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/PO4. In Japan, the major concern on 137Cs 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 131I and 15 PBq of 137Cs according to the Japanese Nuclear and Industrial Safety Agency. Both 137Cs and 131I radioactive nuclides are increasing cancer risk. Nonetheless, 137Cs, with a half-life of about 30 years compared with 8 days for 131I, is a major threat for agriculture and stock farming and, in turn, human life for decades. Therefore, in Japan, the 137Cs 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/NaH2PO4, termed “nano-metallic Ca/PO4.” 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/PO4 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/PO4 over a short milling time also decreases Cs leaching. Therefore, ball milling with nano-metallic Ca/PO4 treatment may be potentially applicable for the remediation of radioactive Cs-contaminated soil in dry conditions.