Cyanide in electroplating

S.SM. Hassan, M.S.A. Hamza, A.E.A. Kelany, A novel spectrophotometric method for batch and flow injection determination of cyanide in electroplating wastewater, Talanta 71 (2007) 1088-1095. 

M. Noroozifar, M. Khorasani-MoEagh, A. Taheri, R. Zare-Dorahei, A comparative study of AgX (X = Cl, Br , 1 and N 3 solid-phase reactors for flow-injection determination of cyanide in electroplating wastewater. Anal. Sci. 24 (2008) 669-672. 

Wet air oxidation has been applied to the destruction of cyanides in electroplating wastewaters. The oxidation reaction for sodium cyanide is the following ... 

Both -hydroxybenzaldehyde and its methyl ether, -methoxybenzaldehyde [123-11-5] (p-anisaldehyde) have found extensive use in electroplating. The most widespread appHcation has been in alkaline bright zinc plating, both in non-cyanide (77) and in cyanide-containing (78) baths. The aldehydes act as both brightening and leveling agents. 

Polarization in metal deposition is highly sensitive to solution composition. When present in the solution, a number of complexing agents and surfactants will strongly enhance it. In electroplating, it is very common that metals are deposited from solutions of their complex salts (e.g., cyanide complexes). In such solutions, the metal exists in the form of different complex anions, of the type with different... 

Cyanide complexes have a venerable history (see CCC S )),1 and find utilization in many industrial processes including as synthetic catalysts e.g., Co cyanides on inorganic supports catalyze alkylene oxide polymerization,187 molecular magnetic materials, in electroplating, and in mining. Their pharmacology and toxicology is well explored... 

Cyanides are used widely and extensively in the manufacture of synthetic fabrics and plastics, in electroplating baths and metal mining operations, as pesticidal agents and intermediates in agricultural chemical production, and in predator control devices. Elevated cyanide levels are normally encountered in more than 1000 species of food plants and forage crops, and this probably... 

Silver-copper (Ag-Cu) ionization systems, environmental limits on, 22 652 Silver-copper system, properties of, 22 644 Silver cyanide, 22 670-671, 674-675 in electroplating, 22 685-686 Silver cyclohexanebutyrate, 22 671 Silver development, corrosion model of, 19 245... 

Several studies of occupational exposures and one study with a human subject were located. In the occupational exposures (summarized in Table 5- 3), neurological symptoms consistent with cyanide intoxication were demonstrated, but the likelihood of concomitant exposure to other chemicals could not be ruled out. For example, cleaners and cutting oils, as well as sodium and copper cyanide, may be present in electroplating operations (ATSDR 1997). The experimental human study involved the exposure of a single subject and a dog to a high concentration for a short exposure period. 

Dyspnea was observed in workers chronically exposed (5-15 years) to 6.4-10.4 ppm of an unspecified cyanide form evolved from sodium cyanide and copper cyanide during electroplating (El Ghawabi et al. 1975) and in workers exposed to 15 ppm hydrogen cyanide (14 ppm cyanide) in a silver-reclaiming... 

Potassium cyanide (KCN) is a white crystalline substance with a slight odor of bitter almonds. It is produced when hydrogen cyanide is absorbed in potassium hydroxide. It is used to extract gold and silver from their ores, in electroplating computer boards, and as an insecticide. Potassium cyanide is very toxic to the skin or when ingested or inhaled, and it is used as a source of cyanide (CN) gas in gas chambers. 

Barium cyanide is used in electroplating and other metallurgical processes. 

Cadmium oxide is used in storage battery electrodes. Its solution, mixed with sodium cyanide, is used in electroplating baths. Other uses are in PVC heat stabilizers as an additive to nitrile rubbers and plastics to improve heat resistance and in ceramic glazes and phosphors. 

Sodium cyanide is used in extracting gold and silver from their ores. It forms soluble complexes with these metals. Other uses are in electroplating baths, heat treatment of metals, fumigation, and preparing other cyanide salts and complexes. 

The nse of complexation to allow codeposition of alloys is well known in electroplating. The best-known example is that of brass (Cu/Zn) plating, where cyanide, which is a stronger complex for Cu than it is for Zn, brings the deposition potentials of the two metals, originally far apart, to almost the same value. There is a direct connection between this effect and the equivalent one for CD. This arises from the fact that, for both CD and electrodeposition of alloys (we in-clnde mixed metal compounds in the term alloy), the effect of the complexant is to lower the concentration of free cations. For CD this affects the deposition throngh the solnbility product, while for electrodeposition it affects the deposition potential through the Nemst equation ... 

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