A Study On The Enhanced Adsorption Of Trace Antimony In Water By Ferric Oxide Loaded Biopolymer Adsorbent

China is a country of huge antimony production,and the problem of antimony pollution has become a more and more serious issue.The treatment of antimony pollution has attracted increasing attention in the world in recent years.The conventional water treatment methods may be effective for high concentration antimony waste water.However,with its discharge standards become more stringent,the conventional method is difficult to meet the requirement,especially for low concentration antimony removal.Therefore,it is urgent to develop the method that can effective remove trace amount of antimony in wastewater.In this paper,the biopolymer adsorbent?CS/CA-Fe?loaded with ferric oxide developed in our group was examined for the removal of different types of antimony in water,including the adsorption properties and mechanism.The surface properties of the adsorbents and their effect on the adsorption of antimony in water were investinged.The method of enhancing the adsorption of antimony by metal cation was also explored.In addition to the static adsorption,the adsorbent was packed into the adsorption column to simulate the treatment of antimony containing wastewater,under continuous flow condition and the parameters of dynamic adsorption column were investigated.The adsorption behaviors of the adsorbent to inorganic antimony?Sb???and Sb????in water,including the effect of solution pH and competitive ions,adsorption kinetics and thermodynamics,and the regeneration performance,were first studied.The results showed that with the increase of pH,the removal efficiency of Sb???decreased gradually,but that of Sb???was less affected.The experimental results with competitive ions of different valences showed that with the increase of valence and strength of the competitive ions,the adsorption of CS/CA-Fe for Sb???reduced gradually,but the adsorption for Sb???was not greatly affected.The regeneration experiments showed that 1M NaOH solution echieved effect regeneration of CS/CA-Fe after adsorption of Sb???;while the ethylene diamine tetraacetic acid disodium salt showed better regeneration for CS/CA-Fe after adsorption of Sb???with the concern of iron oxide leaching,the choice of 1M NaOH solution was selected for the regeneration effect,the regeneration rate of CS/CA-Fe adsorbed with Sb???and Sb???reached 54%and 95%,respectively.The adsorption kinetic study on the adsorption of two types of antimony by CS/CA-Fe showed that the results were better fitted by the pseudo-second order kinetic model.In further examination using the internal diffusion and Elovich model fitting for adsorption dynamics data,it showed that the whole adsorption process included three stages:external diffusion,boundary layer diffusion and intraporn diffusion.The adsorption rate was mainly controlled by external diffusion at pH4.At pH7.5,the adsorption rate of Sb???was mainly controlled by the diffusion inside the pore,and the adsorption rate reduced.The Langmuir model and Freundlish model both can be used to fit the two isotherms,but the regression coefficient of the Langmuir model was lower than that of the Freundlich model.At pH4.0 and 298K,the maximum adsorption capacity was40.13mg/g and 40.45mg/g respectively.The adsorption mechanisms for the two forms of antimony,were that CS/CA-Fe had electrostatic and complexing effects on Sb???,while complexation and oxidation on Sb???.The early research of the project group revealed that CS/CA-Fe has two functions of removing antimony,including electrostatic adsorption and chemical adsorption.In order to further explore the enhancing effect of electrostatic action on the adsorption performance,different metal cations on the surface properties of CS/CA-Fe and its adsorption properties to antimony were investigated in the second part of the study.Particularly,the system using the cation of Cu²⁺was studied in electric detail.The results showed that the introduction of different metal cations increased the surface potential of CS/CA-Fe and enhanced the adsorption efficiency of trace antimony in water.The enhancing effect of Cu²⁺was found to be most obvious,therefore Cu²⁺was selected for further study.From the results,it was found that the presence of Cu²⁺and Sb???at low concentration in the solution,the existence of Cu²⁺inhibited the increase of the solution pH,and thus enhanced the enrichment of Sb???on CS/CA-Fe and increased the adsorption capacity of CS/CA-Fe.The total adsorption capacity was Q_Sb+Cu>Q_Sb+Q_Cu.XPS analysis showed that the Cu²⁺in the solution was adsorbed to CS/CA-Fe surface quickly,formed a coordination bond with the amine group,which enhanced the surface potential and the adsorption capacity of the adsorbent to trace antimony.In summary,CS/CA-Fe was an effective adsorbent in the adsorption of trace antimony in wastewater,especially under acidic conditions.The iron oxides in the material had complexation effect on Sb???and Sb???,and the oxidation of Sb???to Sb???can promote the removal of antimony.When metal cation exists in the solution,it can provide an enhancing effect on the adsorbent,by improving the surface potential,to increase the total adsorption capacity to antimony in water solutions.