Functionalized Multi-walled Carbon Nanotubes For Treating Radioactive Wastewater

The development of nuclear science and technology has brought us all kinds of convenience in ourlives. At the same time, it also brings serious environmental problems. For instance, nuclear powerstations, hospitals, and factories will produce large amounts of radioactive wastewater each year. So theresearch of adsorbent material which can effectively deal with these wastewater becomes more andmore important.In this work, we used the stable isotope of Cu,Sr and Fe to simulate the radioactive Cu, Sr and Feions exist in the wastewater. Then we studied the removal efficiency of Cu²⁺,Sr²⁺and Fe²⁺in waterusing multi-walled cabon nanotubes （MWNTs） and chitosan functionalized multi-walled cabonnanotubes （CS-MWNTs） as adsorbent. The influences of pH, temperature, time, and equilibrium ionconcentration to the adsorption capacity were studied respectively. Results showed that in the sameconditions, the adsorption capacity of CS-MWNTs significantly increased compared to the pristinemulti-walled carbon nanotubes （MWNTs）. Both CS-MWNTs and MWNTs exhibited a better removalefficiency of Cu²⁺, Sr²⁺and Fe²⁺in neutral solutions than in acidic solutions, while in basic solutions,the Cu²⁺and Fe²⁺would precipitate and the removal of Cu²⁺and Fe²⁺was no longer due to theadsorption effect. Sr²⁺didn’t precipited in basic solutions, so the adsorption quantity of Sr²⁺onMWNTs in basic solutions reached an equilibrium. The adsorption equilibrium would be reached inabout3hours and the adsorption of Fe²⁺to MWNTs was endothermic while the adsorption of Cu²⁺andSr²⁺to MWNTs was not effected by temperature. The adsorption of Fe²⁺to CS-MWNTs wasendothermic while the adsorption of Cu²⁺and Sr²⁺to CS-MWNTs was exothermic.At roomtemperature25°C, pH=5, the saturate adsorption capacity of CS-MWNTs for Cu²⁺, Fe²⁺and Sr²⁺was24mg/g,40mg/g and41mg/g, while that of pristine MWNTs was16mg/g,25mg/g and26mg/g.The Freundlich adsorption model could well represent the adsorption of Cu²⁺,Sr²⁺and Fe²⁺to both ofthese two kinds of adsorbent.Prussian blue （PB）, ferrous iron cyanide nickel （NiPB） and ferrous iron cyanide zinc （ZnPB） weredecorated onto the multi-walled carbon nanotubes. The new composite material of MWNTs-PB,MWNTs-NiPB and MWNTs-ZnPB would have both the adsorption ability and ion exchange of metalions in wastewater. TEM, SEM, FT-IR and XRD showed that these three kinds of Prussian materialwere successfully decorated onto MWNTs. We then used these three kinds of composite material toremove Cu²⁺and Sr²⁺in wastewater. MWNTs-ZnPB has shown the best removal efficiency of Cu²⁺andSr²⁺. Mossbauer spectrum were used to analysis the resulting cesium sulfate solution treated with MWNTs-NiPB.