Adsorption Of U(VI) Using Magnetic Chitosan Composites And Their Adsorption Mechanisms

With the development of the nuclear industry,water pollution caused by the heavy metal ions,such as uranium,has become more serious.Adsorption technology was used for handling radioactive pollution,which has the advantages of simple,effective,low cost and secondary pollution.Magnetic chitosan composites are novel materials that exhibit good sorption behavior toward various toxic pollutants in aqueous solution.These magnetic composites have a fast adsorption rate and high adsorption efficiency.It can efficiently remove various contaminants and is easy to recovered and reuse.All these above advantages are expected chitosan and its deviants to develop as an environmental eradicator.However,the fact that chitosan shows poor solubility,chemical stability and adsorptive property limits its application.It is necessary to carry out the modification of chitosan for better apply to practical application.In this paper,the diethylenetriaminepentaacetic acid functionalized magnetic chitosan nano-particles(DTPA-MCS)were facilely synthesized and used to adsorption uranium.The result of FT-IR implied that the amine and carboxyl groups was greatly increased because of the modification.Batch adsorption experiments showed that the DTPA-MCS exhibited fast kinetics for U(VI)due to its high density of N/O-containing groups.The adsorption kinetics followed pseudo-second-order model,whereas the adsorption isotherms agreed well with Langmuir model.After adsorption,uranium were uniform distribution in the surfaces of DTPA-MCS and the maximum adsorption capacity of U(VI)was 157.1 mg/g at pH 5.0 and 298 K.Thermodynamic data indicated a spontaneous and endothermic adsorption process.The U(VI)adsorption mainly proceeds through inner-sphere complexation,as evidenced by the slight influence of ionic strength.The DTPA-MCS could be regenerated by 0.40 M thiourea-0.20 M HNO3 and reused for adsorption.The magnetic chitosan resins functionalized with triethylene-tetramine(TETA-MCR)were in situ prepared for the adsorption of uranium ions from aqueous solution.The adsorption process was spontaneous and endothermic in nature and kinetically followed pseudo-second-order model.The equilibrium data were correlated with the Freundlich models and the maximum adsorption capacity of U(VI)was 166.6 mg/g at pH 5.0 and 298 K.FT-IR analysis indicated that the amine groups of TETA-MCR was the main adsorption sites for complex formation.With the increasing of temperature,the adsorption ability was increased,indicated that the adsorption is endothermic and spontaneous.The TETA-MCR could be regenerated by 0.1 M HNO3-0.1 M EDTA and the desorption efficiency were 92.3%.The TETA-MCR exhibited some excellent high adsorption capacity and easy to magnetic separation.It could be used as a novel magnetic sorbent for actinide separation.The in situ generated Fe0-nanoparticles(FeNPs)were incorporated to tripolyphosphate-crosslinking chitosan membranes(CS-Fe)for enhancing U(VI)adsorption.The specific surface area of membrane reached 46.5 m2/g and the pore volume reached 0.15 cm3/g.The content of FeNPs in membrane was 32%.The adsorption kinetic followed pseudo second-order model,indicating chemisorption as the rate-controlling step.The adsorption capacity of uranium increased with pH,and the maximum adsorption capacity reached 208.8 mg/g at pH 5.0-5.5.The solid to liquid ratio of 0.1 was the best conditions.The FeNPs offered additional adsorption sites,as evidenced by the perfect fitting of the Langmuir model for the adsorption isotherms.The phosphate groups from CS-Fe and the redox reaction from FeNPs play a leading role in remove uranium.The CS-Fe membrane could be regenerated by 0.5 M HNO3 and the desorption efficiency were 97.5%.