Preparation And Properties Study Of Sodium Alginate And Chitosan Composites For Adsorption Of Rare Earth Elements And Phosphorus Elements

The water pollution is increasing significantly every day and becoming more and more serious with the spectacular growth of industrial activities all around the world.The industrial wastewater is discharged directly towards urban or rural areas without performing any detoxifying and cleaning treatment.Such wastewater generally causes great harm to the ecological environment and human health.Among them,rare earth elements are important strategic resources with large-scale exploitation.The excessive rare earth elements which are mostly present in industrial wastewater can cause serious harms to respiratory system,cardiovascular system and nervous system of humans.Phosphorus is also a common pollutant in wastewater.Phosphorus pollution can lead to eutrophication of water,death of aquatic organisms and decline of quality of water.Therefore,it is necessary to decontaminate the wastewater from rare earth elements and phosphorus.The most useful and widely used method for the treatment of wastewater is adsorption method by using natural hydrogel materials.This method has many advantages such as simple,economical and high efficiency.The natural hydrogel material is cheap,has a wide range of sources,good biocompatibility and degradability.Natural hydrogel material also carries a large number of functional groups on the surface which can be used as the adsorption sites to increase the adsorption capacity,and is not easy to produce secondary pollutants,having a huge application potential in wastewater treatment.In this paper,sodium alginate(SA)and chitosan(CS)were modified as the matrix,and two kinds of composite hydrogel materials were prepared for the removal of rare earth elements and phosphorus containing elements from aqueous solution,respectively.The main research contents are as follows:1.Sodium alginate@nitrogen-doped carbon dots composite hydrogels(SA@NCDs composite hydrogels)were synthesized for the removal of La(III)from water using sodium alginate as a substrate and modified with nitrogen-doped carbon dots(NCDs).The results indicated that with the introduction NCDs to modify sodium alginate hydrogel,the adsorption sites of La(III)were increased and the adsorption capacity was significantly improved.The experimental data in the adsorption process were fitted and analyzed,which fit the pseudo-second-order kinetic model(~2=0.9992)and Langmuir isothermal adsorption model(~2=0.9970-0.9989).The theoretical maximum adsorption capacity calculated by Langmuir model at 298.15 K,308.15 K and318.15 K were 217.39 mg/g,225.73 mg/g and 234.74 mg/g,respectively.In competitive adsorption experiments with other ions,the adsorbent had good selectivity for La(III).The SA@NCDs composite hydrogel adsorbent still had a good removal ability for La(III)even after being used for five times.The adsorption effect of SA@NCDs composite hydrogel on other rare earth elements Gd(III)and Yb(III)was also investigated,and the adsorption capacity of SA@NCDs composite hydrogel could reach 249.32 mg/g and300.26 mg/g respectively.The material after La(III)adsorption could also be used for the adsorption of phosphorus elements from wastewater,with an adsorption amount of 9.64 mg-P/g.Therefore,SA@NCDs hydrogel is easy to synthesize and environment friendly and has great potential to be used in the treatment of wastewater.2.Chitosan/polyacrylamide/lanthanumcompositehydrogels(CS/PAM/La composite hydrogels)were synthesized for the removal of phosphorus from aqueous solutions.The addition of lanthanum nitrate and acrylamide resulted in a denser network structure which improved mechanical properties,more functional groups and increasing number of adsorption sites for the adsorption of phosphorus.The experimental data for phosphorus adsorption on CS/PAM/La composite hydrogels were well fitted to the pseudo-second-order model(~2=0.9987)and the Langmuir isothermal adsorption model(~2=0.9926).The adsorption capacity of the CS/PAM/La composite hydrogel for phosphorous was up to 80.07 mg-P/g.The coexisting anions had little effect on the adsorption of phosphorous.It is observed that even after five adsorption-desorption cycles,the CS/PAM/La composite hydrogel still had a good enough efficiency to remove the phosphorus from the aqueous solution.Therefore,the CS/PAM/La composite hydrogels have good application prospects in the treatment of wastewater which is highly contaminated with phosphorus.