Preparation And Adsorption Properties Of Cross-Linked Chitosan-Supported Boron Adsorbents

The salt lake brine contains huge boron resources.The remaining solution with low boron content(about 2000 mg·L^-1)is called as the acidified brine after the boron precipitation.It can be further extracted by a variety of other boron extraction methods,which not only fully recovers boron resources but also avoids low-concentration boron solution polluting the environment.The adsorption method has many advantages for boron extraction at low concentration,and is used as the last step of boron extraction from salt lake brine.It can also be used to treat other low concentration boron-containing water bodies,such as seawater,nuclear power plant wastewater and geothermal water.The key step to the adsorption process is the development of boron adsorbents with excellent performance.For overcoming the shortcomings of existing adsorbents,such as low adsorption capacity,complicated synthesis process and small particle size,new boron adsorbents were developed in this work.The detailed research content and research results obtained are as follows:In order to develop a simple synthetic process,two new types of absorbents(CCTS-2-APD and CCTS-NMDG)were synthesized by grafting 2-amino-1,3-propanediol(2-APD)and N-methyl-D-glucosamine(NMDG)onto the surface of cross-linked chitosan beads to separate boron element.CCTS-2-APD and CCTS-NMDG were examined by FT-IR and SEM analyses.The results indicated that2-APD and NMDG had grafted on CTS successfully.Compared to general surface of pure chitosan bead(CTS),the two adsorbents have a rougher surface.When the p H value is 8?12,CCTS-2-APD has higher adsorption efficiency for boron and it is also affected by competitive ions.While the p H value ranged 3?8,CCTS-NMDG would have a high efficiency of adsorption to boron.CCTS-NMDG had a comparatively high selectivity because general competing ions had little influence on the adsorptive ability of CCTS-NMDG.The adsorption process of CCTS-2-APD and CCTS-NMDG fit to the pseudo-second-order kinetic model and the Langmuir isotherm adsorption model.Chemical reaction is the adsorption rate control step,with 8.56 mg·g^-1 and20.36 mg·g^-1 maximum adsorption capacity,and the adsorption equilibriums were attained in about 2.5 h and 3 h,respectively.Their adsorption capacities could remain above 85%and 94%of initial adsorption capacity after 5 cycles,respectively.The adsorption capacity of CCTS-NMDG is higher than commercial adsorption resins Amberlite IRA-743 and D564,and the adsorption rate is not much different from commercial resin.The maximum adsorption capacity of the currently N-methyl-D-glucosamine functionalized chitosan-based adsorbent is 35.13 mg·g^-1 and it takes 10 h to reach the adsorption equilibrium.The preparation requires four steps and a long reaction time.In contrast,CCTS-NMDG requires only two steps of chlorination and amination,a shorter reaction time,and a higher adsorption rate.