Rhodium arsenide

Rhodium Arsenide, E.hAs2, has been prepared in a pure form by heating rhodium chloride with an excess of arsenic in an atmosphere of hydrogen.8 If finely divided rhodium is heated with excess of arsenic in an atmosphere of an indifferent gas, the arsenide produced is not pure.9... 

Ruthenium Arsenide, RuAs2, may be prepared in an exactly similar manner to rhodium arsenide. The method of analysis described under palladium arsenide (p. 73) may be applied to both of these arsenides. 

More than 200 ores are known to contain cobalt but only a few are of commercial value. The more important are arsenides and sulfides such as smaltite, C0AS2, cobaltite (or cobalt glance), CoAsS, and linnaeite, C03S4. These are invariably associated with nickel, and often also with copper and lead, and it is usually obtained as a byproduct or coproduct in the recovery of these metals. The world s major sources of cobalt are the African continent and Canada with smaller reserves in Australia and the former USSR. All the platinum metals are generally associated with each other and rhodium and iridium therefore occur wherever the other platinum metals are found. However, the relative proportions of the individual metals are by no means constant and the more important sources of rhodium are the nickel-copper-sulfide ores found in South Africa and in Sudbury, Canada, which contain about 0.1% Rh. Iridium is usually obtained from native osmiridium (Ir 50%) or iridiosmium (Ir 70%) found chiefiy in Alaska as well as South Africa. 

An arsenide of rhodium appears to be formed on fusing the two elements together,4 but it has not been definitely isolated. 

Fission products that are compatible with the uraninite crystal stmcture—the REE, yttrium, neodymium, and zirconium—were largely retained in the uraninite core, the reactor clays, minor phosphate phases, and uranium and zirconium silicate phases (Gauthier-Lafaye et ai, 1996). Lighter REE—lanthanum, cerium, and praseodymium—were partially lost from the reactor. Einally, molybdenum, technetium, mthe-nium, rhodium, and other metallic elements were retained in the metal/metal oxide inclusions and arsenide/sulfide inclusions in the core, and in the reactor clays (Hidaka et ai, 1993 Jensen and Ewing, 2001). 

Ruthenium, osmium, rhodium, iridium, palladium and platinum are the six heaviest members of Group VII1. They are rare elements platinum itself is the commonest with an abundance of about 10-6% whereas the others have abundances of the order of 10"7 % of the earth s crust. They occur in Nature as metals, often as alloys such as osmiridium, and in arsenide, sulfide and other ores. The elements are usually associated not only with one another but also with the coinage metals copper, silver and gold. The main suppliers are South Africa, Canada and the USSR. 

The development of a new generation of catalysts and semiconductors will be needed if a photochemical process (using solar radiation) is to be viable, but research and development in this area is growing rapidly. The sources of hydrogen include hydrocarbons, alcohols, and organic acids. Ruthenium, rhodium, and iridium catalysts, and various arsenide, selenide, and telluride semiconductors (see Chapter 15), may lead the way to an efficient system. 

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