Study On Adsorption Of Heavy Metals In Water By Modified Vermiculite And Biochar

Heavy metal pollution of water body has brought great harm to the natural environment and human health,and caused great national economic losses.It is of great significance to develop new materials for pollution remediation and control.In this paper,the performance of a variety of modified vermiculite and biochar prepared for removal of heavy metal ions in water was investigated and the mechanism of removal of Cu(?)and Pb(?)in water was discussed.The specific studies are as follows:(1)Three different methods were used to prepare modified vermiculite and their adsorption properties were compared.The modified vermiculite coated with silica has the best adsorption effect with the maximum adsorption capacity of 22 mg·g-1 and the optimal pH value between 5 and 6.The results show that the adsorption process accords with the quasi second-order adsorption kinetic model and is a chemical adsorption process.The thermodynamic analysis shows that the adsorption process of Cu(?)by this material is a spontaneous endothermic reaction.(2)The vermiculite coated with silica was characterized through methods such as SEM(Scanning electron microscopy),TEM(transmission electron microscopy),XRD(X-ray diffraction)and Zeta potential.The characterization results show that the vermiculite coated by silica is still lamellar structure,but the coating of silica on vermiculite will make the sharp edge of vermiculite particles smooth,appearing different degrees of thickening,and increasing the proportion of SiO2 on the surface,which will affect the crystal structure of the material surface,but will not affect the zeta potential and electrical properties of vermiculite.(3)Amy lose and amylopectin were selected as the raw materials of biochar and different temperature intervals were set for the carbonization modification to produce the corresponding types of biochar.The adsorption experiments show that the amylose biochar prepared at 800? or above had strong adsorption performance.Then the biochar prepared at 850? was selected as the main research object,and the maximum adsorption capacity for Cu(II)and Pb(?)were 86 mg·g-1 and 83.3 mg·g-1 respectively.The kinetic results showed that the adsorption process conforms to the quasi second-order adsorption kinetic model,which is a chemical adsorption process.The thermodynamic analysis showed that the adsorption process of Cu(?)and Pb(?)by this material was spontaneous endothermic reaction,and the adsorption process was easily affected by temperature.(4)AMB(Amylose Biochar)was characterized through the methods of SEM,TEM,XRD,Zeta potential,and BET(Brun Auer-Emmett-Teller model).The characterization results showed that the porous and irregular shaped biochar was formed by the pyrolysis of starch particles after high-temperature carbonization.The higher the temperature,the higher the crystallinity of the lattice in the biochar and the weaker the stability of AMB in the dispersion system.With the increase of carbonization temperature,the specific surface area of AMB increased at first and then decreased.The results of TEM-EDX(TEM and energy dispersive X-ray)analyses showed that the distribution of Cu(?)concentration on the surface of AMB was highly consistent with that of oxygen,indicating that the adsorption of Cu(?)on the surface of AMB might be related to the oxygen functional groups on the surface of AMB.