Selective adsorption and separation of chromium (VI) on the magnetic iron–nickel oxide from waste nickel liquid
Introduction
The increase of hexavalent chromium in the water system has resulted in more stringent effect on the environment from various engineering processes in the recent years. The hexavalent chromium is carcinogenic and mutagenic as a priority list of pollutants, which irritates plant and animal tissues even in small quantities; this is a serious problem worldwide. Many researchers studying the chromium removal have reported in over 30 papers of international journals within 5 years. The conventional treatment process of wastewater is the chemical reduction using ferrous and/or other reduction agents, within subsequent pH is adjustment to precipitate the Cr (III) ions. The most disadvantage is the production of large numbers of chemical sludge during this process, which could generate secondary waste residual that has been considered undesirable due to poor meeting standards of US EPA [1], according to which Cr (VI) is regulated to be discharged to surface water below 0.05 mg/L. Therefore, the removal and recovery of Cr (VI) from industrial wastewaters has been a research hot point. The distinct promising process such as the biosorption with the biomass [2], [3], [4], [5], [6], [7], [8], [9], [10] and adsorption with oxide and other low cost materials [11], [12], [13], [14], [15], [16], [17] was reported. Among these methods, the magnetic particle is one alternative method used for the removal of chromium ions due to the easy separation by the extracting magnetic field in the recent papers [18], [19], [20].
Generally, actual industrial wastewater was produced by mineral engineering, metallurgy process and electroplating which contains many ions together and different ions will have interaction effect on the uptake during adsorption process. Despite, there has been extensive study of the sorption of multi-metal components onto various kinds of bio/adsorbents, such as in bi-system of Cr (VI)–Ni (II), Cr (VI)–Fe (III), Cr (VI)–Cu (II) and Cr-SO42− oxides system [1], [5], [6], [7], [11], [16]. However, the selectivity for the chromium and reversibility of biomass were not very good because there are organic groups not only binding to hexavalent chromium only and but also absorbing to others heavy metal ions. In addition, the Cr (VI) ion was easily or spontaneously reduced to Cr (III) by the same organic carbon owing to the high reduction potential values (above +1.3 V) of Cr (VI) [7], [8], [9]. Therefore, it may affect on the recovery adsorption performance. At present, there is no more information of selective adsorption hexavalent chromium from the binary system of Cr (VI) and Ni (II) in the literature. In practice, pollution with Cr (VI) and Ni (II) waste liquid is frequently encountered together, while there is higher total dissolved substance (TDS) [1], [9]. In this study, selective adsorption of hexavalent chromium onto the iron–nickel oxide is proposed in order to improve the recycle/separation process in mixed solution system. The presence of nickel ions in the adsorbent particle will improve the material magnetic characteristic and stability [21], [22], and it may result in the inhibition of nickel ions adsorption onto the magnetic material. The effect of ions strength on equilibrium performance presented with the Langmuir, Freundlich isotherms and Dubinin–Kaganer–Radushkevich (DKR) equation also in order to understand the in-depth adsorption behaviors and the mechanism was analyzed by FT-IR and energy spectra in this study.
Section snippets
Synthesis of adsorbent
In the laboratory iron–nickel oxide was prepared by the co-precipitation method [22]. 13.5 g FeCl3·6H2O and 7.27 g Ni(NO3)2·6 H2O were dissolved in 200 ml of deionized water with mechanical stirring, 2 mol/L NaOH was dropped into the above mixture under vigorous stirring and henna composite precipitates were formed, when pH reached 9.0. The sediments were filtrated and rinsed with copious quantities of deionized water and calcined to constant weight at 100 °C for 16 h. After that, the oxide was
Effect on the uptake from other ions
The effect on adsorption of chromium ions and plus one anionic as HPO42−, H2PO4−, NO3−, Cl−, F−, SO42− and cations such as Na+, K+, Ca2+, Mg2+, Cu2+, Ni2+, Cd2+ was studied. Some sites of magnetic particles were occupied by other ions at first that may reduce the removal efficiency of chromium. Results are presented in Fig. 1, where “None” means without others competitive ions and chromium only existed. There any date of removal percentage is average values by test 5 times. As can be seen the
Conclusions
The following conclusions can be made from this current study.
Synthetic iron–nickel oxide magnetic particle in co-sedimentation was suitable for selective adsorbing and recycling hexavalent chromium from the binary Cr (VI) and Ni (II) liquid in wastewater. The effect from coexisting ions is really weak, except from phosphate. Langmuir isotherm was employed successfully to describe adsorption equilibrium of Cr (VI) and the maximum adsorption capacity is about 30 mg/g. The ion exchange of HCrO4−
Acknowledgements
This work was supported by the Ministry of Education of China and NSFC (29777011) and the authors would like thank to the reviewers for their suggestions to improve this manuscript.
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