REMOVAL OF COPPER FROM AQUEOUS SOLUTION BY ADSORPTION USING MAGNESIUM ALUMINIUM HYDROGENPHOSPHATE LAYERED DOUBLE HYDROXIDES

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1 JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 8, No. 2, December, REMOVAL OF COPPER FROM AQUEOUS SOLUTION BY ADSORPTION USING MAGNESIUM ALUMINIUM HYDROGENPHOSPHATE LAYERED DOUBLE HYDROXIDES Zaini Hamzah 1, Mohd Najif Ab Rahman 1, Yamin Yasin 2, Siti Mariam Sumari 1 and Ahmad Saat 2 1 Faculty of Applied Science, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia 2 International Education Centre, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia mnajifr@yahoo.com ABSTRACT Layered double hydroxide (LDH) with Mg/Al molar ratio of 4/1 (MAN-4) was synthesized by co-precipitation and followed by hydrothermal method. The compound was allowed to undergo ion exchange with K 2 HPO 4 for 48 hours to produce MgAlHPO 4 (MAHP-4). The solid produced was characterized using X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR). Adsorption of copper solution by MAHP-4 was carried out using batch experiment by mixing the copper solution and the sorbent MAHP-4. The effects of various parameters such as contact time, ph, adsorbent dosage and initial concentration were investigated. The optimum ph for copper removal was found to be 4 and the optimum time of copper removal was found at 4 hours. The isotherm data was analysed using model isotherm Langmuir with the correlation coefficient of was recorded. The maximum adsorption capacity, Q o (mg/g) of mg/g was also recorded from the Langmuir isotherm. The remaining copper solution was determined by using EDXRF (Energy Dispersive X- Ray Fluorescence spectrometry) model MiniPal 4 (PAN analytical). The results in this study indicate that MAHP-4 has potential as an effective adsorbent for removing copper from aqueous solution. ABSTRAK Hidroksida lapisan berganda (LDH) dengan Mg/Al nisbah molar 4/1 (MAN-4) telah disintesis oleh pemendakan bersama dan diikuti oleh kaeadah hidroterma. Bahan itu kemudian menjalani pertukaran ion dengan K 2 HPO 4 selama 48 jam untuk menghasilkan MgAlHPO 4 (MAHP-4). Pepejal yang dihasilkan telah di cirikan menggunakan x-ray pembelauan (XRD) dan Fourier Transform Infrared spektroskopi (FTIR). Penjerapan larutan kuprum oleh MAHP-4 telah dijalankan menggunakan kumpulan eksperimen dengan mencampurkan larutan kuprum dan adsorben MAHP-4. Kesan pelbagai parameter seperti masa sentuhan, ph, dos adsorben dan kepekatan awal telah disiasat. ph optimum untuk penyingkiran kuprum telah didapati 4 dan masa yang optimum penyingkiran kuprum didapati terhasil pada 4 jam. Data sesuhu telah dianalisis menggunakan model sesuhu Langmuir dengan pekali kolerasi pada Kapasitisi maksimum penjerapan Q o (mg / g) bernilai 142,8 mg /g telah diperolehi daripada sesuhu Langmuir. Baki larutan kuprum telah ditentukan dengan menggunakan EDXRF (Pendarfluoran sinar X Serakan tenaga spektrometri) model Minipal 4 (PANanalisis). Keputusan kajian ini menunjukkan bahawa MAHP-4 mempunyai potensi sebagai adsorben yang berkesan bagi menyingkirkan kuprum daripada larutan berair. Keywords: Layered Double Hydroxide (LDH), adsorption, copper removal, anion exchange INTRODUCTION Heavy metals produced and released during domestic, agricultural and industries activities can create a serious hazard to the environment (Sathyavisal et. al., 2008). The presence of heavy metals in the environment can be harmful to a variety of living species. Consequently, the removal of heavy metals from 60

2 JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 8, No. 2, December, wastewater and water is important to protect public health (Donat et. al., 2005). The terms heavy metals refers to any metallic element that has a relatively high density and is toxic or poisonous at low concentration (Duruibe et. al., 2007). Heavy metals such as chromium and lead can accumulate in living organism and causing health disorders and various diseases such as reported by Arivoli et. al., Heavy metals in solution can be removed using several techniques such as precipitation (Karapinar et. al., 2009), coagulation, chemical precipitation, adsorption (Liu et. al., 2010) ozonation, membrane filtration and reverse osmosis (Yasin et. al., 2010). Recently, adsorption has become a widely used technique due its simplicity, potential to regeneration and sludge-free operation (Turk et. al., 2009). Moreover it can be attractive technique if the adsorbent used can be synthesized cheaply and readily. Layered double hydroxide (LDH) is a class of anionic clay with high anion exchange capacities are effective adsorbents for removal of a variety of pollutants. LDH have positively charged layers of metal hydroxides and the anions and water molecules are located between the layers. The positive charges that are produce from the isomorphous substitution of divalent cations and trivalent cations, are counter balanced by anions located between the layers (Hsu et. al., 2007). LDHs have a general formula of [M 2+ 1-x M 3+ x (OH) 2 ] [A n- x/n. m H 2 0], where M 2+ and M 3+ are divalent and trivalent metal cations, respectively, and A is the anions (Hu et. al.,2007). The anions between the layers can be polymers, organic dyes, surfactants and organic acids (Roto et. al., 2009). Wastewater effluents normally contain pollutants carry positive and negative charges. The LDH anion exchange ability, large surface area and regeneration ability ensure that this adsorbent can be excellently utilized in wastewater purification (Yasin et. al., 2010). Therefore, layered double hydroxide was selected in our work to optimize the removal of copper from aqueous solution. EXPERIMENTAL Preparation of layered double hydroxide The co-precipitation method was used for the preparation of the nitrate precursors. In the preparation of Mg- AlNO 3, an aqueous solution of Mg (NO 3 ) 2.6H 2 O (0.1M) was added to Al (NO 3 ) 3.9H 2 O (0.025 M) to give Mg 2+/ Al 3+ with a ratio of 4/1. An aqueous solution of NaOH (1M) was added to the mixture drop wise, with vigorous stirring at room temperature and the ph was adjusted simultaneous to 10.0 ± The coprecipitation method was conducted under a stream of nitrogen gas to avoid, or at least minimize contamination by atmospheric carbon dioxide. The slurry was then aged at approximately 70 C for 24 hours in a thermostated oil bath shaker (hydrothermal method). The precipitate formed was cooled then filtered and washed with excess deionized water and dried at 70 C in an oven for 48 hours. The LDH or MAN-4 thus produced was the ground using a mortar pestle and was kept in air tight bottles for further use and characterization study. Preparation compound MAHP-4 by used of anion exchange reactions were carried out at room temperature with approximately 1 gram of the LDH was suspended in a 0.1 M K 2 HPO 4 solution and stirred for 48 hours at a ph 9. The solid was then filtered and washed several times with deionized water and then dried in an oven at 70 C for 24 hours. Characterization of layered double hydroxide X-ray diffraction (XRD) pattern of the sample was characterized by using a Shimadzu XRD-6000 diffractometer, with Ni- filtered Cu-Kα radiation (λ= 1.54 A ) at 40 kv and 200 ma. Solid samples were mounted on alumina sample holder and basal spacing (d-spacing) was determined via powder technique. Samples scan were carried out at 10-60, 2θ / min at steps. FTIR spectrum was obtained using a Perkin Elmer 1725X spectrometer where samples will be were finely ground and mixed with KBr and pressed into a disc. Spectrums of samples were scanned at 2 cm -1 resolution between 400 and 4000 cm

3 Intensity/Cps JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 8, No. 2, December, Batch adsorption experiment Copper solution 1000 ppm purchased from Merck was used for the adsorption experiment in this study. The batch experiments were carried out using 0.02 g sorbent dosage was put into 25 ml of mg/l solutions of the copper. The amount of copper adsorbed onto the compounds (%) was calculated as: Where C o is the initial copper concentration (mg/l), C t is the concentration of copper (mg/l) at equilibrium time, t. The copper solution is filter through 0.45 µm micro fibre filter attached to a 10 ml syringe. The concentration of copper in the solution was measured using EDXRF (Energy Dispersive X-ray Fluorescence Spectrometry). Adsorption isotherm was recorded over the concentration range between 50 mg/l and 250 mg/l of copper solutions in series of 100 ml Schott bottles containing 25 ml solution of each concentration. All the experiments were carried out in duplicates. (1) RESULTS AND DISCUSSION Characterization of layered double hydroxide The XRD patterns of MAN-4 prepared by anion exchange method with phosphate are presented in Figure 1. As shown in the Figure, original MAN-4 indicates crystallinity with d-spacing of 7.9 Å with the interlayer spacing of compound recorded at 4.1Å. The XRD pattern after anion exchange shows that the d-spacing and interlayer spacing were recorded as 7.8 Å and 3.8 Å, respectively. The crystallinity of MAHP-4 is thus lower than MAN-4 as shown by broadening of the lines and decrease in intensity. d oo3 7.9 Å d Å MAN - d Å d Å MAHP Theta/ Figure 1: XRD pattern of MAN-4 and MAHP-4 The FTIR patterns of MAN-4 prepared by anion exchange with phosphate are presented in Figure 2. As shown in the Figure 2, original MAN-4 compound shows very intense band located approximately around 1380 cm -1 which is attributed to NO 3 vibration. The band at 3440 cm -1, 1625 cm -1 and 825 cm -1, corresponds to vibration of hydroxyl groups, water and of planar lattice hydroxyl group, respectively. FTIR pattern for the compound prepared by used of anion exchange with phosphate shows new bands related to phosphate groups at 1220 cm -1, 1050 cm -1, 870 cm -1 and 550 cm -1 which are attributed to the orthophosphate of (P-OH) and PO 3-4, vibration respectively (Legrouri, et al.,1999). The broadening and dissymmetry of the band was also observed due to the characteristic of hydroxyl groups. The broadening of the band is due to 62

4 JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 8, No. 2, December, the establishment of hydrogen bond between the phosphate groups and water molecules of the interlayer space (Badreddine et. al., 1998). Figure 2. FTIR pattern of MAN-4 and MAHP-4 Calibration of copper using EDXRF The calibration graph for copper solution was conducted using EDXRF (Energy Dispersive X-ray Fluorescence Spectrometry) model MiniPal 4 (30 kv and ma) in the range between 20 ppm to 250 ppm. 5 ml of sample was measured using pipette and placed in cup holder by used of 6.5 µm thin mylar film. The reading from XRF used was count per second (cps) unit. From the data, the cps was plotted against concentration of copper solutions. The correlation coefficient value for the calibration graph is The detector used in this study is high-resolution Si drift detector. Generally, this technique may improve the low atomic elements intensities of elements ranging from beryllium to high atomic elements like uranium. The MiniPal4 consist 2048 multi-channel analyzer was used to determine the present of elements in the sample. EDXRF is non-destructive method and it s suitable for use with solid, liquid or powdered samples. The procedure was fast and highly accurate. Effect of ph The effect of ph on the removal of copper was carried out at a fixed initial concentration of copper (100 ppm) and LDH dosage of 0.05 g for 3 hours of contact time. The range of ph between 2 and 6 were prepared in this study. The range was selected because the copper will be precipitated at high ph (Karapinar et. al., 2009). At the ph values which is higher than 6.0, both ion exchange and aqueous metal hydroxide formation may become significant mechanism in the removal process of metal (Thayyath et. al., 2008) As shown in the Figure 3, it can be observed that the maximum percentage of copper removal from aqueous solution optimized at ph of 4. The percentage removal at this point is 99.4 %. The removal of copper started to decrease at high ph. This is related to the direct sorption of OH - from the solution on LDH compounds (Xuefeng et. al., 2010). The ph solution of 4 subsequently was selected for other optimization experiments in this study. 63

5 Copper removal (%) Copper removal (%) JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 8, No. 2, December, Initial ph of copper solution Figure 3. The effect of ph on the removal of copper solution using MAHP-4 Effect of contact time The adsorption experiments to evaluate the contact time effect on removal of copper using MAHP-4 was carried out ranging from 15 minutes to 5 hours. The experiments were conducted under the standard conditions of: temperature; 298K, ph 4.0 and the concentration copper solution; 40 ppm, 70 ppm and 100 ppm. As shown in Figure 4, the amounts of copper removed increased rapidly within 2 hours and remained constant after 3 hours indicating an equilibrium state. At the contact time of 4 hours, the copper removal (%) for 40 ppm, 70 ppm and 100 ppm are 98.23%, % and 81.94%, respectively. In addition, the MAHP- LDH compound has two types of adsorption sites that are available. Firstly, the external surface which lead to surface adsorption and secondly within the interlayer by which the formation of copper phosphate is believed to occur ppm 70 ppm 40 ppm Time/h Figure 4. The effect of contact time on the removal of copper solution using MAHP-4 64

6 Copper removal (%) JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 8, No. 2, December, Effect of adsorbent dosage The adsorption study with different adsorbent dosage at a fixed ph of 4, temperature of 298K, a contact time of 4 hours and different concentration of copper solution (100 ppm, 150 ppm and 250 ppm) were carried out. The dosages were selected from 0.01 g to 0.05 g. The effect of adsorbent dosage on copper removal is presented in Figure 5. From the graph, it can be seen that the removal of copper increased with increased in adsorbent dosage. The increased in dosage provided more surface and adsorption sites, hence increased adsorbent adsorption (Sumari et. al., 2009) ppm 150 ppm 250 ppm Dosage (g) Figure 5. The effect of adsorbent dosage time on the removal of copper solution using MAHP-4 Adsorption isotherm Adsorption isotherm is important to study in order to understand the interactions between adsorbent and adsorbate. The isotherm is normally obtained at a constant temperature with fix adsorbent dosage by measuring the change of concentration at different initial concentrations of copper solutions after equilibrium has been attained. The Langmuir model is based on assumption that uptake occurs on a homogenous surface by monolayer sorption without interaction between adsorbed molecules (Qaiser et. al., 2009). It is expressed as: (2) Where, q e is the amount of copper adsorbed per unit mass of adsorbent (mg/g); C e is the equilibrium copper concentration (mg/l); and Q 0 and b are the Langmuir constants representing the monolayer adsorption capacity (mg/g) and the energy of adsorption (L/mg), respectively. The plot of C e /q e versus C e gives a straight line with a slope of 1/Q 0 and an intercept of 1/Q 0 b. The isotherm study of copper removal was generated in batch experiments using different initial concentrations range from 50 ppm to 250 ppm at constant temperature of 298 K, a ph of 4 and 0.02 g dosage of MAHP-4. The isotherm is presented in Figure 6 and from the Figure it can be concluded that equilibrium data fitted with the Langmuir Isotherm with high correlation coefficient value of The calculated Langmuir isotherm constant for the maximum capacity of copper removal, Q 0 (mg/g) was mg/g. 65

7 C e /q e (g/l) JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 8, No. 2, December, y = 0.007x R² = C e (mg/l) Figure 6. Langmuir isotherm plot for the removal of copper solution using MAHP-4 CONCLUSION The present study shows that MAHP-4 is suitable adsorbents for the removal of copper from aqueous solution. The removal of copper was shown to be dependent on ph, contact time, adsorbent dosage and initial concentration. The experimental data well fitted to Langmuir equation confirming the monolayer coverage of copper solution onto layered double hydroxide adsorbents. ACKNOWLEDGEMENT The authors would like thank to The Universiti Teknologi MARA (UiTM) Shah Alam and MOSTI Ministry of Science, Technology and Innovation Malaysia. REFERENCES Anirudhan, T.S., Suchithra, P.S., (2008). Synthesis and characterization of tannin-immobilized hydrotalcite as a potential adsorbent of heavy metal ions in effluent treatments. Applied Clay Science 214: Badreddine, M., Khaldi, M., legrouri, A., Barroug, A., Chaouch, M., De, R.A., Besse, J.P., (1998). Chloride hydrogenphosphate ion exchange into the zinc-aluminium-chloride layered double hydroxide. Materials Chemistry and Physics 52, Donat, R., Akdogan, A., Erdem, E., Cetisli, H., (2005). Thermodynamics of Pb 2+ and Ni 2+ adsorption onto natural bentonite from aqueous solution. Journal of Colloid and Interface Science, 286, Duruibe, J., Ogwuegbu, M.O.C., Egwurugwu, J.N., (2007). Heavy metal pollution and human biotoxic Effects. International Journal of Physical Sciences, Vol 2(5), Hu, Q., Xu, Z., Qiao, S., Haghseresht, F., Wilson, M., Lu, G.Q., (2007). A novel color removal adsorbent from heterocoagulation of cationic and anionic clays. Journal of Colloid and Interface Science 308: Hsu, L.C., Wang, S.L., Tzou, Y.M., Chen, J.H., (2007). The removal and recovery of Cr(VI) by Li/Al layered double hydroxide(ldh). Journal of hazardous material 142,

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