Synthesis Of Alkali Lignin Amine And Adsorbability On Heavy Metal Ions

Alkali-lignin was an important by-product of paper industry in China, and current utilization rate was low relatively. For the pollution problem of heavy metal ions derived from wastewater, this paper synthesized two adsorbents named glutamate-based lignin amine (GA-LA) and diethylene triamine-based lignin amine (DETA-LA) via Mannich reaction and immobilization respectively using wheat straw alkali-lignin from alkali pulping black liquor as experimental raw materials. Fourier transform infrared spectroscopy (FT-IR), Elemental analysis (EA) and Nuchear magnetic resonance spectroscopy (1H NMR) were adopted to analysis the structure characteristics of resulting products, and the effects of various factors on adsorbents preparation in synthesis process were investigated in detail. The adsorbability of GA-LA and DETA-LA on Cu2+,Pb2+,Cd2+ and As3+ was researched utilizing simulation wastewater samples of heavy metal ions, and possible adsorption mechanism was also discussed.Optimum synthesis condition of GA-LA based on nitrogen content of product as the main index was determined:n (lignin):n (formaldehyde):n (sodium glutamate)=1.0:1.5:1.0 (molar ratio), reaction temperature=70℃and reaction time=4.0h, and the nitrogen content of GA-LA was 2.62%(quality ratio) according to the condition described above, and FT-IR analysis indicated that glutamate have been grafted onto lignin.The adsorbability of GA-LA on Cu2+,Pb2+,Cd2+ and As3+ was tested in wastewater samples and the results revealed that GA-LA had super adsorption property on four ions. The adsorption capacity of Cu2+,Pb2+,Cd2+ and As3+ was 11.10mg/g,85.25mg/g,3.58mg/g and 3.51mg/g, respectively, and adsorption property was enhanced greatly compared with alkali-lignin which adsorbing capacity was 5.84mg/g,35.07mg/g,1.57mg/g and 9.36mg/g under the same condition. Adsorption equilibrium of Cu2+,Pb2+,Cd2+ and As3+ on GA-LA was reached at around 4.0h,3.0h,4.0h and 4.0h, and the adsorption capacity of Cu2+ and Pb2+ on GA-LA was lagerest when pH was adjusted to about 5.0. As reaction temperature increasing, adsorbing property of Cu2+ and Pb2+ reinforced, which illustrated adsorbing process was endothermic and chemical adsorption might occurred.Adsorption isotherm of Cu2+ and Pb2+ on GA-LA at 25℃conformed well with Langmuir adsorption equation, and monolayer chemisorption was the main adsorption means. Ligand might form between Cu2+ and N, O groups of glutamate introduced into lignin, and ion exchange might occur between Cu2+ and hydroxyl and carboxyl. On the adsorption of Pb2+, ion exchange of carboxyl may be the main way and the coordinate complex with amine also existed. DETA-LA was synthesized through epoxidation and chemical structure was characterized by FT-IR and 1H NMR, Optimum synthesis condition was determined:diethylene triamine, epoxy-lignin and NaOH (solvent, quality ratio was 16.7%) addition was 30.0mL, 1.0g and 30.0mL, respectively, reaction temperature=50℃and reaction time=3.0h, and nitrogen content of DETA-LA was 5.12%(quality ratio) measured by EA according to the condition depicted above.The adsorbability of DETA-LA on Cu2+,Pb2+,Cd2+ and As3+ was tested in wastewater samples adopting static adsorption experiment and the results displayed that DETA-LA had desirable adsorption property on four metal ions. Nitrogen content of DETA-LA had a positive correlation with adsorption capacity of Cu+ and Pb2+. The adsorption capacity of Cu2+,Pb2+,Cd2+ and As3+ was 40.59mg/g,161.97mg/g,5.37mg/g and 10.38mg/g at 25℃, respectively, and adsorption property increased significantly compared with alkali-lignin which adsorbing capacity was 5.84mg/g,35.07mg/g,1.57mg/g and 3.51mg/g under the same adsorbing condition. Rapid adsorption rate of DETA-LA on Cu2+ and Pb2+ was observed with 1.0～2.0h, and adsorption equilibrium was gained at about 3.0h and 4.0h, respectively. Adsorption equilibrium of Cd2+ and As3+ on DETA-LA was reached at both 4.0, which implied that the process of adsorption was short and easy to achieve adsorbing equilibrium. Adsorption capacity of DETA-LA on Pb2+ enhanced as pH inceased, and the largest capacity was gained when pH was adjusted to around 4.5, and ion exchange with amino may explain it.Adsorption isotherm of Cu2+ and Pb2+ on DETA-LA at 25℃and 35℃manifested that two curves fitted with Langmuir adsorption equation well, and and monolayer chemisorption was the main adsorption mode. On the adsorption of Cu2+, adsorption mainly depended on complex action because that complex ability of lone pair electron received by d orbit of Cu2+ strengthed. Cu2+ received lone pair electron from O groups of lignin and amino groups, and complex compound formed which leaded to high adsorption. FT-IR analysis of DETA-LA with Pb2+ adsorbed, and the influence of adsorbing time and pH on adsorption capacity testified that ion exchange might occurred between Pb2+ and amino groups, and the coordinate complex also existed.