Study Of The Adsorption Performance And Mechanism On Re(?) By Different Types And Alkyl Chain Lengths Aminated Chitosan

Rhenium,as one of the scattered metals,has been widely used in the field of petroleum industry,national defence and catalyst industries.Due to its high price,rare resource and scattered distribution,separation and recovery from secondary resources have been broadly acceptance and popularity.It is an environmental friendly and efficient method for the adsorption of rhenium,an oxygen-contaning anionic pollutant,by the use of aminated chitosan.Thus,several aminated chitosan adsorbents with primary,secondary,tertiary and quaternary amines and different lengths of carbon chain were prepared in this work.The physicochemical characteristic and adsorption performance were studied.The adsorption behavior and mechanism towards Re?VII?were investigated through the experimental analysis and quantum chemistry calculation.In this study,chitosan?CS?modified by ethylamine?EA?,diethylamine?DEA?,triethylamine?TEA?,n-octylamine?NOA?,di-n-octylamine?DNOA?and tri-n-octylamine?TNOA?were synthesized as well as a bare one only synthesized by epichlorohydrin?ECH?.The optimum modified pH was 5.The prepared aminated polymers were characterized by SEM,BET,FTIR and potentiometric titration.Morphological details of the sorbents were examined by SEM studies,which shown all the surfaces were porous and distributed differently.The BET surface area were decreased in the order of CS-NOA>CS-EA>CS-DNOA>CS-DEA>CS-TNOA>CS-TEA>CS-ECH;the pK_a were in the order of CS-NOA>CS-DNOA>CS-EA>CS-DEA>CS-TNOA>CS-TEA>CS-ECH.The adsorption perfomances of rhenium including adsorption isotherms,kinetics,selectivity and regeneration were investigated.Compared with the Freundlich model,the Langmuir model represented a better fit of experimental data.The maximum adsorption capacity?q_m?decreased in the order of CS-NOA(937.2 mg g^-1)>CS-DNOA(846.1 mg g^-1)>CS-EA(681.6 mg g^-1)>CS-TNOA(635.4 mg g^-1)>CS-DEA(609.6 mg g^-1)>CS-TEA(602.1 mg g^-1)>CS-ECH(574.2 mg g^-1).The adsorption capacity decreased in the order of:secondary amines>tertiary amines>quanternary amines and the adsorbents with longer alkyl chains were more favorable for adsorption.Kinetic experiments revealed that sorption equilibrium couled reach within 400 min for all aminated chitosan.CS-NOA,CS-DNOA and CS-TNOA exhibited the selectivity for Re?VII?in the 800 mg L^-1 ternary-metal solution and multiple-metal solution.After five adsorption-desorption cycles,all of the adsorbents showed desorption efficiency over 90%.The results of FTIR and XPS analysis of polymer sorbents before adsorption,after adsorption and desorption indicated that electrostatic interaction was the main binding mechanism between the rhenium ions and protonated amines as well as the ion-exchange menchanism involved in the desorption process.According to the quantum chemical calculation study,the rhenium ions interacted with surfaces by electrostatic attraction and hydrogen bonding.Among them,rhenium ions mainly formed N-H…O hydrogen bond with primary,secondary and tertiary amines and formed C-H…O hydrogen bond with quaternary ammounium.Besides,the order of adsorption energy of ReO₄^-on aminated chitosan surfaces were as follows:secondary amines>tertiary amines>quanternary amines adsorbents.The adsorption energy increased with the alkyl chain length.