Trivalent ions arsenic

Redox reactions may cause mobile toxic ions to become either immobile or less toxic. Hexavalent chromium is mobile and highly toxic. It can be reduced to be rendered less toxic in the form of trivalent chromium sulfide by the addition of ferrous sulfate. Similarly, pentavalent (V) or trivalent (III) arsenic, arsenate or arsenite are more toxic and soluble forms. Arsenite (III) can be oxidized to As(IV). Arsenate (V) can be transformed to highly insoluble FeAs04 by the addition of ferrous sulfate. 

Chemical precipitation is used in porcelain enameling to precipitate dissolved metals and phosphates. Chemical precipitation can be utilized to permit removal of metal ions such as iron, lead, tin, copper, zinc, cadmium, aluminum, mercury, manganese, cobalt, antimony, arsenic, beryllium, molybdenum, and trivalent chromium. Removal efficiency can approach 100% for the reduction of heavy metal ions. Porcelain enameling plants commonly use lime, caustic, and carbonate for chemical precipitation and pH adjustment. Coagulants used in the industry include alum, ferric chloride, ferric sulfate, and polymers.10-12... 

The forward reaction is favored because lewisite oxide and polymerized lewisite oxide are insoluble. In a basic solution, the trauj-lewisite isomer is cleaved by the hydroxyl ion to give acetylene and sodium arsenite this reaction may occur even at low temperatures (Rosenblatt et al, 1975 Clark, 1989). C/5-lewisite heated to over 40° C reacts with sodium hydroxide to yield vinyl chloride, sodium arsenite, and acetylene (Rosenblatt et al, 1975). In aqueous solution, the cA-isomer imdergoes a photoconversion to the trans-isomer (Rosenblatt et ah, 1975). Epstein (1956) reported that the toxic trivalent arsenic of lewisite oxide in standing water is converted to the less toxic pentavalent arsenic. 

Pentavalent arsenic compounds occur most frequently but trivalent arsenic ions are also found, particularly in arsenical subterranean waters. If the trivalent arsenic is to be detected separately the water should be sampled in the absence of air since As (III) is very sensitive to oxidation and is converted to the pentavalent oxidation stage merely by the oxygen in the air. 

In the arsenal of spectroscopic techniques, fluorescence measurements offer particular advantages, since they are sensitive and can be employed at relatively low concentrations of the luminescent species(4). Thus, we have initiated a study of the structures of ion-containing polymers using trivalent lanthanide ions as fluorescent probes. 

When chromium and arsenic are present as an oxyanions, they are not to be precipitated as a hydroxides even if the pH of the solution is in the alkaline region. Immobilization of chromate, arsenate and arsenite ions using calcium alumino-zincate is described in this review. It should be noted that the oxyanions of hexavalent chromium and those of both trivalent and pentavalent arsenic are referred to as Cr[VI], As[nr, and As[V], respectively, in this manuscript. 

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