Sulfide precipitants

Adding sulfide precipitates the Hg + as HgS. This is important because NH3 forms stable complexes with many metal ions, including Hg +. Any NH3 that is complexed with Hg + will not be collected by distillation, providing another source of determinate error. 

The removal of copper from the pregnant nickel solution in the Sherritt-Gordon process is an example of purification by precipitation of a fairly insoluble compound. First, in the copper boil step, ammonia is driven off by heating the solution, and some copper sulfide precipitates. The residual copper is removed by a dding hydrogen sulfide for the chemical precipitation of mote copper sulfide. 

Thiosulfates. The ammonium, alkaU metal, and aLkaline-earth thiosulfates are soluble in water. Neutral or slightly alkaline solutions containing excess base or the corresponding sulfite are more stable than acid solutions. Thiosulfate solutions of other metal ions can be prepared, but their stabiUty depends on the presence of excess thiosulfate, the formation of complexes, and the prevention of insoluble sulfide precipitates. 

As a result, sulfide precipitation is frequendy used as a polishing step following hydroxide precipitation. 

Many heavy metals are removed on activated carbon. A primary mechanism is sulfide precipitation on the carbon. 

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 ... 

An alternative procedure for removing an ion from solution is to change its identity by changing its oxidation state. The metal ions in very insoluble heavy metal sulfide precipitates can be dissolved by oxidizing the sulfide ion to elemental sulfur. For example, copper(II) sulfide, CuS, takes part in the equilibrium... 

Which sulfide precipitates first when sulfide ions are added to a solution containing equal concentrations of Co2"1", Cu2+, and Cd2+ For CoS, Kip = 5 X 10 22. Explain your conclusions. 

You decide to use sulfide precipitation to separate the copper(II) ions from the manganese(II) ions in a solution that is 0.20 m Cu2+(aq) and 0.20 m Mn2+(aq). Determine the minimum sulfide ion concentration that will result in the precipitation of one cation (identify the cation) hut not the other. 

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). 

Figure 4.23. Comparison of results on four batches using four different methods. The results are grouped according to batch, and within a group, the methods are sulfide precipitation, polarography. X-ray fluorescence, and inductively coupled plasma absorption (left to right).

Sato (1973) and Ohmoto et al. (1983) calculated the amounts of sulfides precipitated due to the mixing of ascending hydrothermal solution and cold seawater. Their calculations showed that the calculated ratios of the amounts of minerals precipitated are generally consistent with those in Kuroko ore deposits. 

If sulfur isotopic equilibrium between coexisting sulfates and sulfides was attained, using average values of sulfates and sulfides, -i-22%c and +5%c, respectively, we could estimate temperature using the equation by Ohmoto and Rye (1979). This temperature seems too high compared with temperature estimated from fluid inclusions and mineral assemblages (section 1.3.3). That means that sulfates and sulfides precipitated under the condition far from equilibrium. 

M. M. Brezinski. Methods and acidizing compositions for reducing metal surface corrosion and sulfide precipitation. Patent US 6315045, 2001. 

There are several potential treatment technologies that may be applicable, but are more expensive than the methods currently used. These potential treatments include sulfide precipitation, ultrafiltration, reverse osmosis, deep-well disposal, activated carbon adsorption or activated alumina adsorption, solidification, or ion exchange.19-21... 

Removal of Pollutants by Sulfide Precipitation at Three Plants... 

Pretreatment of metal-bearing wastewater before sulfide precipitation so that the formation of hazardous gaseous hydrogen sulfide does not occur... 

Ferrous sulfide itself is also a relatively insoluble compound. Thus, the sulfide ion concentration is limited by its solubility, which amounts to only about 0.02 g/L, and the inherent problems associated with conventional sulfide precipitation are significantly minimized. 

In addition to these three treatments, there are several alternative treatment technologies applicable to the treatment of common metals wastes. These technologies include electrolytic recovery, electrodialysis, reverse osmosis, peat adsorption, insoluble starch xanthate treatment, sulfide precipitation, flotation, and membrane filtration.1516... 

Cr(III) hydroxide, carbonate, and sulfide precipitate (pH > 6) Cr(VI) does not precipitate in these conditions. 

Toxic pollutants found in the mercury cell wastewater stream include mercury and some heavy metals like chromium and others stated in Table 22.8, some of them are corrosion products of reactions between chlorine and the plant materials of construction. Virtually, most of these pollutants are generally removed by sulfide precipitation followed by settling or filtration. Prior to treatment, sodium hydrosulfide is used to precipitate mercury sulfide, which is removed through filtration process in the wastewater stream. The tail gas scrubber water is often recycled as brine make-up water. Reduction, adsorption on activated carbon, ion exchange, and some chemical treatments are some of the processes employed in the treatment of wastewater in this cell. Sodium salts such as sodium bisulfite, sodium hydrosulfite, sodium sulfide, and sodium borohydride are also employed in the treatment of the wastewater in this cell28 (Figure 22.5). 

Wastewater treatment in the copper sulfate industry can further be improved, particularly the removal of the toxic metals, through sulfide precipitation, ion exchange, and xanthate processes. Addition of ferric chloride alongside alkaline precipitation can improve the removal of arsenic in the wastewater. 

Aspirate through ammoniacal cadmium chloride strip sulfur dioxide by aeration dissolve cadmium sulfide precipitate in concentrated HC1 titrate with iodine using a starch indicator. Iodometric titration 0.7 qg/L NR EPA 1978... 

Balasco AA, Santhanam CJ, Stevens JI, et al. 1986. Soluble sulfide precipitation study. Report to the U S. Army Toxic and Hazardous Materials Agency, Aberdeen Proving Ground, MD, by Arthur D. Little, Inc., Cambridge, MA. Report no. ADL-54144. 

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