Arsenic(V) sorption using chitosan/Cu(OH)2 and chitosan/CuO composite sorbents
Introduction
The contamination of natural waters by heavy metals is a serious problem in several countries (Sun et al., 2013). Among contaminating metal ions arsenic is well known for its toxicity: it is often called the Poison of Kings and the King of Poisons (Litovitz et al., 1990, Vahidnia et al., 2007). Toxicological studies on the effects of arsenic on human health showed that a long-term intake of As-contaminated water even at very low arsenic concentration (0.01–0.05 mg L−1) can cause lethal diseases such as conjunctivitis, hyperkeratosis, hyper pigmentation, cardiovascular diseases, disorders of the central nervous system and peripheral vascular system, skin cancer and gangrene of the limbs (Bhattacharya et al., 2007). Due to the weathering and erosion of rocks and soils (which naturally contain arsenic) and to volcanic emissions, arsenic-containing particles can enter in contact with surface water and contribute to contaminate water bodies and groundwater. Apart from natural sources, arsenic contamination is also due to anthropogenic activities such as dissemination of arsenic pesticides, and sub-products of mining, industrial and chemical wastes and also burning of fossil fuels. At industrial scale, arsenic is mainly used as a wood preservative and in the production of dyes, paints and pigmenting substances. It is also used in glass-making, electronics manufacturing and leather tanning industries. Arsenic is also used, at low concentration, in both human and animal medications and care products.
The presence of arsenic ions in natural waters has become an important issue around the world. The World Health Organization (WHO) has recommended an allowable drinking water arsenic concentration of 0.01 mg L−1 (WHO, 2011). It is generally considered that more than 140 million people worldwide are exposed to water exceeding the WHO's allowable concentration (Ravenscroft, Brammer, & Richards, 2009).
The treatment of arsenic contaminated water is necessary before intake in several regions and countries. Various technologies for removing arsenic from contaminated water have been developed, including oxidation-precipitation (Nitzsche et al., 2015), coagulation-flocculation associated to filtration (Wang et al., 2014a, Wang et al., 2014b, Wang et al., 2014c), sorption (Hokkanen, Repo, Lou, & Sillanpaa, 2015) and nanofiltration (Maher, Sadeghi, & Moheb, 2014). A large variety of non-conventional sorbent materials have been studied for As removal (Chowdhury and Balasubramanian, 2014, Dax et al., 2014, Pontoni and Fabbricino, 2012, Yadav et al., 2014, Yu et al., 2013). New sorbents with high sorption capacities are still under development to reduce the sorbent dose and minimize disposal problems (Gomez-Pastora, Bringas, & Ortiz, 2014).
Chitosan (one of the most abundant polysaccharides) is an efficient low cost sorbent due to the presence of amine groups (Wang & Chen, 2014). Chitosan binds metal cations at near neutral pH by chelation through the free electron doublet of nitrogen on free amino groups, while the biopolymer can sorb metal anions in acidic solutions through an ion exchange/electrostatic attraction mechanism (Guibal, 2004). However, chitosan has relatively poor sorption capacities for As(V) (and even lower for As(III)): sorption capacity, in most cases does not exceed 14 mg As g−1 (Kwok et al., 2014, Pontoni and Fabbricino, 2012). Sophisticated physical modifications of the biopolymer are necessary for substantially increasing its sorption properties: for example, electrospun nanofiber membranes have been successfully designed for As(V) sorption (with sorption capacities as high as 30 mg As g−1). However, best As sorption properties on chitosan-based materials were obtained incorporating in the biopolymer matrix other functional groups (Pontoni & Fabbricino, 2012) or other compounds having a strong affinity for arsenic (for example molybdate, which is strongly bound to chitosan in acidic solutions (Dambies, Vincent, & Guibal, 2002)).
The sorption properties of metal oxides for arsenic species have already been reported (Beker et al., 2010, Lunge et al., 2014, Raul et al., 2014, Uwamariya et al., 2014, Zhu et al., 2013). Due to the possible dispersion of metal contaminated micro-particles (which contain arsenic fraction after metal sorption) it is generally preferable immobilizing or depositing the metal oxides or metal hydroxides on a mineral support (Uwamariya et al., 2014, Zaspalis et al., 2007), in the framework of a polymer support (Beker et al., 2010, Ocinski et al., 2014), or at the surface of agriculture waste materials (Cope et al., 2014, Cumbal et al., 2003, Cumbal and Sengupta, 2005, DeMarco et al., 2003, Sarkar et al., 2007). Chitosan can also be used for the incorporation or immobilization of metal ions, metal oxides or metal hydroxides that can have a further interaction with target molecules (Dambies et al., 2000, Dambies et al., 2002, Demey et al., 2014, Guibal et al., 2014, Sarkar et al., 2012) (Hong et al., 2014, Vu et al., 2013, Yamani et al., 2012).
While in most cases metal oxides and hydroxides that were immobilized in chitosan matrix were iron-, aluminum- or titanium-based, in the present study, the composite sorbents were prepared by incorporation of copper oxide (CuO) and copper hydroxide (Cu(OH)2) into chitosan matrix. This work describes the synthesis and the characterization of sorbent particles before investigating their sorption properties. The effect of pH on As(V) removal is discussed in relation with charge properties of the materials. The uptake kinetics and the sorption isotherms are carried out and modeled. Thermodynamic parameters are also determined. Finally, the desorption of arsenic from loaded sorbent and the recycling of the sorbents are studied along a series of sorption/desorption cycles.
Section snippets
Chemicals
Chitosan was supplied by Aber Technologies (France); its deacetylation degree (87%, determined by FT-IR spectrometry on KBr pellets using the intensity ratio for absorbance bands of Amide I band (at 1655 cm−1) and non-specific 3450 cm−1 band (Baxter, Dillon, Taylor, & Roberts, 1992)) and its molecular weight (125,000 g mol−1, determined by size exclusion chromatography coupled with light scattering and refractometry) were previously reported (Ruiz, Sastre, Zikan, & Guibal, 2001). Copper chloride
Physico-chemical characterization of sorbents
The principle of sorbent synthesis is based on the co-precipitation of a mixture of copper chloride and chitosan in solution using sodium hydroxide. After precipitation the sorbent is cross-linked with epichlorohydrin before being freeze-dried. The main advantage of this drying method is that the porous structure of the original hydrogel is less affected by the drying procedure than a simple uncontrolled drying (at room temperature or in an oven) (Ruiz, Sastre, & Guibal, 2002). After drying the
Conclusion
Chitosan/Cu(OH)2 and chitosan/CuO sorbents have been prepared by co-precipitation of copper chloride/chitosan solution in alkaline solution: the alkalization controls the type of copper oxide deposited in the framework of the polymer particles. These sorbents are quite efficient for the sorption of As(V). SEM and SEM-EDX analyses show irregular objects with very rough surfaces. Optimum arsenic sorption is obtained at equilibrium pH close to 6; this pH is also favorable in terms of sorbent
Acknowledgements
This study was supported by the French Government through a fellowship granted from the French Embassy in Egypt (Institut Français d’Égypte). The authors would like to thank Thierry Vincent, André Brun and Jean-Marie Taulemesse for their technical and scientific contributions to this work. The authors also acknowledge Prof. Sayed El Sawey for XRD analysis.
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