Adsorb Uranyl Ion With Synthesized Amidoxime Polyacrylonitrile Fibers

With the development of nuclear industry,both uranium extraction from seawater and dispose uranium-containing waste water from industrial production become significant.The aim of this task is to dispose the uranium-containing waste water,whose concentration is about 100 ?g/L.The amidoxime polyacrylonitrile fibers(PAO fibers)synthesized from polyacrylonitrile fibers(PAN fibers)through a heterogeneous reaction were used to decrease the concentration of uranium under 10 ?g/L.The as-prepared PAO fibers were characterized by using Fourier transform infrared spectroscopy(FT-IR),scanning electron microscope(SEM),energy dispersive spectroscopy(EDS),thermal gravimetric analyzer(TGA),X-ray photoelectron spectroscopy(XPS),and X-ray diffraction(XRD)measurements.Batch adsorption and desorption experiments were conducted,and then the adsorption process was fitted with kinetic and thermodynamic models.The appropriate modification temperature was explored firstly.Fibers will be in polycondensation state under high temperature,whereas fibers nearly won't be modified under low temperature.Therefore,the modification temperature was chosen at 323 K.The modified reaction of nitrile groups transform into amidoxime groups was verified by FT-IR and XPS.Batch adsorption experiments were conducted to explore the best adsorbent concentration,pH,contact time,temperature,and initial uranium concentration.The optimum pH for this adsorption experiment is 5.0,and the results of adsorption become better with the increasing of temperature.PAO fibers are better than silica gel,activated carbon,and zeolite in adsorbing uranium about 100 ?g/L.Twelve kinds of reagent were used to desorb uranyl ions,such as hydrochloric acid,sulfuric acid,tartaric acid,DL-aspartic acid,and potassium hydroxide etc.The desorption percentage of strong acid reach 90% or higher,and it needs no more than 10 min to reach desorption equilibrium,however,all of them will damage PAO fibers to make it gelatinous.The desorption speed of tartaric acid is high enough,and it only takes 5 min to reach equilibrium.But its desorption percentage is lower than 40%.It costs 8 h to reach desorption equilibrium of potassium hydroxide,but the desorption percentage is nearly 50%,what's more,fibers won't be gelatinized.The adsorption process fit well with Intraparticle diffusion model and pseudo-second-order model.In addition,Langmuir,Freundlich,Temkin,and Dubinin–Radushkevich(D-R)models were used to explain the adsorption thermodynamic process.The adsorption process is spontaneous and endothermic.