Modified Walnut Shell Material Adsorption Experiments Of Mercury In Water

In this paper,forestry waste walnut shell as base material,uses the sulfide,alkali modification,carbonized modified different ways such as the preparation of various modified walnut shell material,and through the Scanning Electron Microscope（SEM）,Brunauer Emmett Teller（BET）,compares the differences between the modified walnut shell material surface morphology,and uses the modified walnut shell as an adsorbent for the removal of Hg（Ⅱ）in water.The adsorption kinetic model,isotherm model and particle diffusion model were used to fit the experimental data.Comparing the difference between the adsorption efficiency between different materials,using X-ray diffraction（XRD）,Fourier infrared spectrum（FTIR）characterization methods such as comparative analysis of different modification methods of adsorbent materials for the adsorption of Hg（Ⅱ）in the water function and mechanism.The main findings of this paper are as follows:（1）Using Na₂S and KOH modified two walnut shell material.Along with the water Hg（Ⅱ）higher initial concentration,walnut shell and modified materials removal of Hg（Ⅱ）in water decreased,when the initial concentration of Hg（Ⅱ）>0.3 mg/L,the removal rate of different materials for Na₂S modified walnut shell>KOH modified walnut shell>walnut shell.When the solution is in a strong acid state,the modified walnut shell material has an unsatisfactory effect on the removal of Hg（Ⅱ）in water;then the removal rate also increases with the increase of p H,and reaches the best at p H 5～6.In the relationship between the removal rate and the reaction time,the Na₂S modified walnut shell has the fastest adsorption rate for Hg（Ⅱ）in water and the largest adsorption capacity,followed by KOH modified walnut shell,and finally walnut shell.Which is the same as walnut shell,two modified walnut shell materials conform to the pseudo-second-order kinetic equation and are mainly chemical adsorption.The KOH modified walnut shell is the same as the walnut shell,Langmuir isotherm model can better simulate the reaction process and is a kind of monolayer homogeneous adsorption.Na₂S modified walnut shell better conforms to the Freundlich isotherm model and is a multi-layer non-uniform adsorption process.The maximum adsorption capacities of Na₂S modified walnut shell and KOH modified walnut shell were 1.34mg/g and 0.65 mg/g respectively obtained by Langmuir isotherm model fitting,which were higher than 0.42 mg/g of walnut shell.The two modifications were effective,and the effect of sulfide modification was better than that of alkali modification.The surface functional group structure of the two modified walnut shell materials is not significantly different from that of walnut shell.During the adsorption of Hg（Ⅱ）in water,four chemical groups-OH,C=C,C-O,-COOH participated in the reaction The process has changed significantly compared to before adsorption.The surface morphology of the walnut shell after Na₂S modification has not changed significantly,but the S%content of the material is significantly higher than that of walnut shell,which proves that the modified successfully loads sulfide ions on the surface of the material;The surface morphology of walnut shell material modified by KOH was rougher and more pores appeared,which proved that alkali modification could effectively modify the surface and pore structure of the material.The structure of the two modified walnut shell materials has not changed obviously.（2）Under the condition of high temperature,biochar was prepared by carbonization to observe the structural changes of walnut shell compared with that of walnut shell.At the same time compared to the same type on the market the carbon adsorbent material of activated carbon,analysis of the two carbon materials on the surface structure,and the removal efficiency of Hg（Ⅱ）in water and the adsorption mechanism of differences.Walnut shell after high temperature carbonization of the preparation of biological carbon materials morphology structure has certainly changed,presents the honeycomb porous,specific surface area increased obviously,and C%content compared with walnut shell increased obviously,and active carbon for non-uniform block structure,also a part of the reunion,rough surface drape,some appeared gap between block structure,decentralized structure.In removing the water Hg（Ⅱ）experiments,the initial concentration of 0.05 mg/L,bicohar removal rate up to 76.95%higher than that of walnut shell material,less than84.99%of the active carbon;When the p H value of both biochar and activated carbon was 6,the best removal performance could be obtained.Pseudo-second-order kinetics could better simulate the reaction process of the two materials,both of which were mainly based on chemical adsorption.Both biochar and activated carbon can be simulated refer to using the Freundlich isotherm model,and both are heterogeneous multilayer adsorption.Langmuir isotherm was used to fit the two carbon materials,and the results showed that the maximum adsorption capacity of biochar was 2.87mg/g,which was significantly increased compared with the 0.42 mg/g of walnut shell material,while the theoretical maximum adsorption capacity of activated carbon was4.80mg/g.In the process of adsorption of Hg（Ⅱ）in water,the chemical groups of the biochar-OH、C=C、-COOH participated in the reaction;Activated carbon is involved in the reaction process of the group is-OH,C=C.In the test of recycling,the adsorption performance of biochar and activated carbon is stable and can be reused.（3）Na₂S modified biochar and KOH modified biochar were obtained.The content of S%of Na₂S modified biochar increased significantly,while the specific surface area of KOH modified biochar increased significantly.In the initial concentration range of 0.05～0.5mg/L,Na₂S modified biochar showed better adsorption performance than KOH biochar and biochar.In the p H range of 2～6,the adsorption efficiency of Na₂S modified biochar is better than that of KOH biochar than the original biochar.Like the original biochar,the adsorption of Hg（Ⅱ）in water by the two modified biochar materials is mainly chemical adsorption,which conforms to pseudo-second-order kinetics;Freundlich isotherm model can well fit the adsorption process of two kinds of modified materials,Langmuir isotherm model fitting the Na₂S biochar and KOH biochar maximum adsorption capacity compared with walnut shell increase 88.12%and 36.49%respectively,proved sulfide modification is to improve the adsorption of Hg（Ⅱ）.Like biochar,the two modified biochar are also composed of-OH,C=C and-COOH groups,which are mainly involved in the reaction process.The two kinds of modified materials have good structural stability and can be reused,and the structure has not changed obviously.