Polonium reduction

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

Because of its radioactivity and alpha emission, polonium forms many types of radiolytic oxidation-reduction products. 

Bipositive polonium in hydrochloric acid solution (pink) is oxidized to polonium(lV) by hydrogen peroxide, by hypochlorous acid or by the radiolysis products of the alpha bombardment of the solvent. Solutions of polonium(II) in acid are obtained by the reduction of polonium(lV) with sulfur dioxide or hydrazine in the cold, or with arsenious oxide on warming. Polonium (IV) is not reduced in hydrochloric acid by either hydroxylamine or oxalic acid, even on boiling 6). 

Its solutions in dilute hydrobromic acid are a carmine-red (0.025 M PoBr4) and in more dilute solution (10 3 M), orange red. The tetrabromide is soluble in ethanol, acetone and some other ketones, and is sparingly soluble in liquid bromine. It is hygroscopic and is easily hydrolyzed to a white, basic bromide of variable composition. It forms a yellow ammine in ammonia gas and this yields polonium dibromide and polonium metal on standing, presumably because of radiation decomposition of the ammonia and subsequent hydrogen reduction of the tetrabromide (7). 

The aquatic samples in 8 M HN03 are evaporated and the dry residue is dissolved in 20 mL 0.5 M HC1. After the addition of approximately 50 mg of ascorbic acid (reduction of Fe3+ to Fe2+), the solution is transferred to PTFE vessels equipped with a silver sheet bottom. Polonium is electrodepos-ited at 90°C for 4 h.34-36... 

The tetrachloride of polonium is prepared by dissolving the metal in hydrochloric acid and evaporating to dryness. P0CI4, is a hydroscopic yellow solid which melts at 300° and is soluble in ethanol and acetone. The tetrachloride can be converted to dichloride, P0CI2, by reduction with sulfur... 

Polonium dibromide is purple-brown in color and sublimes at 110° at reduced pressure with some decomposition. It is prepared by the reduction of PoBr4 with H2S or by heating PoBr4 to 200° in vacuo. The dibromide is soluble in ketones as well as in dilute, aqueous HBr in which it forms a purple solution. In the latter solution, the dibromide is oxidized rapidly to Po(IV). 

Polonium metal was formed by the reduction of P0CI4, P0OCI2 as well as from the nitrate or the acetate. The solvents involved were hydrochloric acid and polar organics such as acetone, ethanol, and methyl ethyl ether. Mercury served as the reducing agent and a polonium-mercury amalgam is formed. 

From a solution containing iron and some rare earth metals, Debierne precipitated a mixture of hydroxides. It was radioactive, an activity that could not have its origin in uranium, radium or polonium. A new element could be isolated by fractional crystallization of magnesium lanthanum nitrate. The element was named actinium after the Greek word aktinos, meaning ray . Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300°C. 

Polonium-210 Reactor Static discharge reduction in the making of photographic film and phonograph records... 

---