Precipitated solids sulfide

Heavy metals often can be removed effectively by chemical precipitation in the form of carbonates, hydroxides, or sulfides. Sodium carbonate, sodium bisulfite, sodium hydroxide, and calcium oxide are all used as precipitation agents. The solids precipitate as a floe containing a large amount of water in the structure. The precipitated solids need to be separated by thickening or filtration and recycled if possible. If recycling is not possible, then the solids are usually disposed of to a landfill. 

The occurrence of sulfide strongly affects the speciation and solubility of numerous trace elements. Solid sulfide phases may be precipitated, and dissolved sulfide and polysulfide complexes may be formed (21-23). The influence of sulfide on trace... 

Sulfide. Sulfide appears in the water column of Lake Greifen only at the end of stagnation time and in the deepest water layers. This distribution indicated the biological reduction of sulfate in sediments. The reactions involved in the sulfur cycle are described in ref. 65. The occurrence of sulfide indicates a very low pe (p < 0) sulfide is an efficient reductant for many elements, including Fe(III), Mn(IV), As(V), and Cr(VI). The occurrence of sulfide also implies the possible precipitation of solid sulfide phases of various elements and the formation of dissolved complexes (21-23). 

Dissolve 100 grams of 2,4,6-trinitrotoluene into 200 milliliters of p-dioxane, and then place the mixture into a cold-water bath. Then stir the mixture, and add 2 milliliters of 28 - 30% ammonium solution. Then bubble 46 grams of hydrogen sulfide gas into the mixture over a 2-hour period while keeping the reaction temperature at 20 Celsius by means of the cold-water bath, and stir the reaction mixture continuously during the addition. After the addition of the hydrogen sulfide gas, filter off the precipitated sulfur, and then add the filtered reaction mixture to 1000 milliliters of ice water. After which, filter off the yellow precipitated solid, and then wash the solid with 400 milliliters of water. Then vacuum dry or air-dry the solid. The result is a mixture of the desired 4-amino-2,6-dinitrotoluene (61%), and the by-product, 4-hydroxylamino-2,6-dinitrotoluene (39%). 

To a hot solution of 12.1 g. (0.05 mole) of 3 nitro-4-methylbenzo-phenone (p. 228) in 300 ml. of ethanol is added dropwise a hot solution of 22.5 g. of crystalline sodium sulfide in 30 ml. of ethanol and 30 ml. of water. The reaction mixture is poured into 500 ml. of water, and the precipitated oil solidifies on cooling. The solid product is suspended in 600 ml. of boiling water and treated with concentrated hydrochloric acid until no more solid dissolves. The mixture is filtered rapidly, and the filtrate is treated with excess aqueous ammonia. The precipitated solid is recrystallized from methanol to give 9 g. (85%) of amine, m.p. 109-110°. 

A solution of 990 g. (4.40 moles) of stannous chloride dihydrate in 975 ml. of concentrated hydrochloric acid is added to 165 g. (0.598 mole) of di-(p-nitrophenyl) sulfide [Org. Syntheses, 28, 82 (1948)]. To initiate reaction, the mixture is warmed on the steam bath to 65°. The reaction mixture is heated to 80-90° for 5 hours and then poured into an ice-cold solution of 1290 g. of sodium hydroxide dissolved in 3230 ml. of water. The precipitated solid is removed by filtration and... 

The chemical processes leading to different minerals are diverse. Highly incompatible lithophilic elements (e.g. Li, Be, Zr and lanthanides) are concentrated in the final stages of solidification of molten rocks, known as pegmatites. Many sulfide minerals (e.g. of Cu, Zn, Mo and Pb) are formed by hydrothermal processes, in which water circulates deep in the crust and at high temperatures and pressures, and forms soluble complexes of these elements with anions such as CF and HS-, which may subsequently precipitate solids when they cool. 

Sulfides of alkali- and alkaline-earth metals including magnesium, manganese(II) and thallium(III) were found to be soluble in the melt and their solutions were colourless. On the contrary, the addition of Na2S to solutions of other cations caused precipitation of solid sulfides which were black, apart from ZnS (white), CdS (orange) and Ce2S3 (grey). It should be... 

Under reducing conditions, As(III) may precipitate with sulfide as orpi-ment, As2S3(s), realgar, As4S4(s), or arsenopyrite, EeAsS(s). However, even if such solids form, the dissolved As(III) concentrations in equilibrium with them are not necessarily low. A study of orpiment solubility demonstrated that, in... 

But the fact is that the precipitation of sulfides by the iron oxide is essentially an oxidation-reduction reaction between the gas and the solid, which actually proceeds faster at low pH (Ray et al. 1979). 

Precipitates. Mercuric sulfide is highly insoluble. In fact, its solubility is so low that there is some spread in reported values of the solubility product, but all are in the general region of 10 . Precipitation with sulfide or a sulfur-containing compound therefore is a common technique. The solids are removed by filtration. Again, mercury can form anionic complexes with sulfur, and so overtreatment with a sulfide solution can be counterproductive. 

Procedure. A drop of the test solution, or a few grains (or more) of the solid sulfide, according to the expected arsenic content, is placed in a micro crucible and warmed with a few drops of ammonia and 10 % hydrogen peroxide. Sulfides must be completely dissolved, or made colorless. The mixture is then acidified with dilute acetic acid, and 1 or 2 drops of 1 % silver nitrate solution added. A red-brown precipitate or coloration appears if arsenic is present. 

G) Add to large excess water, precipitate as sulfide, neutralize, oxidize excess sulfide with hypochlorite. Solids to secure landfill, liquid to drain. 

Water-insoluble salts are dissolved in dilute acids and can be isolated by extraction, steam distillation, or even filtration if the liberated acid is solid and insoluble in water. Insoluble salts of alkaline-earth metals can be converted to soluble sodium salts by boiling with sodium carbonate solution. Insoluble silver, copper, lead, and similar salts are decomposed in an aqueous suspension with hydrogen sulfide and filtered from the precipitated metal sulfide. The acid can then be isolated from the filtrate. 

In-situ immobilization is used to convert wastes to insoluble forms that will not leach from the disposal site. Heavy metal contaminants including lead, cadmium, zinc, and mercury, can be immobilized by chemical precipitation as the sulfides by treatment with gaseous H2S or alkaline Na2S solution. Disadvantages include the high toxicity of H2S and the contamination potential of soluble sulfide. Although precipitated metal sulfides should remain as solids in the anaerobic conditions of a landfill, unintentional exposure to air can result in oxidation of the sulfide and remobilization of the metals as soluble sulfate salts. 

Note that this reduction reaction is the reverse of the photos)mthetic reaction shown in Eq. (2.51b). This reaction produces sulfide species, such as H2S (hydrogen sulfide), HS (bisulfide), and (sulfide ion), which are the most reduced forms of sulfur, with sulfur in the (—11) oxidation state. Sulfides are toxic most popularly known is H2S, which forms in rotten eggs and gives them their characteristic pungent odor. Sulfides are also important in causing the chemical precipitation of many metals, such as iron, copper, lead, and zinc, which form solids (such as FeS, CuS, PbS, and ZnS) upon reaction with. Precipitation with sulfide promotes long-term retention of metals in bottom sediments, and enables the geologic formation of many metal ore deposits. 

Solid Compounds. The tripositive actinide ions resemble tripositive lanthanide ions in their precipitation reactions (13,14,17,20,22). Tetrapositive actinide ions are similar in this respect to Ce . Thus the duorides and oxalates are insoluble in acid solution, and the nitrates, sulfates, perchlorates, and sulfides are all soluble. The tetrapositive actinide ions form insoluble iodates and various substituted arsenates even in rather strongly acid solution. The MO2 actinide ions can be precipitated as the potassium salt from strong carbonate solutions. In solutions containing a high concentration of sodium and acetate ions, the actinide ions form the insoluble crystalline salt NaM02(02CCH2)3. The hydroxides of all four ionic types are insoluble ... 

Wlien solid soda ash is used to supply all the carbonate v alues in the precipitation step (eq. 9), a ca 10% Na2S solution results from the primary filtration step wliich can be concentrated to 40% Na2S in a three-effect evaporator train. Final concentration to 60%Na2S occurs in a high v acuurn single-effect evaporator. Hiis concentrated solution can then be fed to a Baker to produce a 60% sodium sulfide flake wliich is sold as co-product. 

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. 

D. ci - -Thiabicyclo[4 .. Q]nonan S,S-Dioxide [Benzo[c]thiophene 2,2-dioxide, cis-octahydro-]. A solution of the sulfide (43.0 g., 0.303 mole) in 11. of ether is cooled to 0° and treated dropwise while magnetically stirred with 1.01. of 0.65iV ethereal monoperphthalic acid (0.65 mole). The mixture is kept overnight at 0°, after which time the precipitated phthalic acid is separated by filtration and the filtrate concentrated with a rotary evaporator. Bulb-to-bulb distillation of the residual oil at 0.05-0.1 mm. affords the sulfone as a eolorless liquid (48.5-50 g., 92-95%) (Note 11). This product is crystallized from ether-hexane to give a colorless solid, m.p. 39-41° (Note 12). 

Technology Description To achieve precipitation, acid or base is added to a solution to adjust the pH to a point where the constituents to be removed have their lowest solubility. Chemical precipitation facilitates the removal of dissolved metals from aqueous wastes. Metals may be precipitated from solutions as hydroxides, sulfides, carbonates, or other soluble salts. A comparison of precipitation reagents is presented in Table 7. Solid separation is effected by standard flocculation/ coagulation techniques. 

Extension of these studies to medium rings produced interesting results (73). The mercuric acetate oxidation of 1-methyl-1-azacyclooctane (64), when worked up in the usual manner, gave no distillable material. When an equivalent amount of hydrochloric acid was added to the solution which had been saturated with hydrogen sulfide to precipitate the excess mercuric acetate and filtered, evaporation of the solution to dryness gave a solid which was subsequently identified as 2,4,6-tris(6 -methylaminohexyl)-trithiane trihydrochloride (65). Two plausible routes to the observed... 

Precipitation involves the alteration of the ionic equilibrium to produce insoluble precipitates. To remove the sediment, chemical precipitation is allied with solids separation processes such as filtration. Undesirable metal ions and anions are commonly removed from waste streams by converting them to an insoluble form. The process is sometimes preceded by chemical reduction of the metal ions to a form that can be precipitated more easily. Chemical equilibrium can be affected by a variety of means to change the solubility of certain compounds. For e.xample, precipitation can be induced by alkaline agents, sulfides, sulfates, and carbonates. Precipitation with chemicals is a common waste stream treatment process and is effective and reliable. The treatment of sludges is covered next. 

You are given a solution and asked to analyze it for the cations Ag t, Ca2+, and Hg24. You add hydrochloric acid. Nothing appears to happen. You then add dilute sulfuric acid, and a white precipitate forms. You filter out the solid and add hydrogen sulfide to the solution that remains. A black precipitate forms. Which ions should you report as present in your solution ... 

Many carbonate, sulfite, and sulfide precipitates can be dissolved by the addition of acid, because the anions react with the acid to form a gas that bubbles out of solution. For example, in a saturated solution of zinc carbonate, solid ZnCO, is in equilibrium with its ions ... 

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