Removal Of Cobalt Ions From Low And Medium Level Radioactive Wastewater By Pressure Driven Membrane

The rapidly development of nuclear power industry in our country result in plenty of radioactive wastewater, most of which was at the low and medium radioactive level and bring a potent effect on environmental protection. With principle of higher efficiency and lower energy, nuclear waste comes from nuclear power plant is stored first and then discharged if it reaches standard; for example, low and medium radioactive level waste should be compressed or divided into two part, the part of high radioactive level will be sealed storage forever, the other part which radioactive level reach discharge standard will be sent to dilute in environment.In this thesis, we use two types of pressure driving membrane: nanofiltration and reverse osmosis to treat the low and medium radioactive wastewater, considering the characteristic, source and harming degree of wastewater from nuclear power plants, we choose cobalt ions (⁶⁰Co) as research object. It studies the flux and removal rate of cobalt ions in several conditions such as pressure, pH, competing ions and complex agent. It also includes the illustrations of Physical model to make the interpretation of experimental results easily.The concentration of Co²⁺ in raw water is 400ug/L. The following experimental conclusions can be obtained:(1)In nanofiltration experiments, membrane flux is over 80L·m^-2·h-1, which is much more than reverse osmosis. And general removal rate of Co²⁺ is over 90%, that is lower about 5 percentage to reverse osmosis.(2)The concentration of Co²⁺ will be constant in acid solution especially the solution is at especial pH. In the condition of weakly basic solution, there is cobalt-water balance and produce a certain amount of Co(OH)2 precipitation. Due to the experimental results, both nanofiltration and reverse osmosis have a good effect on retention at pH 10, the retention of nanofiltration is 95.4%, reverse osmosis is 98.02%.(3) Competing ions in raw water make a potent effect on removal rate of Co²⁺, Competing ions with different valence states generate different functions, such as Na+ and Ca²⁺ will make the removal rate of Co²⁺ lower and higher. This result implies us that selective membrane can not only be applied in removal of particular ions, but also can squeeze valuable metal ions from dilute solution.(4)At a suitable pH and the radio of cobalt to complex agent, the retention of cobalt ions by nanofiltration membrane reaches 98.06%. It available and effective to plunge into complex agent, but high polymer induces serious concentration polarization and makes membrane flux rather low. So how to choose complex agent should study further.(5)In the experiment of nanofiltration- reverse osmosis cascade, the retention of cobalt ions reaches 98.68%. It is relatively poor than anticipated results because of concentration polarization. In accordance with Physical model of reverse osmosis membrane we shall obtain the retention of cobalt ions more than 99.7%, which can not test by Chemistry method.