三乙烯四胺固化单宁吸附剂制备及性能研究OACSTPCD

An amine-modified tannin adsorbent(TETA-TA)was prepared by Mannich reaction,in which triethylenetetramine(TETA)was used to cure tannin,and its preparation process was optimized by orthogonal experiment.The structure of TETA-TA was characterized by FT-IR,SEM and BET,and the adsorption properties of the adsorbent to Cd2+ and Pb2+ were investigated at different pH,different adsorption time and different initial concentrations of metal ions.The results of orthogonal experiment showed that,when the molar ratio of tannin to TETA to formaldehyde was 1∶2∶2.5,the reaction temperature was 80℃,the reaction time was 4 h and the dosage of acetic acid was 4%,the experiment had the best preparation conditions.The results of adsorption indicated that,the adsorption capacity for Cd2+ and Pb2+ greatly depended on the pH,and the optimal pH values for Cd2+ and Pb2+ were both 5.0.The adsorption of Cd2+ was rapid,which could quickly reach adsorption equilibrium within 60 min,but the adsorption of Pb2+ could continue for 24 h.The adsorption process of Cd2+ and Pb2+ by TETA-TA conformed to the pseudo-second-order kinetic model,which was a chemical adsorption process.Higher initial concentrations of metal ions could lead to higher equilibrium adsorption capacity.The adsorption isotherm of Cd2+ could be well described by Langmuir equation(R2=0.995),and the theoretical maximum adsorption capacity was 150.41 mg/g.The adsorption isotherm of Pb2+ could be well fitted with Sips equation,and the theoretical maximum adsorption capacity was 210.45 mg/g.The main adsorption mechanism for Pb2+was speculated to be chelation and redox reaction between Pb2+ and hydroxyl/amine groups on the surface of the adsorbent,which were accompanied with ion exchange and electrostatic adsorption.It was also found that when more than one kind of metal ions coexisted in aqueous solution,the equilibrium adsorption capacity for each was not affected by others,implying that the TETA-TA adsorbent was effective in simultaneous removal of these ions.The test results of regeneration and reusability indicated that the TETA-TA adsorbent was suitable for repeated use for more than five times.