Research On Preparation And Performance Of Modified Animal Bone Char Materials For Removal Of Heavy Metal Ions

In this paper,pig bone was used as raw material to prepare bone char material（BC）by chemical activation method.Cellulose modified bone char material（MCC-BC）was prepared by chemical modification,and MCC-BC particle was prepared by granulation.FTIR,XPS,XRD,BET analysis,Zeta potential analysis and SEM-EDAX were used to characterize the structure of the materials before and after modification,and the static adsorption properties,dynamic adsorption properties,and adsorption of the materials before and after modification and the adsorption mechanism was studied.BC was prepared by chemical activation using sodium hydroxide as activators,and the effects of three factors（activator concentration,pyrolysis temperature,and heating rate）on the adsorption performance of BC were investigated.The optimum conditions for the preparation of bone char are as follows:activator concentration 1 mol/L,pyrolysis temperature 500℃,heating rate 10℃/min.MCC-BC was prepared by chemical modification using microcrystalline cellulose as a modifier.The effects of three factors（mass ratio of MCC to BC,modification temperature,modification time）on the adsorption performance of MCC-BC were investigated.The optimum conditions for the preparation of MCC-BC are as follows:MCC:BC1:4,modification temperature 80℃,and modification time 4 h.FTIR,XPS,XRD,BET,Zeta potential,and SEM-EDAX were used to characterize the two adsorbents.The results showed that after activation treatment,the main component of bone char was hydroxyapatite（HAP）,and after modification,cellulose was successfully loaded on the surface of bone char.The effects of temperature,p H,adsorbent dosage,contact time,initial concentration of the Pb（Ⅱ）solution and number of cycles on the Pb（Ⅱ）adsorption performance of BC and MCC-BC were studied.The results show MCC-BC has higher adsorption capacity and shorter adsorption equilibrium time than BC,and the two adsorbents both have good recycling performance,especially MCC-BC still has more than 90%removal efficiency after 5cycles.It is found that the adsorption process by BC and MCC-BC can be well fitted by the second-order kinetic model.The adsorption capacities obtained by the model fitting are in good agreement with the experimental results.This indicates the adsorption process is mainly controlled by the chemical adsorption.The fitting by the intraparticle diffusion model shows that the adsorption rate on BC is controlled by both intraparticle diffusion and surface diffusion,while the adsorption rate on MCC-BC is only controlled by the surface chemical adsorption.The analysis of the adsorption isotherms by Langmuir model reveals that the adsorption process belongs to the single layer adsorption.The adsorption thermodynamics analysis confirms that the adsorption of Pb（Ⅱ）on BC and MCC-BC is a spontaneous and endothermic process.The adsorption mechanisms are summarized as the chemical precipitation of Ca_xPb_（10-x）（PO4）₆（OH）₂ via ion exchange of Ca（Ⅱ）and Pb（Ⅱ）,accompanied by the coordination of Pb（Ⅱ）with the hydroxyl groups.MCC-BC particle was prepared by granulation,the optimum conditions for granulation are as follow:binder polyvinyl butyral（PVB）,the mixing mass ratio（PVB:MCC-BC:H₂O）4:10:10,The stability time of the particles in water is up to 40 hours.The effects of bed depths,initial concentration and flow rate on the adsorption performance of MCC-BC particles were studied through dynamic adsorption experiments,the penetration time,depletion time,and removal rate increased with the increase of bed depths,and decreased with the increase of initial concentration and flow rate.The equilibrium adsorption capacity also decreased with the increase of bed depths and flow rate,and increased with the increase of initial heavy metal ion concentration.Moreover,the dynamic adsorption process by MCC-BC can be well fitted by Thomas model,which provides important parameters for the dynamic adsorption design of the bone char adsorbent.