Performance Of Uranium(Ⅵ) In Soil Of Uranium Tailings Fixed By NZVI/nHAP Composites

With the development of the nuclear industry,the amount of mining of radioactive materials such as uranium has been increasing,and the amount of tailings and slag has gradually increased.These tailings and slags are treated and stored in the tailings pond.The uranium in the tailings,which has been routinely treated by lime alkalizing,will be released into the environment again as the environment changes,endangering human health.Soil is the first barrier to prevent uranium from entering the environment in the tailings pond.Therefore,it is of great significance for the restoration of uranium-contaminated soil.In this paper,nano-zero-valent iron(nZVI),nano-hydroxyapatite(nHAP),nano-zero-valent iron/hydroxyapatite three fixatives are used to uranium in uranium tailings soil.The immobilization treatment was carried out,and the uranium tailings soil before and after the nanomaterials were fixed by SEM and XRD were characterized by stepwise chemical extraction,toxic leaching(TCLP)and magnetic separation test.The nanomaterials were studied at different dosages and pH.Effects of morphological distribution and fixation on uranium in tailings pond soil under conditions,and discussion on the fixing mechanism.The main conclusions are as follows:(1)nZVI mainly promotes exchangeable state(including water-soluble state)in carbonate tailings,conversion of carbonate-bound uranium to amorphous iron-manganese oxide-hydroxide state,and residual uranium;the amount of nZVI is At 8% and pH=5,the uranium content in the residual state increased by 13.84%,and the MF value reached a minimum of 24.88%.At this time,the toxic leaching amount of uranium in the soil sample was only 13.98%,and the fixation effect was the best;the treatment by nZVI After the magnetic separation of the soil samples,it was found that the concentration of uranium in the non-magnetic soil was significantly reduced,and the toxicity leaching value was close to the toxic leaching limit of the US Environmental Protection Agency.(2)nHAP mainly promotes the exchangeable state(including water-soluble state),carbonate-bound uranium to crystalline iron-manganese oxide-hydroxide state,and residual uranium in the uranium tailings reservoir;n is added in nHAP When the amount is 6% and pH=4,the uranium content in the residual state increases by 16.58%,and the MF value reaches 41.79%.At this time,the toxic leaching value of uranium is only 9.14%,and the fixation effect is optimal.(3)Nano-HAP/ZVI mainly promotes the exchangeable state(including water-soluble state),carbonate-bound uranium to amorphous iron-manganese oxide-hydroxide state,and residual uranium in the uranium tailings reservoir soil;When the dosage of HAP/ZVI is 8% and pH=5,the uranium content in the residual state increases by 11.05%,the proportion of residual uranium is up to 30.10%,and the MF value reaches a relatively stable value of 31.72%.At this time,the toxic leaching of uranium The amount of urethane was only 8.57%,and the fixation effect was the best.The magnetic separation of the soil samples treated with nano-HAP/ZVI showed that the uranium content in the non-magnetic soil after separation was lower than that in the non-magnetic soil after nZVI single treatment.And its toxicity leaching value is lower than the US Environmental Protection Agency uranium element toxicity leaching characteristics limit.