Calcium arsenite

Calcium Arsenites.—The ternary system Ca0-As203-H20, investigated at 0°, 25° and 99° C. by the method indicated under barium arsenites11 (p. 162), gives evidence of the formation of two arsenites,... 

Calcium Arsenite. (CAS 52740-16-6. CadAsOit , white precipitate, formed by reaction of soluble calcium salt solution and sodium arsen-ite solution. 

Shih and Lin (2003) investigated the solidification/stabilization of arsenic-rich flyash from an abandoned copper smelter in northern Taiwan. The flyashes (2-40 % total arsenic, mostly as As(III)) were collected from three flue gas discharge tunnels. Extremely high cement dosages (cement/waste mass ratio of greater than 6) were required to stabilize the wastes so that they would pass the US TCLP for arsenic (<5 mg L 1 Appendix E). (The TCLP is often used in research outside of the United States.) Cement dosages could be reduced and the mixtures would still pass the TCLP for both arsenic and lead if municipal waste incinerator flyash was added. Lime alone was able to stabilize arsenic and pass the TCLP however, the leachates exceeded the TCLP lead standard of 5mgL 1. The immobilization of arsenic in lime may be due to the formation of sparsely water-soluble calcium arsenites and arsenates, such as CaHAsC>3 //1LO or Ca3(AsC>4)2 H20, where n > 0 (Shih and Lin, 2003, 692). 

Arsenic is a frequent contaminant in metal ores (especially sulfides) and therefore appears in hydrometallurgical processes applied to these ores. Because of its toxicity, it must be efficiently removed from aqueous process streams before discharge. Traditionally this has been done with lime, but a large excess is required and the product (calcium arsenite and arsenate) can re-release some arsenic under the influence of atmospheric carbon dioxide. A more reliable process is co-precipitation with iron salts under near-neutral conditions. This requires both element ores to be in their higher oxidation states and hydrogen... 

SYNS ARSENENOUS ACID. CALCIUM SALT (2 1) CALCIUM ARSENITE, soUd (DOT) PROTARS... 

Nishimura, T, and Robins, R. G., 1998, A re-evaluation ofthe solubility and stability regions of calcium arsenites and calcium arsenates in aqueous solution at 25°C Mineral Processing and Extractive Metallurgy Reviews, v. 18, p. 283-308. 

Agent Index A108 Calcium Arsenate CAS 7778-44-1 Agent Index A109 Calcium Arsenite CAS 52740-16-6 Agent Index A110... 

Calcium Arsenite, Variable composition. Prepd by passing steam over a dry mixture of CaO and As203 Altwegg, Dutel, U.S. pat. 1,700,756 (1929). 

The leach solution containing arsenic and tin is treated with a controlled addition of lime (CaO) to firstly precipitate tin as calcium stannate (CaSn03.3H20), and then by further Ume addition after dilution to a NaOH concentration of less than 80 g/L to precipitate arsenic as calcium arsenite (Ca3(As04)2). In some instances calcium carbonate is used for tin precipitation followed by lime addition, firstly to remove carbonate as calcium carbonate and then to precipitate arsenic. This approach may give a cleaner separation of tin if required. 

Bullion commonly contains np to two per cent arsenic. Arsenic is preferentially oxidised in the softening or Harris processes, bnt more readily than antimony. Conseqnently when softener slag is reduced to form an antimonial lead alloy, arsenic can be retained in the residual slag from where it can be extracted by leaching and precipitation as arsenic trioxide or as calcium arsenite. Alternatively it can be extracted from canstic slags from the Harris process by leaching and precipitation with lime as calcium arsenite, which can contain around 20 per cent As. 

Differentiation between Calcium Arsenite and Calcium Arsenate... 

Calcium arsenite yields yellow silver arsenite under these conditions. Accordingly, a comparsion test with pure calcium arsenite is advisable when small amounts of arsenate are to be detected in mixture with much arsenite. Calcium arsenite can be detected by treating a portion of the test material on a spot plate with one drop of a 5 % solution of sodium hydroxide followed by one drop of 5 % silver nitrate. The resulting silver oxide is reduced by the arsenic i. 

After several minutes strong ammonia water is added. The excess silver oxide is dissolved immediately, whereas the black elemental silver remains. Less than 0.1 mg of calcium arsenite can be detected in this manner with no interference by calcium arsenate. 

Calcium Arsenate and Calcium Arsenite Mixtures, solid 1574 53 Caprylyl Peroxide 2199 52... 

Tanneries (historical) 0.1-1% sulphides, sodium arsenite, calcium arsenite in tannery landfills... 

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