Competitive Removal Of Cd(?) And Pb(?) By Biochars:Performance And Mechanism

In recent years,many studies have been devoted to investigate the application of biochar for pollutants removal from aqueous solutions.Biochar is porous carbon material,which made by pyrolyzing biomass under the limited or no oxygen condition.The main properties of biochar are the following:high surface area with many functional groups and the developed porous structure.Biochar exhibits a great potential to efficiently tackle water contaminants considering the wide availability of feedstock and its low-cost and favorable physical/chemical surface characteristics.Three biochars converted from water hyacinth biomass at 300,450,and 600?,respectively were used to investigate the adsorption properties of Cd2+ and Pb2+.BET,XPS,FTIR and SEM were applied to analyze the physical and chemical properties of biochar.Experimental data were better fitted by pseudo-second-order kinetic equation and Langmuir isotherm model.Adsorption kinetics and isotherms indicated that the maximum adsorption capacity of Pb2+ was larger than that of Cd2+.The maximum adsorption capacities of Pb and Cd on 450? biochar were 129 mg g-1 and 75 mg g-1,respectively at 30?.Thermodynamic analysis indicated that these adasorption processes wer spontaneous and endothermic.In addition,the influence of background ionic strength on adsorption was studied at appropriate pH with the addition of different concentration of NaCl(0-1 mol L-1).The results demonstrated that adsorption capacities of biochar decreased with increasing the concentration of NaCl.The competitive adsorption mechanisms between Cd2+ and Pb2+ were also conducted.The adsorption process in the mixed solutions of two heavy metals(Cd2+and Pb2+)was more favorable for Pb2+.Further investigation about the characterization of biochars demonstrated that cation exchange,surface complexation,cation-? interaction and precipitation were the main mechanisms responsible for the heavy metal removal.In this study,competitive adsorption may also be explained by these mechanisms.These results are useful for the application of biochars in selective adsorption and in practical wastewater treatment.In conclusion,water hyacinth biochar can effectively remove Cd2+ and Pb2+from wastewater,and it is a great potential cost-effective adsorbent for water heavy metal pollutants.This study can lay the foundation on selective adsortption by biochar in wastewater which contained multiple pollutants.