Characterization Of The Adsorption Behaviour Of Aqueous As(Ⅲ) And Cd(Ⅱ) Ions On Nanoparticles Of Zero-valent Iron

Recent years, heavy metal pollution caused by arsenic and cadmium frequentlyoccured with the development of industry. Nano zero-valent iron(NZVI) has beendeveloped as an efficient absorbent materials to treat various heavy metals fromcontaminated water which has not been widely used in our country. On this ocassion,it is necessary to investigate the adsorption property of laboratory-synthesized NZVIfor the remediation of As(III) and Cd(Ⅱ) based on the characteristic of pollution inChina and provides theoretical basis for the practical applications of NZVI.This study focuses on the synthesis of NZVI, characterization of the material andits application for the removal As(Ⅲ)and Cd(Ⅱ) ions under different experimentalconditions. Finally, the possible adsortiom mechanisms involved were discussed.The traditional liquid-phase reduction for preparation of NZVI was improved byinviting the polyvinylpyrrolidone K-30(PVP) as a kind of surfactant. In thisnew approach, no mechanical agitation was needed. TEM results showed theaggregates of NZVI can reach to several micrometers in length but less than100nm indiameter. The iron particles were enclosed by a layer of oxide film that is less than10nm, demonstrated that the NZVI possess a core-shell structure. BET results indicatethe specific surface area of the NZVI was20.3159m2/g.This study provides comprehensive investigation about the effects of initial metalconcentration, initial pH of solution, dose of NZVI, negative ion and competing ionson the absorption efficiency of NZVI. Results showed lower initial metalconcentration, higher dose of NZVI and lower initial pH(if for Cd(Ⅱ), higher) ofsolution can stimulate the adsorption reaction of As(Ⅲ). PO43-、CO32-、SO42-andH2PO4-had a similar inhibitory effect on the reaction between As(Ⅲ) and NZVI, butfor Cd(Ⅱ), the HCO3-and PO43-can promote the adsorption process. Cu(Ⅱ)、Pb(Ⅱ)、Cr(Ⅲ) and Zn(Ⅱ) had a significant impact on the adsorption of Cd(Ⅱ) but onlyhad marginal effect on that of As(Ⅲ). Three factors and three levels orthogonalexperiments were employed to find out the dominant factor among the effects ofinitial metal concentration, initial pH of solution and dose of NZVI that affect theremoval rate of As(Ⅲ)and Cd(Ⅱ) by NZVI. Based on the range values the initial pHof the solution was found to be the most significant factor. TEM、XRD、desorption experiment、simulation results and the correlation between adsorption efficiency ofdifferent metals by NZVI and eduction potential suggested the adsorptionmechanism to be chemisorption.The adsorption isotherm data could be well described by the Langmuir as well asFreundlich equations. The data of As(Ⅲ) fitted the Langmuir equation better and thatof Cd(Ⅱ) fitted the Freundlich equation better. The maximum As(III) and Cd(Ⅱ)adsorption capacity in batch experiments calculated by adsorption isotherm were11.586mg/g and153.9621mg/g.