Research On The Remove Of Cr(?) By Green Synthesized Shell Powder Supported Nanoscale Zero-valent Iron

Hexavalent chromium is one of the most toxic heavy metals in the world,which is harmful to human health and ecological environment.Hexavalent chromium in nature mainly exists in water and soil,especially Cr(?)in water is difficult to degrade and easy to migrate,which can be transmitted and enriched through the food chain,and ultimately harm human health.Therefore,it is an urgent environmental problem to solve the problem of hexavalent chromium pollution in water.In recent years,nano zero valent iron has been widely used in the removal of Cr(?)and other heavy metals due to its strong reducibility and significant advantages in the remediation of water pollution.However,nano zero valent iron is easy to agglomerate and oxidize in preparation and practical application,which affects its application in practical engineering.In this paper,the nano zero valent iron(SP@NZ?)loaded on the shell was prepared by using Kudingcha extract as reducing agent and shell powder as loading group,in order to improve the oxidation resistance and dispersion of nano zero valent iron.At the same time,after the shell is crushed,screened and pyrolyzed,it has a certain adsorption on Cr(?)in water body.In this study,nano iron and shell powder are combined by load to make them have a synergistic effect on the removal of Cr(?),so as to achieve the purpose of efficient removal of Cr(?).At the same time,it also opens a new way for the utilization of Kudingcha,shell and other natural resources.In this paper,the effects of the pyrolysis temperature of shell powder,the particle size of shell powder and the loading ratio of shell to nano iron on the removal of Cr(?)from water by SP@NZ? were studied.The optimal preparation parameters of SP@NZ? were obtained by response surface method,and then the SP@NZ? synthesized under the optimal preparation conditions was characterized by SEM,IR and XRD,At the same time,the effect of adsorption conditions on the removal of Cr(?)was also studied.The adsorption conditions include the dosage of SP@NZ?,the initial p H of the solution and the temperature of the solution.Finally,through the analysis of adsorption isothermal model,adsorption kinetics and XPS characterization before and after SP@NZ? adsorption,the following conclusions were obtained:(1)Through the study of the effect of single factor of preparation conditions on the removal of Cr(?)by SP@NZ?,it can be seen that:with the increase of pyrolysis temperature of shell powder,the removal rate of Cr(?)by SP@NZ? increases,and when the temperature is higher than 500?,the removal rate of Cr(?)decreases;the smaller the particle size of shell powder,the greater the removal rate of Cr(?)by SP@NZ?;with the quality of shell powder and nano iron When the mass ratio is 4:1,the removal rate reaches the maximum.(2)Through the optimization of the preparation conditions of SP@NZ? by response surface method,the optimal preparation conditions are:SP/NZ? mass ratio3.43,shell powder pyrolysis temperature 517?,particle size 210 mesh.With SEM,FTIR and XRD.The shell powder and SP@NZ? were characterized.The results showed that the structure of the shell powder after pyrolysis was porous.The extract of Kudingcha could reduce Fe²⁺to particle size 32?79 successfully.The nano-sized zero valent iron particles(NZ?)were loaded on the surface of the shell powder,which effectively reduced the agglomeration of NZ? and enhanced the oxidation resistance of NZ? in the air.(3)SP@NZ? composite,shell powder(SP)and their physical mixture(SP+NZ?)were added to the same Cr(?)solution at the same time.The results showed that the removal efficiency of SP@NZ? to Cr(?)in water was 92.35%,SP removal efficiency was only 11.99%,SP+NZ? physical mixture maximum removal efficiency was only65.06%,compared with the unloaded SP+NZ? mixture The removal rate of SP@NZ? increased by 53.47%,which indicated that the adsorption performance of SP loaded NZ? could be effectively improved,and SP also played a role in the removal of Cr(?).Therefore,it can be concluded that SP@NZ? has synergistic effect on the removal of Cr(?).(4)Taking SP@NZ? as the adsorbent,the influence of adsorption conditions on the adsorption effect was discussed.The adsorption conditions included the amount of adsorbent,p H and temperature.The results showed that in a certain range of parameters,with the increase of the amount of adsorbent,the decrease of p H and the increase of temperature,the removal rate of Cr(?)also increased.Through the orthogonal test,the best adsorption conditions were obtained:the dosage of SP@NZ? was 3.0g/l,the solution p H 2.0,and the adsorption temperature was 45?.(5)The adsorption isotherm model of removing Cr(?)from water by SP@NZ? was studied.It was found that the adsorption process had the best fitting effect on Langmuir model.Through XPS,quasi-1 and quasi-2 dynamics analysis,the adsorption process was in accordance with the quasi-2 dynamics model.It was revealed that the removal of Cr(?)by SP@NZ? was mainly through oxidation-reduction reaction and belonged to chemical adsorption behavior.