Arsenic, vaporization

Arsenic vapor [12187-88-5] As, does not combine direcdy with hydrogen to form hydrides. However, arsine (arsenic hydride) [7784-42-17, AsH, a highly poisonous gas, forms if an intermetaUic compound such as AlAs is hydrolyzed or treated with HQ. Arsine may also be formed when arsenic compounds are reduced using zinc in hydrochloric acid. Heating to 250°C decomposes arsine into its elements. 

Metafile arsenic can be obtained by the direct smelting of the minerals arsenopyrite or loeUingite. The arsenic vapor is sublimed when these minerals are heated to about 650—700°C in the absence of air. The metal can also be prepared commercially by the reduction of arsenic trioxide with charcoal. The oxide and charcoal are mixed and placed into a horizontal steel retort jacketed with fire-brick which is then gas-fired. The reduced arsenic vapor is collected in a water-cooled condenser (5). In a process used by Bofiden Aktiebolag (6), the steel retort, heated to 700—800°C in an electric furnace, is equipped with a demountable air-cooled condenser. The off-gases are cleaned in a sembber system. The yield of metallic arsenic from the reduction of arsenic trioxide with carbon and carbon monoxide has been studied (7) and a process has been patented describing the gaseous reduction of arsenic trioxide to metal (8). 

Arsenic peroxides, 13 404 Arsenic removal, in municipal water treatment, 26 124 Arsenic trioxide, 3 264, 265-266 Arsenic vapor, 3 264, 264t Arsenious acid, presence in water and food, 3 276t... 

Elemental arsenic is stable in dry air but exposure to moist air tarnishes its surface to a golden bronze color which converts to a black oxide on further exposure. Arsenic vapors react with oxygen to form arsenic trioxide (sesquiox-ide) ... 

Gallium arsenide is prepared by passing a mixture of arsenic vapor and hydrogen over gallium(lll) oxide heated at 600°C ... 

Phosphorus and arsenic vapors consist of molecules P4 and AS4, respectively, in which the four atoms occupy the vertices of a regular tetrahedron. Suggest reasons for the difference between these structures and that of gaseous nitrogen (which is also in Group 15). 

Most particulate arsenic in the atmosphere is inorganic As(V) and As(III) rather than organoarsenicals (Mandal and Suzuki, 2002), 207. Any arsenic vapors would mostly consist of AS4O6 with trace amounts... 

Sterling, R.O. and Helble, J J. (2003) Reaction of arsenic vapor species with fly ash compounds kinetics and speciation of the reaction with calcium silicates. Chemosphere, 51(10), 1111-19. 

Sulfur dioxide coproduced by this method was generally converted to sulfuric acid in these early operations by using the chamber process. Using this source for the sulfur dioxide for acid making put all of the vaporized arsenic from the pyrites directly into the sulfuric acid product. At the time this aspect was not considered to be serious since most of the sulfuric acid was consumed in the Le Blanc process to produce sodium carbonate (Eqs. 9.4 and 9.5), causing arsenic vaporization and loss again, with the hydrogen chloride produced by the first step [11]. 

At least six forms of sohd arsenic have been reported, of which three are amorphous. The most stable and most common form of arsenic at room temperature is a brittle, steel-gray solid (a-As) with a structure analogous to that of rhombohedral black phosphorus. Arsenic vapor contains tetrahedral As4 molecules, which are thought to be present in the yellow tmstable arsenic formed by condensation of the vapor. Arsenic occurs naturally as a-As and also as the mineral arsenolamprite, which may have the same structure as orthorhombic black phosphorus. 

The preparation of CdgASg is similar to that ofZngASg (method I) heating the metal in a stream of hydrogen that carries arsenic vapor (see p. 1083). 

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