title: Removal of uranium and gross radioactivity from coal bottom ash by CaCl2 roasting followed by HNO3 leaching.
abstract: A roast-leach method using CaCl2 and HNO3 to remove uranium and gross radioactivity in coal bottom ash was investigated. Heat treatment of the ash with 100% CaCl2 (900°C, 2h) significantly enhanced uranium leachability (>95%) compared with direct acid-leaching (22.6-25.5%). The removal efficiency of uranium and gross radioactivity increased steeply with increasing CaCl2 content, from 10% to 50%, and a HNO3 leaching time from 5 min to 1h, but remained nearly constant or decreased slightly with increasing CaCl2 dosage >50% or acid-leaching time >1h. The majority of the uranium (87.3%), gross α (92.9%) and gross β (84.9%) were removed under the optimized roast-leach conditions (50% CaCl2, 1M HNO3 leaching for 1h). The mineralogical characteristics of roasted clinker indicated that molten CaCl2 promoted the incorporation of Ca into silica and silicates and resulted in its progressive susceptibility to acid attack. Uranium and other radionuclides, most likely present in the form of silicates or in association with miscellaneous silicates in the highest density fraction (>2.5g mL(-1)), were probably leached out as the result of the acid decomposition of newly formed "gelatinizing silicates".
authors.affiliation: Department of Environmental Engineering, School of Environment, Tsinghua University, Beijing 100084, China.
authors.forename: Xuefei
authors.initials: X
authors.lastname: Lei
authors.affiliation: Department of Environmental Engineering, School of Environment, Tsinghua University, Beijing 100084, China.
authors.forename: Guangxia
authors.initials: G
authors.lastname: Qi
authors.affiliation: Department of Environmental Engineering, School of Environment, Tsinghua University, Beijing 100084, China.
authors.forename: Yinglong
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Department of Environmental Engineering, School of Environment, Tsinghua University, Beijing 100084, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Xu
authors.affiliation: Department of Environmental Engineering, School of Environment, Tsinghua University, Beijing 100084, China. Electronic address: yi_wang@tsinghua.edu.cn.
authors.forename: Yi
authors.initials: Y
authors.lastname: Wang
mesh_terms: D002122:Calcium Chloride / Q000737:chemistry; D060729:Coal Ash; D017942:Nitric Acid / Q000737:chemistry*; D011868:Radioisotopes / Q000302:isolation & purification*; D014501:Uranium / Q000302:isolation & purification*
chemical_list: D060729:Coal Ash; D011868:Radioisotopes; D017942:Nitric Acid; D014501:Uranium; D002122:Calcium Chloride
keywords: Coal bottom ash; Radionuclides; Roast-leach method; Uranium