Treatment Of Wastewater Containing Cobalt And Strontium By Combined Process Of Coprecipitation And Microfiltration

The radioactive liquid waste was generated from milling of nuclear fuel, recycling the spent nuclear fuel, operation and maintenance of nuclear reactors, nuclear research and nuclear medical examination and treatment. Nuclear accident, such as the 2011 Fukushima nuclear crisis, would release large amounts of radioactive waste. In general, such radioactive waste contained a variety of radionuclides that are fission byproducts generated from these processes. Among the byproducts, 60 Co and 90 Sr were considered as the most dangerous radionuclides to human health due to their high transferability, high solubility, long half-lives and easy assimilation in living organisms. Therefore, it is necessary to research on an appropriate treatment for the removal of these radionuclides.A pellet coprecipitation microfiltration?PCM? was feasible for the removal of the cobalt and strontium elements from the wastewater, which combine the advantages of chemical precipitation and membrane methods. The mean DFs of cobalt and strontium were 1536 and 504. The microfiltration membrane in the membrane reactor could separate the mixed liquid efficiently, so the precipitation of cobalt and strontium could be retained. In the PCM process, less sludge volume was produced. After sedimentation for 24 h, the concentration factor?CF? value was more than 1.0×103.The results showed that the PCM process had better treatment effect on the removal of the cobalt with the coexistence of strontium, but had worse treatment effect on the removal of strontium with the coexistence of cobalt. When the raw water contained cobalt only, the sludge showed poor stability which would increased again. However the raw water contained cobalt and strontium, the sludge showed better sedimentation performance, which made subsequent process easier. In the pellet reactor, CaCO3 and Na₂CO₃ were dosed as induced crystal seed and precipitating agent. Cobalt carbonate, cobalt hydroxide and strontium carbonate adhered on the surface of the crystal seed and coprecipitated from the solution. Moreover, Sr2+ and Co2+could incorporated into CaCO3 lattice to form strontianite and Co-bearing calcite. The generated particles were dense with good settling performance.The influencing factors such as temperature, the dosage of Na₂CO₃ and coexisting ions on the removal of strontium and cobalt were investigated. In the lab-scale tests, the PCM had a higher removal rate for strontium and cobalt ions with the higher temperature and especially the change of temperature between 9 °C to 19 °C. Reducing the Na₂CO₃ dosage could reduce the p H value of the effluent, but decreasing the DFs. As the concentration of calcium ion was increased, strontium removal efficiency was improved, but decreased the removal efficiency of cobalt.