Elsevier

Talanta

Volume 79, Issue 5, 15 October 2009, Pages 1454-1463
Talanta

On-line preconcentration and recovery of palladium from waters using polyaniline (PANI) loaded in mini-column and determination by ICP-MS; elimination of spectral interferences

https://doi.org/10.1016/j.talanta.2009.06.008Get rights and content

Abstract

The applicability of polyaniline (PANI) for the on-line preconcentration and recovery of palladium from various water samples has been investigated. Batch experiments were performed to optimize conditions such as pH and contact time to achieve quantitative separation of Pd spiked at high (μg ml−1) and low levels (ng ml−1). During all the steps of the removal process, it was found that Pd was selectively removed by PANI even in the presence of various ions. Quantitative removal of Pd occured in the entire studied pH range (1–12) and the Kd value was found to be >106. Kinetic studies show that a contact time of <4 min was adequate to reach equilibrium. The retained Pd was subsequently eluted with a mixture of HCl and thiourea, optimized using a factorial experimental design approach. ICP-OES was used for the micro-level determinations of Pd whereas ICP-MS was used for the determination of Pd at sub-ppb levels.

Breakthrough curve using column experiments demonstrated that PANI has an excellent ability to accumulate up to ∼120 mg g−1 of Pd from synthetic sample solutions. A preconcentration factor of about 125 was achieved for Pd when 250 ml of water was passed. PANI columns prepared were used up to 10 times in consecutive retention–elution cycles without appreciable deterioration in their performance. The proposed on-line method also has the ability to remove interfering elements Cu and Y for the determination of Pd in waters by ICP-MS. The reported method has been applied successfully for the determination of Pd in ground water, lake water sea-water and waste water samples. The recoveries were found to be >95% in all cases. These studies indicate that PANI has an excellent ability to preconcentrate Pd from various waters making the method very promising for the determination of Pd.

Introduction

In recent years, palladium has found a variety of applications (e.g. medicine and dentistry (25–40% of annual consumption); electrical products and electronics (30–40%), chemical industry (10–15%), automotive industry (5–15%), jewelry (2–5%), glass industry, etc.) because of its attractive physical and chemical properties such as high melting point, corrosion resistance and extraordinary catalytic properties [1], [2], [3], [4]. Although the benefits of automotive catalysts are undisputable, they result in significant amounts of Pt, Rh and Pd being released into the atmosphere leading to contamination of food and water-bodies [5], [6] which finally lead to bioaccumulation in the living organisms through diverse pathways. Although Pd in its elemental form is rather inert with respect to its biological activity, all ionic species of Pd are regarded as highly toxic and carcinogenic to humans, causing asthma, allergy, rhino-conjunctivitis, etc. [7], [8]. But, the trends in their production, demand and prices show that there has been a significant growth in the demand for PGMs, particularly palladium, over the years [9]. In order to meet this increasing demand and in view of the limited resources, there is a need to look for new sources of palladium. One way is to recover and recycle Pd from various wastewaters generated from industries that use PGEs extensively. This process also contributes significantly to the protection of the environment by reducing any negative impact associated with metal waste disposal. Therefore, the development of new methods for the effective separation, preconcentration and determination of Pd in waters has been of a great interest.

Palladium in environmental matrices, in particular waters, usually occurs at sub-ppb levels [10] and its direct measurement is often difficult even with highly sensitive and selective techniques such as inductively coupled plasma-mass spectrometry (ICP-MS), electro-thermal atomic absorption spectrometry (ETAAS) and inductively coupled plasma optical emission spectrometry (ICP-OES) [11], [12], [13] due to matrix and spectral interferences. Therefore, coupling of a separation/preconcentration procedure and elimination of interfering species in single step prior to detection is necessary.

Fire assay, solvent extraction, co-precipitation, ion-exchange and solid-phase extraction (SPE) techniques have been employed widely for the preconcentration of Pd [14], [15], [16]. Among the techniques reported, column configuration SPE has found increasing application for the preconcentration of trace amounts of Pd and effective elimination of matrix interferences prior to analysis because of high selectivity, high enrichment capacity and operational simplicity [12], [13]. Different sorbents such as Amberlite XAD resins [17], [18], alumina [19], modified silica gel [20], [21] and various chelating resins such as Metalfix-Chelamine [13], [22], dithiozone anchored poly(vinylpyridine) [23] have been extensively used for the preconcentration of palladium from aqueous media. In recent years, a variety of anion-exchange resins for the removal and preconcentration of palladium have also been reported in the literature [24], [25].

Along with complex-forming and ion-exchange sorbents, a number of different sorbents such as natural and synthetic zeolites, activated carbon [26] and biosorbents, etc. [27], [28], have been employed. But most of the reported methods suffer from various disadvantages such as high cost of the sorbents, high detection limits, low enrichment factors, poor reusability of the sorbents, need for large amount of organic reagents and generation of large volumes of secondary wastes. Thus there is a need for developing a method that can overcome these limitations.

Polyaniline (PANI) is well known for its ion-exchange and conducting properties [29], [30]. Applicability of PANI as ion-exchange resin and conducting polymer, has attracted a considerable scientific interest in recent decades because of its good combination of properties, diverse structure, thermal and radiation stability, low cost, ease of synthesis and thus resulted in its wide applications in different fields such as micro-electronics, corrosion protection, sensors and electrodes for batteries [29], [31], [32], [33]. PANI can be easily synthesized either chemically or electrochemically from acidic solutions [29], [31]. PANI can exist in various oxidation states characterized by the ratio of imine to amine nitrogen. Upon alkaline treatment of the polymer with dilute NH3 or NaOH solutions, it changes into a material called emeraldine which comprises an equal number of repeating reduced and oxidized units.

The physicochemical properties of polyaniline and its potential applications in diverse fields have been reviewed [29], [31]. PANI has been used as base material for the preparation of mercury standard for use in neutron activation analysis [34]. The applicapability of polyaniline for the separation and determination of Cd, Cu, Pb and Sb in KI medium in biological matrices was also studied [35]. In our earlier studies, PANI was applied successfully for the removal and speciation of inorganic and methylmercury in waters [36]. More recently, studies were conducted to evaluate the performance of PANI synthesized on jute surface for the removal of hexavalent chromium [Cr(VI)] in aqueous environment [37]. Despite the extensive literature on various applications of PANI, to our knowledge, no application of PANI for preconcentration and removal of Pd from waters has been reported.

This paper deals with the potential application of polyaniline as an anion exchanger suitable for environmental protection through water and wastewater treatment. In this work, the efficacy of PANI, probably for the first time, has been investigated for the removal and preconcentration of low levels of palladium from various waters such as ground waters, lake waters, sea-waters and wastewaters. After optimizing all the experimental parameters such as influent pH, equilibration time, eluent composition, etc., using batch experiments, extensive studies were carried out with PANI loaded in home made mini-column for preconcentration of Pd and elimination of interfering species followed by optimization of the eluent volume. Using this optimal procedure, capacity studies were carried out using a breakthrough curve.

Section snippets

Instrumentation

Palladium concentrations when at sub-ppb levels were determined using an ICP-MS (VG Plasma Quad 3, VG Elemental, Winsford, Cheshire, U.K.) system. The data were collected by monitoring the most abundant isotopes of Pd m/z 105, 106 and 108 using the peak jump mode. For the experiments with on-line preconcentration, a time resolved mode of data acquisition available with the Plasma Quad was used for obtaining a chromatogram. The optimized conditions are given in Table 1a. The experimental set-up

Results and discussion

The effect of various parameters on Pd removal was studied with PANI through both, batch and column experiments. In the first set of batch experiments, Platinum, Rhodium, Iridium and Ruthenium were included along with Pd to study the removal behavior by PANI under different pH conditions. These studies clearly demonstrated that PANI has an excellent ability for the quantitative removal (>99%) of Pt group elements from aqueous solutions, however present study aimed at the sorption of Pd from

Experiments with mini-column loaded with PANI

Generally column methods are more favored over batch methods because of various advantages such as continuous operation, ease of separation and repeated use. Thus the possibility of using the sorbent filled in a column in a flow mode was studied. Under the conditions previously optimized in batch experiments, effect of flow rate, sample volume and capacity of PANI were studied a using PANI loaded mini-column in an off-line procedure. The experimental set-up for optimization of Pd removal is

On-line preconcentration studies with PANI mini-column using FI-ICP-MS

The PANI column was coupled to the ICP-MS for on-line preconcentration of Pd in order to obtain low detection limits, thereby improving the sensitivity of the proposed preconcentration method. The experimental set-up for on-line preconcentration shown in Fig. 1b was connected to the ICPMS by coupling the outlet of the column directly to the nebuliser inlet. Different volumes of sample solutions (10 ml, 20 ml, 40 ml, etc.) containing 0.5 ng ml−1 of Pd were passed through the column with the injection

Effect of sample volume/concentration of sample solution

In order to estimate the achievable preconcentration factor for very dilute sample solutions containing the analyte of interest, the maximum applicable volume of sample that can be passed through the column loaded with PANI must be determined. To study this effect, a series of solutions with increasing sample volumes 50 ml, 100 ml, 150 ml, 250 ml, and 300 ml of sample solutions containing a total amount of 25 ng of Pd was passed through the column under the optimised conditions. After following the

Limit of detection (LOD) and precision of the method

Analytical response characteristics of Pd with ICP-MS and ICP-OES are shown in Table 4. The detection limit for Pd was evaluated as the concentration corresponding to three times the S.D. of the blank signal. Detection limit for Pd when determined based on 105Pd isotope was found to be 0.0004 ng ml−1 and 0.22 ng ml−1 for ICP-MS and ICP-OES respectively. Correlation coefficient values and the detection limits obtained for other isotopes of Pd are shown in Table 4. As no standard reference material

Capacity of PANI for Pd using breakthrough curves

In this work, breakthrough capacity is used to determine the capacity of PANI for palladium. A feed solution containing 10 μg ml−1 of Pd was passed through a column loaded with PANI at optimized conditions described in previous sections. The pH and flow rate of the feed solution were maintained at ∼6.5 ml min−1 and 2 ml min−1 respectively. Samples were collected from the column periodically and analysed for residual Pd content using ICP-MS. A breakthrough curve for Pd was obtained by plotting %

Interference studies with FI-ICPMS system

As described in the previous sections, the determination of Pd at its environmental concentration levels requires the use of very sensitive analytical techniques such as ICP-MS. Pd determination by ICPMS in many environmental samples such as waters, road dust or airborne particulate matter especially sub-ppb levels, is hampered by the combined factors of very low Pd concentration and a high content of interfering elements (such as Cu, Y, Zn, Zr and Cd) arising from catalyst abrasion or

Analytical application

The proposed removal and preconcentration method was applied to real-life samples; experiments were carried out by adding known amounts of Pd to different water samples—ground water, lake (Hussain Sagar, Hyderabad, India), sea-water and waste water samples obtained from an industrial area and applying the general procedure previously described. The water samples were collected in pre-cleaned polyethylene bottles and samples were used immediately after collection. A 50 ml portion of these samples

Conclusion

An on-line preconcentration method using PANI has been proposed for the recovery of Pd and its determination by ICP-MS in various water samples. Quantitative removal of Pd was achieved with a mini-column loaded with PANI even at low ng ml−1 levels. Another advantage of the use of PANI is the capability of being used within a wide range of pH values. The capacity of the prepared PANI for Pd was determined to be ∼120 mg g−1 for Pd. The on-line preconcentration method also has the ability to remove

Acknowledgement

The authors are thankful to Dr. J. Arunachalam, Head, CCCM for his constant support and encouragement.

References (48)

  • C.R.M. Rao et al.

    Trends Anal. Chem.

    (2000)
  • S. Tokalioglu et al.

    Anal. Chim. Acta

    (2004)
  • K. Ravindra et al.

    Sci. Total Environ.

    (2004)
  • R. Merget et al.

    Sci. Total Environ.

    (2001)
  • K. Farhadi et al.

    Talanta

    (2005)
  • M. Muzikar et al.

    Talanta

    (2006)
  • K. Pyrzynska

    Talanta

    (1998)
  • R.R. Barefoot et al.

    Talanta

    (1999)
  • Pei Liang et al.

    Talanta

    (2009)
  • I.A. Kovalev et al.

    Talanta

    (2000)
  • M. Moldovan et al.

    Anal. Chim. Acta

    (2003)
  • R. Vlasankova et al.

    Talanta

    (1999)
  • F.S. Rojas et al.

    Talanta

    (2006)
  • M. Iglesias et al.

    Talanta

    (2003)
  • R. Shah et al.

    Anal. Chim. Acta

    (1997)
  • Z. Hubicki et al.

    Desalination

    (2005)
  • Z. Hubicki et al.

    J. Hazard. Mat.

    (2008)
  • S. Lin et al.

    Talanta

    (1995)
  • A.A. Syed et al.

    Talanta

    (1991)
  • A. Airoudj et al.

    Talanta

    (2009)
  • R. Verma et al.

    J. Radioanal. Nucl. Chem.

    (1997)
  • M.V. Balarama Krishna et al.

    Talanta

    (2005)
  • P.A. Kumar et al.

    J. Hazard. Mater.

    (2009)
  • P. Kovacheva et al.

    Anal. Chim. Acta

    (2002)
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