Suitability of microcrystalline cellulose as an ion exchanger : a radiochemical approach to the determination of ion exchange properties of AaltoCellTM materials

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http://urn.fi/URN:NBN:fi:hulib-201912094070
Title: Suitability of microcrystalline cellulose as an ion exchanger : a radiochemical approach to the determination of ion exchange properties of AaltoCellTM materials
Author: Järvenpää, Jenna
Contributor: University of Helsinki, Faculty of Science
Publisher: Helsingin yliopisto
Date: 2019
Language: eng
URI: http://urn.fi/URN:NBN:fi:hulib-201912094070
http://hdl.handle.net/10138/308240
Thesis level: master's thesis
Discipline: Radiokemia
Abstract: The suitability of AaltoCellTM materials as ion exchangers to the purification of radioactive waste waters is researched through structural studies and batch sorption experiments. The aim of these experiments is to determine if AaltoCellTM materials are suitable for sorption of 57Co, 85Sr and 134Cs in NaNO3 (aq), NaClO4 (aq) or phosphate buffer solutions. Three different AaltoCellTM materials are produced from bleached sulfate (MCC1), unbleached oxygen delignified (MCC2) and unbleached pulps (MCC3) given by a Finnish kraft pulp mill. Their morphology, specific surface area, particle size and molecular distributions, carbohydrate and lignin content as well as surface lignin coverage are measured. The batch sorption experiments are focused on kinetics, sorption as a function of pH and ionic strength and the electrolyte exclusion by the Donnan potential. The experimental work revealed the order of the lignin content, MCC2 > MCC3 > MCC1, and the sorption order for 57Co, MCC3 > MCC2 > MCC1. MCC2 had the highest total lignin, surface lignin coverage and the BET surface area of the AaltoCellTM materials. MCC1 had the widest size range of particles and the lowest lignin contents, whereas MCC3 had the narrowest particle size distribution. The batch sorption experiments indicated the AaltoCellTM materials, except MCC1, to be suitable for sorption of 57Co in phosphate buffer solutions at pH ~ 7. Also, MCC2 was noticed to be suitable in solutions with inert electrolytes and low ionic strength, such as 0,01 M NaClO4 (aq) at pH ~ 4,7 or in active electrolytes and high ionic strength, such as 1 M NaNO3 (aq) at pH ~ 6,5. The sorption of 57Co was discovered to be dependent on the solution, swelling and experiment method used. No sorption of 57Co was detected in 10 mM NaNO3 (aq) at any pH level tested, 0,1–1 M NaClO4 (aq) at pH ~ 4,6 and 0,1 M NaNO3 (aq) at pH ~ 4,8–4,9. On the other hand, MCC2 was found to be suitable for sorption of 85Sr in 10 mM NaNO3 (aq) at pH range of 1–9 and not consistently suitable for sorption of 134Cs in 10 mM NaNO3 (aq) at the same pH range due to the divergent results of two batch sorption experiments. The performed experiments indicated that the AaltoCellTM materials, except MCC1, could have a significant sorption of 57Co in phosphate buffer solutions, especially in those without disturbing K+ ions. Moreover, MCC2 was found to act as a pure cation exchanger with 85Sr in 10 mM NaNO3 (aq). Since the results were promising, the AaltoCellTM materials containing lignin may be seen as inexpensive, non-toxic and environmentally friendly bases for chemical modifications to achieve better ion exchangers in the nuclear industry and to reduce the volume and the costs of their final disposal.


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