Preparation Of New Chelating Nanofiber Membrane As Adsorbent For Removal Of Cu²⁺and Cd²⁺from Water

In recent years,industries such as mining,smelting,pesticide have been developing rapidly in China.However,the absence of appropriate management and supervision indirectly leaded to the heavy metal pollution accidents occurring frequently.Many methods were used to treat heavy metal wastewater including coagulation,chemical precipitation method,electrochemical method,membrane separation and adsorption.Among these technologies,chelating fibers is considered as an efficient adsorbent to remove heavy metal ions from water due to its high selective adsorption capacity and easy regeneration.In this paper,new PAN nanofiber was prepared by electrospinning and its diameter was about 100 nm.Then amidoxime chelating fiber PAN-AM was synthesized by chemical modification in hydroxylamine hydrochloride aqueous solution.The adsorption behavior and mechanism of PAN-AM on heavy metal ions(Cu2+and Cd2+)were studied.The adsorption-desorption performance was investigated,and the effect of pH value,the coexistence of alkaline earth metal ions and natural organic matter on the adsorption performance were studied.At last,the membrane filtration adsorption process is simulated.The result can provide theoretical guidance for the application of PAN-AM in wastewater treatment.The main results are as follows:(1)PAN nanofiber membranes are prepared by electrostatic spinning method.After chemical modification of amidoxime,chelating fiber PAN-AM was successfully synthesized.Optimum reaction conditions were confirmed as:pH=7.0,T=60?,Time=2h,and concentration of hydroxylamine hydrochloride solution=4g/100mL.SEM,EA and FT-IR analysis were used to characterize PAN-AM.The BET specific surface area of PAN-AM was 75.6m2/g.(2)The adsorption kinetics curves indicated that the adsorption of heavy metal ions onto PAN-AM could reach equilibrium in 80 minutes.Within the nitial 25 min,more than 50%of the equlibrilium adsorption capacity was reached.Both the pseudo-first-order kinetic and pseudo-second-order kinetic equations could fit the kinetic adsorption curves well,suggesting both film diffusion and intra-particl diffusion process as the rate-limiting steps of adsorption in solution.Langmuir equation could fit adsorption isotherms well,which indicated that maximum monolayer adsorption capacity of Cu2+and Cd2+were 153.09mg/g and 269.12mg/g,respectively.(3)The adsorption thermodynamic parameters indicated that adsorption process was an endothermic and spontaneous process which was propelled by entropy.XPS analysis indicated that 'N' and 'O' chelated heavy metal ion.Both 0.1 M hydrochloric acid solution and 0.1 M EDTA solution could be used as eluant to desorb heavy metal ions from PAN-AM.After continuous adsorption and desorption for 5 cycles,the adsorption capacity and desorption rate of PAN-AM for heavy metal ions still maintained 80%and 90%,respectively.(4)At pH 4.0,the adsorption capacity of Cu2+and Cd2+ by PAN-AM fiber was the highest.As the temperature increased,the adsorption capacity of Cu2+and Cd2+increased.The effect of Ca2+on adsorption depends on the concentration of Ca2+.Low concentration of Ca2+showed slight adverse effect on Cu2+and Cd2+removal.When the concentration of Ca2+increased to 10mmol/L,the adsorption capacity of PAN-AM fiber decreased 30%.The natural organic matters had no significant effect on adsorption of metal ions by PAN-AM.(5)The membrane filtration experiment was based on PAN-AM fiber.Three pieces of PAN-AM membrane were used in series as filters.The influent rate was 4mL/min.The initial concentration of Cu2+and Cd2+were 50mg/L and 100mgL,respectively.The breakthrough point appeared at 100min.Thomas model can fit the adsorption process well.We can predict the breakthrough curves by the Thomas model.