Adsorption Performance Of Pb(?) And Cd(?) On Organically Modified Magnetic Bentonite

Heavy metal contamination has posed serious ecological and human health threats.Raw bentonite?RB?,an abundant and inexpensive clay adsorbent,can be successively modified with Fe₃O₄ and organic modifier to improve its adsorption performance,solid-liquid separation efficientcy and magnetic stability.In this study,magnetic bentonite?Fe₃O₄/bentonite,MB?was prepared first,and then the modifier carboxymethyl cellulose?CMC?and polyethyleneimine?PEI?were combined to form copolymers on MB surface,to obtain the modified organic magnetic bentonite?CMC and PEI modified MB,MB/CP?.The corresponding morphology and structure of MB/CP were characterized by a series of echniques including XPS,XRD,FT-IR,BET,VSM and SEM.Whereas,the adsorption performance of MB/CP was evaluated by choosing Pb???and Cd???as the target pollutants.Furthermore,the effects of adsorption time,initial pH value,initial concentration of heavy metal ions and coexistence of humic acid?HA?on the adsorption were also investigated.Moreover,the adsorption isotherm models and adsorption kinetic models were fitted,and the reusability efficiency of MB/CP was examined for 5 consecutive cycles.In addition,the main adsorption mechanism of MB/CP for Pb???and Cd???were proposed.The main outcomes of this study were as follows:?1?MB/CP contains elements such as Fe,C,N,Si,Al,O,H.et al.Moreover,the characteristic peaks for montmorillonite,Fe₃O₄ and quartz were exhibited in MB/CP XRD pattern,which suggested that Fe₃O₄ had been successfully loaded on MB and MB/CP.The corresponding magnetic saturation value of MB and MB/CP were 10.12 emu×g^?1 and 17.87 emu×g^?1,respectively,which indicated that quick solid-liquid separation could be achieved.The organic copolymer organic generated by the reaction of CMC can PEI could effectively modified the MB and which could prevent the corrosion and oxidation of Fe₃O₄ composition in MB.Consequently,the excellent magnetic saturation could be obtained,which would be beneical for efficient solid-liquid separation of MB/CP with the help of an external magnet field.Compared with RB and MB,the larger pore volume and average pore size were exhibited in MB/CP,which indicated the enhanced adsorption capability of MB/CP for heavy metals.?2?The adsorption experiment of Pb???and Cd???on MB/CP indicated that the adsorption of 200 mg×L^?1 Pb???and 100 mg×L^?1 Cd???on 1.0 g×L^?1MB/CP firstly quickly increased and then slowly attained equilibrium.The adsorption equilibrium time were 45 min and 30 min,corresponding the removal efficiency were 99%,respectively.The adsorption equilibrium time of200 mg×L^?11 Pb???adsorpted on RB and MB were 90 min?removal efficiency was 69%?and 120 min?removal efficiency was 59%?,which correspond to adsorption equilibrium time of 100 mg×L^?11 Cd???adsorpted on RB and MB were58 min?removal efficiency was 42%?and 120 min?removal efficiency was43%?,respectively.When the pH value was 1 to 7,as the increase of pH,the removal efficiency of Pb???and Cd???by RB and MB gradually increased.With the pH increased from 1 to 3,the removal efficiency of Pb???and Cd???by MB/CP significantly increased.In addition,the removal efficiency of Pb???and Cd???not exhibite significant changes at pH 3⁷.The removal efficiency of Pb???and Cd???can reach about 90%,which suggested that the MB/CP possessd stronger torlerance ability to the changes of pH.The coexistence of HA could enhance the adsorption efficiency of Pb???and Cd???on MB/CP than that of RB and MB.With the increase of HA concentration,the adsorption efficiency of Pb???on MB/CP decreased at first then attained the highest adsorption efficiency.Conversely,the adsorption of Cd???by three bentonite materials increased with the increase of HA concentration at first,then decreased slightly and then maintained a stable trend.The adsorption process of Pb???and Cd???on MB and MB/CP coincide with Langmuir isothermal model.The adsorption capacities of MB/CP for Pb???and Cd???were 760 mg×g^?1 and 470 mg×g^?1,respectively.Which were significantly higher than the adsorption efficiency of MB for Pb???(324 mg×g^?1)and Cd???(126 mg×g^?1).The adsorption process of Pb???and Cd???by MB and MB/CP was best fitted with quasi-second-order kinetics model implied that the adsorption process of heavy metals by MB and MB/CP was fast at first,then slowand finally stable.After five times recycles on adsorption-desorption,the removal efficiency of Pb???and Cd???remained above 90%suggested that the stronger stability was achieved in MB/CP and its recycling performance was more superior than that of RB and MB.?3?The main adsorption mechanisms of Pb???and Cd???on MB/CP included ion exchange,complexation,electrostatic attraction and pore diffusion.When the pH value was 1 to 3,the adsorption of Pb???and Cd???by MB/CP mainly depended on ion exchange.With the increase of pH value from 3 to 7,MB/CP gradually deprotonated and then Pb???and Cd???could complexation with functional groups such as—NH₂,—CH₃ belonged to the surface of MB/CP.Moreover,the electrostatic attraction occurred between on Pb???,Cd???and charged negative MB/CP.In conclusion,the MB/CP modified with organic modifier can effectively improve the adsorption properties of Pb???and Cd???,solid-liquid separation ability,magnetic stability and recycling performance,which exhibited promising application prospect in heavy metal wastewater treatment.