Preparation Of Amino-phosphoric Acid Functionalized Polyacrylonitrile Fibers And Adsorption Properties On Gadolinium Ions

Rare earth elements（REEs）,including all lanthanides as well as scandium and yttrium,are critical industrial metals.Due to their rare and unique physicochemical properties,REEs are widely used in high technologies and futuristic industries such as automotive,fluorescent lamps,high performance permanent magnets,electrometallurgical alloys,laser and renewable energy.However,the large amount of consumption makes REEs inevitably released into the environment,posing a great threat to ecosystems and human health.Not only that,China’s rare earth mining and export volume has long ranked first in the world,which has led to the gradual depletion of rare earth deposits,coupled with the difficulty in resourcefulness of impurity components such as associated minerals phosphorus,fluorine and thorium,imperfect rare earth industrial reprocessing technology has also resulted in the generation of large amounts of rare earth tailings,industrial wastes,magnetic wastes and electronic wastes.Therefore,the development of suitable technologies for the enrichment and recovery of rare earth elements in secondary resources is of great significance to realize the efficient utilization of rare earth resources and promote the clean production of rare earth smelting process in China.For example,the impurity concentration in the acid leaching waste stream is several orders of magnitude higher than that of rare earth ions,and there is an urgent need to discover materials with high selectivity and capacity for rare earth elements.Solid phase adsorption is often used for the removal of rare earth ions due to its low cost,ease of operation,wide range of application and high efficiency.To address the problem of low Gd（III）ion content in wastewater which is difficult to separate efficiently,a novel functionalized fiber with high selectivity and high adsorption capacity of Gd（III）ions was developed by a simple synthesis method of amination and phosphorylation using polyacrylonitrile fiber as raw material.The structure and properties of the functionalized fibers were characterized by various modern analytical testing techniques such as SEM,FTIR,XRD,TGA,zeta potential and XPS,etc.The FIIR and SEM/EDS results confirmed the successful grafting of phosphate groups on the surface of the acrylic fibers and the maintenance of good fiber integrity.The TGA and XRD results showed that the physical properties of the modified acrylic fibers were slightly improved,but the crystallinity decreased significantly,and the zeta potential results showed that the adsorbent exhibited a positive charge at p H below 3.By investigating the adsorption behavior of Gd（III）at different p H values,the strongest adsorption capacity of PAN-Phos fibers was observed at p H 6.In the phosphorylation modification stage,the maximum adsorption was achieved at a phosphite to aminated fiber dosage ratio of 1.The adsorption process of PAN-Phos fibers on Gd（III）was consistent with the proposed secondary kinetics and Langmuir isotherm model,indicating that the effective adsorption of Gd（III）ions was controlled by the chemisorption mechanism.The maximum adsorption capacity was 120.9 mg/g at p H 6 at 25 °C.The thermodynamic adsorption results verified that the inner surface complexation process of phosphate groups with Gd（III）was spontaneous heat absorption and the highest adsorption capacity was observed at 45 °C.The effect of in single competing ions on the adsorption performance of Gd（III）was further investigated,and the results showed that the adsorption effect of Gd（III）was less affected when Mg（II）,Ca（II）,Al（III）and Fe（III）ions were present in the solution.In addition,the desorption of PAN-Phos-Gd was studied by various eluents,and it was found that the strong acid-based eluent had the best desorption effect,and the PAN-Phos fiber could still reach the adsorption amount of 75.0 mg/g after four consecutive adsorption and desorption cycles,which showed good adsorption performance and recycling effect compared with other existing reported rare earth ion adsorption materials.In conclusion,the recyclable phosphorylated polyacrylonitrile fibers with high adsorption capacity and high selectivity were successfully constructed in this work,which are expected to be potential adsorbents for the extraction of rare earth elements from wastewater environment due to their simple process and remarkable adsorption effect.