Synthesis of hydrotalcite powder and bead to remove arsenate - Tung Nguyen Thanh

Vietnam Journal of Science and Technology 55 (4C) (2017) 204-209 SYNTHESIS OF HYDROTALCITE POWDER AND BEAD TO REMOVE ARSENATE Tung Nguyen Thanh 1 , Thuy Ly Bich 1, * , Shinya Echigo 2 1 School of Environmental Science and Technology, Hanoi University of Science and Technology, No.1 Dai Co Viet Street, Ha Noi, Viet Nam 2 National Institute of Public Health, 2-3-6 Minami, Wako 351-0197, Japan * Email: thuy.lybich@hust.edu.vn; nguyentung2407@gmail.com; shinyae@gmail.com Received: 15 July 2017; Accepted for publication: 15 October 2017 ABSTRACT The affecting factors on the synthesis of hydrotalcite (HT) powder and bead for effective arsenate removal were investigated. HTs with a ratio of Mg:Al = 2:1 (MA) were synthesized by the co-precipitation method at 70 o C with reaction times of 1 and 120 - 300 min. The synthesis of MA with a reaction time of 1 min was done under high supersaturation condition, the others under low supersaturation conditions. The characteristics of MA were examined by X-ray diffraction (XRD), scanning electron microscopy, and nitrogen adsorption/desorption isotherms. According to the XRD patterns, pure HT was obtained for all tested conditions. With increasing reaction time from 1 to 300 min, the crystal size of MA increased from 4.9 to 11.3 μm, the surface area of MA increased from 9.3 to 71.4 m 2 /g. Batch-mode experiments showed that 1-min reaction time MA had the highest As(V) removal capacity. MA beads were separately synthesized using alginate and poly acrylamide (PAM) as binding agents. For alginate/MA, heat drying (110 o C) and freeze drying were applied to test the effect of these drying methods on the beads. The results showed that As(V) adsorption capacity of PAM/MA was the highest, closely followed by freeze drying/alginate/MA, much higher than that of heat drying/alginate/MA bead. Keywords: hydrotalcite, arsenate, adsorption. 1. INTRODUCTION HT is a promising adsorbent to treat environmental pollutants [1 - 3]. However, the common form of HT (powder) limits its application to environment treatment system. Thus, HT in bead forms had been synthesized to overcome this disadvantage [4, 5]. The problem of arsenic pollution in Viet Nam is serious [6]. The research on As removal by different materials has been done by several researchers in Vietnam as presented elsewhere [7]. In this study, we synthesized powder HT with the formula of Mg4Al2(OH)12CO3•3H2O named MA under low and high super saturation conditions with different reaction times. As(V) removal capacities and other characteristics of the synthesized MAs were compared. Then, MA Synthesis of hydrotalcite power and bead to remove arsenate 205 beads with either alginate or PAM as binder were fabricated. As(V) removal capacities of the synthesized MA beads were compared. 2. MATERIALS AND METHODS 2.1. Materials Mg(NO3)2 Al(NO3)3 Na2CO3 (England-PA) were used for synthesis experiments. Standard solution of As(V) (H3AsO4 in HNO3) with concentration of 1000 mg/L (MERCK) was used as stock solution for As(V). 2.2. Synthesis of HT powder and bead a. HT powder formation under low supersaturation condition: MA was synthesized by injecting the mixture of 100 mL of 1 M Mg(NO3)2 and 50 mL of 1 M Al(NO3)3 at a rate of 150 mL/h into 260 mL of 1 M Na2CO3 at 70 o C with mixing (300 rpm). Soaking intervals of 2, 3, 4, 5 hr were applied, and the materials were named MA2, MA3, MA4, MA5, respectively. The obtained crystals were then filtered and washed with distilled water for three times, in which once under sonication. The MAs were then dried at 110 o C for 24 hr and grinded by a ball grinner (Retsch MM200) and sieved (150 m mesh) to obtain the MA powder. The reaction time interval was chosen from the fact that the lowest reaction time for HT formation under low supersaturation condition in literature was 2 hr [8-12]. b. HT powder formation under high supersaturation condition: Our results later on showed that even at the shortest reaction time (i.e., 2 hr), HT can be formed at 100% efficiency and As(V) removal capacity was not significantly different. Therefore, we conducted HT formation experiment under high super saturation condition in which the mixture of 100 mL of 1 M Mg(NO3)2 and 50 mL of 1 M Al(NO3)3 was quickly added to into 260 mL of 1 M Na2CO3 at 70 o C and shaking shortly until the solution become completely homogenous (about 1 min). This material was named MA0. c. HT bead fabrication: Three grams of the mixture of sodium alginate and MA with an alginate ratio of 5 % was dispersed in 20 mL of distilled water. The mixture was added dropwise with a syringe into 10 % CaCl2 solution to produce beads in spherical form with diameter of 2 mm. The alginate/beads were dried by two methods: heating at 105 o C until completely dried and freeze drying. The freeze drying was done by completely freezing the bead at -20 o C before drying with a Labconco freezer dryer. PAM binder was applied at a ratio of 6 % by a similar process with the heat dried bead by alginate binder. The ratios of alginate and PAM binder were chosen from pre-experiment that the minimum binder percentages to keep beads stable after shaking in water at 150 rpm for 1 hr were used. 2.3. HT powder characteristic analysis XRD analysis was carried out by D8 Advance-Bruker XRD. SEM image was taken by Nova nanoSEM 450-FEI. Nitrogen adsorption/desorption isotherms (BET) was measured by Germini VII 2390. Thanh Tung Nguyen, Bich Thuy Ly, Shinya Echigo 206 2.4. As(V) removal experiments Batch mode adsorption tests of powder: The tests were carried out in 50 mL Erlenmeyer flasks containing 50 ml of 500 g/L As(V) solutions with a solid-to-liquid ratio of 0.2 g/L (pH, 7; temperature, 25 o C; mixing, 150 rpm; contact time,1 hr). The solution was then filtered and As(V) in the filtrate was measured by ICP-MS (Perkin Elmer). Batch mode adsorption test for bead: The absorption tests for MA bead were carried similarly with the test for MA powder except that they were done in 100 mL solution for time interval of 1, 3, 6, 16, 24, 48 hr. 3. RESULTS AND DISCUSSION 3.1. Structure of materials Figure 1. XRD patterns of MA materials, the numbers above peaks are Miller Index. Figure 2. SEM images of MA materials: a) MA0, b–e) MA(2-5). XRD patterns of the synthesized MAs were presented in Fig.1. For all the MAs, crystallized HT-like phase peaks were presented with typical peak at 2θ of 11.5o, 23.5o, 35o and 39.5 o [13] No other crystalline phase peak was detected. Synthesis of hydrotalcite power and bead to remove arsenate 207 The average weights of obtained MA(0-5) (n = 2 each) were 11.7 0.1 g. This value was equal with theoretical mass of MA (calculated from its chemical formula) of 11.7 g, proving that the formation efficiency of HT was about 100 %. XRD pattern and weights analysis results indicated that initial reactants reacted completely. More interestingly, the obtained results showed that HT could be synthesized with short reaction time which, so far, has not been reported for MA synthesis as far as we know. 3.2. Effect of reaction period on crystal size The sizes of single crystal were calculated following Debye-Scherrer formula [8] and summarized in Table 1. The data in Table 1 showed that crystal sizes increased with the increasing of reaction time. MA0 had the smallest crystal size of 49 Å, clearly lower than crystal size of other MAs(95-113 Å). Those sizes were smaller than those in other researches, such as 230 Å [8] and 526 – 1653 Å [9]. The differences in those sizes were because the reaction periods in this study were shorter than those of previous researches (18 h and 200 o C [8] and at 200 o C and 24 h [9]). This increase of crystal sizes with reaction period was well explained because of the smaller crystals were consumed by larger particle by Ostwald rippening mechanism. SEM results (Fig. 2) showed that polycrystal sizes increased with reaction times. Hexagonal shape can be observed in SEM image of MA(2-5) even though they were not so clear. Those crystals were significantly different from the crystals forming under high supersaturation condition with short reaction time (MA0), in which the crystal form was hardly observed. Table.1. Single crystal size of Mas. Samples Full width at half maximum (angle) Single crystal size(Å) MA0 1.622 49 MA2 0.840 95 MA3 0.737 108 MA4 0.704 113 MA5 0.736 108 3.3. As(V) treatment efficiency of powder MA The treatment efficiencies of MA on As(V) were presented in Fig 3. The removal efficiency of MA0 was the best (99.1 %). MA2, MA3, MA4, MA5 showed no significant difference in As(V) removal efficiency. This highest adsorption capacity of MA0, however, interestingly in contrast with BET results indicated that the specific area of MA0 (9.3 m 2 /g) was significantly lower than those of MA(2-5) of 70.4 - 71.4 m 2 /g. Further research about this phenomenon to apply MA to environment treatment should be conducted. 3.4. As(V) removal capacity of MA bead The As(V) removal efficiencies of MA beads are presented in Fig. 4. The data showed that the fabricated MA with PAM as the binder had highest As(V) removal efficiency. The removal efficiency reached equilibrium at 72 % after 24 hr. Thanh Tung Nguyen, Bich Thuy Ly, Shinya Echigo 208 Figure 3. As(V) removal efficiency and crystal size of MAs in powder form (V = 50 mL, Co = 500 g/l, solid-to-liquid ratio = 0.2 g/l, pH = 7; temperature 25 o C, ; mixing = 150 rpm; contact time = 1 hr). Figure 4. As(V) removal efficiency by MA beads (V = 100 mL, Co = 500 g/l, solid-to-liquid ratio = 0.2 g/l, pH = 7; temperature 25 o C; mixing = 150 rpm). The adsorption rates of alginate/MA were high in the first 6 hr and slowed down in the later phase reached equilibrium after around 16 hr. The alginate MA bead finished by heat drying had As(V) removal efficiency of 42 % much lower than the ones finished by freezer drying (68 %). This result can be explained by comparing SEM data of heat drying and freeze drying alginate bead presented in other research [14, 15]. The heat drying bead had almost no pore whereas the freezed ones had pores [14, 15]. Further investigation in freeze drying method of HT/alginate bead may help to increase their As(V) removal efficiency. 4. CONCLUSIONS Powder HT was synthesized at low and high super saturation condition. The HT formation under high super saturation condition with short reaction time had the highest As(V) removal efficiency. It could remove As(V) from 500 g/L to 6 g/L; met Vietnamese standard for drinking water of 10 g/L (QCVN01-2009/BYT). The high As(V) removal efficiency of HT synthesized with short reaction time is a new finding in this study. Bead HT were fabricated with alginate and PAM binders. PAM binding bead had the highest As(V) removal efficiency. The As(V) removal of freeze drying alginate/MA was close to that of MA with PAM binder and much higher than that of heat drying alginate/MA. Freeze drying alginate/MA also had advantage of higher adsorption rate than PAM binding MA. Further investigation to improve the capacity of freeze drying alginate/MA is needed. Acknowledgements. This research is financially supported by GSGES seeds research funding program for overseas field campuses of Kyoto University (Fiscal year 2015). REFERENCES 1. Lin Deng, Zhou Shi - Synthesis and characterization of a novel Mg-Al hydrotalcite-loaded kaolin clay and its adsorption properties for phosphate in aqueous solution. Journal of Alloys and Compounds 627 (2015) 188-196. Synthesis of hydrotalcite power and bead to remove arsenate 209 2. Eduardo Perez, Isabel Diaz, Girum Getachew - Removal of chromium (VI) using nano- hydrotalcite/SiO2 composite. Journal of Enviromental Chemical Engineering 3 (3) (2015) 1555-1561. 3. Dongjin Wan, Yongde Liu, Shuhu Xiao, Jing Chen, Jian Whang - Uptake fluoride from water by calcined Mg-Al-CO3 hydrotalcite: Mg/Al ratio effect on its structure, electrical affinity and adsorptive property. Colloids and Surface A: Physicochemical and Engineering Aspects 469 (2015) 307-314. DOI: 10.1016/j.colsurfa.2015.01.045 4. Nguyen Thi Kim Phuong - Entrapment of Mg−Al layered double hydroxide into alginate/polyvinyl alcohol beads for water remediation, Journal of Environmental Chemical Engineering 2 (2) (2014) 1082-1087. 5. Yong-un Han, ChangGu Lee - Immobilization of layered double hydroxide into polyvinyl alcohol/alginate hydrogel beads for phosphate removal. Journal of Environmental Engineering Research 17 (2012) 133-138. 6. Michael Berg, Hong Con Tran, Thi Chuyen Nguyen, Hung Viet Pham, Roland Schertenleib, Walter Giger - Arsenic contamination of groundwater and drinking water in Vietnam: A human health threat. Environmental Science and Technology 35 (2001) 2621–2626. 7. Dao Thi Hong Nhung, Vo Thi Le Ha, Akio Furuta, Ly Bich Thuy - Removal efficiency of an aluminum based hydrotalcite-like-compound on arsenic. Journal of Science and Technology. Technology Universities (in press). 8. Frantisek Kovanda, David Kolousek, Zuzana Cilova - Crystallization of synthetic hydrotalcite under hydrothermal condition. Applied Clay Science 28 (1-4) (2004) 101- 109. 9. Shigeo Miyata - Physico-Chemical properties of synthetic hydrotalcites in relation to composition. Clays and Minerals 28 (1) (1980) 50-56. 10. Nguyen Thị Mai Tho - Synthesis hydrotalcite and research for its application of arsenic removal in aqueous solution. Master thesis. University of Science, Hochiminh city National University (2006) pp. 90（in Vietnamese). 11. Tran Thị Huong - Synthesis and determination of characteristics of some hydrotalcite double layer structure application in environmental treatment. University of Science, Hochiminh city National University (2011) pp. 94 (in Vietnamese). 12. Labajos F. M., Ulibarri M. A. - Effect of hydrothermal and thermal treatments on physicochemical properties of Mg-Al hydrotalcite like materials. Journal of Material Science 27 (1992) 1546-1552. 13. Duan X. and Evans D. G. (Volume Editors) - Layered Double Hydrotalcites. Springer (2006) pp.234. 14. Sung Wook Choi, Yu Zhang, Yi Chun Yeh - Biofradable porous beads and their potential applications in regenerative medicine. Journal of Material Chemistry 23 (2012) 11442- 11451. 15. Luca Coluccino, Paola Stagnaro, Massimo Vassalli, Silvia Scaglione - Bioactive TGF- B1/HA alginate-based scaffolds for osteochondral tissue repair. Journal of Applied Biomaterials and Functional Materials 14 (2016) e42-52.