Reactions between americium ions

Keenan et al. have carried out a brief survey on the exchange reactions AmO +Am -  

In perchlorate media the latter reaction was found to be rapid (100 % exchange in 60 sec) and the former reaction slow (half times of 200 hours at 100 °C). The isotopic method was used ( Am). 

undergoes disproportionation and redox reactions in aqueous acidic media, which can be followed by spectrophotometry at wavelengths of 812 m/ii for Am(III), 715 m t for Am(V) and 992 mpt for Am(VI). The earlier work on solutions of Am(V) in hydrochloric, nitric , sulphuric , and perchloric acid media, which were hindered by a-radiation reactions ( Am), led to the conclusion that the rate law 

In 1962, Coleman , using the relatively stable Am, was able to study the reaction of Am(V) in various media in more detail and found a rate law 

In perchlorate media, values of k and k at 75.7 °C (/r = 2.0 M) are 7 x 10 l .mole .sec and 4.6x 10 l . mole . sec , respectively. The rate increased in the solvent order HCIO4. HNO3 HCl H2SO4. No rate measurements in dibutylphosphoric acid media were possible. 

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The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

Pearson s principle simplifies the treatment of the results of investigations performed by Lambertin et al. [40]. The authors of this work examined the effect of the addition of fluoride ion on the equilibrium between different oxidation states of americium in the molten KCl-LiCl eutectic at 743 K. The increase of fluoride ion concentration was shown to result in a shift to the right of the following reaction ... 

Desire, Hussonnois and GuUlaumont (1969) determined stability constants for the species AnOH + for the actinides, plutonium(III), americium(III), curium (III), berkelium(III) and californium (III) using a solvent extraction technique. The stability constants obtained for americium(III) and curium(III) are two orders of magnitude larger than other similar data available in the literature. The stability constants of the lanthanide(III) and actinide(III) ions are very difficult to obtain using solvent extraction due to problems associated with attainment of maximum extraction into the solvent phase before the narrow band of pH between the onset of hydrolysis reactions and the precipitation of solid hydroxide phases. Consequently, the data of Desire, Hussonnois and GuUlaumont (1969) are not retained in this review. 

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