Calcium thiosulfate

The most common form of calcium thiosulfate is the hexahydrate [10035-02-6] CaS202 6H20, which has triclinic crystals and a density of 1.872 g/cm at 16°C (84). Heating, however, does not give the anhydrous salt because of decomposition at 80°C. At lower temperatures, dehydration stops at the monohydrate [15091-91-5]. The solubiUty of calcium thiosulfates in water is as follows ... 

Calcium thiosulfate has been prepared from calcium sulfite and sulfur at 30—40°C, or from boiling lime and sulfur in the presence of sulfur dioxide until a colorless solution is obtained. Alternatively, a concentrated solution of sodium thiosulfate is treated with calcium chloride the crystalline sodium chloride is removed at low temperature. Concentrated solutions of calcium thiosulfate are prepared from ammonium thiosulfate and lime the Hberated ammonium ion is recycled to the ammonium thiosulfate process (85). 

Calcium thiosulfate is not produced commercially in the United States. Uses include fungicide formulations (86), a noncorrosive concrete-set accelerator (87), and a catalyst for polyolefin manufacture (88). 

Calcium thiosulfate [10124-41-11 M 152.2, m 43-49°, pKj 0.6, pKj 1.74 (for H2S2O3). Recrystd from water below 60° in a N2 atmosphere, followed by drying with EtOH and Et20. Stored in a refrigerator. [Pethybridge and Taba J Chem Soc, Faraday Trans 7 78 1331 1982.]... 

The powdered sulfide, admixed with small amounts of calcium thiosulfate and sulfur, has been involved in several fires and explosions, some involving initiation by static discharges. 

Kiss An obsolete process for extracting silver from its ores. The ores were roasted with sodium chloride, producing silver chloride, and this was leached out with a solution of calcium thiosulfate. The process was replaced by the cyanide process. 

This category of admixture is based mainly on the major raw materials, calcium chloride, calcium nitrate, calcium formate [2] and calcium thiocyanate, with minor amounts of other materials occasionally being included in the formulations, such as calcium thiosulfate [3] and triethanolamine (TEA). TEA is not normally used alone but because it is sometimes used in other categories of admixture to compensate for retarding influences it will be included in this section. 

BeH808Se beryllium selenate tetrahydrate 10039-31-3 25.00 2.0300 1 745 CaH1209S2 calcium thiosulfate hexahydrate 10124-41-1 25.00 1.8700 1... 

Calcium thiosulfate is a clear crystalline substance, with a faintly sulfurous odor. It reacts with free as well as combined chlorine. Calcium thiosulfate undergoes the following reactions with chlorine (20) ... 

Approximately 0.99 mg of calcium thiosulfate is required to neutralize 1 mg of residual chlorine at pH 7.35. At pH 11,0.45 mg/L of calcium thiosulfate is sufficient to neutralize 1 mg of chlorine residual. On a weight basis, approx 1.30 parts are needed per part of chlorine at pH 6.5. Although calcium thiosulfate is reported to neutralize combined chlorine effectively, the reactions involved are not currently known. Chlorine neutralization produces HCl and H2SO4 that may result in lower pH. It does not scavenge oxygen significantly, and does not produce SO2. 

The 96-h LC q of calcium thiosulfate for fathead minnows is greater than 750 mg/L (21). Other toxicity information on calcium thiosulfate is not currently available. Hazardous reporting is not required for calcium thiosulfate. Exposure may cause eye and skin irritation. Hazard rating of calcium thiosulfate is 0, 0, 0, 0 for health, fire, reactivity, and persistence. 

The field study indicated that, when no chemical was added, free chlorine concentration in the water did not decrease significantly. Chlorine concentrations decreased from 1.2 to approx 1.0 mg/L after a travel of 450 ft (4 min, 10 s) on the semi-paved, asphalt road. When stoichiometric concentrations of dechlorination chemicals were added, most of the chemicals neutralized chlorine instantaneously. Samples analyzed 2 ft (reaction time approx 1 s) downstream of the diffuser contained less than 0.1 mg/L of chlorine. An exception to this trend was calcium thiosulfate. When calcium thiosulfate was added, chlorine concentrations decreased to 0.2 mg/L within 2 ft and residual chlorine was reduced to less than 0.1 mg/L after a travel of 200 ft (reaction time 1 min 40 s). 

When twice the stoichiometric concentration of chemicals was added, residual chlorine in all the tests (including calcium thiosulfate) decreased to below 0.1 mg/L immediately (approx 2 s). 

Bureau of Water Works, Portland, OR Combined chlorine Sodinm bisnlfite Sodium sulfite Sodium thiosulfate Calcium thiosulfate Ascorbic acid Sodium ascorbate 1% solution Stoichiometric concentrations needed for dechlorination 1.1 8.0 Surface water 300... 

When no dechlorination chemical was added, the dissolved oxygen concentration of the released water decreased from an initial concentration of 11 by less than 0.3 mg/L after traveling 450 ft in one test. When stoichiometric amounts of dechlorination chemicals were added, the DO decreased by 1.18,0.3,0.55, and 0.5 mg/L in the presence of sodium metabisulfite, sodium sulfite, sodium thiosulfate, and calcium thiosulfate, respectively. When twice the stoichiometric amounts of dechlorination chemicals were added, the dissolved oxygen concentration decreased hy 1, 0.9, 0.9, and 0.7 mg/L, respectively, in the presence of these chemicals. With the addition of stoichiometric concentrations of ascorbic acid and sodium ascorbate, the DO of the water increased by 0.3 mg/L, after a travel of 450 ft. When twice the stoichiometric concentrations of these chemicals were used, the DO decreased hy 0.2 mg/L. 

In summary, results indicated that sodium metabisulfite had a greater impact (1.0-1.18 mg/L depletion) on the DO concentrations of the water tested. Sodium sulfite, sodium thiosulfate, and calcium thiosulfate decreased the DO concentration hy 0.3-0.9 mg/L, depending on the amount of dechlorination chemical used. Ascorbic acid and sodium ascorbate had the least impact on the DO of the water tested. 

The initial pH of the hydrant water, prior to chemical addition, was between 8.8 and 9.0. Sodium metabisulfite, at either concentration used, decreased the water pH about 0.8 unit after a travel of 450 ft. After a travel of 450 ft, ascorbic acid decreased the pH of the water by 0.3 and 0.6 unit when stoichiometric and twice the stoichiometric amounts, respectively, were used. The pH decreased by less than 0.1 unit when sodium sulfite, calcium thiosulfate, or sodium ascorbate was used at stoichiometric or twice the stoichiometric amounts. 

When no dechlorination chemical was added, the chlorine concentration decreased from 1.05 to 0.95 mg/L after 1000 feet (Fig. 2). This indicated that only a small amount (0.1 mg/L) of the chloramines dissipated through chlorine demand of paved surfaces. Sodium bisulfite, sodium sulfite, ascorbic acid, and sodium ascorbate neutralized all detectable chlorine to below 0.1 mg/L within 2 ft downstream of the mixing hose (approx 2 s). Sodium thiosulfate neutralized more than 80% of the chlorine within 2 ft. However, chlorine concentrations decreased below 0.1 mg/L (the discharge limit in most states) after about 500 ft (elapsed time 3 min, 2 s). Calcium thiosulfate neutralized 60% of the chlorine within 2 ft and neutralized 90% of the chlorine after 1000 ft (elapsed time 7 min, 10s). 

The field studies indicated that all of the dechlorination chemicals were effective in neutralizing free and combined chlorine to below 0.1 mg/L. In most cases the stoichiometric amount of dechlorination chemicals removed more than 90% of the chlorine. However, the reaction rates and the water quality impacts varied with the type, amount, and form of the chemicals used. In general, the rates of dechlorination using sodium/calcium thiosulfate were slower than those using the other chemicals. However, studies by others indicated that dechlorination of wastewater samples using sodium thiosulfate was more rapid that using ascorbic acid (24). 

Leaching Pure Gold in Calcium Thiosulfate based Leach Solutions... 

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