High immobilization of soil cesium using ball milling with nano-metallic Ca/CaO/NaH2PO4: implications for the remediation of radioactive soils

Abstract

This report shows that cesium can be immobilized in soils with an efficiency of 96.4% by ball milling with nano-metallic Ca/PO 4 . In Japan, the major concern on 137 Cs deposition and soil contamination due to the emission from the Fukushima Daiichi nuclear power plant showed up after a massive quake on March 11, 2011. The accident rated 7, the highest possible on the international nuclear event scale, released 160 petabecquerels (PBq) of iodine 131 I and 15 PBq of 137 Cs according to the Japanese Nuclear and Industrial Safety Agency. Both 137 Cs and 131 I radioactive nuclides are increasing cancer risk. Nonetheless, 137 Cs, with a half-life of about 30 years compared with 8 days for 131 I, is a major threat for agriculture and stock farming and, in turn, human life for decades. Therefore, in Japan, the 137 Cs fixation and immobilization in contaminated soil is the most important problem, which should be solved by suitable technologies. Ball milling treatment is a promising treatment for the remediation of cesium-contaminated soil in dry conditions. Here, we studied the effect, factors and mechanisms of soil Cs immobilization by ball milling with the addition of nano-metallic Ca/CaO/NaH 2 PO 4 , termed ''nano-metallic Ca/PO 4 .'' We used scanning electron microscopy combined with electron dispersive spectroscopy (SEM/EDS) and X-ray diffraction. Results show that immobilization efficiency increases from 56.4% in the absence of treatment to 89.9, 91.5, and 97.7 when the soil is ball-milled for 30, 60 and 120 min, respectively. The addition of nano-metallic Ca/PO 4 increased the immobilization efficiency to about 96.4% and decreased the ball milling time. SEM/EDS analysis allows us to observe that the amount of Cs decreased on soil particle surface. Use of nano-metallic Ca/PO 4 over a short milling time also decreases Cs leaching. Therefore, ball milling with nano-metallic Ca/PO 4 treatment may be potentially applicable for the remediation of radioactive Cs-contaminated soil in dry conditions.

Dynamic immobilization of simulated radionuclide 133 Cs in soil by thermal treatment/vitrification with nanometallic Ca/CaO composites

“…This mixture was found to be more suitable for trapping heavy metals in soil with an efficiency of more than 99% (Mallampati et al, 2012a). The same Ca/CaO mixtures proved to be effective in retaining 133 Cs after a ball-milling process (Mallampati et al, 2012b). Further, the nanometallic Fe/Ca/CaO system was found to be equally efficient in fixing and encapsulating heavy metals in a pozzolanic cemented shell (Mallampati et al, 2013).…”

Immobilization and volume reduction of heavy metals in municipal solid waste fly ash using nano-size calcium and iron-dispersed reagent

“…Therefore, the particle surface area increases and the heavy metal mobility decreases because the adsorption area increases (Orumwense, 2006). However, during grinding with nano-Fe/Ca/CaO/PO 4 additives, fly ash particles are subjected to collisions that are expected to promote aggregation and breakage phenomena (Montinaro et al, 2007 (Figure 4b) (Mallampati et al, 2012a(Mallampati et al, , 2014. The X-ray diffraction (XRD) patterns of fly ash before treatment consisted mainly of a glassy phase and some minerals with crystalline phases of mullite and quartz (SiO 2 ), magnetite (Fe 3 O 4 ), anorthite (CaAl 2 Si 2 O 8 ), and hematite (Fe 2 O 3 ).…”

“…Our recent investigations revealed that a nanometallic Ca/ CaO mixture was the most effective for hydrodechlorination of about 98% of polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) in contaminated fly ash, and also for cesium immobilization of about 96% in soil by ball-milling treatment (Mallampati et al, 2012a(Mallampati et al, , 2014Mitoma et al, 2011;Lee et al, 2015). For the present study, we developed a dry method for separating and immobilizing heavy metals in fly ash samples that is being applied to large volumes.…”

“…Grinding a mixture of heavy metalcontaminated fly ash and nano-calcium reduces the particle size and coats each particle with nano-calcium, thereby immobilizing the heavy metals on surfaces. They might be enclosed or bound with Ca-associated (CaCO 3 /Ca(OH) 2 ) salts, whereby high heavy metal immobilization can occur (Mallampati et al, 2012a(Mallampati et al, , 2014. This process produces a dry sample that is separable by particle size at room temperature.…”

“…The coated particles are placed in water underneath a strong magnet. The smallest particles, which have the highest concentrations of cesium, are attracted to the magnet even against gravity (Mallampati et al, 2012a(Mallampati et al, , 2014. In addition, to diminish further heavy metal leaching, it was decided to evaluate the potential combination of Fe/Ca/ CaO/NaH 2 PO 4 [PO 4 ] in the in situ formation of hydroxyapatite, which can further enhance heavy metal immobilization and harden the cemented shell (Mallampati et al, 2012a(Mallampati et al, , 2014Lee et al, 2015).…”