Zinc sulfide precipitation

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... 

The Na2S solution is mixed with a cobalt-treated zinc salt solution under precisely controlled conditions. The resulting zinc sulfide precipitate is calcined and processed to give the finished product. 

Production. The raw material for the production of cadmium yellow pigments is high-purity cadmium metal (99.99 %), cadmium oxide, or cadmium carbonate. If the metal is used it is first dissolved in mineral acid. A zinc salt is then added to the solution the amount added depends on the desired shade. The zinc salt is followed by addition of sodium sulfide solution. An extremely finely divided cadmium sulfide or cadmium zinc sulfide precipitate is formed, which does not possess any pigment properties. This intermediate product can also be obtained by mixing the cadmium or cadmium-zinc salt solution with sodium carbonate solution. An alkaline cadmium carbonate or cadmium zinc carbonate precipitate is formed which reacts in suspension with added sodium sulfide solution. 

Presence of oxidizable substances in the sample would interfere in the test, thus giving high results. These include S2. S 0,2. and certain metal ions such as Fe2+ in lower oxidation state. Sulfide should be removed by adding 0.5 g zinc acetate, allowing the zinc sulfide precipitate to settle and drawing out the supernatant liquid for analysis. If thiosulfate is present, determine its concentration in an aliquot of sample by iodometric titration using iodine standard. Subract the concentration of thiosulfate from the iodometric sulfite results to calculate the true value of SO,2. ... 

Whether lead(ll) sulfide and zinc sulfide precipitate from the hydrogen sulfide solution depends on the solubility product constants of the sulfides, and on the sulfide-ion... 

Finally, selective separation and dewatering of one suspended substance in a slurry containing different minerals or precipitates is possible by selectively adsorbing a magnetic material (usually hydrophobic) onto a soHd that is also naturally or chemically conditioned to a hydrophobic state. This process (Murex) was used on both sulfide ores and some oxides (145). More recently, hydrocarbon-based ferrofluids were tested and shown to selectively adsorb on coal from slurries of coal and mineral matter, allowing magnetic recovery (147). Copper and zinc sulfides were similarly recoverable as a dewatered product from waste-rock slurries (148). 

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 ... 

The luminescence of macrocrystalline cadmium and zinc sulfides has been studied very thoroughly The colloidal solutions of these compounds also fluoresce, the intensity and wavelengths of emission depending on how the colloids were prepared. We will divide the description of the fluorescence phenomena into two parts. In this section we will discuss the fluorescence of larger colloidal particles, i.e. of CdS particles which are yellow as the macrocrystalline material, and of ZnS particles whose absorption spectrum also resembles that of the macrocrystals. These colloids are obtained by precipitating CdS or ZnS in the presence of the silicon dioxide stabilizer mentioned in Sect. 3.2, or in the presence of 10 M sodium polyphosphate , or surfactants such as sodium dodecyl sulfate and cetyldimethylbenzyl-ammonium... 

Rao SR, Finch JA, Zhou ZA, Xu Z (1998) Relative flotation response of zinc sulfide mineral and precipitate. Sep Sci Tech 33 819-833... 

The platinum asbestos is filtered off. The product which has deposited on the catalyst is washed off with a minimum amount of water and the washings are combined with the filtrate. To avoid contamination of the final product with zinc, the zinc is removed from the solution by addition of about 55 ml. of a 20% ammonium sulfide solution (or ammonium sulfide is added until precipitation is complete). The zinc sulfide is removed by filtration, the solid is washed, and the washings are added to the solution. Alcohol is added to the filtrate and washings until some cloudiness appears, then the mixture is cooled to precipitate the product. Additional product may be obtained by concentrating the solution under vacuum, adding hydrochloric acid to obtain a pH below 1, and cooling. The crystals are washed with alcohol. 

Some of the discharged sulfide particles settle onto the chimney s exterior, where they are buried by the outward growth of anhydrite. Sulfide precipitation within the chimneys, causes copper, zinc, and iron sulfides to deposit and partially replace the anhydrite. Chimneys can build to several meters in height and their orifices range in diameter from 1 to 30 cm. Both the smoke and the chimneys are composed of polymetallic sulfide minerals, chiefly pyrrhotite (FeS), pyrite (FeS2), chalcopyrite (CuFeS2), and sphalerite or wurtzite (ZnS). 

GaUium may be recovered from zinc sulfide ores by a series of steps that include oxidation, acid treatments, neutralization, precipitation, alkali treatment, and electrolysis (Foster, L.M. 1968. Gallium. In the Encyclopedia of Chemical Elements, ed. C. L. Hampel, pp. 231-237, New York Reinhold Pubhshing Corp.). The process is described below. 

Also, zinc sulfide may be prepared in the laboratory by passing hydrogen sulfide through an aqueous solution of a soluble zinc salt, such as zinc chloride or zinc nitrate. The precipitate is filtered, washed, and dried. 

The manufactnring process for the important zinc and cadmium sulfide phosphors involves precipitation of the sulfide from purified salt solutions, e.g. the snlfate, with hydrogen snlfide. For ZnS Cu, the copper activator is added, as a readily decomposed derivative, to the sulfides and after grinding the components are fired in fnmaces at temperatures in the range 800-1200 °C. ZnS Ag, the bine phosphor nsed in CRTs, is prepared by firing zinc sulfide with silver nitrate at 1000 °C, nsnally in the presence of sodinm chloride to give the co-activating chloride ions. 

Although gallium sulfide does not precipitate from a solution of the pure salt, it is readily carried down with zinc sulfide. Boisbaudran therefore added ammonium acetate and acetic acid to the hydrochloric acid solution of the above precipitate, and passed in hydrogen sulfide. As long as the line Ga a (417 0) continued to show in the spectrum of the precipitate, he kept on adding zinc to the filtrate until finally all the gallium had been precipitated. 

The zinc concentrate is first roasted in a fluid-bed roaster to convert the zinc sulfide to the oxide and a small amount of sulfate. Normally, roasting is carried out with an excess of oxygen below 1000°C so that comparatively htde cadmium is eliminated from the calcined material in this operation (3). Since the advent of the Imperial Smelting Zinc Furnace, the preliminary roasting processes for zinc and zinc—lead concentrates result in cadmium recovery as precipitates from solution or as cadmium—lead fame, respectively, as shown in Figure 1. 

Fender, R.G., A MacGregor, and K.E. Patterson, "Sulfide Precipitation Investigation and System Design for Zinc-Laden Foundry Wastewater," Proc. 14th Mid-Atlantic Industrial Waste Conf.. 14 268-277, (1982). 

Zinc and Cadmium Sulfides and Sulfoselenides. The raw materials for the production of these sulfide phosphors are high-purity zinc and cadmium sulfides, which are precipitated from purified salt solutions by hydrogen sulfide or ammonium sulfide [5.291], [5.296], [5.307], [5.310], The concentration of contaminants such as Fe, Co, or Ni must be below 1 % of the activator concentration. The Zn, Cd S can be produced by mixing precipitated zinc sulfide and cadmium sulfide. However, coprecipitation from mixed zinc-cadmium salt solutions is preferred because of the better homogeneity. 

Most of the heavy-metal impurities present in zinc salt solutions must be removed before the precipitation reaction, or these form insoluble colored sulfides that reduce the whiteness of the zinc sulfide pigment. This end is usually achieved by the addition of zinc metal which reduces most heavy-metal ions to their metallic form. The brightness of zinc sulfide can be improved by the addition of a small amount of cobalt salts (ca 0.04% on a Co/Zn basis) (20). Barium sulfate [7727-43-7] formed in the first step is isolated and can be used as an extender. 

Both zinc sulfide and barium sulfate are insoluble in water. To improve the stability of lithopone, a small amount of a cobalt salt is added to the precipitated mixture. The mixture has to be filtered off, dried, and calcined. The calcination is carried out in rotary calciners at temperatures between 600 and 700°C. During calcination, the particle size of zinc sulfide grows from its original size (about 0.1 Jim) to the pigmentary optimal size of 0.4—0.6 Jim. 

Pure solutions of zinc sulfate can only be used for the preparation of lithopone having a low (up to 30%) percentage of zinc sulfide. Additional zinc compound must be added for the preparation of lithopone having a higher concentration of ZnS. Most often that compound is zinc chloride. One can either use a mixture of sulfuric and hydrochloric acid for the dissolution of zinc-containing raw materials, or direcdy mix separately prepared solutions of zinc sulfate and zinc chloride. The precipitation of 60% of the lithopone can be approximated by the following reaction ... 

Ray et al. [77] used an indirect method based on AAS for the determination of sulfide in flooded acid sulfate soils. Hydrogen sulfide, evolved during the anaerobic metabolism of sulfate, is readily converted into insoluble metal sulfides, chiefly iron sulfide, in flooded acid sulfate soils. A method for determining sulfide is based on the precipitation of the sulfide as zinc sulfide and subsequent determination by methylene blue formation or iodine titrimetry. 

Ray et al. [77] have also described a method for determining sulfide in soil extracts involving the precipitation of zinc sulfide by the action of zinc on the hydrogen sulfide-flooded acid sulfate soil, and then indirect determination of sulfide by determining the zinc in the precipitate and also the zinc remaining in solution, after the precipitation by AAS. Over 85% of the sulfide was recovered in this procedure. 

---