Speaker
Description
Ivanets A.I.1, Prozorovich V.G.1, Kouznetsova T.F.1, Radkevich A.V.2, Milutin V.V.3
1Institute of General and Inorganic Chemistry of the National Academy of Sciences of Belarus
2Joint Institute for Power and Nuclear Research – Sosny of the National Academy of Sciences of Belarus
3A.N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS
Ivanets@igic.bas-net.by
Currently, sorption technologies are developed very intensively for the decontamination of liquid radioactive waste (LRW) containing strontium radionuclides (the half-life of 90Sr isotope is 28.79 years). The study of novel sorbents for strontium removal is the subject of research around the world. Due to the chemical and thermal stability and radiation resistance inorganic sorbents are the most promising materials for these purposes [1]. One of the main required characteristics for sorbents is the high selectivity towards radionuclides due to the complex composition of LRW. Selective removal of strontium ions from solutions with high salinity, including LRW, is a challenging task due to the presence of competing ions in solutions, especially calcium, magnesium and sodium that reduce the uptake of strontium [2].
There is a number of sorbents that demonstrate sorption-selective properties towards Sr2+-ions in saline solutions, e.g. natural and synthetic zeolites and other raw materials, composite magnetic nanoparticles, manganese oxides, titanates and titanosilicates etc. High exchange capacity, stability in alkaline media allow to consider manganese oxides with a layered and channel structure as a promising materials for the removal of radioactive metal ions from aqueous media. Manganese oxides have a structure of octahedral molecular sieves (OMS) with tunnels 2×2 or 3×3, which are formed of octahedra MnO6. The dimensions of the tunnels of OMS-2 (cryptomelane with ions K+) and OMS-1 (type todorokite with ions Ca2+ or Mg2+) depend on the cations located inside and are about 0.46 and 0.70 nm respectively [3, 4].
At present work mesoporous manganese oxides with developed specific surface area, layered and/or tunnel structure and high ion-exchange capacity were prepared using non-template sol-gel technique by reducing KMnO4 in aqueous media. Physical and chemical properties of manganese oxide sorbents were characterized by means of X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential-thermal analysis (DTA), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and low temperature adsorption-desorption of nitrogen. Sorption of the 85Sr and 90Sr radionuclides from model LRW was studied in batch mode. The influence of inorganic (MnCl2 and H2O2) and organic reducing agent (ethanol and polyvinilalchohol), nature of „host” ions (Na+, K+ and Сa2+), conditions of sol-gel process (time, temperature) and calcination temperature on the chemical and phase composition, porous structure, surface morphology and sorption properties on sorption properties were studied for prepared manganese oxides.
The results of sorption study for manganese oxides prepared via sol-gel technique by reducing KMnO4 in ethanol/aqueous media is presented in tables 1 and 2. All sorbents are characterized by developed specific surface area (ABET) – up to 293 m2/g. Sample 2 demonstrated the highest sorption (Kd 90Sr=10.6×103 cm3/g) and selective (DSr/Ca=99.8) properties towards 90Sr in the presence of 0.01M CaCl2 background electrolyte. It was established that manganese oxides with tunnel structure (samples 2,3 and 5,6) had higher affinity towards 90Sr radionuclide in comparison with layered modifications (samples 1 and 4). Sorbents in Na+-form is more effective than in Ca2+-form due to lower charge and higher mobility of Na+ ions.
Table 1. Synthesis conditions and characteristics of manganese oxide sorbents prepared via sol-gel technique by reducing KMnO4 by ethanol in aqueous media.
Sample Temperature of sol-gel synthesis, °С Time of sol-gel synthesis, h Calcination temperature, °С Ion-form ABET, m2/g
1 25 5 150 К+ 208
2 350 Na+ 203
3 Ca2+ 165
4 80 48 150 К+ 284
5 350 Na+ 293
6 Ca2+ 213
Table 2. Sorption properties of manganese oxide sorbents towards 90Sr (0,01 M CaCl2, рН=6.0, V/m=200 cm3/g).
Sample Ion exchange capacity for Са2+, mmol/g Distribution coefficient,
Kd (90Sr) ×10-3, cm3/g Separation coefficient, DSr/Ca
1 0.852 0.75 5.6
2 0.739 10.6 99.8
3 <0.01 5.77 -
4 0.243 1.23 47.7
5 0.44 3.83 66.3
6 - 2.89 67.2
The relationship between the conditions of preparation, physical-chemical and sorption-selective properties of sorbents allow to define general regularities and approaches to the directed synthesis of highly selective materials of strontium radionuclides. The comparison study of developed manganese oxides with others sorbents (zeolites, zirconia and titanosilicates) has showed their higher sorption and selective properties towards strontium radionuclides.
References
[1] Abdel-Rahman R.O., Ibrahium H.A., Hung Y.-T. (2011) Liquid Radioactive Wastes Treatment: A Review, Water doi:10.3390/w3020551.
[2] Tu Y-J, You C-F, Zhang Z, et al. (2016) Strontium removal in seawater by means of composite magnetic nanoparticles derived from industrial sludge. Water doi:10.3390/w8080357
[3] Ivanets AI, Prozorovich VG, Kouznetsova TF, et al. (2016) Mesoporous Manganese Oxides Prepared by Sol-Gel Method: Synthesis, Characterization and Sorption Properties towards Strontium Ions. Environ Nanotechnol Monitoring & Management doi:10.1016/j.enmm.2016.11.004
[4] Ivanets AI, Katsoshvili LL, Krivoshapkin PV, et al. Sorption of strontium ions onto mesoporous manganese oxide of OMS-2 type. Radiochemistry doi: 10.1134
