Characterization and adsorption capacity of raw pomegranate peel biosorbent for copper removal
Introduction
Heavy metals are natural elements characterized by a relatively high density, greater than 6 g/cm3 (OConnell et al., 2008). Currently, 41 metals and 5 metalloid are identified (Atteia, 2005). Some of these elements present in trace amounts, are essential for living organisms (Zn, Fe, Mn, Ni, Cr, V, Mo, Se, Sn), but the increase in their concentration can lead to toxicity phenomena. Other elements produce harmful effects (Pb, Hg, Cd). The heavy metal toxicity against living organisms depends on their nature, concentration, mode of action, specification and bioavailability (Bonnet et al., 2000). They are characterized by their significant persistence, toxicity and accumulation in the natural environment especially in water, considered the most important medium, for it can distribute these metals along the food chain. Among the important natural metal sources, we cite, the volcanic activity, continent weathering and forest fires. In terms of anthropogenic sources, effluents from mining extractions, industrial, domestic and atmospheric sources we can mention, the burning of fossil fuels, waste incineration and industrial emissions into water courses which lead to environmental problems. This situation has attracted recently a worldwide interest. Among other metals, Copper(II) is a dangerous and toxic heavy metal when its concentration exceeds the standard limit. Several technologies have so far been employed to remove copper from wastewater such as precipitation, cementation, classical and advanced oxidation process and ion exchange. Yet, these techniques become too expensive and ineffective when the metal ion concentrations in solution are less than 100 mg/L (Benaissa and Elouchdi, 2007). Contrariwise, the removal of copper from the effluent by an adsorption process provides an attractive alternative therapy, especially when the adsorbent is inexpensive and readily available. Waste agricultural materials may constitute an important source of this type of adsorbent. They include shells of wheat, bran and rice (Aydın et al., 2008), orange peels (Romero-Cano et al., 2016), sunflower leaf (Benaissa and Elouchdi, 2007), olive stones (Bohli et al., 2015), litchi pericarp (Kong et al., 2014) and others materials detailed in overviews (Bhatnagar et al., 2015, At and Olugbenga, 2015, Abas et al., 2013). Another waste agricultural material that could be very efficient as biosorbent for metal removal is the pomegranate peel. Pomegranate peel is a byproduct of the pomegranate juice industry, wine industries, and tanneries. In Tunisia, pomegranate production is about 71 597 tons/year in 2010 (Saad et al., 2012). Hence, pomegranate peel constitutes a low-cost renewable source of biosorbent. However, few studies have so far been done to investigate the potential capacity of modified pomegranate peel for metal removal from wastewater, the maximum adsorption capacity obtained are summarized in Table 1. Untreated pomegranate peel is not sufficiently studied. El-Ashtoukhy et al. (2008) had studied raw pomegranate peel treated at low temperature (378 K), potential capacity for copper and lead removal was investigated, the maximum adsorption capacities found are 1.318 mg/g for Cu(II) and 13.87 mg/g for Pb(II). Ay et al. (2012) had also studied pomegranate peel treated at low temperature (353 K) for adsorption of lead (II) ions and the maximum adsorption capacity obtained is 193.94 mg/g. Therefore, the purpose of this work is to assess the ability of natural pomegranate peel biosorbent to adsorb copper Cu(II) from aqueous solution. Any treatment is used to activate PGP, furthermore the applied temperature for washing and drying is below 323 K. The physical and chemical characteristics of the adsorbent, including point of zero charge (pHpzc) and surface functional groups are determined. The effect of different experimental parameters on the removal of copper(II) such as the pH solution, the initial metal concentration, the particle size and the contact time has been studied. The experimental data obtained have been treated using equilibrium isotherms models, and kinetic models.
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Preparation and characterization of the adsorbent
Pomegranate peel (PGP) was collected in the southern part of Tunisia (Gabes). It was initially washed with preheated double distilled water, several times. Then, it was dried in an air oven at 323 K overnight, crushed manually with a ceramic mortar and sieved to the desired particle size. The adsorbent was then characterized with Boehm titration, Iodine number, Point of zero charge, TG/DTA, and FTIR spectrum analysis.
Physical and chemical characterization of the adsorbent
Fig. 1 shows the particle size distribution. The class weight is plotted versus the particles diameter. Three particle size ranges are selected: < 630 μm, 630 μm-1600 μm and 1600 μm-3150 μm. Mean particle size are found to be 205 μm, 850 μm and 2375 μm respectively.
The determination of the surface area was carried out on the basis of the Iodine adsorption number. Iodine number obtained is 602 mg/g for particle size of 500 μm. The iodine molecule is relatively small with an area of 0.4 nm2 and
Adsorption mechanism
The adsorption capacity depends upon porosity as well as chemical functional groups at the adsorbent surface. Fourier Transform Infrared Spectroscopy (FTIR) analysis have been carried out to identify active sites for adsorption mechanism. The FTIR spectra of PGP before and after copper Cu(II) ions adsorption are shown in Fig. 12. In both spectra, the broad brand region and intense absorption peaks at about 3330 cm−1 correspond to the OH stretching vibrations. The peak shifting from 3280 to
Conclusion
The purpose of this work is to consider the potential of natural materials, the non-modified pomegranate peel (PGP) derived from agricultural activities for copper removal from a polluted wastewater. In literature, different natural agricultural wastes had been used to remove copper ions (Zhu et al., 2009) (Wan et al., 2010) (Tong et al., 2011) (Milicevic et al., 2012) (Kong et al., 2014). Only El-Ashtoukhy et al. (2008) had studied the adsorption capacity of natural PGP for copper removal and
Acknowledgement
This work was supported by the Ministry of the Higher Education and Scientific Research in Tunisia.
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