Treatment of Heavy Metals in Contaminated Soils Around an Abandoned Mine Using Magnetically Modified Alginic Acid and XYZ

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1 Treatment of Heavy Metals in Contaminated Soils Around an Abandoned Mine Using Magnetically Modified Alginic Acid and XYZ Choong Jeon and Sung Ho Yeom Department of Environmental & Applied Chemical Engineering, Kangnung National University, Kangwondo , Korea Received October 7, 200; Accepted February 23, 2006 Abstract: To efficiently remove heavy metals from contaminated soils around an abandoned mine, new magnetically modified alginic acid and XYZ samples were prepared. The Kahak mine, which is located in KwangMyung City in Korea, was chosen to provide a model contaminated soil. Among the heavy metals in this contaminated soil, the concentration of Zn 2+ was the highest (ca. 00 mg/l); the concentrations of Pb 2+, Cu 2+,andCd 2+ were 300, 4, and mg/l, respectively. In the case of alginic acid containing carboxyl groups only, the removal efficiencies of Pb 2+ and Cu 2+ were high ( and 8 %, respectively), but those of Cd 2+ and Zn 2+ were low (ca. 40 %). Meanwhile, most of these heavy metals could be completely removed when the XYZ adsorbent, including amine and xanthate functional groups, was used. The sorption mechanism involves chelating the heavy metals to S and N atoms of a variety of functional groups. Heavy metals could be removed within 30 sec with no reelution. Therefore, this process seems to be a very safe method for removing heavy metals from the contaminated soils of the Kahak mine. Keywords: heavy metals, contaminated soils, adsorption, alginic acid, abandoned mine Introduction 1) The increased contamination of soils by means of toxic heavy metals is a very serious problem. Especially, concerns about contaminated metals in farmlands around abandoned mines has been increased greatly because of their toxicity and other adverse effects. The metals can be adsorbed onto the soil, discharged into rivers or lakes, and leached into the groundwater, which is an important source of drinking water. Exposure to toxic metals through drinking water and food can lead to their accumulation in animals, plants, and human. According to the literature, remediation techniques for soil contaminated with toxic metals include chemical treatment [1,2], electrokinetics [3], biochemical processing [4], and phytoremediation []. However, chemicals used in the chemical methods may destroy the soil structure and result in secondary pollution. Cline and Reed [6] reported that soil contaminated by heavy metals is effectively leached by EDTA, but this approach To whom all correspondence should be addressed. ( metaljeon@kangnung.ac.kr) destroyed the soil structure. Although phytoremediation takes a long time to remove heavy metals, it is a very simple and cheap process. Machenbrock [7] mentioned that it is more economical and competitive to remove heavy metals from leaching solutions by using a biosorption process. Therefore, in this study, among all of the biological methods, the biosorption process was chosen to treat leaching solutions containing heavy metals. Alginic acid is a linear, binary copolymer of 1,4linked αlguluronic acid and βdmannuronic acid units. It is usually isolated from brown algae, but it is also present in some species of bacteria. It is well known that alginic acid is a very useful material for removing heavy metals; its carboxyl groups play a very important role [8]. On the other hand, to investigate the effect of functional groups on the removal efficiency of heavy metals leached from contaminated soils, the XYZ adsorbent, which was supplied by a Korean company, was also used. It is a kind of polymer that contains two functional groups: i.e., dithiocarbamic acid (NHCS 2 Na) and thiol (SNa) groups. A serious problem often encountered in adsorption

2 Treatment of Heavy Metals in Contaminated Soils Around an Abandoned Mine Using Magnetically Modified Alginic Acid and XYZ 363 treatment systems is the presence of suspended solids. For this reason, magnetic carrier methods are widely used in processes such as the separation of biological cells, the treatment of wastewater, coal desulphurizations, and mineral processing []. Magnetite has been used a carrier in precipitationadsorptioncoagulation schemes for the treatment of wastewater containing PO 4,Cu 2+, and Hg [10]. We previously studied heavy metal removal in metal solutions using magnetically modified alginic acid (MMA) and obtained satisfactory results [11]. In this study, MMA and MMXYZ were applied to heavy metal solutions (Pb, Cu, Cd, Zn) leached from contaminated farmland around an abandoned mine. was ca. 1.2 T. The equilibrium metal concentration was measured using an Atomic Absorption Spectrometer (PerkinElmer, U.S.A). All sorption experiments were performed three times; average values are shown. The uptake capacity of heavy metals was calculated using following equation: Q=(C i V i C f V f )/M where Q is the metal uptake capacity (mg/g), C i is the initial metal concentration (mg/l), V i is the initial volume (L), C f is the final metal concentration (mg/l), V f is the final volume (L), and M is the initial MMA loading (g). Materials and Methods Alginic acid was obtained from Alfa Aesar; XYZ was supplied by a Korean company. All reagents were of analytical grade and distilled waster was used to prepare all solutions. Soil Leaching The soil was sampled from farmland around an abandoned mine and dried in air. The soil was then sieved through a Taylor s standard sieve mesh to constant size (<1 mm). To extract the heavy metals in the soil, the standard operation test method using 00 ml of 0.1 N HCl and 100 g of soil was used. The soil leaching time was fixed at 1 hr and the agitation rate was set at 200 rpm. Extracted metal solutions were stored at room temperature. Preparation of Magnetically Modified Alginic Acid and XYZ Alginic acid or XYZ ( g) was mixed with 1.0 g of iron oxide powder (Bayferrox, Bayer) in 1.0 g of urethane (UT78, Kumgang Korea Chemical Co.) and 1 4 ml of distilled water for 1 h. The sample was then placed in a vacuum oven dryer 0 o C for 3 hrs and then it was ground for use as an adsorbent for heavy metals. Adsorption Experiments All sorption experiments were performed through batchtype operation using 100 ml of a metal solution extracted from contaminated soils in a shaking incubator at room temperature for 1 hr. To control the ph of the metal solutions, HNO 3 and NH 4 OH were used. When the adsorption of the metal solutions approached an equilibrium state, the magnetically modified adsorbents were separated from the metal solutions by using a permanent magnet. The magnetic field strength used in this study Results and Discussions Analysis of Sample Soils (Kahak Mine) The concentrations of heavy metal ions extracted from contaminated soils around the Kahak mine were measured by means of ICP (Inductively Coupled Plasma). As shown in Table 1, the concentration of Zn 2+ was the highest (ca. 00 mg/l); the concentrations of Pb 2+,Cu 2+, and Cd 2+ were 300, 4, and mg/l, respectively. In the case of Ni 2+, the concentration as (0. mg/l) was very low in the contaminated soils. Therefore, Ni 2+ was excluded from our present study. Treatment of Heavy Metals Using Magnetically Modified Alginic Acid (MMA) To test the feasibility of using magnetically modified alginic acid, comparisons with commercial adsorbents, such as ion exchange resin (Amberlite IR 120 plus) and activated carbon, were performed. Figure 1 shows the uptake capacities of heavy metal ions for each adsorbent. In the case of MMA, the uptake capacity of Pb 2+ (ca. 0.7 mmol/g) was much higher than those of the ion exchange resin (0.14 mmol/g) and activated carbon (0.10 mmol/g). For Cu 2+ ions, however, the uptake capacity of the ion exchange resin was the highest. On the other hand, adsorbents could adsorb Cd 2+ ions at all. The Zn 2+ ions were removed relatively well by the activated carbon, although its uptake capacity was very low. The selectivity order of MMA toward heavy metal ions was as follows: Pb > Cu >> Cd, Zn In general, among the various functional groups, it is well known that the carboxyl groups, which are a major component of alginic acid, have excellent selectivity toward Pb 2+ ions [12]. The effect of the MMA dosage on the removal effi

364 ChoongJeonandSungHoYeom Table 1. Heavy Metal Concentrations of the Sample Soil (Kahak Mine) Unit : mg/l Analysis Method Zn Pb Cu Cd Ni Standard operation test 00 ± 12. 300 ± 6. 4 ± 1.8 ± 0.3 0.

3 364 ChoongJeonandSungHoYeom Table 1. Heavy Metal Concentrations of the Sample Soil (Kahak Mine) Unit : mg/l Analysis Method Zn Pb Cu Cd Ni Standard operation test 00 ± ± 6. 4 ± 1.8 ± ± 0.02 Table 2. Effect of StepBy Step Addition of MMA on the Removal Efficiencies of Heavy Metal Ions Second step 0.2 g 0.4 g 0.6 g 0.8 g First step : 0.2 g First step : 0.4 g First step : 0.6 g First step : 0.8 g Pb Cu Cd Zn Pb Cu Cd Zn Pb Cu Cd Zn Pb Cu Cd Zn Figure 1. Uptake capacities of heavy metal ions extracted from soils with MMA, ion exchange resin, and activated carbon (equilibrium ph: 4.0). Figure 2. Effect of amount of MMA added on the removal efficiencies of heavy metal ions extracted from contaminated soils (working volume: 0 ml) ciencies of heavy metal ions was investigated. As shown in Figure 2, Pb 2+ ions were removed over 80 % when 0.4 g of MMA was added into the metal solutions. In Figure 3. Uptake capacity of heavy metal ions extracted from soils using a cosorbent of MMA and activated carbon (equilibrium ph of metal solution: 4.0). contrast, Cu 2+, Cd 2+, and Zn 2+ ions showed very low removal efficiencies (below 70, 20, and 23 %, respectively), even when 4.0 g of MMA was added. We believe that the differences in the removal efficiencies of these heavy metal ions is due to the selectivity of each metal toward carboxyl groups. To decrease the selectivity of Pb 2+ ion and, at the same time, to increase the removal efficiencies of the other metal ions, a stepbystep addition process was applied to the system. The Pb 2+ ions were removed preferentially in the first step and then, in the second step, some new amount of MMA was added to the remaining metal solutions. The total amount of MMA added was set at 1.0 g. The results are shown in Table 2; the removal efficiency of each heavy metal ion was almost the same as that in Figure 2. Therefore, this stepbystep process had no effect on reducing the selectivity of Pb 2+ ions. Generally, there are many kinds of organic materials found in wastewater extracted from contaminated soils; the adsorption of heavy metal ions by means of MMA can be interfered accordingly. To decrease any interfer

4 Treatment of Heavy Metals in Contaminated Soils Around an Abandoned Mine Using Magnetically Modified Alginic Acid and XYZ 36 (a) (b) Figure 4. Removal efficiencies of heavies metals extracted from soils using various amounts of MMA (equilibrium ph of metal solution: 4.0; working volume: 100 ml). ence from organic materials on MMA and, simultaneously, to increase the adsorption capacity of heavy metals, especially Cd 2+ and Zn 2+, activated carbon was applied to the system. Activated carbon is used widely as a good adsorbent of many organic materials [13]. No additional cost is necessary to setup an activated carbon system because the removal of organic materials using activated carbon is also an adsorption process. As mentioned above, the selectivity toward Zn 2+ on activated carbon was much higher than that of MMA. Therefore, coadsorbent containing a 1: 1 ratio of MMA and activated carbon was used; the results are shown in Figure 3. The adsorption capacity of each heavy metal was very low. Especially, in the case of Cd 2+ and Zn 2+, no adsorption capacity was observed on the coadsorbent. Therefore, the effect of activated carbon on heavy metal removal was slight. As mentioned above, heavy metal ions were adsorbed Figure. Uptake capacity and removal efficiency of heavy metals in synthetic wastewater using magnetically modified XYZ (adding amount: 0.1 g/100 ml; initial concentration of heavy metals: 100 ppm). mainly by the carboxyl groups of alginic acid. Therefore, among the components of MMA, the content of alginic acid was increased. Figures 4(a) and (b) show the removal efficiencies of the heavy metal ions when using MMA samples including 0 and 66.7 % of alginic acid, respectively. In the case of MMA (0 %), the removal efficiency for each heavy metal ions was higher than that of MMA (33.3 %). Especially, the removal efficiencies of Cd 2+ and Zn 2+ (ca. 40 and 30 %, respectively) much higher than those of MMA (33.3 %). However, there was almost no improvement in these removal efficiencies when MMA (66.7 %) was used as the adsorbent. The Treatment of Heavy Metals Using Magnetically Modified XYZ When magnetically modified alginic acid was used to remove heavy metals ions extracted from contaminated soils, the economics efficiency was not satisfactory because of the high loading of MMA required, causing concern of soils contamination. Therefore, a study of the removal of heavy metals using XYZ as a new adsorbent was performed. As mentioned in the Materials and Methods section, XYZ was supplied by a Korean company; it has two functional groups with amino and xanthate units. The adsorption mechanism inrolves chelating the heavy metals by means of the S and N functional groups. The XYZ was also magnetized and its content was fixed at 0 %. Firstly, the uptake capacities and removal efficiencies of each heavy metal ion in synthetic wastewater on magnetically modified XYZ were investigated; the results are shown in Figure. Among these heavy metal ions, the uptake capacity of Zn 2+ was the highest (ca. 1.2 mmol/gdry mass); its removal efficiency was also ca. %. The removal efficiencies of Pb 2+ and Cu 2+ were

5 366 ChoongJeonandSungHoYeom (a) Figure 7. Effect of time on the removal efficiency of heavy metals extracted from soils using magnetically modified XYZ (content of adsorbent XYZ: 0 %; adding amount: 1.0 g/100 ml). Therefore, all of the heavy metals leached from contaminated soils could be removed completely with 1.0 g of chemically modified XYZ. It is very important to investigate the effect of time on the removal efficiency of heavy metals in the batch process. As shown in Figure 7, all of the heavy metals were removed completely within 30 sec. Consequently, the efficiency of the magnetically modified XYZ with its amino and xanthate functional groups was much higher than that of the magnetically modified alginic acid, containing carboxyl groups only, for the removal of heavy metals from contaminated soils. (b) Figure 6. (a) Uptake capacity and (b) removal efficiency of heavy metals extracted from contaminated soils using magnetically modified XYZ (content of XYZ: 0 %; working volume: 100 ml). also very high (ca. % each). Magnetically modified XYZ was also applied to the heavy metal solution extracted from contaminated soils around the Kahak mine. Figures 6(a) and (b) show the uptake capacity and removal efficiency of heavy metals on magnetically modified XYZ. For Pb 2+ and Cd 2+, as expected, the uptake capacities decreased as the amount of adsorbent added increased [14]. However, in the case of Zn 2+,the uptake capacity increased greatly when the added amount increased. These results can be explained by considering the different selectivities among the heavy metals toward magnetically modified XYZ. In the case of the removal efficiency, Pb 2+,Cu 2+,andZn 2+ could be removed almost completely with 0.3 g of chemically modified XYZ. Zn 2+ could be removed completely with 1.0 g of adsorbent. Conclusions To remove heavy metals efficiently from contaminated soils around an abandoned mine, two new adsorbents (magnetiteimmobilized alginic acid and XYZ) were tested. In the case of alginic acid (containing carboxyl groups only), the removal efficiencies of Pb 2+ and Cu 2+ were as high as and 8 %, respectively. However, the removal efficiency of Cd 2+ and Zn 2+ was low (ca. 40 %). On the other hand, most of these heavy metals could be removed completely when a very small amount of the XYZ sorbent (containing amino and xanthate functional groups) was used. The heavy metals could be removed within 30 sec; there was no reelution of there heavy metals. References 1. C. R. Evanko and D. A. Dzombak, Remediation of metalscontaminated soils and groundwater, Tech

6 Treatment of Heavy Metals in Contaminated Soils Around an Abandoned Mine Using Magnetically Modified Alginic Acid and XYZ 367 nology evaluation report. Groundwater remediations technologies analysis center, Pittsburgh (17). 2. R. G. Robins, Arsenic chemistry in relation to the disposal and stability of metallurgical wastes. Arsenic and mercuryworkshop on removal, recovery, treatment and disposal, Alexandria, Virginia, 4 (12). 3. Y. B. Acar and R. J Gale, J. Hazard. Mater., 40, 117 (1). 4. C. N. Mulligan, R. N. Yong, and B. F. Gibbs, J. Soil. Contam., 8, 231 (1).. A. J. M. Baker, R. D. Reeves, and S. P. McGrath, In situ bioreclamation, RE, Hinchey, R.F. Offenbach (Eds.), Butterworth Heinemann, Boston, pp (11). 6. S. R. Cline and B. E. Reed, J. Environ. Eng., (1). 7. K. Mackenbrock, Treatment of contaminated soils by a combination of suitable, proven technologies contaminated soil, Kluwer Academic Publishers, Netherlands (13). 8. C. Jeon, J. Y. Park, and Y. J. Yoo, Water Res., 36, (2002).. P. Parsonage, Colloid Chem. Miner. Process., (12). 10. M. Benjamin, J. Water Pollut. Control Fed., 4, 1472 (182). 11. C. Jeon, I. W. Nah, and K. Y. Hwang, Water Res. (200). 12. C. Jeon, Y. D. Kwon, and K. H. Park, J. Ind. Eng. Chem., 11, 1 (200). 13. V. Gaur, A. Sharma, and N. Verma, Chem. Eng. Process., 4, 1 (200). 14. B. D. Honeyman and A. H. Santschi, Environ. Sci. Technol., 22, 862 (188).

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