Cesium adsorption from aqueous solutions onto Japa

Authors: Shigeru Yamauchi Takayuki Yamagishi Kazuko Kirikoshi Mitsuyoshi Yatagai

Publish Date: 2016/08/04

Volume: 62, Issue: 6, Pages: 562-566

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Abstract

To remove group 1 and 2 metal ions from Japanese oak Quercus serrata Thunb and/or Quercus crispula Blume charcoal OC a waterextraction treatment was employed The treatment was repeated 1 4 8 or 12 times The amounts of four metal sodium potassium magnesium and calcium ions eluted from nontreated and treated OC were determined using an ion chromatographic apparatus The effects of waterextraction treatment on the ability of OC to adsorb cesium were investigated using 250 × 10−5 and 250 × 10−6 mol/L aqueous cesium chloride solutions As for both aqueous solutions an unexpected result was obtained in that the cesiumadsorption ability of OC decreased suddenly when the repetition of waterextraction treatments exceeded a certain threshold We explain the results in terms of pH of the sample solutions and the point of zero charge for OCThe disaster at the Fukushima Daiichi nuclear power stations in 2011 widely dispersed various radioisotopes As a result many victims are still living in temporary dwellings because the radioactivity in their hometowns remains above the safety levels established by the Japanese government In addition contaminated water containing radioisotopes is produced constantly at the power stations Two cesium nuclides 134Cs and 137Cs whose halflives are about 2 and 30 years respectively are the main targets for decontamination although the pollutants contain many kinds of radioisotopes To remove and collect these radioactive cesium nuclides it is essential to develop an ideal adsorbent for capturing themMany studies have already reported the cesiumadsorption performance of synthetic zeolites and Prussian blue type complexes but only a few reports on cesiumfixation using biochar have been published 1 2 3 Advantages of biochar include its ease of largescale production and capability to reduce its volume markedly by combustion after used as an adsorptive Kobayashi suggested that a highly practical adsorptive for cesium may be readily developed from biochar 4Our attention focused on Japanese oak Quercus serrata Thunb and/or Quercus crispula Blume charcoal OC because it is the most popular charcoal manufactured in Japan We previously investigated several factors such as pH and specific surface area that were predicted to affect adsorption ability of charcoal in aqueous solution 5 Moreover we clarified that group 1 and 2 metals whose content is not negligible in ordinary charcoal 6 7 have blocking effects on cesium adsorption onto charcoal 8 Furthermore we reported that partial removal of the metals from charcoal clearly raised the amount of cesium adsorbed from aqueous solution 9 Therefore it was expected that charcoal may exhibit much higher adsorption ability when metal elements are completely removed from itTo better understand the effects of metal removal from OC we studied changes in the cesiumadsorption isotherm of OC after waterextraction waterwashing treatment However an unexpected result was obtained the amount of cesium adsorbed onto OC decreased drastically when the repetitions of extraction treatments exceeded a certain threshold A likely explanation is provided for these results in terms of pH of the sample solutions and the point of zero charge PZC for OCCharcoal used in this study was produced in Iwate Prefecture and commercially available In previous studies 5 8 9 its physicochemical properties were described in detail Small OC blocks were ground in a porcelain mortar and then OC powder was put through a 60mesh sieve The powder was kept in a desiccator over silica gel after drying at 105 °C for over 24 h From Raman spectra it was estimated that the carbonization temperature of the OC was in the range of 600–800 °C 5 Specialgrade cesium chloride anhydride was obtained commercially

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