Studies On Capability And Mechanism Of Heavy Metal Ions Adsorption On Modified Silk

Using waste silk as raw materials and NaClO solution as modifier,the modified silk was produced by single-factor method and response surface analysis method.Both static adsorption and dynamic adsorption of Zn2+,Cu2+,Pb2+on modified silk were studied.The silk and modified silk were characterized to explore the mechanism of modified silk absorbing heavy metal ions.The main researched contents and conclusions were as follows:1.Silk modificationSilk was modified with NaClO solution by single-factor method.Using adsorption amount of heavy metal ions on modified silk as evaluation index,the influences of concentration of NaCIO solution,time,temperature and bath ratio on results of modification were investigated.The results showed as follows:The adsorption amount of heavy metal ion on modified silk was increaed with the increasing of concentration of NaCIO solution,time and bath ratio,but decreased with the rising of temperature.The concentration of NaCIO solution,time and bath ratio were determined as three significant factors for their big effects on modification results of silk.Modification conditions of silk were optimized by response surface analysis mothed.The experiment was designed by Box-Behnken to investigate the influences of concentration of NaCIO solution,time and bath ratio on results of modification.The results showed as follows:The concentration of NaCIO was the most significant factor,the bath ratio was second and the time was last one.The best modification process which under experimental conditions were that the concentration of NaClO solution was 2.4%,the modification time was 10 h and the bath ratio was 600 mL/g.2.The static adsorption of heavy metal ions on modified silkThe static adsorption experiments of Zn2+?Cu2+?Pb2+on modified silk were conducted to investigate the influences of the pH,adsorption time,initial concentration of heavy metal ions,temperature and coexisting ions on adsorption amount of silk.Some of the experimental data were fitted by isothermal adsorption model and adsorption kinetic model.The results showed as follows:The pH has a great influence on the adsorption of heavy metal ions on modified silk and the higher pH was better to adsorption.When pH was 7,the adsorption amount of Zn2+on modified silk was 13.48 mg/g,which was the biggest;when pH was 6,the adsorption amount of Cu2+,Pb2+ on modified silk were 17.175mg/g and 40.77 mg/g,which were the biggest.The static adsorptions of Zn2+?Cu2+?Pb2+ on modified silk were so fast that the adsorption amount could reach 90%of the balanced one in 30 mins,and the adsorption could reach balance just in 3 hours.All of the adsorption processes are endothermic and the adsorption amount increased with the rising of temperature.The adsorption isotherm fitted the Langmuir isothermal adsorption model better,and the adsorption kinetic fitted the Lagergren pseudo-second kinetic model better.The oexisting ions had negative influences on the adsorption of Zn2+?Cu2+?Pb2+ on modified silk and the adsorption amount varied with sorts and concentrations of the heavy metal ions.When the concentrations of anions such as SO42-?Cl?CH2COOH were 800 mg/L,the adsorption amount decreased to the 85%?90%of the original one;When the concentrations of cations such as K2+?Na2+?Ca2+?Mg2+were 800 mg/L,the adsorption amount decreased to the 60%?85%of the original one.3.Dynamic adsorption of heavy metal ions on modified silkThe dynamic adsorption experiments of Zn2+?Cu2+?Pb2+on modified silk were conducted to investigate the influences of the ratio of height to diameter,the initial concentrations of heavy metal ions and the flow speed of solution on breakthrough curve and adsorption amount of silk.The results showed as follows:With the increasing of the ratio of height to diameter,the penetration point of dynamic adsorption moved to right of the breakthrough curve and the penetration time extended,but moved to left of the breakthrough curve and the penetration time shortened with the increasing of the initial concentrations of heavy metal ions and the flow speed of solution.The adsorption amount of Zn2+?Cu2+?Pb2+on modified silk decreased with the increasing of the ratio of height to diameter,but added with the increasing of the initial concentrations of heavy metal ions and the flow speed of solution.4.The characterization of silk and modified silk and the research of adsorption mechanismThe silk and modified silk were characterized by the method of Scanning Electron Microscope(SEM)analysis,Fourier(FTIR)Infrared Spectroscopy analysis,Thermogravimetric(TG)analysis and X-ray diffraction analysis.The results showed as follows:After modified,the molecular structure of silk was not completely destroyed,but part of it ' s Peptide bond have been hydrolyzed and cut,which result to the adding of-OH,-NH3,the becoming rough of surface and the increasing of specific surface area.The silk had the better adsorption amount of Zn2+?Cu2+?Pb2+and it' s thermal stability increased after modified.What' s more,the addition of heavy metal ions could also increase thermal stability of modified silk but decrease its crystallization.