Study On Preparation Of Juncus Effuses-Based Adsorbents And Their Adsorption Properties For Chromium And Phosphorus

With the increase of industrial production and human activities,the discharge of a large number of wastewater containing Cr（Ⅵ）and phosphorus has an adverse impact on the aquatic ecological environment and human health.Therefore,it is of great significance to reduce its concentration to the standard limit or below.Adsorption method is widely used in wastewater treatment because of its simple operation,low cost and high removal efficiency.At present,most of the commonly used adsorbents are powder,which is difficult to separate and recover in use.Adsorbents with macro size and three-dimensional network structure can not only solve the problem of separation and recovery in the use of adsorbents,but also conducive to the exposure of active sites and the mass transfer of pollutants.In recent years,they have become a research hotspot at home and abroad.However,at present,the preparation of three-dimensional network structure materials is either difficult to construct and control the microstructure,or the preparation process is cumbersome,the reagent consumption is large,or the strength of the materials obtained is poor.Juncus effuses（JE）is an ideal adsorbent carrier with high surface area and porosity due to its three-dimensional network structure and internal interconnecting pipe structure.In this paper,based on the infiltration characteristics of ethanol/water system on Juncus effuses fiber,the active groups were successfully introduced without any acid,alkali and oxidant pretreatment,and the Juncus effuses based chromium and phosphorus removal adsorption materials were prepared respectively.The adsorption characteristics of the two materials were studied,and the relevant adsorption mechanisms were discussed.This research has certain theoretical and practical significance for the research,development and application of natural three-dimensional network structure and its adsorption materials.The main research contents and conclusions are as follows:1.Preparation and Cr（Ⅵ）removal performance of Juncus effuses based chromium removal adsorbent（PEI-JE）.Based on the wetting characteristics of Juncus effuses fiber in ethanol/water system,polyethyleneimine and glutaraldehyde were quickly introduced into the structure of Juncus effuses for crosslinking loading without any acid,alkali and oxidant pretreatment.A Juncus effuses based chromium removal adsorbent（PEI-JE）with macro size and three-dimensional network structure was prepared.The morphology and structure were characterized by SEM,EDS,XPS and FTIR.The removal characteristics of Cr（Ⅵ）by PEI-JE were studied,and the related mechanism was discussed.The results showed that PEI was successfully loaded on Juncus effuses fiber,and the prepared PEI-JE maintained the three-dimensional network structure of Juncus effuses.The adsorption of Cr（Ⅵ）by PEI-JE is p H dependent.When p H is 3,the removal efficiency of Cr（Ⅵ）is the highest.The removal rate of Cr（Ⅵ）is positively correlated with adsorption time,adsorbent dosage and adsorption temperature,and negatively correlated with Cr（Ⅵ）concentration;The adsorption capacity of PEI-JE was negatively correlated with the dosage of adsorbent and positively correlated with the concentration of Cr（Ⅵ）.The adsorption kinetics of PEI-JE on Cr（Ⅵ）accorded with the quasi second-order kinetic equation,indicating that the adsorption process was dominated by chemical adsorption.Langmuir model and Freundlich model have high fitting degrees for adsorption heat,indicating that there are monolayer adsorption and multilayer adsorption on PEI-JE surface at the same time.The adsorption thermodynamics shows that the adsorption of Cr（Ⅵ）on PEI-JE is a spontaneous endothermic reaction.The coexistence of Na⁺,K⁺,Al³⁺,H₂PO₄^-,Cl^-and NO₃^-had little effect on Cr（Ⅵ）removal,but the presence of SO₄^2-,HCO₃^-and CO₃^2-reduced the removal of Cr（Ⅵ）by PEI-JE,and the efficiency loss was 10.9%,41%and 66%,respectively.After 10 adsorption desorption cycles,the removal rate of Cr（Ⅵ）by PEI-JE is basically unchanged,indicating that PEI-JE has good recycling performance.The mechanism study shows that the Cr（Ⅵ）removal process involves three steps,the membrane diffusion is the rate-limiting step of the adsorption process,and the chemical adsorption is the main mechanism of Cr（Ⅵ）removal.Cr（Ⅵ）adsorbed on the surface of PEI-JE was completely reduced to Cr（III）.2.Preparation and phosphorus removal performance of Juncus effuses based phosphorus removal adsorption material（La-JE）.Taking natural Juncus effuses as the carrier,using ethanol/water system,La³⁺was quickly introduced into the three-dimensional network structure of Juncus effuses,and then reacted with ammonia to form La（OH）₃ in situ on Juncus effuses fiber,and a Juncus effuses based phosphorus removal adsorption material（La-JE）was prepared.The morphology and structure were characterized by SEM,XRD,FTIR.The removal characteristics of phosphate radical by La-JE were studied,and the related mechanism was discussed.The results showed that the prepared La-JE completely retained the three-dimensional network structure of Juncus effuses,the lanthanum containing active species loaded on Juncus effuses was La（OH）₃,and the regenerated cellulose formed a dense film on the outer surface of Juncus effuses.The removal rate of phosphorus by La-JE first increases and then decreases with the increase of p H,and the optimal p H is 6.The removal rate of phosphoric acid was positively correlated with adsorption time,adsorbent dosage and adsorption temperature,but negatively correlated with phosphorus concentration.The adsorption capacity of La-JE was negatively correlated with the amount of adsorbent and positively correlated with the concentration of phosphorus.The adsorption kinetics of phosphorus by La-JE conforms to the quasi second-order kinetic equation,indicating that the adsorption process is dominated by chemical adsorption.Freundlich model can better describe the adsorption heat of phosphorus by La-JE,indicating that the surface of La-JE is mainly multi-layer heterogeneous adsorption.The adsorption thermodynamics shows that the adsorption of phosphorus on La-JE is a spontaneous endothermic reaction.The co-existing ions SO₄^2-,Cl^-,NO₃^-,NH₄⁺,HCO₃^-and CO₃^2-had little effect on the phosphorus removal performance of La-JE,and their removal rate fluctuated within±4%.After La-JE phosphorus removal,the three-dimensional network structure and regenerated cellulose wrapped on the outer surface of Juncus effuses were not damaged;The phosphorus removal process is that phosphate and La（OH）₃ loaded on Juncus effuses are removed by precipitation reaction.