Citric Acid Enhanced Copper Removal by a Novel Multi-amines Decorated Resin.

Chen Ling,Xiaopeng Zhang,Yanhong Zhang,Zhiguo Pei,Lirong Zheng,Aimin Li,Baoshan Xing,Jing Zhang,Mengmeng Wei,Fuqiang Liu

doi:10.1038/srep09944

Abstract

Cu removal by a novel multi-amines decorated resin (PAMD) from wastewater in the absence or presence of citric acid (CA) was examined. Adsorption capacity of Cu onto PAMD markedly increased by 186% to 5.07 mmol/g in the presence of CA, up to 7 times of that onto four commercial resins under the same conditions. Preloaded and kinetic studies demonstrated adsorption of [Cu-CA] complex instead of CA site-bridging and variations of adsorbate species were qualitatively illustrated. The interaction configuration was further studied with ESI-MS, FTIR, XPS and XANES characterizations. The large enhancement of Cu adsorption in Cu-CA bi-solutes systems was attributed to mechanism change from single-site to dual-sites interaction in which cationic or neutral Cu species (Cu2+ and CuHL0) coordinated with neutral amine sites and anionic complex species (CuL− and Cu2L22−) directly interacted with protonated amine sites via electrostatic attraction, and the ratio of the two interactions was approximately 0.5 for the equimolar bi-solutes system. Moreover, commonly coexisting ions in wastewaters had no obvious effect on the superior performance of PAMD. Also, Cu and CA could be recovered completely with HCl. Therefore, PAMD has a great potential to efficiently remove heavy metal ions from wastewaters in the presence of organic acids.

Highlights

In the past years, many kinds of adsorbents were developed but suffered the following drawbacks: (1) OAs markedly suppressed HMIs adsorption due to either competing for the same adsorption sites or forming complex species with lower adsorption affinity[9,15]; (2) HMIs was hardly adsorbed from wastewater without the presence of high load of OAs16; and (3) application of soil- and bio-materials was much restricted because of their low capacity, poor mechanical strength or unsatisfactory recyclability[15,17,18,19]
We hypothesize that HMIs adsorption by amine adsorbents in HMIs-OAs bi-solutes systems is driven by hybrid mechanisms of both coordination and electrostatic attraction, in which HMIs in cationic or neutral species coordinate with neutral amine sites and anionic complex species directly interact with protonated amine sites
Cu species was investigated by theoretical calculation and Electrospray ionization mass spectra (ESI-MS)

Summary

Introduction

Many kinds of adsorbents were developed but suffered the following drawbacks: (1) OAs markedly suppressed HMIs adsorption due to either competing for the same adsorption sites or forming complex species with lower adsorption affinity[9,15]; (2) HMIs was hardly adsorbed from wastewater without the presence of high load of OAs16; and (3) application of soil- and bio-materials was much restricted because of their low capacity, poor mechanical strength or unsatisfactory recyclability[15,17,18,19]. Markton et al.[22] proposed two mechanisms: first, PEI competitively bound Cu from anionic Cu-citrate complex along with the release of citrate ligands; second, protonated PEI binds anionic citrate to form a PEI–citrate complex and excess carboxylic groups in PEI-citrate complex could bind additional Cu. the aim of this study is to develop a new amine decorated adsorbent possessing high capacity to HMIs regardless of the presence of OAs or not, and futher explore the interaction mechanisms between HMIs, OAs and the adsorbent. We hypothesize that HMIs adsorption by amine adsorbents in HMIs-OAs bi-solutes systems is driven by hybrid mechanisms of both coordination and electrostatic attraction, in which HMIs in cationic or neutral species coordinate with neutral amine sites and anionic complex species directly interact with protonated amine sites. Electrospray ionization mass spectra (ESI-MS) of the aqueous phase, Fourier Transform Infrared Spectra (FTIR), X-ray Photoelectron Spectra (XPS) and X-ray absorption near edge structure spectra (XANES) of the resin phase were used to further examine the mechanisms of Cu adsorption in the absence and presence of CA

Objectives

Methods

Results

Conclusion