Treatment Of Simulated Radioactive Wastewater From Nuclear Power Plant By Sulfide Coprecipitation

With the development of nuclear technology and the expansion of the proportion of nuclear power in energy structure,the treatment of liquid radioactive waste in nuclear power plant has received extensive concern and attention of international society.60Co is the typical activated corrosion product,its proportion is more than 40%in liquid radioactive waste,and it is also one of main sources of radioaction.Therefore,it is significant to remove 60Co in liquid radioactive waste.In this paper,sulfide coprecipitation was used to remove 59Co which acted as the simulation of non-radioactive isotope.The best technological parameters were optimized,and the removal mechanism was preliminarily investigated.It could provide technical assistance to use sulfide coprecipitation for the treatment of the actual liquid radioactive waste.Experimental results are as follows:1)Sulfide coprecipitation process can efficiently remove Co2+in the simulated liquid radioactive waste.The optimal process parameters were pH=9.5,S2-/(Fe2++Co2+)molar ratio=0.65:1,reaction temperature=65?,Fe2+/Co2+molar ratio=75:1 and reaction time=40min.Under these reaction parameters,the removal rate was 99.927%and residual concentration of Co2+was 3.67?g/L in effluent.Water content of the solid product was 80.8%while treating 500mL liquid waste.Some process parameters could affect sulfide coprecipication and their order for influence degree is reaction pH>S2-(Fe2++Co2+)molar ratio>Fe2+/Co2+molar ratio>reaction temperature>reaction time.The water quality of influent could affected the process,the lower concentration of Co2resulted in the lower removal rate.The concentration of boric acid in influent directly affected the particle size of products and finally affected the removal rate,the higher boric acid concentration in influent resulted in the smaller particle size and lower removal rate.2)The existence of other heavy metal ions could affect the removal rate of Co2+.With the existence of Zn2+the formation of cobalt sulphide precipitation exhibited an induction period and decreased the removal rate of Co2+.Different molar ratio of Mn2+/Co2+had the different effect,when Mn2+/Co2+molar ratio was higher than 2:1.With the existence of Mn2+ the formation of cobalt sulphide precipitation also exhibited an induction period and decreased the removal rate of Co2+,but its influence was less obvious than that of Zn2+.The existence of Sr2+helped the formation of cobalt sulphide precipitation,enlarged particle size and increased the removal rate of Co2+3)The solid product was black,the particle size was big,the sedimentation velocity was fast,and the reaction solution clarified after 15min sedimentation time.The sulfide precipitation process used in this study greatly improved the poor precipitation performance of the traditional sulfide coprecipitation.4)The sulfide coprecipitation formation mechanism was complex.In this study,Co2+was removed by forming sulphide precipitate,hydroxide precipitate and adsorption,the proportion of hydroxide precipitate and adsorption was about 16.4%.The removal of Co2+had two steps.When the reaction time reached 10min,the demarcation point appeared.XRD analysis showed that the cobalt sulphide precipitate in solid products mainly included CoS and CoS2.