Investigation On RSM Optimization Of Amino-modified Chitosan And Its Adsorption Mechanism On Re(?)

Because of its high temperature resistance and strong catalytic performance,rhenium is used in aerospace,reforming catalysts,automobile exhaust gas purification and other fields,however rhenium is less distributed in natural minerals and its cost being mined is high.How to realize the recovery rhenium from the secondary resource shows a great research significance.In this work,an efficient and environmentally friendly aminated chitosan?NOA-CST?adsorption material was developed to adsorb ruthenium from an acidic multi-metal solution.The mechanism of Re???adsorption onto NOA-CST was explored through a series of sequential batch and column experiments and,characterization analyse.The grafting of amine groups on the surface of chitosan?CST?was affected by many factors.The results of single factor experiments showed that the dose of pre-crosslinker epichlorohydrin?ECH?,the dose of modifier n-octylamine,the dose of ECH used in the intermediate synthesis,intermediate synthesis pH and modification pH value were the key factors.Through the five-factor and three-level Box-Behnken design of Response Surface of Methodology,the interaction between each level and the influence of factors were simulated.The optimal preparation conditions for NOA-CST after model optimization were 0.63mL of pre-crosslinker ECH,2.10 mL of modifier n-octylamine,1.10 mL of ECH used in the intermediate synthesis,intermediate synthesis with pH 12.0 and,modified condition under pH 7.0.The adsorption capacity of Re???obtained by prepared NOA-CST under optimal conditions was verified as 187.83?±1.17?mg/g,which was similar to the predicted value of191.08 mg/g with 1.7%of relative error.Isothermal adsorption results showed that the Langmuir model was fitted better to describe Re???adsorption equilibrium.The maximum adsorption capacity was 747.11mg/g,which was much larger than that of unmodified chitosan?ECH-CST?with uptake of467.49 mg/g and many adsorbents in the literature.The kinetic adsorption result showed that the quasi-second-order kinetics could better describe the adsorption behavior of Re???on the surface of NOA-CST.In the competitive adsorption experiments,Re???could be selectively adsorbed onto NOA-CST from multi-metal solution in HCl or HCl-HNO₃system,however,Cu???and Zn???were barely adsorbed.The desorption efficient of Re???by 0.5M hydrochloric acid could be obtained over 95%.The adsorption mechanism was investigated by FTIR,XPS analyse,and the surface electrostatic potential energy of NOA-CST and atomic charge distribution obtained quantum chemical calculation based on density functional theory?DFT?.The FTIR and XPS analysis showed that amine group played a predominant role in the Re???adsorption onto NOA-CST,electrostatic potential energy and the atomic charge distribution on the surface of NOA-CST indicated a same result with FTIR and XPS analyse.The main adsorption mechanism was the electrostatic attraction bewteen Re???and the protonated amine group on the surface of NOA-CST in an acidic solution.The desorption mechanism was proposed to ion exchange,which meaned that the high concentration of chloride ions in the solution destroyed the force between NOA-CST and ReO₄^-.The experimental results of adsorption column experiments showed that the Thomas model fitted well with the adsorption breakthrough curve of Re???in the single ruthenium influent.After two or three cycles of regeneration experiments,the adsorption capacity of ruthenium in single ruthenium solution and synthetic wastewater remained above 400.00mg/g and 300.00 mg/g,respectively.The desorption curve using 0.5 M hydrochloric acid as eluent reached the maximum concentration factor of 45.0 and 21.8 within 30-40 min.Adsorption column experiments provided technical support for the further industrial-scale applications and,indicating the potential value of NOA-CST for industrial applications.