The synthesis and ion-exchange chemistry of vanadium doped natisite and paranatisite

Abstract

With 440 commercial nuclear reactors in use globally, nuclear energy contributes to 11 % of the world’s energy demands[1]. Like most forms of energy, nuclear energy generates waste. To help manage contaminated aqueous streams generated from the nuclear cycle, i.e., reactor primary coolant and the clean-up of spent fuel systems, ion exchange media are being utilised[2].
This thesis focuses upon the synthesis of vanadium-paranatisite and vanadium-natisite, inorganic zeotypes[3], which have not been previously reported. Optimisation of the synthesis showed that with an increased percentage of vanadium the time taken for the progressive transformation of vanadium-paranatisite to vanadium-natisite increased. 5 %-vanadium-paranatisite and natisite formed during 7 and 72 hours of synthetic heating, whilst 10 %-vanadium-paranatisite and natisite formed during 72 and 288 hours, respectively. Increasing the percentage of vanadium also showed to increase the crystallinity of the vanadium-paranatisite framework, with attempts to form Ti-paranatisite failing.
The respective abilities of vanadium-paranatisite and vanadium-natisite to remove ions commonly found within nuclear waste such as strontium, cesium, cobalt, cerium (inactive surrogate for plutonium) and neodymium (inactive surrogate for uranium) was also investigated. The results showed that both vanadium-paranatisite and vanadium-natisite have the potential to act as ion exchange media for the removal of radioactive ions from aqueous effluent within the nuclear industry.
Vanadium-paranatisite and vanadium-natisite frameworks showed higher affinities towards strontium and cobalt. During ion exchanges involving vanadium-paranatisite, up to 32 % (± 0.62) and 29 % (± 0.82) of strontium and cobalt ions respectively, were exchanged during a 24 hour period. Ion exchanges involving vanadium-natisite showed that up to 30 % (± 0.53) and 28 % (± 0.26) of strontium and cobalt ions respectively, were exchanged in the same 24 hour period.
Further to this, vanadium-paranatisite frameworks showed increased affinities for all the ions tested when compared with vanadium-natisite. A plausible reason for the increased affinity shown by vanadium-paranatisite could be due to the structure. Unlike natisite, which is a layered titanium silicate, the framework of paranatisite is less regimented, with exchangeable cations fragmented throughout the framework.