Study On Distribution And Species Of Uranium In Bottom Ash And Its Recovery Technique

The severe environmental issues have been produced by the tremendously massive uranium-rich coal bottom ash in China.In this paper,a novel technique was developed for recovery of valuable constituents from uranium-rich coal bottom ash.The speciation of uranium in ash and the recycling technique were clarified around reduction of radioactivity and recovery of valuable components in bottom ash.Base on the research of speciation of uranium in ash,an integrated separation and recovery method was studied within a scale of laborotary.Meanwhile,the mechanism for uptake of uranium from ash and the environmental impact of ash heap were also discussed.The environmental impact of ash heap was mainly heavy metals and radionuclides pollution,the heavy metal concentrations of bottom ash,soil,plant were high,the order was Ba>>Mn>Sb>Cr>Pb>U>Cu>Ni>Cd>Co,and the concentration of Ba,Mn and Sb was much higher than others,they were 15492,2417,281 mg/kg,respectively.In soil and ash,the concentration of totalαwas 3000-5000 Bq/kg,concentration of totalβwas11000-14000 Bq/kg.According to the heavy metal concentration and distribution,the significant positive correlation between Co,Mn and Ni had been clearified,also the migration behavior.Herein,the measures of environmental maganement were also provided.The content of uranium bound to Fe oxides and residual in ash were 34.9%and59.1%respectively.Residual uranium was mainly incorporated into aluminosilicates,i.e.combined with glass and cristobalite,whereas uranium bound to Fe oxides was especially enriched in the magnetic fraction,of which about 50%was present with magnetite（Fe₃O4）and the rest in other iron oxides.In addition,the results of a linear combination fit（LCF）of the X-ray absorption near edge structure（XANES）spectrum revealed that in the raw CBA,the uranium mainly occurred as U3O8（71.8%）and UO3（12.1%）,however,in the iron-rich particles,the uranium mainly occurred as UO2（91.9%）after magnetic separation.According to the distribution and speciation of uranium in bottom ash,a highly effective method for recovery of uranium and other valueable components was developed by using roast with CaCl2 and leach with HNO3.This method could not only destroy the uranium-bearing mineral phases,but also recovery multi-components simultaneously.Furthermore,the mass-material ratio,roast temperature,duration,leaching temperature,acidity were optimized and 99%of leaching efficiency for uranium acquired under the condition of the mass-material ratio of 0.5:1,roasting temperature of 900℃for 2h and leaching at 80℃for 4h.Meanwhile,the leaching efficiency of alumina is more than 93.21%,uranium and alumina had been recovered effectively in alone procedure.The reaction mechanism of uranium recovery processes was investigated.The new minerals,i.e andradite,anorthite,wollastonite,mayenite and cristobalite were founded in the roasted clinker,which were susceptive to acid leaching.The residue originated from acid leaching was mainly composed of amorphous silicon dioxide,which could be utilized as construction materials.The reclaimed uranium and alumina can be recovered to produce triuranium octoxide and alumina.