Competitive adsorption and mechanism of hexahydroxy metallic system by aminated solution-blown polyacrylonitrile micro/nanofibers

Huiqing Lou,Xiangwei Feng,Siyu Li,Xianzhong Cao

doi:10.2166/wpt.2021.084

Abstract

AbstractAdsorptive properties for Cd(II), Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) onto amidoxime-functionalized polyacrylonitrile (APAN) micro/nanofibers were systematically investigated in a hexahydroxy metallic solution system using batch experiments. The interactive effect of multi-metal ions in multi- metal systems was antagonistic in nature, and the adsorption capacity in a multi-metal system was lower than that in a single-metal system. The Langmuir isotherm model could explain respectively the isotherm and kinetic experimental data for the hexahydroxy metallic system with much satisfaction. The maximum adsorption capacity in hexahydroxy metallic for Cd(II), Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) was calculated to be 98 mg/L, 158 mg/L, 80 mg/L, 76, 312 and 58 mg/L individually. The APAN micro/nanofibers possessed good selectivity toward Pb(II) and Cr(III), over Cd(II), Cu(II), Ni(II), and Zn(II), having the highest selectivity coefficients at 17.52 and 6.07 in the test range. The five adsorption-desorption cycle experiments exhibited that APAN micro/nanofibers adsorbent are readily reusable, and have potential for heavy metal removal from wastewater. The adsorption behavior in multi-metal systems was shown to be complex, including surface complexation, antagonistic competition and displacement reactions. The diversity and selectivity in metal ion adsorption onto the micro/nanofibers relate mainly to the stability constants, and the microscopic coupling mechanism between the heavy metal ions and the functional groups on the fiber surface. This interaction mechanism between the favorable component and other metal ions could contribute significantly to the direct displacement impact illustrated schematically.

Highlights

Heavy metals are among the most important pollutants in source and treated waters, and are becoming a severe public health problem
Modified Langmuir isotherm model successfully fitted the competitive adsorption of Cd(II), Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) onto amidoxime-functionalized polyacrylonitrile (APAN) micro/nanofibers, and the maximal adsorption capacities for Cd(II), Cr(III), Cu(II), Ni(II), Pb(II), and Zn(II) were 98, 158, 80, 76, 312 and 58 mg/g, respectively
The distribution coefficients and selectivity coefficients of Pb(II) and Cr(III) were higher than whose of Cd(II), Cu(II), Ni(II) and Zn(II) at initial concentrations ranging from 20 to 200 mg/L, which indicated that APAN micro/nanofibers had higher selectivity for Pb(II) and Cr(III) in the multi-metal system

Summary

Introduction

Heavy metals are among the most important pollutants in source and treated waters, and are becoming a severe public health problem. Special attention should be given to heavy metal pollution – such as Cd, Cr, Pb, Ni, Zn and Cu – which are the commonest in industrial wastewater and pose serious threats to ecological systems and public health, because of their high toxicity, and non-biodegradable and carcinogenic properties even at very low concentrations (Saeed et al 2008; Kampalanonwat & Supaphol 2010; Li et al 2011; Neghlani et al 2011; Ihsanullah et al 2016). Among the modified adsorbents, chelating polymer fibers, with one or more reactive functional groups containing O, N, S and P donor atoms and extensive structural diversity, are capable of forming stable complexes with metal ions, and induce large adsorption capacity, high selectivity, and excellent mechanical properties as well as easy recovery

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