XANES evidence of molybdenum adsorption onto novel fabricated nano-magnetic CuFe2O4

doi:10.1016/j.cej.2014.01.084

Chemical Engineering Journal

Volume 244, 15 May 2014, Pages 343-349

https://doi.org/10.1016/j.cej.2014.01.084 Get rights and content

Highlights

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A technology for preparation of CuFe₂O₄ is developed from industrial sludge.
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The CuFe₂O₄ is effective in removing Mo from wastewater, groundwater and tap water.
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The K-edge XANES spectra show that Mo(VI) was the dominant species on CuFe₂O₄.
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The data implies that 0.001 N NaOH solution is sufficient for Mo desorption.
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The CuFe₂O₄ could be rapidly separated and recycled by a magnet in 20 s.

Abstract

An efficient Molybdenum (Mo) removal technology in aqueous solutions was developed for the first time using nano-magnetic CuFe₂O₄ manufactured from printed circuit board (PCB) industrial sludge. This nano-magnetic CuFe₂O₄ adsorbent displayed a nonlinear L-type isotherm that fitted well with the Langmuir isotherm, suggested limited adsorption sites and monolayer sorption on surface. The K-edge X-ray absorption near-edge structure (XANES) spectra demonstrated that Mo(VI) was the predominant oxidation species on nano-magnetic CuFe₂O₄ and the maximum adsorption capacity was found to be 30.58 mg g⁻¹ at pH 2.75. When pH became higher, more negative charges would occur at the surface of adsorbent and lead to more electric repulsion. Consequently, Mo adsorption was sharply reduced in alkaline condition. Importantly, these adsorbed Mo anions were replaced easily by OH⁻ ions in NaOH solution and showed huge potential for removal/concentration of Mo in industrial wastewater, groundwater, and tap water. This unique Mo separation technique can also be potentially applied for geochemical investigation in various natural aqueous solutions.

Graphical abstract

Introduction

Molybdenum (Mo) is a trace element which presents widely in nature and is required by the human body for many important biological and physiological processes [1], [2], [3]. The estimated daily demand of Mo in adults and older children is 75–250 μg per day [4], [5]. However, high concentration of Mo uptake may cause some health problems such as anemia, gout, digestive problems, growth retardation, bone deformities, and sterility [5].

Mo also plays an important role in industrial society and is economically important as a component of metal alloys, additive in stainless-steel, leather, anti-corrosive agent, rubber, catalyst, and fertilizer [5], [6], [7], [8], [9]. The growing production and usage of Mo represents a hazardous potential for increased release and distribution in the natural environments.

It was reported that Mo concentrations in surface waters are normally less than 5 μg L⁻¹ [2]. However, much higher concentrations (several tens μg L⁻¹ to mg L⁻¹ level) could be found in aquatic systems due to anthropogenic activities. For example, according to the effluent database of Environmental Protection Administration in Taiwan, the effluent Mo concentration in photo-electric industries range between 66 and 260 μg Mo L⁻¹. If there is no suitable method for treating the Mo anthropogenic contamination, human health and aquatic ecosystems will be threatened. An effective and economic technology for Mo removal from water systems has consequently become an important issue.

Adsorption could be considered as a fast, efficient, and economical method for removing trace metals from water. Many literatures have been focused on the removal of most toxic heavy metals such as Cd, Cr, Cu, Pb, Hg [10], [11], [12], [13], [14]. However, the investigation of Mo removal from water is still paucity. It should be mentioned that Mo is the most concentrated trace metal in seawater, in part owing to its stability and weak adsorption behavior [15]. Thus, to find a fast and efficient adsorbent for removing Mo from water is a critical issue.

Several adsorbents have been studied for their removal feasibility of Mo from water. For instance, EI-Moselhy et al. investigated the removal of Mo(VI) from wastewater using carminic acid modified anion exchanger. The result showed that the maximum Langmuir adsorption capacity was found to be 13.5 mg Mo(VI) g⁻¹ of the adsorbent [15]. Lian et al. reported that the sulfuric acid modified cinder can remove Mo(VI) with a maximum adsorption capacity of 10.8 mg Mo(VI) g⁻¹ adsorbent at pH between 4.0 and 6.0 [16]. However, the mentioned adsorbents showed only low Mo adsorption capacity in water system. Besides, the high price of these adsorbents may obstruct their development when performing in the actual industrial plants.

Nano-magnetic CuFe₂O₄, with the spinel structure, has a cubic close-packed arrangement of the oxygen ions with Cu²⁺ and Fe³⁺ ions at two different crystallographic sites [17]. It has been reported that CuFe₂O₄ has the potential to remove some hazardous materials (As, Cd, acid orange II) from water [18], [19], [20]. Nevertheless, the cost of CuFe₂O₄ synthesized from sol–gel method [21], auto-combustion [22], or co-precipitation [23] is still high because the raw materials used to produce CuFe₂O₄ are adopted from the pure chemicals. If the raw materials used to produce CuFe₂O₄ can be replaced by industrial sludge, the cost of CuFe₂O₄ would be reduced dramatically.

This study aims to investigate the Mo removal process using the nano-magnetic CuFe₂O₄, which is recycled from the sludge in printed circuit board (PCB) industry. Our previous study has successfully recycled copper powder from PCB sludge by combination of acid leaching and chemical exchange [24]. After these two combinations of technologies, ferrite process (FP) has been conducted not only to make sure the supernatant but also the sludge can meet the environmental rules.

It should be noticed that FP is used to treat wastewater containing heavy metals for many years [25], [26], [27], [28], [29]. The product generated from FP such as Fe₃O₄, is a magnetic iron oxide containing Fe²⁺ and Fe³⁺ in the spinel structure. It can be synthesized through the reaction expressed by Eq. (1) [29], [30]. $3 {Fe}^{2 +} + 6 {OH}^{-} + 1 / 2 O_{2} \to {Fe}_{3} O_{4} + 3 H_{2} O$

When heavy metal ions coexist with Fe²⁺, they can be incorporated into the structure through co-precipitation [29], [30]. The principle of FP to catch heavy metals is presented in Eq. (2). $x M^{2 +} + (3 - x) {Fe}^{2 +} + 6 {OH}^{-} + 1 / 2 O_{2} \to M_{x} {Fe}_{(3 - x)} O_{4} + 3 H_{2} O$

The sludge (M_xFe₍₃₋_x₎O₄) generated from ferrite process thus is regarded as a novel adsorbent and is used for testing its capability for Mo removal efficiency.

A series of systematic experiments were designed to evaluate the feasibility of Mo removal from aqueous solutions by nano-magnetic CuFe₂O₄ under various conditions. The basic physical/chemical properties inclusive of adsorbent crystalline phase, density, saturation magnetization, point of zero charge, specific surface area, and primary particle size were carefully examined. The adsorption kinetics and isotherms of Mo on nano-magnetic CuFe₂O₄ were also calculated and discussed. Furthermore, Mo K-edge X-ray absorption near edge spectra (XANES) were used to realize the oxidation state of Mo after the adsorption of nano-magnetic CuFe₂O₄. The information gained here demonstrates the great potential for developing an effective adsorbent for uptake Mo using nano-magnetic CuFe₂O₄.

Section snippets

Preparation of nano-magnetic CuFe₂O₄

The preparation of nano-magnetic CuFe₂O₄ was followed as our earlier study by a combination of acid leaching, chemical exchange and ferrite process [24]. Briefly, acid leaching was conducted using 500 g of the industrial sludge as 10 L diluted sulfuric acid was added for extracting Cu from solids. Fe powder was used as sacrificed metal to substitute Cu²⁺ in the liquids during chemical exchange reaction. To ensure the supernatant fulfill the effluent standards, ferrite process was performed after

Basic properties of the adsorbent

The physical/chemical properties of the adsorbent were examined using standard procedures and the results were displayed in Table 1 and Fig. S1. Briefly, SEM image of the synthesized adsorbent presents numerous particles are in almost spherical shape and the primary particle size ranged from 20 to 120 nm, with a mean particle size of 60 nm (Fig. S1a). The density and the point of zero charge (PZC) of the manufactured adsorbent were found to be around 5.2 g cm⁻³ and 7.3 (Fig. S1b). The BET surface

Conclusion

The evaluated nano-magnetic CuFe₂O₄ manufactured from industrial sludge is fast and effective for Mo removal in solutions. The optimum pH for maximum removal is 2.75 at the pH range of 2.75–11.02. These nano-particles were identified as CuFe₂O₄ in spinel structure and their SEM morphology showed that the primary particle size fall in a range between 20 and 120 nm. Their adsorption behavior followed Langmuir and Freundlich isotherm models and the Langmuir adsorption capacity was found to be 30.58

Acknowledgments

This research is financially supported by MOE and NCKU to CFY. The authors would like to thank Prof. Jiang Wei-Teh and Mr. Lee Po-Shu for their support on XRD analysis under the project of NSC1002116M006002. We also thank NSRRC staff for useful discussions and experimental support.

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XANES evidence of molybdenum adsorption onto novel fabricated nano-magnetic CuFe2O4

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Preparation of nano-magnetic CuFe2O4

Basic properties of the adsorbent

Conclusion

Acknowledgments

J. Biol. Chem.

Colloids Surf. A: Physicochem. Eng. Aspects

Chem. Geol.

J. Hazard. Mater.

J. Hazard. Mater.

J. Hazard. Mater.

Chem. Eng. J.

Chem. Eng. J.

Handbook of ferromagnetic materials

Chem. Eng. J.

Chemosphere

J. Hazard. Mater.

Mater. Sci. Eng. B

Mater. Res. Bull.

J. Magn. Magn. Mater.

J. Hazard. Mater.

J. Hazard. Mater.

J. Hazard. Mater.

Bioresour. Technol.

Chemosphere

Geochim. Cosmochim. Acta

Water Res.

XANES evidence of molybdenum adsorption onto novel fabricated nano-magnetic CuFe₂O₄

Preparation of nano-magnetic CuFe₂O₄