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IRIDIUM Natural Abundance, Stable Isobars Ir191, 38.5%, None Ir193, 61.5% Powdered iridium metal is the only charge material which has been used for the separation of iridium isotopes. The metal is used in a special graphite source block which is heated by electron bombardment. Due to its high cost, unresolved Ir is recycled and recovered. Iridium remains in the calutron source as small globules of metal which are readily recovered and reused as feed material. Washing the calutron components and sanding the carbon parts serves to recover Ir which is in the elemental form. Filtering the wash solutions concentrates Ir, and the filtrates are discarded. The solids are dried and combined with the ash resulting when all carbon salvage is ignited in oxygen at 650° C. The combined solids are leached successively with 1:1 hydrochloric acid and 1:1 nitric acid, then washed with water. The filtrates and washings are discarded; the solids are dried and fused with sodium chloride at 850° C in a stream of chlorine using 10 parts sodium chloride for each part of solid used. The resulting product, sodium chloroiridate, is dissolved in 0.1 N hydrochloric acid and filtered. Any remaining solids are re-fused with sodium chloride until no more Ir is recovered. The 0.1 N hydrochloric acid filtrate is treated with powdered zinc metal, reducing Ir to the metal. Acidity is maintained in the solution using dilute hydrochloric acid. Reduced Ir metal is recovered by filtering, leaching with 2:1 nitric acid followed by leaching with 2:1 aqua regia, and washing several times with water. The recovered Ir is dried and stored as the metal. Soluble iridium compounds are considered toxic; however, no industrial data are available upon which to base a maximum allowable concentration in air. Safety clothing plus a respirator should be used when dusting, misting, or vaporizing of iridium or its compounds may be encountered. |
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