Study On Treatment Of Radioactive Rare Earth Wastewater With Orthophosphate Complexation And Flocculation Process

Radioactive rare earth wastewater contained uranyl (UO22+) and lead ions (Pb2+) was treated using orthophosphate complexing and flocculation process. Effect on the UO22+、Pb2+removing efficiency and stability of different initial pH, reaction time, reaction temperature, phosphate concentration and flocculant species were investigated through variable test including orthogonal test, flock leaking test and single factor test in which uranyl and lead were well resolved. Main results are:(1) Initial pH, reaction time, phosphate concentration and flocculant species were studied in orthogonal test, uranyl removal efficiency upraised with pH rising, went up first, then down with time elapsed and phosphate concentration rising. The best uranyl and lead removing conditions were:pH=9,30min reaction time, using PAFC as flocculant, and making phosphate concentraion at17.5mg.L-(2) Effect on uranyl removal of factors examined in orthogonal test took in turn as pH>reaction time>phosphate concentration>flocculant species. And pH was the only remarkable influence factor among all of them.(3) Uranyl leaking efficiency of different lixiviants took an proper order like HNO3>KNO3. Uranyl removed was more stable at lower pH using orthophosphate complexing and flocculation process and having a smaller leaking ratio. Uranyl flock was leaked at a90%scale formed at pH>5when using HNO3as an lixiviants, wheras no uranyl was leaked at pH=3. As a result, if taking the resistance against acid and alkali into consideration, pH should be3to make phosphoric uranyl complexation.(4) Uranyl and lead ion would be fully dissolved in solution at pH=3, they possessed a good mobility and were the most hazardous to environment. The effects of very factors including temperature, phosphate concentration and flocculant species on the uranyl and Pb2+removal were examined. The result showed that, high temperature are favorable to the formation of phosphate-uranyl and phosphate-lead, the optimum temperature examined was30℃; phosphate concentration should neither be too high nor too low to make uranyl and lead complexation. the most suitable concentration was about50.0mg·L-1; phosphate-lead complexation formed faster and more than phosphate-uranyl complexation. Iron-based flocculation had a higher proportion iron, it polymerized better in the presence of phosphate and showed a better result treating REE wastewater. PAFC presented a better flocculent ability under neutral and alkaline medium, wheras SPFS possessed a better adaptability at a wide pH range, it is suggested to choosing SPFS as a flocculant removing uranyl and lead phosphate complex at acidic conditions.In short, treatment of radioactive rare earth wastewater contained uranyl (UO22+) and lead ions (Pb2+) was efficient, quick and stable using orthophosphate complexing and flocculation process, and it could lead the treatment of radioactive wastewater in rare earth element company theoretically and practically.