Adsorption Of Several Metal Ions By Modified Biochar And Study Of The Mechanism

Water pollution is a major environmental problem worldwide.Heavy metals in water environment can cause adverse effects on human health and aquatic organisms,and the harm of heavy metals at low concentrations can not be underestimated.In recent years,biochar has shown great potential for remediation of polluted water,which has attracted extensive attention.Biochar is the pyrolysis product of biomass in low oxygen or no oxygen environment,which has the potential of soil conditioning and carbon fixation and adsorption capacity.Biochar can also contain tiny mineral particles of silica,calcium carbonate,calcite and potassium salt to facilitate the adsorption of metal ions through electrostatic reactions and ion exchange.In this reseach,pine sawdust and other pine wood residues were used as raw materials to prepare biochar,and the effects of traditional modification and economic and environmental modification methods were compared to explore the adsorption characteristics of biochar on heavy metals and trace elements in the solution.This research also study the relationship between the structure characteristics and adsorption capacity,and the adsorption characteristics and mechanism for metal elements in solution though different characterization methods.The main research contents and results are as follows:(1)Pine biochar(PW)was modified with H2O2,KMnO4 and Mn(CH3COO)2·4H2O.Through adsorption experiments and characterization,the removal capacity and mechanism of Pb2+ were investigated,and the contribution rates of various adsorption mechanisms(functional group complexation,mineral precipitation,ion exchange and π electron bonding)were quantitatively analyzed.The adsorption capacity of PW-H2O2,PW-Mn and PW-MnC to Pb in solution was 6,8.5 and 7.9 times of that of original biochar,and the contribution rates of surface complexation to the adsorption were 36.8%,31.6%,16.8%and 8.9%,respectively.The specific surface area of the two Mn-modified biochar was significantly increased,and MnO2 was formed on its surface.The contribution rate of cation exchange to the adsorption of Pb accounted for 74.6%and 87.5%of PW-Mn and PW-MnC adsorption.It is indicated that BC-MnC is a kind of material with excellent comprehensive performance for Pb removal from industrial waste water.(2)Pine biochar was modified with urea and thiourea.Adsorption experimentsand characterization were conducted to investigate the adsorption properties of Cu2+,Cd2+and Pb2+.The removal effect of heavy metal ions in mixed metal solutions(Pb2+,Cd2+and Cu2+)was studied,the competitive adsorption rules of the three metal ions were explored as well.The results demonstrated that the modified biochar can increase the-NH2 and C-S groups,and can expand the surface area of biochar by dissolving the coordination of metal inorganic compounds.The modification of thiourea makes the surface adsorption sites of Cu2+more effective than those of Pb2+or Cd2+.In the polymetallic system,the adsorption sequence of competitive adsorption is as follows:Pb2+>Cu2+>Cd2+,indicating that the removal of Cd2+in the polymetallic system has a more significant pH effect.(3)Pine biochar was modified by KOH and CH3COOK.The adsorption effect of Pb2+in solution and the adsorption rule of mono-metal and polymetal systems under different pH conditions were investigated,and the adsorption mechanism was studied by characterization analysis.The results showed that the adsorption capacity of Pb2+by PW-CHK and PW-KOH reached 23.1 mg/g and 15.67 mg/g,respectively,which were 7 and 5 times of the original biochar adsorption capacity,respectively.The specific surface area of PW-CHK increased by 3.5 times and showed more surface functional groups(mainly carboxylate functional groups).The adsorption of trace elements Fe2+,Mn2+,Cu2+and Zn2+by biochar was investigated using PW-CHK as adsorbent.Compared with PW,the adsorption capacity of Fe2+,Mn2+,Cu2+and Zn2+by PW-CHK increased to different degrees,especially the adsorption capacity of Cu2+increased by 20 times.Pb2+and Cu2+were selectively adsorbed by PW-CHK.The Freundlich adsorption isotherm and the quasi-second-order kinetic equation fit the adsorption process well,indicating that the adsorption of Pb2+,Fe2+,Mn2+,Cu2+and Zn2+is mainly controlled by chemisorption.Furthermore,carbonate mineral precipitation and complexation with functional groups are also important mechanisms of Pb2+,Fe2+,Mn2+,Cu2+and Zn2+in PW-CHK adsorption solution.