Silver thiosulfate

Silver Thiosulfate. Silver thiosulfate [23149-52-2], Ag 2 y is an insoluble precipitate formed when a soluble thiosulfate reacts with an excess of silver nitrate. In order to minimize the formation of silver sulfide, the silver ion can be complexed by haUdes before the addition of the thiosulfate solution. In the presence of excess thiosulfate, the very soluble Ag2(S203) 3 and Ag2(S203) 3 complexes form. These soluble thiosulfate complexes, which are very stable, are the basis of photographic fixers. Silver thiosulfate complexes are oxidized to form silver sulfide, sulfate, and elemental sulfur (see Thiosulfates). 

Sulfur Complexes. Silver compounds other than sulfide dissolve in excess thiosulfate. Stable silver complexes are also formed with thiourea. Except for the cyanide complexes, these sulfur complexes of silver are the most stable. In photography, solutions of sodium or ammonium thiosulfate fixers are used to solubilize silver hahdes present in processed photographic emulsions. When insoluble silver thiosulfate is dissolved in excess thiosulfate, various silver complexes form. At low thiosulfate concentrations, the principal silver species is Ag2(S203) 2j high thiosulfate concentrations, species such as Ag2(S203) 3 are present. Silver sulfide dissolves in alkaline sulfide solutions to form complex ions such as Ag(S 2 Ag(HS) 4. These ions are... 

Silver compounds having anions that are inherently toxic, eg, silver arsenate and silver cyanide, can cause adverse health effects. The reported rat oral LD values for silver nitrate, silver arsenate [13510-44-6] and silver cyanide are 500—800 (29), 200—400 (29), and 123 mg/kg (30), respectively. Silver compounds or complexes ia which the silver ion is not biologically available, eg, silver sulfide and silver thiosulfate complexes, are considered to be without adverse health effects and essentially nontoxic. 

The impact that a silver compound has in water is a function of the free or weaMy complexed silver ion concentration generated by that compound, not the total silver concentration (3—5,27,40—42). In a standardized, acute aquatic bioassay, fathead minnows were exposed to various concentrations of silver compounds for a 96-h period and the concentration of total silver lethal to half of the exposed population (96-h LC q) deterrnined. For silver nitrate, the value obtained was 16 )-lg/L. For silver sulfide and silver thiosulfate complexes, the values were >240 and >280 mg/L, respectively, the highest concentrations tested (27). 

The chronic aquatic effects which relate silver speciation to adverse environmental effects were studied on rainbow trout eggs and fry. The maximum acceptable toxicant concentration (MATC) for silver nitrate, as total silver, was reported to be 90—170 ng/L (43). Using fathead minnow eggs and fry, the MATC, as total silver, for silver thiosulfate complexes was reported as 21—44 mg/L, and for silver sulfide as 11 mg/L, the maximum concentration tested (27). 

In secondary wastewater treatment plants receiving silver thiosulfate complexes, microorganisms convert this complex predominately to silver sulfide and some metallic silver (see Wastes, INDUSTRIAL). These silver species are substantially removed from the treatment plant effluent at the settling step (47,48). Any silver entering municipal secondary treatment plants tends to bind quickly to sulfide ions present in the system and precipitate into the treatment plant sludge (49). Thus, silver discharged to secondary wastewater treatment plants or into natural waters is not present as the free silver ion but rather as a complexed or insoluble species. 

Other Uses. Photochromic glass contains silver chloride (80) and silver molybdate [13765-74-7] (81) (see Chromogenic materials). An apparatus coated with silver nitrate has been described for the detection of rain or snow (82). Treatment with silver-thiosulfate complex has been reported as dramatically increasing the post-harvest life of cut carnations (83). Silver sulfate has been used in the electrolytic coloring of aluminum (84). Silver sulfate also imparts a yellowish red color to glass bulbs (85). 

Wood, C.M., C. Hogstrand, F. Galvez, and R.S. Munger. 1996b. The physiology of waterborne silver toxicity in freshwater rainbow trout (Oncorhynchus mykiss). 2. The effects of silver thiosulfate. Aquat. Toxicol. 35 111-126. 

Uptake of small organic metal complexes over transport systems of organic metabolites may be possible, for example, of small organic acids like citrate or amino acids. However, only few examples of such processes have been studied so far. Increased uptake of cadmium by an alga has been observed in the presence of citrate and has been attributed to accidental transport of the metal-citrate complex over a citrate transporter [212]. Transport systems of inorganic anions may also play a role in metal transport. Silver uptake by algae was enhanced in the presence of thiosulfate. In this case, the silver thiosulfate complex was transported over a sulfate uptake system [213]. It remains to be demonstrated how widespread these processes may be for metal uptake in the aquatic environment [12]. 

Silver tetrafluoroborate, 22 674, 23 715 Silver thiocyanate, 22 674 Silver thiosulfate, 22 674, 675 in floristry, 22 659, 669 wastewater treatment plants and, 22 683... 

In this method, a metal (usually iron) in a chemical recovery cartridge (CRC) reacts with the silver thiosulfate in the spent fixer and goes into solution. The less active metal (silver) settles out as a solid. To bring the silver into contact with the iron, the spent fixer is passed through the CRC container, which is filled with steel wool. The steel wool provides the source of iron to replace the silver. The main advantages of this CRC method are the very low initial cost (cartridges cost about US 60) and the simplicity of installation only a few simple plumbing connections (shown in Fig. 2) are required. 

Initial stages of Ag electrocrystallization from silver thiosulfate complexes have been studied by Simons et al. [368] and Gonnissen et al. [369] The formation of subcritical 2D silver clusters, preceding the formation of supercritical, stable 3D nuclei and their growth, has been suggested. 

Scow et al. (1981) reported that the median silver concentrations in sewage treatment plant influent and effluent were 0.008 mg/L and 0.002 mg/L, respectively. Treated effluents from a large photographic processing plant contained an average of 0.07 mg/L silver (range <0.02-0.30 mg/L) in the form of silver thiosulfate complexes, silver bromide, and silver sulfide (Bard et al. 1976). 

When the film paper is exposed to light, silver ions are reduced to silver atoms. Next excess silver ions are removed by combining them with thiosulfate ions to form a silver thiosulfate complex ion. This happen when the exposed film paper is placed in a hypo solution. To completely stop the developing process, the film paper is next placed in a fixer such as acetic acid to neutralize the basic hypo solution. 

Metal salts can be used in two ways. First, pretreatment with a trihydroxyben-zene compound such as pyrogallol [87-66-1] is followed by treatment with an ammoniacal silver salt solution. This allows rapid dyeing due to the formation of metallic silver and oxidation products of the trihydroxybenzene derivative. If pre-treatment is performed with thiosulfate instead of a benzene derivative, the process yields unstable silver thiosulfate and finally black silver sulfide. 

Decolorized a colorless solution of tetrathionate ions is formed White precipitate of barium thiosulfate White precipitate of silver thiosulfate... 

An overworked fixing bath contains complex silver thiosulfate compounds that can be retained by negatives or prints and cannot be removed completely by washing. This formula... 

Silver ions923 and 2,5-norbornadiene (NBD)924 are well known as effective inhibitors of ethylene action. Silver, applied in the form of thiosulfate (silver thiosulfate (STS)), is a very effective inhibitor of ethylene action. It has been used with much success on cut flowers and potted plants. But as it is a heavy metal it cannot be used on food and feed, and is harmful to environment. As NBD requires continuous exposure and a high concentration, and has a strong odor, it also cannot be used on cut flowers and food. Furthermore, both compounds are toxic for plant growth in high concentration. 

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