An analysis of the hydrolytic polymerization of Pu(IV) and its reaction paths in nitric acid solution
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An analysis of the hydrolytic polymerization of Pu(IV) and its reaction paths in nitric acid solution Hu Zhang1 · Jing Chen1 · Yong‑zhi Ning1 · Guang‑hui Chen2 Received: 26 July 2020 / Accepted: 4 November 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Reaction conditions for the hydrolysis polymerization of Pu(IV) in a nitric acid solution were studied by a dynamic light scattering method, and the reaction paths of the Pu(IV) hydrolysis polymerization and its thermodynamic functions were calculated. The results showed that the acidity and concentration of Pu(IV) in the solution and the temperature of the solution were correlated with the hydrolysis polymerization of Pu(IV). The particle size distribution of the polymerized Pu(IV) colloidal particles increased with increasing temperature and decreasing Pu(IV) concentration. Quantum chemistry calculations showed that the more likely reaction path of the Pu(IV) hydrolysis polymerization consisted of the following: first, Pu(IV) hydrolysed to form Pu(OH)4 and then polymerized to form a bioxygen-bridged polymer molecule, which had a low reaction energy. Keywords Plutonium · Hydrolytic · Polymerization · Reaction paths · Nitric acid molarity
Introduction Plutonium is often considered one of the most interesting actinide elements. In spent nuclear fuel-enriched uranium (3–5% 235U, 97–95% 238U) of light water reactors, plutonium accounts for approximately 0.9% of the heavy metal content in which the most common plutonium isotopes are 238 Pu, 239Pu, 240Pu, 241Pu and 242Pu [1]. Plutonium exhibits long-term serious harm to the ecological environment due to its extreme radioactive toxicity; therefore, the chemical behaviours of plutonium in aqueous solution are an important concern during the reprocessing of spent nuclear fuel and the disposal of nuclear waste. Pu in solution commonly exists in Pu(III), Pu(IV), Pu(V), Pu(VI) oxidation state. The most common oxidation states in open seawater are Pu(IV) and Pu(V) [2, 3]. Pu(III) only presents in anoxic waters and in the presence of enhanced levels of organics, Pu(III) is often complexed to humics. The most likely actinide oxidation states in groundwater as * Hu Zhang [email protected] 1
China Institute of Atomic Energy, P. O. Box 275 (26), Beijing 102413, China
Department of Chemistry, Shantou University, Shantou 515063, Guangdong Province, China
2
a function of the microbial activity and the corresponding biogeochemical zone [2]. The oxidation state distribution of plutonium in natural waters can be affected by a number of variables including Eh, pH, hydrolysis, complexation, disproportionation, solubility, and redox interchange. In general, the reduced (III, IV) oxidation states of the actinides are stabilized in acidic media, while the oxidized (V, VI) states become more stable as the pH increases. Pu is particle reactive and readily absorbed onto nanoparticles/colloids in the surface waters and groundwater. Plutonium sorbs more extensively in the (III) and (IV) oxidation states than in the higher state
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