| With the rapid development of industrialization and urbanization, more and moreheavy metals are transferred into the natural water and soil，and the heavy metalpollution will cause a great harm to the environment and humans. Biochars derivedfrom low-cost agricultural wastes are proven to be promising for its extensive, low-costand effective adsorption capacity. Nevertheless, the method of chemical modificationfor the biochars in order to improve their adsorption capacity are facing a risk ofsecondary pollution, so it is necessary to develop a method of modification that isefficient, environmentally friendly, and easy to operate.In this paper, pine wood char（PWC）,bamboo char（BC）and activated carbon（AC）was used to study the feasibility of modification by ultraviolet radiation(UV-R),and the effects of UV-R were investigated. The mechanism of modification by UV-Rwas discussed through elemental analysis, functional groups on the surface, the specificsurface area and pore structure, and other characterization of the carbon materials beforeand after modification. Based on this, further study was designed to test the effect forthe removal of Pb2+、Cd2+in the simulated wastewater with the modified adsorbents.Finally, several important factors in adsorption process for Pb2+、Cd2+with the modifiedadsorbents was discussed, such as reaction time, initial pH value of solution, initialconcentration of heavy metal ions and temperature. The adsorption kinetics andisotherm models had been analyzed for a preliminary study of adsorption mechanism.Following conclusions were drawn in this study.1) The modification by UV-R can improve the adsorption properties of carbonmaterials, especially the biochars, that is mean UV-R can be served as an effectivemodification for biocars. The optimum parameters of the modification by UV-R are asfollows: radiation wavelength365nm (UVA),16h,60mm between the sample and tube.Further significant analysis shows that the factor of distance is more significant than thefactor of time.2) The modification by UV-R not only reduce the pH value and the content ofcarbon, hydrogen, nitrogen, but also improve the CEC, the specific surface area, oxygencontent, and the oxygen functional groups, such as carboxyl group, a hydroxyl and soon. Meanwhile, compared to the chars before modification, the chars after modificationare better hydrophilic and more uniform pore structure. 3) Compared to the chars before modification, the chars, especially the biochars,after modification have a bigger capacity for the adsorption of Pb2+, Cd2+in thewastewater. In our experimental conditions, the maximum adsorption capacity for theremoval of Pb2+increased a amount of135.98percent, however, only25.34percent forCd2+. There is an order for the removal of Pb2+, Cd2+among the carbon materials beforeand after modification, and the order is Pb2+: MPWC> MAC> AC> MBC> PWC> BC>Cd2+: MAC> MPWC> PWC> AC> MBC> BC.(4) The optimum initial pH value of the carbon materials modified for Pb2+is4.0to5.0, while the optimum pH value for Cd2+is complicated. The optimum initial pHvalue for Cd2+is5.0for MPWC, and6.0for MBC.5) The kinetics of the process for the removal of Pb2+,Cd2+could be well describedby pseudo-second-order kinetic model, which means the adsorption of Pb2+, Cd2+bycarbon materials modified is chemical adsorption. For chemical adsorption, theabsorption rate is controlled by the outer membrane diffusion firstly, and by the innermembrane diffusion at last.6) The equilibrium adsorption data of the process for Pb2+could be well describedby Langmuir. However, For the bamboo char（BC）modified, the equilibrium adsorptionfor Cd2+could be well described by Freundlich. |
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