Study On Adsorptive Removal Of Pb²⁺ And Congo Red Using Magnetic Chitosan Modified Diatomite

The magnetic chitosan modified diatomite composite,which can be rapidly separated from liquid,was synthesized by coprecipitation method using chitosan,diatomite and Fe₃O₄ as raw material.The new composite was characterized with SEM,XRD,VSM,FTIR and more.The optimum proportion of chitosan,diatomite and Fe₃O₄ was studied,and then the new composite was used in the treatment of lead wastewater and congo red wastewater.Its adsorption of Pb²⁺ and congo red was investigated under the condition of solution initial pH,adsorbent dosage,contact time,solution initial concentration and co-existing ions,as well as its regenerability.The adsorption kinetics and thermodynamics of Pb²⁺ and congo red adsorption by the composite was investigated,so did the possible adsorption mechanism in this study.The characterization results indicated that both chitosan and Fe₃O₄ were coated on the diatomite.The composite presented a coarser surface and a larger specific surface area.XRD results of composite showed one more Fe characteristic peak,while FTIR indicated the Fe-O stretching vibration and the protonation of amino group in all three substances.The composite had a saturation magnetization of 14.59emu/g,and it can be easily magnetically separated in the aqueous solut ion.The isoeletric point of the composite was 7.01.The optimum proportion of chitosan,diatomite and Fe₃O₄ was 0.5:10:2.5 in the preparation of the composite.The adsorption of Pb²⁺ by the composite indicated that the optimum pH was 5.When solution pH was 5,initial concentration was 10mg/L for 50 m L and adsorbent dosage was 0.5g,the adsorption efficiency could achieve up to 96.3%.Co-existing cations could inhibit the reaction and the interference followed: Mg²⁺ > Na⁺ > K⁺.The adsorption of congo red by the composite indicated that the optimum pH was also 5.And the adsorption efficiency could reach to 97.04% under the condition of initial pH at 5,initial concentration at 50mg/L for 50 m L and adsorbent dosage at 0.08 g.Co-existing anions could also inhibit the reaction and the interference followed: SO₄^2->Cl^->NO₃^-.Na OH was used as regenerant and after three times,the adsorption efficiency of Pb²⁺ and congo red was 44.76% and 56.13%,respectively.The adsorption kinetic indicated that the adso rption of Pb²⁺ and congo red both followed the pseudo-second-order kinetic model and reaction reached equ ilibrium within 540 min and 120 min,respectively.The adsorption thermodynamics indicated that adsorption of Pb²⁺ and congo red both followed the Langmuir adsorption isotherm model,and adsorption capacity increased with the rising of temperature.Thermodynamic parameters indicated that both adsorption process was endothermic and spontaneous.The study on adsorption mechanism revealed that the adsorption of Pb²⁺ and congo red by the composite was mainly con trolled by electrostatic attraction.The composite prepared in the experiment could adsorb Pb²⁺ and congo red in aqueous solution to some extent,and could also be rapidly magnetically separated from solution,thus having some practical value.