH regimes. As it is, the only Fe-O-H solids we have considered are Fe metal, Fe(OH)2, and Fe(OH)3, whereas in practice magnetite (Fe30,i), hematite (a-Fe2C>3), goethite [a-FeO(OH)], and other Fe-O-H phases could be present. Indeed, our choice of solubility products for Fe(OH)2 and... 

Another secret-ink system used by the Germans during the war involved the chemical reactions between lead nitrate and sodium sulfide. As any high school student should know, solutions of these compounds are colorless, but form a black precipitate of lead sulfide when mixed. A spy can inscribe a message with the lead solution, and its recipient can read the missive by spraying it with the sodium sulfide solution. 

Dilute hydrochloric acid or sulfuric acid Silver nitrate Lead acetate Sodium nitroprusside solution Sulfides, S2 Hydrogen sulfide gas is evolved and detected by odor or lead acetate paper Black precipitate of silver sulfide soluble in hot, dilute nitric acid Black precipitate of lead sulfide Transient purple color in the presence of solutions of alkalis... 

Add 100 mg of spironolactone to a mixture of 10 mL of water and 2 mL of IN NaOH, boil for 3 minutes, and cool. Add 1 mL of glacial acetic acid and 1 mL of lead acetate solution a brown to black precipitate of lead sulfide is produced. 

B. Dissolve about 5 mg of sample in a mixture of 1 mL of lead acetate TS and 1 mL of a 1 10 sodium hydroxide solution. A yellow color appears. Heat the mixture for several minutes on a steam bath. The color changes to brown, and on standing, a precipitate of lead sulfide forms. 

The sulfide ion then reacts with the lead ion in the gel to precipitate lead sulfide. Crystals up to a millimeter in length can be produced in 2 weeks. Temperatures range from room temperature to 35°, with best results reported at the higher temperature. The same sulfide source is used for the growth of zinc sulfide crystals.25,27 The crystals grow to a size of 3-4 mm in 2 months. It should be mentioned that a modified U-tube system has been used to produce this size crystal and it is expected that smaller crystals will be produced if a simple U-tube is employed. 

The solution is again brought to a boil and a calculated amount of silver oxide (Note 7) is added to remove the last of the chlorides. The silver chloride is filtered off and the lead is precipitated with hydrogen sulfide. A light straw-colored solution remains. 

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