碱性材料对独居石废渣中U、Th的稳定化效应

Stabilization Effect of Alkaline Materials on U and Th in Monazite Waste Residue

采用CaO、Mg(OH)_(2)、Ca_(3)(PO_(4))_(2)、海泡石、CaCO_(3)等碱性材料对放射性独居石废渣进行稳定化处理,进行不同投加比试验与长期浸出试验,监测U、Th、pH的变化规律,借助XRD、SEM-EDS、组分形态变化等手段揭示U、Th稳定化机理。结果表明,在5.0%、7.5%的投加比条件下,各材料试验组浸出液均满足pH=6~9的要求;在长期浸出试验中,仅有Ca_(3)(PO_(4))_(2)具备对U、Th核素的长期稳定能力;短期内废渣pH升高对U具有稳定化效应,稳定后U的活化重新溶出是一个长期过程,与反酸无关;Th的稳定性主要受pH影响,pH>6即可实现Th长期稳定。稳定化过程中,废渣表面由于沉淀的生成而变得粗糙,沉淀的U、Th次生相多为无定形态;U、Th核素的稳定化主要与促进可交换态、碳酸盐结合态向铁锰氧化态、残余态转变有关。

Several materials such as CaO,Mg(OH)_(2),Ca_(3)(PO_(4))_(2),sepiolite,CaCO_(3) were used to stabilize radioactive monazite waste residue.Different dosing ratios and long-term leaching experiments were carried out,the changes in U,Th,and pH were monitored,and the stabilization mechanism of U and Th was revealed by means of XRD,SEM-EDS,and variation of the distribution and forms.The results show that under the condition of 5.0%and 7.5%dosage ratio,the leaching solution of all experimental groups meet the standard requirements of pH=6~9.In subsequent long-term leaching experiments,only Ca_(3)(PO_(4))_(2) has the long-term stability ability for U and Th nuclides.In the short term,the increase in pH of waste residue has a stabilizing effect on U,and the activation and redissolution of U after stabilization is a long-term process unrelated to acid reflux.The stability of Th is mainly affected by pH,pH>6 can achieve long-term stability of Th.During the stabilization process,the surface of the waste residue become rough due to the formation of precipitation,and the precipitated U and Th secondary phases are mostly amorphous.The stabilization of U and Th nuclides is mainly related to promoting the transition of exchangeable state and carbonate complex state to iron-manganese oxidation state and residual state.