- Email: [email protected]
Clearance and recovery of Cd(II) from aqueous solution by magnetic separation technology
Chemosphere 83 (2011) 1214–1219
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Clearance and recovery of Cd(II) from aqueous solution by magnetic separation technology YongLe Chen, Hao Qian ⇑, Fan Wu, Jian Zhou College of Materials Science and Engineering, HuaQiao University, XiaMen 361021, Fujian, China
a r t i c l e
i n f o
Article history: Received 3 September 2010 Received in revised form 20 March 2011 Accepted 22 March 2011 Available online 12 April 2011 Keywords: Magnetic beads Adsorption Desorption Regeneration Cd(II)
a b s t r a c t An effective method to actualize the recycling use of Cd(II) in industrial wastewater was developed by using the magnetic beads, which was modified with ethylenediamine. When the industrial wastewater was treated with these magnetic beads, the Cd(II) concentration in the solution was sharply reduced to the governmental standard (0.1 lg mL 1) of China. Based on the monolayer adsorption of Cd(II) on the surface of these magnetic beads, the saturation capacity for Cd(II) reached to 68 mg g 1 dried magnetic beads. On the other hand, the binding Cd(II) could be easily recovered in acid conditions and the recovery efficiency exceeded 99%. Thus, in the process of the wastewater purification, the recycling utilization of Cd(II) was realized. Additionally, the excellent capability of regeneration and recycling utilization of these magnetic beads made this technology much suitable for the large-scale application. Compared with the conventional purification methods, the rapid process, simple equipments, easy operation and high efficiency, brought this technology with great potentialities in the treatment of industrial wastewater. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction In many regions of the world, heavy metal contamination of soil and water has caused great harm to people’s health (Robinson-Lora and Brennan, 2009). In China, the environmental situation became very serious in recent decades. The poisoning effect of cadmium contamination has aroused great vigilance because its gradual accumulation in human body results in a number of adverse health effects, for example, nephrotoxicity and osteotoxicity (Min et al., 2004; Wang and Xing, 2004). Majority cadmium contamination is caused by human activities, such as mining, waste disposal, vehicle exhausts and phosphate fertilizer application (Matheickal et al., 1999). And significant quantities of cadmium are released to environment as Cd(II) in industrial wastewater. On the other hand, as an important kind of rare metals, cadmium becomes more deficient as the economic development. To effectively extract the heavy metal ions from industrial effluents, many purification technologies have been developed (Babel and Kurniawan, 2003; Kurniawan et al., 2006). Although magnetic separation based on paramagnetic beads has been successfully applied in many biotechnology fields (Jun et al., 2009), its potential application in purification of contamination water is attracting ⇑ Corresponding author. Address: Huaqiao University, College of Materials Science and Engineering, Department of Polymer Science and Engineering, JiMei Avenue, 668 XiaMen, China. Tel.: +86 595 22691285; fax: +86 595 22692508. E-mail address: [email protected] (H. Qian). 0045-6535/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2011.03.043
much attention (Rikers et al., 1998; Feng et al., 2000; Karapinar, 2003; Marius et al., 2005; Chin et al., 2006; Oka et al., 2008). Because of the advantages of high sensitivity and convenient isolation, the technology of magnetic microsphere has been developed to purify many target products (Ritter et al., 2004; Ma et al., 2006; Chen et al., 2008; Qian et al., 2008, 2010; Chung et al., 2009). A new technology of magnetically stabilized bed was developed based on magnetic carriers (Hristov and Fachikov, 2007). Compared with the fixed bed, this technology has a higher velocity to enhance heat and mass transfers, which results in a higher treatment capacity. Compared with the fluidized beds, smaller magnetic particles could be employed in this technology. Therefore, this technology had great potential in massive purification of heavy metal ions from aqueous solution due to its easy operation, highly efficient regeneration, convenient equipments and sufficient reutilization of heavy metal ions. In this paper, we designed to prepare a new magnetic carrier with small particle size. We utilized the amino groups to capture Cd(II) in aqueous solution depending upon the complexation interaction between amino groups and Cd(II) (Su and Zang, 2004). After the micro-sized paramagnetic polymer beads were synthesized with micro-suspension polymerization, the amino groups were sufficiently modified on their surface. To realize the essential manner of the responding adsorption, several sorption models were used to analyze the adsorption process. Furthermore, the recovery of absorbed Cd(II) was investigated. The regeneration and repeated use of these magnetic beads were both studied. In addition, some
Y. Chen et al. / Chemosphere 83 (2011) 1214–1219
potential applications to deal with industrial wastewater by these magnetic beads were explored. 2. Experimental 2.1. Materials and chemicals Methyl methacrylate (MMA) and divinylbenzene (DVB) were distilled under reduced pressure to remove the inhibitor and stored at 4 °C prior to use. The initiator of 2,2-azobis-(isobutyronitrile) (AIBN) was recrystallized before used. Polyvinyl alcohol (PVA), ferric chloride hexahydrate, ferrous chloride tetrahydrate, ammonium hydroxide (NH3H2O, 25% w/v), hexadecane (HD) and oleic acid (OA) were all used as received. All materials to prepare magnetic beads were provided by China National Pharmaceutical Industry Corporation in ShangHai. 2.2. Preparation of paramagnetic beads containing abundant amino groups The OA-modified magnetic nano-particles were prepared by the chemical co-precipitation method. The magnetic beads were synthesized by micro-suspension polymerization (Qian et al., 2008, 2010). A typical recipe is described as follows. A mixture of MMA (8.0 g), DVB (2.0 g) and HD (0.3 g) was added to 2.0 g dried OAmodified Fe3O4 powder. After ultrasonic dispersion in an icecooled bath, AIBN (0.3 g) was added into the mixture and shook for 30 min to form the organic phase. The water phase was prepared with PVA solution (0.75% w/v in relation to water). The two phases were first mixed together with high-shear treatment at 3000 rpm to form polymerisable micro-suspension. Then, the polymerization was initiated by increasing the temperature to 80 °C and processed for 8 h under constant stirring at 400 rpm. The resulted magnetic beads (PMMA–DVB) were separated by magnetic decantation and thoroughly washed with distilled water and ethanol to remove excess stabilizer and other impurities. The prepared magnetic PMMA–DVB beads were converted into PMMA–DVB–NH2 beads by an aminolysis reaction. Some magnetic beads were added into ethylene diamine, and then, the mixture was reacted under refluence temperature for certain hours. Finally, the resulted magnetic PMMA–DVB–NH2 beads were separated by magnetic decantation and repeatedly washed with distilled water until neutral. There are about 0.2485 g dry beads in each gram of waterish magnetic beads. 2.3. Characterization The infrared spectrometry (FTIR) measurement was performed with a Nicolet Nexus FTIR spectrometer at a resolution of 2 cm 1. The spectra were recorded in the range from 4000 to 400 cm 1 in KBr pellets. The particle size and surface morphology of the magnetic beads were observed by scanning electron microscopy (SEM, JSM-6700F, Japan). Magnetite content of the dried samples was measured by thermogravimetric analysis (TGA, TA Instruments). The content of N in modification magnetic beads was measured by elemental analyzer. The concentration of Cd(II) was detected by Atomic Absorption Spectrometer, which was provided by Analysis of General Instrument Corporation in Beijing. 2.4. Adsorption and recovery of Cd(II) The adsorption studies were carried out in batch-wise mode. In a typical adsorption experiment, the magnetic adsorbents were suspended in a 30 mL aqueous solution containing different Cd(II) concentration. The mixture was stirred on shaker at room temper-
1215
ature (25 °C) for certain period in certain pH, which is different from each experiment. The responding conditions were listed in every figure or table. After completion of the adsorption, the supernatants were magnetically separated with the help of a handhold magnet. Finally, the adsorbed Cd(II) was recovered by elution with H2SO4 aqueous solution. The supernatants of each step were collected and analyzed. 2.5. Regeneration of magnetic beads The regeneration of magnetic beads was carried out in NaOH aqueous solution. The magnetic beads were directly washed with NaOH solution for half an hour. Then, these magnetic beads were fully washed with distilled water. A series of NaOH concentrations were employed to investigate the regeneration of these magnetic beads. 3. Results and discussion 3.1. Preparation of magnetic beads with abundant amino groups The successive technologies are much important for the large scale treatment of industrial wastewater. The conventional technologies are both focused on the fixed beds and fluidized beds. But, the flow velocity in the fixed beds is too low to satisfy the large treatment capacity. The small particles (<50 lm) are usually limited in fluidized beds for its loss with the liquid or gas although they have large specific surface. While in magnetically stabilized bed, some small magnetic particles could be used due the assistance of the external magnetic field. And these small particles could effectively improve its performance of adsorption and recovery. Thus, some micron sized magnetic beads were designed and synthesized in this paper. The magnetic beads were prepared with MMA and DVB in the presence of modified magnetite fluid by micro-suspension polymerization (Qian et al., 2010). The independent distribution of these magnetic beads was observed in Fig. 1. It is clear that the particles present spherical shape and the main diameter of these magnetic beads falls between 1 and 6 lm. Because of the addition of hydrophobic agent (HD), the mass exchange and coalescence between monomer droplets were effectively suppressed resulting in the stability of these small particles. This key step distinguished it from the conventional suspension polymerization. Certainly, the responding magnetic nano-beads could be prepared with emulsion polymerization, but the magnetism of these beads was too weak to satisfy the need of rapid isolation. Because the designed adsorption is mainly based on the complexation interaction between amino group and Cd(II), the obtained magnetic beads were fully modified with ethylene diamine. The reaction was performed under the reflux temperature of ethylene diamine. After 8 d, the N content of these magnetic beads reached to 2%. These modification processes were recorded by FTIR, which was showed in Fig. 1. As expected, both the magnetic beads (MB) and the magnetic beads modified with amino groups (MBA) showed similar spectral profiles, but some details are different. The presence of low intensity peaks at 3210 cm 1 is attributed to N–H symmetrical stretching of –NH2 on the modification magnetic beads. The intense absorption peak at 1729 cm 1 is assigned to carbonyl groups of methyl methacrylate. The less intense adsorption at 1630 cm 1 is associated to N–H flexural vibration of –NH2 groups on MBA. The weak peaks at 1355 and 1543 cm 1 correspond to plane flexural vibration and deformation vibration of N–H in –C– NH–C– groups, respectively (Ying et al., 2010). A strong adsorption peak at 585 cm 1 corresponds to the characteristic stretching
1216
Y. Chen et al. / Chemosphere 83 (2011) 1214–1219
Fig. 1. FTIR spectra and SEM photo of these magnetic beads.
vibration band of the magnetite (Fe3O4). From the above analysis, it is clear that abundant amino groups were modified on the surface of these magnetic beads. 3.2. Efficient extraction of Cd(II) by these magnetic beads In the treatment of the industrial wastewater, the principle target is to effectively eliminate the heavy metal ions from aqueous solution. The results in Fig. 2 were so inspiring that Cd(II) concentration was reduced to 0.1 lg mL 1 after its solution was absorbed by these magnetic beads. This concentration is lower than the governmental standard of China for cadmium pollutants discharge (GB 8978-1996). Furthermore, after the recovery, the Cd(II) concentra-
tion reached 44 lg mL 1, which meant that more than 99% Cd2+ could be recycled. To further reveal the essential interaction between the magnetic beads and Cd(II), several adsorption models were used to describe the adsorption process. From Table 1, it was found that theoretical saturation adsorbance (qmax) obtained from Langmuir model was 68 mg g 1, which was much close to the practical saturation adsorbance. For obtaining the practical saturation adsorbance, some waterish magnetic beads (5 g) were employed to capture Cd2+ in high concentration, including 7019 and 12 353 lg mL 1. The equilibrium adsorbances were 67 and 68 mg g 1 dried magnetic beads, respectively. Then, the practical saturation adsorbance of Cd(II) onto magnetic beads was estimated
Fig. 2. Clearance and recovery of Cd(II) from its aqueous solution. The adsorption was carried out with 5 g waterish magnetic beads in 30 mL aqueous solution containing Cd(II) (44 lg mL 1), and the pH value of solution was 6, the sample was collected after 15 min. And the absorbed Cd(II) were recovered with 30 mL 0.1 M H2SO4 solution, the sample was collected after 15 min. The shaking speed was 120 rpm.
Y. Chen et al. / Chemosphere 83 (2011) 1214–1219 Table 1 Parameters of adsorption isotherm models. 1
)
b (mL mg 11 ± 4
1
)
R2 0.999
Langmuir constants
am (mg g 68 ± 1
Freundlich constants
logkf 1.21 ± 0.05
1/n 0.18 ± 0.02
R2 0.952
BET constants
1/VmC 0.97 ± 1.40
(C 1)/VmC 37 ± 4
R2 0.936
as 68 mg g 1. Moreover, from the square error (R2) of the fitting curves, Langmuir model becomes more suitable to fit the adsorption data. Langmuir model is favorable to describe the chemical adsorption, which is generally occurred on monolayer between the adsorbent and the adsorbate (Gupta et al., 2003). Contrary to it, the BET model, which is usually employed to describe the physical multilayer adsorption, has a larger error to fit the responding experimental data (Do et al., 2010). Therefore, a conclusion could be drawn that this adsorption of Cd2+ on magnetic beads was mainly attributed to chemical adsorption and only monolayer of Cd(II) was adsorbed on these magnetic beads. Furthermore, from the N content of these magnetic beads (2%), it was found about 0.71 mmol amino groups existed in each gram of magnetic beads. But, the saturation adsorption amount of Cd(II) onto magnetic beads reached 0.60 mmol g 1 magnetic beads. It means that each amino group could capture a Cd2+. However, in the conventional complexation interaction between Cd(II) and amino group, at least two amino groups are required to complex with a Cd2+ (Su and Zang, 2004). Thus, this complexing force between Cd(II) and amino groups on magnetic beads was not as strong as usual. It provided possible for the easy recovery of absorbed Cd2+ from these magnetic beads in mild conditions. When the initial Cd2+ concentration was different, the change of the responding adsorption capacity was shown in Fig. 3a. The equilibrium adsorbance reached the theoretical saturation capacity when the initial Cd2+ concentration is higher than 4817 lg mL 1. However, the clearance efficiency of Cd(II) greatly decreased. When the initial concentration was below 1000 lg mL 1, the clearance efficiency exceeded 99%. In other words, the ratio of the Cd2+ concentration to the amount of magnetic beads took an important role in the Cd(II) clearance. Allowing for the complete elimination of Cd(II) from aqueous solution, an appropriate proportion between the Cd(II) amount and dried magnetic beads is drawn to 23.3 (mg):1 (g). Another advantage of this magnetic technology, revealed from Fig. 3a, is the rapid adsorption process. No matter what initial Cd2+ concentration was employed, the adsorption equilibrium could be reached within 20 min because of the small particles. Furthermore, compared with the centrifugation and precipitation,
1217
the rapid magnetic separation makes this technology more convenient and accessible. The adsorption of metal ions is highly dependent on the pH value of its aqueous solution (Kula et al., 2008). Thus, the effect of pH value on the adsorption behavior was investigated in Fig. 3b. The initial Cd2+ concentration was 1759 lg mL 1, and 3 g waterish magnetic beads were employed to absorb Cd2+ in each experiment. After adsorption, the residual Cd2+ concentration was detected. In the acidic conditions, the magnetic beads could effectively capture Cd(II) due to the protonation of Cd2+. But, in neutral aqueous solution, the adsorption was greatly inhibited. When the pH value continuously increased to 9–11, some Cd2+ might generated as the deposition of Cd(OH)2. As an example, in the condition of pH 11, the solubility-product constant of Cd(OH)2 was only 7.2 10 15 (Sun and Skold, 2001). Thus, in alkaline conditions, the sharply decrease of Cd(II) concentration is mainly attributed to the precipitation of Cd(OH)2, but not to the adsorption by these magnetic beads. Therefore, this technology based on magnetic beads should be carried out in the pH range of 3–6. 3.3. Complete recovery of adsorbed Cd(II) In the treatment of heavy metal ions in aqueous solution, much attention is mainly being focused on their complete removal from water to avoid pollution. However, in view of the enormous economic value and the rapid depletion of these rare metals, the recyclable application of these heavy metal ions has aroused great interests. Thus, the factors to influence the recovery of adsorbed Cd(II) were investigated in Fig. 4. A series of different acids were used to release Cd2+ from the magnetic beads. It shows that strong acids, such as HNO3, HCl and H2SO4, have strong effects on the desorption and the weak acid (HAc) has an inferior result. In addition, the salt solution has little effect on desorption. Therefore, the Fig. 4 arrived at a conclusion that H+ played an important role in releasing Cd(II) from the surface binding-sites on the adsorbent. Due to the sufficient protonation of amino groups in acidic environment, the binding Cd(II) could be easily released from these magnetic beads. Moreover, the complexation interaction between Cd(II) and magnetic beads, as described, is weaker than usual. It was reasonable to the desorption efficiency even reached 100% in 0.05 M H2SO4 solution, which meant that all binding Cd(II) could be completely recovered. Considering of the oxidation and corrosion of these magnetic beads by acid, the influence of its concentration was investigated in Table 2. It found that only a few Cd(II) were released in the low acid concentration (0.01 M). As the acid concentration exceeded 0.1 M, an overwhelming majority of absorbed Cd2+ were released. Because there was no loss of magnetic performance when
Fig. 3. (a) Effect of initial concentration of Cd(II) on the adsorption. The adsorption was carried out with 5 g waterish magnetic beads in 30 mL aqueous solution containing Cd(II). The pH value of solution was 6. And the sample was collected every 15 min until two hours. (b) Effect of pH on the adsorption. The adsorption was carried out with 3 g waterish magnetic beads in 30 mL Cd(II) aqueous solution (1759 lg mL 1). After 15 min, the sample was collected with the help of the magnetic separation.
1218
Y. Chen et al. / Chemosphere 83 (2011) 1214–1219
Fig. 4. Desorption of Cd(II) in the different reagents. The waterish magnetic beads (4.5 g) were employed to capture Cd(II). The different reagents including H2SO4, HCl, HNO3, NaNO3 and HAc were used to recover the absorbed Cd(II). The reagent volume was always kept 30 mL.
Table 2 Complete recovery of Cd(II) and easy regeneration of these magnetic beads.
protonated by strong acid in the process of the recovery, these magnetic beads could not be directly reused. From the results in Table 2, it found the adsorption capacity of these magnetic beads could be effectively recovered by NaOH solution. If NaOH solution with high concentration was frequently employed, some surface functional groups on the magnetic beads might be destroyed resulting in the decrease of adsorption capacity (Deng et al., 2010). Therefore, the NaOH aqueous solution (0.1 M) was selected to regenerate the magnetic beads. The repeat utilization of these magnetic beads was investigated in Fig. 5. It is obvious that the adsorption capacity of these magnetic beads changed little within first ten cycles. But, after fifteen cycles, the adsorption capacity declined rapidly because some surface functional groups on these magnetic beads were damaged by the acid or alkaline conditions during the reduplicate regeneration. Finally, the adsorption capacity reached platform again after 25 cycles and the relative adsorption capacity decreased 80%. Therefore, to enhance the stability of surface structure of these magnetic beads is much significant for their further application in the industry.
3.5. Clearance of the simulated wastewater
Effect of acid concentration on the desorption Concentration of H2SO4 (M) 1 Amount of desorption (mg g 1) 54 Desorption efficiency (%) 100
0.1 53 98
0.01 8 14
Effect of NaOH concentration on the regeneration Concentration of NaOH (M) 1 Adsorbance (mg g 1) 51 Regeneration efficiency (%) 95
0.1 51 96
0.01 8 15
The adsorption was carried out with 5 g waterish magnetic beads and the pH value of solution was 6, then the responding recovery was performed in 30 mL H2SO4 solution with different concentration. After the recovery, these magnetic beads were regenerated with 30 mL NaOH aqueous solution.
these magnetic beads were washed with H2SO4 solution (0.1 M), it was selected to recover captured Cd(II). 3.4. Repeated use of these magnetic beads The absorbent regeneration is an important factor to influence its service efficiency. Because the amino group was fully
In the real industrial wastewater, there were many coexisting substances such as metal ions, anions and caustic acid. Therefore, these magnetic beads were employed to recover Cd(II) in the simulated wastewater (Escobar et al., 2006). The chemical composition of this simulated wastewater is as following: K+ (2 mg dm 3), Ca2+ (102 mg dm 3), Mg2+ (48 mg dm 3), Na+ (94 mg dm 3), SO24 (192 mg dm 3), HCO3 (250 mg dm 3), Cl (182 mg dm 3) and Cd2+ (2916 mg dm 3). The coexisting ions had a great effect on the adsorption of Cd2+ on these magnetic beads. Although the Cd2+ concentration could be still reduced to the governmental standard by the adsorption with these magnetic beads, the equilibrium adsorbance of Cd2+ was only 29 mg g 1, which is lower than half of the saturation adsorbance in pure Cd2+ aqueous solution. Additionally, it was found the adsorbance of Mg2+ was about 0.26 mg g 1, which meant that other metal ions disturbed the adsorption of Cd2+ on magnetic beads. It is reasonable that amino group could generate complexation interaction with many metal ions. The selectivity of these magnetic beads to Cd(II) was not very satisfied. But, as an effective method to concentrate the metal ions
Fig. 5. Investigation of repeated use of these magnetic beads. The adsorption was carried with 5 g waterish magnetic beads in 30 mL solution containing Cd(II) (888 lg mL 1), the pH value of solution was 6. After sufficient washing, the captured Cd(II) was recovered from the magnetic beads in 30 mL 0.1 M H2SO4 solution. Then, these beads were regenerated with 30 mL 0.1 M NaOH solution.
Y. Chen et al. / Chemosphere 83 (2011) 1214–1219
from some industrial wastewater, this technology is much convenient and efficient.
4. Conclusions The magnetic polymer beads with sensitive magnetic response were employed to remove Cd(II) from aqueous solution. Depending on the large specific surface area of these beads, the saturation absorbance for Cd(II) reached 68 mg g 1 dried magnetic beads. In order to keep a high clearance efficiency (>99.5), an appropriate proportion is drawn to 23.3 (mg Cd2+):1 (g dried magnetic beads). The suitable pH range for the adsorption was in 3–6. Moreover, the absorbed Cd(II) could be completely recovered in acid conditions and these magnetic beads could be easily regenerated in alkaline solution. Additionally, the excellent performance of repeated use (more than 10 cycles) makes this technology become more efficient. Therefore, by using these magnetic beads in magnetically stabilized bed, it becomes much potential to actualize the successive treatment of industrial wastewater containing Cd(II). At the same time, the complete recovery of Cd(II) could be achieved. This technology makes it possible not only to avoid the Cd(II) pollution, but also to actualize the recyclable utilization of Cd(II). Acknowledgements The authors gratefully acknowledge financing from Program for New Century Excellent Talents in University of Fujian Province (07FJRC02) and the Fundamental Research Funds for HuaQiao University (JB-GJ1007). References Babel, S., Kurniawan, T.A., 2003. Low-cost adsorbents for heavy metals uptake from contaminated water: a review. J. Hazard. Mater. 97, 219–243. Chen, M.Q., Lin, Z.Y., Qian, H., 2008. Preparation of thiophilic paramagnetic adsorbent for separation of antibodies. Chin. Chem. Lett. 19, 1495–1498. Chin, C.M., Chen, P.W., Wang, L.J., 2006. Removal of nanoparticles from CMP wastewater by magnetic seeding aggregation. Chemosphere 63, 1809–1813. Chung, T., Chang, J., Lee, W., 2009. Application of magnetic poly(styrene–glycidyl methacrylate) microspheres for immunomagnetic separation of bone marrow cells. J. Magn. Magn. Mater. 321, 1635–1638. Deng, W., Wang, M.Y., Chen, G., Kan, C.Y., 2010. Morphological evolution of multistage polymer particles in the alkali post-treatment. Eur. Polym. J. 46, 1210–1215. Do, D.D., Do, H.D., Nicholson, D., 2010. A computer appraisal of BET theory, BET surface area and the calculation of surface excess for gas adsorption on a graphite surface. Chem. Eng. Sci. 65, 3331–3340.
1219
Escobar, C., Soto-Salazar, C., Toral, M.I., 2006. Optimization of the electrocoagulation process for the removal of copper, lead and cadmium in natural waters and simulated wastewater. J. Environ. Manage. 81, 384–391. Feng, D., Aldrich, C., Tan, H., 2000. Removal of heavy metal ions by carrier magnetic separation of adsorptive particulates. Hydrometallurgy 56, 359–368. Gupta, V.K., Jain, C.K., Ali, I., Sharma, M., Saini, V.K., 2003. Removal of cadmium and nickel from wastewater using bagasse fly ash – a sugar industry waste. Water Res. 37, 4038–4044. Hristov, J., Fachikov, L., 2007. An overview of separation by magnetically stabilized beds: state-of-the-art and potential applications. China Particuol. 5, 11–18. Jun, B.H., Noh, M.S., Kim, G., Kang, H., Kim, J.H., Chung, W.J., Kim, M.S., Kim, Y.K., Cho, M.H., Jeong, D.H., Lee, Y.S., 2009. Protein separation and identification using magnetic beads encoded with surface-enhanced Raman spectroscopy. Anal. Biochem. 391, 24–30. Karapinar, N., 2003. Magnetic separation of ferrihydrite from wastewater by magnetic seeding and high-gradient magnetic separation. Int. J. Miner. Process. 71, 45–54. Kula, I., Ugurlu, M., Karaoglu, H., Çelik, A., 2008. Adsorption of Cd (II) from aqueous solutions using activated carbon prepared from olive stone by ZnCl2 activation. Bioresour. Technol. 99, 492–501. Kurniawan, T.A., Chan, G.Y.S., Lo, W., Babel, S., 2006. Physico–chemical treatment techniques for wastewater laden with heavy metals. Chem. Eng. J. 118, 83–98. Ma, Z., Liu, X., Guan, Y., Liu, H., 2006. Synthesis of magnetic silica nanospheres with metal ligands and application in affinity separation of proteins. Colloids Surf. 275, 87–91. Marius, M.S., James, P.A.B., Bahaj, A.S., Smallman, D.J., 2005. Development of a highly magnetic iron sulphide for metal uptake and magnetic separation. J. Magn. Magn. Mater. 293, 567–571. Matheickal, J.T., YU, Q., Woodburn, G.M., 1999. Bisorption of cadmium (II) from aqueous solutions by pre-treated biomass of marine alga Durvillaea potatorum. Water Res. 33, 335–342. Min, S.H., Han, J.S., Shin, E.W., Park, J.K., 2004. Improvement of cadmium ion removal by base treatment of juniper fiber. Water Res. 38, 1289–1295. Oka, T., Kanayama, H., Fukui, S., Ogawa, J., Sato, T., Ooizumi, M., Terasawa, T., Itoh, Y., Yabuno, R., 2008. Application of HTS bulk magnet system to the magnetic separation techniques for water purification. Physica 468, 2128–2132. Qian, H., Chen, M.Q., Lin, Z.Y., 2008. The effective and specific isolation of antibodies from human serum by using thiophilic paramagnetic polymer beads. Colloids Surf. 67, 224–229. Qian, H., Li, C., Lin, Z.Y., Zhang, Y.X., 2010. Using thiophilic magnetic beads in purification of antibodies from human serum. Colloids Surf. 75, 342–348. Rikers, R.A., Rem, P., Dalmijn, W.L., 1998. Improved method for prediction of heavy metal recoveries from soil using high intensity magnetic separation (HIMS). Int. J. Miner. Process. 54, 165–182. Ritter, J.A., Ebner, A.D., Daniel, K.D., Stewart, K.L., 2004. Application of high gradient magnetic separation principles to magnetic drug targeting. J. Magn. Magn. Mater. 280, 184–201. Robinson-Lora, M.A., Brennan, R.A., 2009. Efficient metal removal and neutralization of acid mine drainage by crab-shell chitin under batch and continuous-flow conditions. Bioresour. Technol. 100, 5063–5071. Su, X., Zang, X., 2004. Engineering Inorganic Chemistry. East China University of Science and Technology Press, Shanghai. Sun, Z.X., Skold, R.O., 2001. A multi-parameter titration method for the determination of formation pH for metal hydroxides. Miner. Eng. 14, 1429– 1443. Wang, K., Xing, B., 2004. Mutual effects of cadmium and phosphate on their adsorption and desorption by goethite. Environ. Pollut. 127, 13–20. Ying, W., Bao, Y.Y., Zhou, Q.X., 2010. Simultaneous adsorption and desorption of cadmium and tetracycline on cinnamon soil. Chemosphere 80, 807–812.
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Clearance and recovery of Cd(II) from aqueous solution by magnetic separation technology YongLe Chen, Hao Qian ⇑, Fan Wu, Jian Zhou College of Materials Science and Engineering, HuaQiao University, XiaMen 361021, Fujian, China
a r t i c l e
i n f o
Article history: Received 3 September 2010 Received in revised form 20 March 2011 Accepted 22 March 2011 Available online 12 April 2011 Keywords: Magnetic beads Adsorption Desorption Regeneration Cd(II)
a b s t r a c t An effective method to actualize the recycling use of Cd(II) in industrial wastewater was developed by using the magnetic beads, which was modified with ethylenediamine. When the industrial wastewater was treated with these magnetic beads, the Cd(II) concentration in the solution was sharply reduced to the governmental standard (0.1 lg mL 1) of China. Based on the monolayer adsorption of Cd(II) on the surface of these magnetic beads, the saturation capacity for Cd(II) reached to 68 mg g 1 dried magnetic beads. On the other hand, the binding Cd(II) could be easily recovered in acid conditions and the recovery efficiency exceeded 99%. Thus, in the process of the wastewater purification, the recycling utilization of Cd(II) was realized. Additionally, the excellent capability of regeneration and recycling utilization of these magnetic beads made this technology much suitable for the large-scale application. Compared with the conventional purification methods, the rapid process, simple equipments, easy operation and high efficiency, brought this technology with great potentialities in the treatment of industrial wastewater. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction In many regions of the world, heavy metal contamination of soil and water has caused great harm to people’s health (Robinson-Lora and Brennan, 2009). In China, the environmental situation became very serious in recent decades. The poisoning effect of cadmium contamination has aroused great vigilance because its gradual accumulation in human body results in a number of adverse health effects, for example, nephrotoxicity and osteotoxicity (Min et al., 2004; Wang and Xing, 2004). Majority cadmium contamination is caused by human activities, such as mining, waste disposal, vehicle exhausts and phosphate fertilizer application (Matheickal et al., 1999). And significant quantities of cadmium are released to environment as Cd(II) in industrial wastewater. On the other hand, as an important kind of rare metals, cadmium becomes more deficient as the economic development. To effectively extract the heavy metal ions from industrial effluents, many purification technologies have been developed (Babel and Kurniawan, 2003; Kurniawan et al., 2006). Although magnetic separation based on paramagnetic beads has been successfully applied in many biotechnology fields (Jun et al., 2009), its potential application in purification of contamination water is attracting ⇑ Corresponding author. Address: Huaqiao University, College of Materials Science and Engineering, Department of Polymer Science and Engineering, JiMei Avenue, 668 XiaMen, China. Tel.: +86 595 22691285; fax: +86 595 22692508. E-mail address: [email protected] (H. Qian). 0045-6535/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2011.03.043
much attention (Rikers et al., 1998; Feng et al., 2000; Karapinar, 2003; Marius et al., 2005; Chin et al., 2006; Oka et al., 2008). Because of the advantages of high sensitivity and convenient isolation, the technology of magnetic microsphere has been developed to purify many target products (Ritter et al., 2004; Ma et al., 2006; Chen et al., 2008; Qian et al., 2008, 2010; Chung et al., 2009). A new technology of magnetically stabilized bed was developed based on magnetic carriers (Hristov and Fachikov, 2007). Compared with the fixed bed, this technology has a higher velocity to enhance heat and mass transfers, which results in a higher treatment capacity. Compared with the fluidized beds, smaller magnetic particles could be employed in this technology. Therefore, this technology had great potential in massive purification of heavy metal ions from aqueous solution due to its easy operation, highly efficient regeneration, convenient equipments and sufficient reutilization of heavy metal ions. In this paper, we designed to prepare a new magnetic carrier with small particle size. We utilized the amino groups to capture Cd(II) in aqueous solution depending upon the complexation interaction between amino groups and Cd(II) (Su and Zang, 2004). After the micro-sized paramagnetic polymer beads were synthesized with micro-suspension polymerization, the amino groups were sufficiently modified on their surface. To realize the essential manner of the responding adsorption, several sorption models were used to analyze the adsorption process. Furthermore, the recovery of absorbed Cd(II) was investigated. The regeneration and repeated use of these magnetic beads were both studied. In addition, some
Y. Chen et al. / Chemosphere 83 (2011) 1214–1219
potential applications to deal with industrial wastewater by these magnetic beads were explored. 2. Experimental 2.1. Materials and chemicals Methyl methacrylate (MMA) and divinylbenzene (DVB) were distilled under reduced pressure to remove the inhibitor and stored at 4 °C prior to use. The initiator of 2,2-azobis-(isobutyronitrile) (AIBN) was recrystallized before used. Polyvinyl alcohol (PVA), ferric chloride hexahydrate, ferrous chloride tetrahydrate, ammonium hydroxide (NH3H2O, 25% w/v), hexadecane (HD) and oleic acid (OA) were all used as received. All materials to prepare magnetic beads were provided by China National Pharmaceutical Industry Corporation in ShangHai. 2.2. Preparation of paramagnetic beads containing abundant amino groups The OA-modified magnetic nano-particles were prepared by the chemical co-precipitation method. The magnetic beads were synthesized by micro-suspension polymerization (Qian et al., 2008, 2010). A typical recipe is described as follows. A mixture of MMA (8.0 g), DVB (2.0 g) and HD (0.3 g) was added to 2.0 g dried OAmodified Fe3O4 powder. After ultrasonic dispersion in an icecooled bath, AIBN (0.3 g) was added into the mixture and shook for 30 min to form the organic phase. The water phase was prepared with PVA solution (0.75% w/v in relation to water). The two phases were first mixed together with high-shear treatment at 3000 rpm to form polymerisable micro-suspension. Then, the polymerization was initiated by increasing the temperature to 80 °C and processed for 8 h under constant stirring at 400 rpm. The resulted magnetic beads (PMMA–DVB) were separated by magnetic decantation and thoroughly washed with distilled water and ethanol to remove excess stabilizer and other impurities. The prepared magnetic PMMA–DVB beads were converted into PMMA–DVB–NH2 beads by an aminolysis reaction. Some magnetic beads were added into ethylene diamine, and then, the mixture was reacted under refluence temperature for certain hours. Finally, the resulted magnetic PMMA–DVB–NH2 beads were separated by magnetic decantation and repeatedly washed with distilled water until neutral. There are about 0.2485 g dry beads in each gram of waterish magnetic beads. 2.3. Characterization The infrared spectrometry (FTIR) measurement was performed with a Nicolet Nexus FTIR spectrometer at a resolution of 2 cm 1. The spectra were recorded in the range from 4000 to 400 cm 1 in KBr pellets. The particle size and surface morphology of the magnetic beads were observed by scanning electron microscopy (SEM, JSM-6700F, Japan). Magnetite content of the dried samples was measured by thermogravimetric analysis (TGA, TA Instruments). The content of N in modification magnetic beads was measured by elemental analyzer. The concentration of Cd(II) was detected by Atomic Absorption Spectrometer, which was provided by Analysis of General Instrument Corporation in Beijing. 2.4. Adsorption and recovery of Cd(II) The adsorption studies were carried out in batch-wise mode. In a typical adsorption experiment, the magnetic adsorbents were suspended in a 30 mL aqueous solution containing different Cd(II) concentration. The mixture was stirred on shaker at room temper-
1215
ature (25 °C) for certain period in certain pH, which is different from each experiment. The responding conditions were listed in every figure or table. After completion of the adsorption, the supernatants were magnetically separated with the help of a handhold magnet. Finally, the adsorbed Cd(II) was recovered by elution with H2SO4 aqueous solution. The supernatants of each step were collected and analyzed. 2.5. Regeneration of magnetic beads The regeneration of magnetic beads was carried out in NaOH aqueous solution. The magnetic beads were directly washed with NaOH solution for half an hour. Then, these magnetic beads were fully washed with distilled water. A series of NaOH concentrations were employed to investigate the regeneration of these magnetic beads. 3. Results and discussion 3.1. Preparation of magnetic beads with abundant amino groups The successive technologies are much important for the large scale treatment of industrial wastewater. The conventional technologies are both focused on the fixed beds and fluidized beds. But, the flow velocity in the fixed beds is too low to satisfy the large treatment capacity. The small particles (<50 lm) are usually limited in fluidized beds for its loss with the liquid or gas although they have large specific surface. While in magnetically stabilized bed, some small magnetic particles could be used due the assistance of the external magnetic field. And these small particles could effectively improve its performance of adsorption and recovery. Thus, some micron sized magnetic beads were designed and synthesized in this paper. The magnetic beads were prepared with MMA and DVB in the presence of modified magnetite fluid by micro-suspension polymerization (Qian et al., 2010). The independent distribution of these magnetic beads was observed in Fig. 1. It is clear that the particles present spherical shape and the main diameter of these magnetic beads falls between 1 and 6 lm. Because of the addition of hydrophobic agent (HD), the mass exchange and coalescence between monomer droplets were effectively suppressed resulting in the stability of these small particles. This key step distinguished it from the conventional suspension polymerization. Certainly, the responding magnetic nano-beads could be prepared with emulsion polymerization, but the magnetism of these beads was too weak to satisfy the need of rapid isolation. Because the designed adsorption is mainly based on the complexation interaction between amino group and Cd(II), the obtained magnetic beads were fully modified with ethylene diamine. The reaction was performed under the reflux temperature of ethylene diamine. After 8 d, the N content of these magnetic beads reached to 2%. These modification processes were recorded by FTIR, which was showed in Fig. 1. As expected, both the magnetic beads (MB) and the magnetic beads modified with amino groups (MBA) showed similar spectral profiles, but some details are different. The presence of low intensity peaks at 3210 cm 1 is attributed to N–H symmetrical stretching of –NH2 on the modification magnetic beads. The intense absorption peak at 1729 cm 1 is assigned to carbonyl groups of methyl methacrylate. The less intense adsorption at 1630 cm 1 is associated to N–H flexural vibration of –NH2 groups on MBA. The weak peaks at 1355 and 1543 cm 1 correspond to plane flexural vibration and deformation vibration of N–H in –C– NH–C– groups, respectively (Ying et al., 2010). A strong adsorption peak at 585 cm 1 corresponds to the characteristic stretching
1216
Y. Chen et al. / Chemosphere 83 (2011) 1214–1219
Fig. 1. FTIR spectra and SEM photo of these magnetic beads.
vibration band of the magnetite (Fe3O4). From the above analysis, it is clear that abundant amino groups were modified on the surface of these magnetic beads. 3.2. Efficient extraction of Cd(II) by these magnetic beads In the treatment of the industrial wastewater, the principle target is to effectively eliminate the heavy metal ions from aqueous solution. The results in Fig. 2 were so inspiring that Cd(II) concentration was reduced to 0.1 lg mL 1 after its solution was absorbed by these magnetic beads. This concentration is lower than the governmental standard of China for cadmium pollutants discharge (GB 8978-1996). Furthermore, after the recovery, the Cd(II) concentra-
tion reached 44 lg mL 1, which meant that more than 99% Cd2+ could be recycled. To further reveal the essential interaction between the magnetic beads and Cd(II), several adsorption models were used to describe the adsorption process. From Table 1, it was found that theoretical saturation adsorbance (qmax) obtained from Langmuir model was 68 mg g 1, which was much close to the practical saturation adsorbance. For obtaining the practical saturation adsorbance, some waterish magnetic beads (5 g) were employed to capture Cd2+ in high concentration, including 7019 and 12 353 lg mL 1. The equilibrium adsorbances were 67 and 68 mg g 1 dried magnetic beads, respectively. Then, the practical saturation adsorbance of Cd(II) onto magnetic beads was estimated
Fig. 2. Clearance and recovery of Cd(II) from its aqueous solution. The adsorption was carried out with 5 g waterish magnetic beads in 30 mL aqueous solution containing Cd(II) (44 lg mL 1), and the pH value of solution was 6, the sample was collected after 15 min. And the absorbed Cd(II) were recovered with 30 mL 0.1 M H2SO4 solution, the sample was collected after 15 min. The shaking speed was 120 rpm.
Y. Chen et al. / Chemosphere 83 (2011) 1214–1219 Table 1 Parameters of adsorption isotherm models. 1
)
b (mL mg 11 ± 4
1
)
R2 0.999
Langmuir constants
am (mg g 68 ± 1
Freundlich constants
logkf 1.21 ± 0.05
1/n 0.18 ± 0.02
R2 0.952
BET constants
1/VmC 0.97 ± 1.40
(C 1)/VmC 37 ± 4
R2 0.936
as 68 mg g 1. Moreover, from the square error (R2) of the fitting curves, Langmuir model becomes more suitable to fit the adsorption data. Langmuir model is favorable to describe the chemical adsorption, which is generally occurred on monolayer between the adsorbent and the adsorbate (Gupta et al., 2003). Contrary to it, the BET model, which is usually employed to describe the physical multilayer adsorption, has a larger error to fit the responding experimental data (Do et al., 2010). Therefore, a conclusion could be drawn that this adsorption of Cd2+ on magnetic beads was mainly attributed to chemical adsorption and only monolayer of Cd(II) was adsorbed on these magnetic beads. Furthermore, from the N content of these magnetic beads (2%), it was found about 0.71 mmol amino groups existed in each gram of magnetic beads. But, the saturation adsorption amount of Cd(II) onto magnetic beads reached 0.60 mmol g 1 magnetic beads. It means that each amino group could capture a Cd2+. However, in the conventional complexation interaction between Cd(II) and amino group, at least two amino groups are required to complex with a Cd2+ (Su and Zang, 2004). Thus, this complexing force between Cd(II) and amino groups on magnetic beads was not as strong as usual. It provided possible for the easy recovery of absorbed Cd2+ from these magnetic beads in mild conditions. When the initial Cd2+ concentration was different, the change of the responding adsorption capacity was shown in Fig. 3a. The equilibrium adsorbance reached the theoretical saturation capacity when the initial Cd2+ concentration is higher than 4817 lg mL 1. However, the clearance efficiency of Cd(II) greatly decreased. When the initial concentration was below 1000 lg mL 1, the clearance efficiency exceeded 99%. In other words, the ratio of the Cd2+ concentration to the amount of magnetic beads took an important role in the Cd(II) clearance. Allowing for the complete elimination of Cd(II) from aqueous solution, an appropriate proportion between the Cd(II) amount and dried magnetic beads is drawn to 23.3 (mg):1 (g). Another advantage of this magnetic technology, revealed from Fig. 3a, is the rapid adsorption process. No matter what initial Cd2+ concentration was employed, the adsorption equilibrium could be reached within 20 min because of the small particles. Furthermore, compared with the centrifugation and precipitation,
1217
the rapid magnetic separation makes this technology more convenient and accessible. The adsorption of metal ions is highly dependent on the pH value of its aqueous solution (Kula et al., 2008). Thus, the effect of pH value on the adsorption behavior was investigated in Fig. 3b. The initial Cd2+ concentration was 1759 lg mL 1, and 3 g waterish magnetic beads were employed to absorb Cd2+ in each experiment. After adsorption, the residual Cd2+ concentration was detected. In the acidic conditions, the magnetic beads could effectively capture Cd(II) due to the protonation of Cd2+. But, in neutral aqueous solution, the adsorption was greatly inhibited. When the pH value continuously increased to 9–11, some Cd2+ might generated as the deposition of Cd(OH)2. As an example, in the condition of pH 11, the solubility-product constant of Cd(OH)2 was only 7.2 10 15 (Sun and Skold, 2001). Thus, in alkaline conditions, the sharply decrease of Cd(II) concentration is mainly attributed to the precipitation of Cd(OH)2, but not to the adsorption by these magnetic beads. Therefore, this technology based on magnetic beads should be carried out in the pH range of 3–6. 3.3. Complete recovery of adsorbed Cd(II) In the treatment of heavy metal ions in aqueous solution, much attention is mainly being focused on their complete removal from water to avoid pollution. However, in view of the enormous economic value and the rapid depletion of these rare metals, the recyclable application of these heavy metal ions has aroused great interests. Thus, the factors to influence the recovery of adsorbed Cd(II) were investigated in Fig. 4. A series of different acids were used to release Cd2+ from the magnetic beads. It shows that strong acids, such as HNO3, HCl and H2SO4, have strong effects on the desorption and the weak acid (HAc) has an inferior result. In addition, the salt solution has little effect on desorption. Therefore, the Fig. 4 arrived at a conclusion that H+ played an important role in releasing Cd(II) from the surface binding-sites on the adsorbent. Due to the sufficient protonation of amino groups in acidic environment, the binding Cd(II) could be easily released from these magnetic beads. Moreover, the complexation interaction between Cd(II) and magnetic beads, as described, is weaker than usual. It was reasonable to the desorption efficiency even reached 100% in 0.05 M H2SO4 solution, which meant that all binding Cd(II) could be completely recovered. Considering of the oxidation and corrosion of these magnetic beads by acid, the influence of its concentration was investigated in Table 2. It found that only a few Cd(II) were released in the low acid concentration (0.01 M). As the acid concentration exceeded 0.1 M, an overwhelming majority of absorbed Cd2+ were released. Because there was no loss of magnetic performance when
Fig. 3. (a) Effect of initial concentration of Cd(II) on the adsorption. The adsorption was carried out with 5 g waterish magnetic beads in 30 mL aqueous solution containing Cd(II). The pH value of solution was 6. And the sample was collected every 15 min until two hours. (b) Effect of pH on the adsorption. The adsorption was carried out with 3 g waterish magnetic beads in 30 mL Cd(II) aqueous solution (1759 lg mL 1). After 15 min, the sample was collected with the help of the magnetic separation.
1218
Y. Chen et al. / Chemosphere 83 (2011) 1214–1219
Fig. 4. Desorption of Cd(II) in the different reagents. The waterish magnetic beads (4.5 g) were employed to capture Cd(II). The different reagents including H2SO4, HCl, HNO3, NaNO3 and HAc were used to recover the absorbed Cd(II). The reagent volume was always kept 30 mL.
Table 2 Complete recovery of Cd(II) and easy regeneration of these magnetic beads.
protonated by strong acid in the process of the recovery, these magnetic beads could not be directly reused. From the results in Table 2, it found the adsorption capacity of these magnetic beads could be effectively recovered by NaOH solution. If NaOH solution with high concentration was frequently employed, some surface functional groups on the magnetic beads might be destroyed resulting in the decrease of adsorption capacity (Deng et al., 2010). Therefore, the NaOH aqueous solution (0.1 M) was selected to regenerate the magnetic beads. The repeat utilization of these magnetic beads was investigated in Fig. 5. It is obvious that the adsorption capacity of these magnetic beads changed little within first ten cycles. But, after fifteen cycles, the adsorption capacity declined rapidly because some surface functional groups on these magnetic beads were damaged by the acid or alkaline conditions during the reduplicate regeneration. Finally, the adsorption capacity reached platform again after 25 cycles and the relative adsorption capacity decreased 80%. Therefore, to enhance the stability of surface structure of these magnetic beads is much significant for their further application in the industry.
3.5. Clearance of the simulated wastewater
Effect of acid concentration on the desorption Concentration of H2SO4 (M) 1 Amount of desorption (mg g 1) 54 Desorption efficiency (%) 100
0.1 53 98
0.01 8 14
Effect of NaOH concentration on the regeneration Concentration of NaOH (M) 1 Adsorbance (mg g 1) 51 Regeneration efficiency (%) 95
0.1 51 96
0.01 8 15
The adsorption was carried out with 5 g waterish magnetic beads and the pH value of solution was 6, then the responding recovery was performed in 30 mL H2SO4 solution with different concentration. After the recovery, these magnetic beads were regenerated with 30 mL NaOH aqueous solution.
these magnetic beads were washed with H2SO4 solution (0.1 M), it was selected to recover captured Cd(II). 3.4. Repeated use of these magnetic beads The absorbent regeneration is an important factor to influence its service efficiency. Because the amino group was fully
In the real industrial wastewater, there were many coexisting substances such as metal ions, anions and caustic acid. Therefore, these magnetic beads were employed to recover Cd(II) in the simulated wastewater (Escobar et al., 2006). The chemical composition of this simulated wastewater is as following: K+ (2 mg dm 3), Ca2+ (102 mg dm 3), Mg2+ (48 mg dm 3), Na+ (94 mg dm 3), SO24 (192 mg dm 3), HCO3 (250 mg dm 3), Cl (182 mg dm 3) and Cd2+ (2916 mg dm 3). The coexisting ions had a great effect on the adsorption of Cd2+ on these magnetic beads. Although the Cd2+ concentration could be still reduced to the governmental standard by the adsorption with these magnetic beads, the equilibrium adsorbance of Cd2+ was only 29 mg g 1, which is lower than half of the saturation adsorbance in pure Cd2+ aqueous solution. Additionally, it was found the adsorbance of Mg2+ was about 0.26 mg g 1, which meant that other metal ions disturbed the adsorption of Cd2+ on magnetic beads. It is reasonable that amino group could generate complexation interaction with many metal ions. The selectivity of these magnetic beads to Cd(II) was not very satisfied. But, as an effective method to concentrate the metal ions
Fig. 5. Investigation of repeated use of these magnetic beads. The adsorption was carried with 5 g waterish magnetic beads in 30 mL solution containing Cd(II) (888 lg mL 1), the pH value of solution was 6. After sufficient washing, the captured Cd(II) was recovered from the magnetic beads in 30 mL 0.1 M H2SO4 solution. Then, these beads were regenerated with 30 mL 0.1 M NaOH solution.
Y. Chen et al. / Chemosphere 83 (2011) 1214–1219
from some industrial wastewater, this technology is much convenient and efficient.
4. Conclusions The magnetic polymer beads with sensitive magnetic response were employed to remove Cd(II) from aqueous solution. Depending on the large specific surface area of these beads, the saturation absorbance for Cd(II) reached 68 mg g 1 dried magnetic beads. In order to keep a high clearance efficiency (>99.5), an appropriate proportion is drawn to 23.3 (mg Cd2+):1 (g dried magnetic beads). The suitable pH range for the adsorption was in 3–6. Moreover, the absorbed Cd(II) could be completely recovered in acid conditions and these magnetic beads could be easily regenerated in alkaline solution. Additionally, the excellent performance of repeated use (more than 10 cycles) makes this technology become more efficient. Therefore, by using these magnetic beads in magnetically stabilized bed, it becomes much potential to actualize the successive treatment of industrial wastewater containing Cd(II). At the same time, the complete recovery of Cd(II) could be achieved. This technology makes it possible not only to avoid the Cd(II) pollution, but also to actualize the recyclable utilization of Cd(II). Acknowledgements The authors gratefully acknowledge financing from Program for New Century Excellent Talents in University of Fujian Province (07FJRC02) and the Fundamental Research Funds for HuaQiao University (JB-GJ1007). References Babel, S., Kurniawan, T.A., 2003. Low-cost adsorbents for heavy metals uptake from contaminated water: a review. J. Hazard. Mater. 97, 219–243. Chen, M.Q., Lin, Z.Y., Qian, H., 2008. Preparation of thiophilic paramagnetic adsorbent for separation of antibodies. Chin. Chem. Lett. 19, 1495–1498. Chin, C.M., Chen, P.W., Wang, L.J., 2006. Removal of nanoparticles from CMP wastewater by magnetic seeding aggregation. Chemosphere 63, 1809–1813. Chung, T., Chang, J., Lee, W., 2009. Application of magnetic poly(styrene–glycidyl methacrylate) microspheres for immunomagnetic separation of bone marrow cells. J. Magn. Magn. Mater. 321, 1635–1638. Deng, W., Wang, M.Y., Chen, G., Kan, C.Y., 2010. Morphological evolution of multistage polymer particles in the alkali post-treatment. Eur. Polym. J. 46, 1210–1215. Do, D.D., Do, H.D., Nicholson, D., 2010. A computer appraisal of BET theory, BET surface area and the calculation of surface excess for gas adsorption on a graphite surface. Chem. Eng. Sci. 65, 3331–3340.
1219
Escobar, C., Soto-Salazar, C., Toral, M.I., 2006. Optimization of the electrocoagulation process for the removal of copper, lead and cadmium in natural waters and simulated wastewater. J. Environ. Manage. 81, 384–391. Feng, D., Aldrich, C., Tan, H., 2000. Removal of heavy metal ions by carrier magnetic separation of adsorptive particulates. Hydrometallurgy 56, 359–368. Gupta, V.K., Jain, C.K., Ali, I., Sharma, M., Saini, V.K., 2003. Removal of cadmium and nickel from wastewater using bagasse fly ash – a sugar industry waste. Water Res. 37, 4038–4044. Hristov, J., Fachikov, L., 2007. An overview of separation by magnetically stabilized beds: state-of-the-art and potential applications. China Particuol. 5, 11–18. Jun, B.H., Noh, M.S., Kim, G., Kang, H., Kim, J.H., Chung, W.J., Kim, M.S., Kim, Y.K., Cho, M.H., Jeong, D.H., Lee, Y.S., 2009. Protein separation and identification using magnetic beads encoded with surface-enhanced Raman spectroscopy. Anal. Biochem. 391, 24–30. Karapinar, N., 2003. Magnetic separation of ferrihydrite from wastewater by magnetic seeding and high-gradient magnetic separation. Int. J. Miner. Process. 71, 45–54. Kula, I., Ugurlu, M., Karaoglu, H., Çelik, A., 2008. Adsorption of Cd (II) from aqueous solutions using activated carbon prepared from olive stone by ZnCl2 activation. Bioresour. Technol. 99, 492–501. Kurniawan, T.A., Chan, G.Y.S., Lo, W., Babel, S., 2006. Physico–chemical treatment techniques for wastewater laden with heavy metals. Chem. Eng. J. 118, 83–98. Ma, Z., Liu, X., Guan, Y., Liu, H., 2006. Synthesis of magnetic silica nanospheres with metal ligands and application in affinity separation of proteins. Colloids Surf. 275, 87–91. Marius, M.S., James, P.A.B., Bahaj, A.S., Smallman, D.J., 2005. Development of a highly magnetic iron sulphide for metal uptake and magnetic separation. J. Magn. Magn. Mater. 293, 567–571. Matheickal, J.T., YU, Q., Woodburn, G.M., 1999. Bisorption of cadmium (II) from aqueous solutions by pre-treated biomass of marine alga Durvillaea potatorum. Water Res. 33, 335–342. Min, S.H., Han, J.S., Shin, E.W., Park, J.K., 2004. Improvement of cadmium ion removal by base treatment of juniper fiber. Water Res. 38, 1289–1295. Oka, T., Kanayama, H., Fukui, S., Ogawa, J., Sato, T., Ooizumi, M., Terasawa, T., Itoh, Y., Yabuno, R., 2008. Application of HTS bulk magnet system to the magnetic separation techniques for water purification. Physica 468, 2128–2132. Qian, H., Chen, M.Q., Lin, Z.Y., 2008. The effective and specific isolation of antibodies from human serum by using thiophilic paramagnetic polymer beads. Colloids Surf. 67, 224–229. Qian, H., Li, C., Lin, Z.Y., Zhang, Y.X., 2010. Using thiophilic magnetic beads in purification of antibodies from human serum. Colloids Surf. 75, 342–348. Rikers, R.A., Rem, P., Dalmijn, W.L., 1998. Improved method for prediction of heavy metal recoveries from soil using high intensity magnetic separation (HIMS). Int. J. Miner. Process. 54, 165–182. Ritter, J.A., Ebner, A.D., Daniel, K.D., Stewart, K.L., 2004. Application of high gradient magnetic separation principles to magnetic drug targeting. J. Magn. Magn. Mater. 280, 184–201. Robinson-Lora, M.A., Brennan, R.A., 2009. Efficient metal removal and neutralization of acid mine drainage by crab-shell chitin under batch and continuous-flow conditions. Bioresour. Technol. 100, 5063–5071. Su, X., Zang, X., 2004. Engineering Inorganic Chemistry. East China University of Science and Technology Press, Shanghai. Sun, Z.X., Skold, R.O., 2001. A multi-parameter titration method for the determination of formation pH for metal hydroxides. Miner. Eng. 14, 1429– 1443. Wang, K., Xing, B., 2004. Mutual effects of cadmium and phosphate on their adsorption and desorption by goethite. Environ. Pollut. 127, 13–20. Ying, W., Bao, Y.Y., Zhou, Q.X., 2010. Simultaneous adsorption and desorption of cadmium and tetracycline on cinnamon soil. Chemosphere 80, 807–812.