The first result of study on Zn2+ adsorption on Phuoc Long basalt, Vietnam

JOURNAL OF SCIENCE OF HNUE Natural Sci., 2008, Vol. 53, N ◦ . 5, pp. 73-80 THE FIRST RESULT OF STUDY ON Zn2+ ADSORPTION ON PHUOC LONG BASALT, VIETNAM Nguyen Duc Chuy Hanoi National University of Education Nguyen Trung Minh Vietnam Academy of Science and Technology Abstract. This study reported adsorption capacity of Zn 2+ on Phuoc Long basalt, Vietnam in comparison with powder activated carbon (PAC). The adsorption of Zn 2+ from aqueous solution on basalt and PAC was inves- tigated in aqueous solution of pH: 4.51 ÷ 4.67, at temperature of 31 ± 0.5 0 C. Experimental values indicated that the first plateau is at 12.5 mM concentration of Zn 2+ and the second at 50 mM. The linear Langmuir-2 and Freundlich models were applied to describe isotherm adsorption equilibrium and models fitted well. At the concentration 12.5 mM of Zn 2+ the adsorption capacity (qe) of basalt and PAC was 8.003 mg/g and 3.787 mg/g, respec- tively. The monolayer Langmuir adsorption capacity of basalt and PAC was found 19.42 mg/g and 76.92 mg/g; R 2 : 0.9893 and 0.998; respectively. At the concentration 50mM of Zn 2+ the adsorption capacity (qe) of basalt and PAC was equal 37.881 mg/g and 15.438 mg/g, respectively. The Lagergren pseudo-first-order; pseudo-second-order were used to describe kinetics data of basalt. The experimental data fitted well to the pseudo-first-order and pseudo-second-order kinetic with parameters R 2 = 0.9431 and 0.9333. Keyword: Basalt, adsorption of Zn(II), linear Langmuir-2 and Freundlich models, Lagergren pseudo-first and pseudo-second-order. 1. Introduction Pollution is one of the great problems in the world and in Vietnam. The pop- ulation explosion together with industrialization and urbanization makes the living environment more polluted with every passing day and directly affects the life of people, animals and plants, it poses a significant health problem throughout the world. The treatment of waste from factories before eliminating into the environ- ment are really necessary. Using natural soil or rock (even waste itself) to treat the environment is a new and good idea because it is cheap and easy to find. For the last 10 years, The Asian countries (such as Japan, Korea, China, Iran, Thailand, Vietnam,. . . ) have been studying the adsorption of natural soil and rock or waste from agriculture and industry [1,2]. 73 Nguyen Duc Chuy and Nguyen Trung Minh For bringing advantages to the design of equipment to treat waste, the study of kinetic parameters is important. In this paper, we present the first results of study on Zn 2+ adsorption on Phuoc Long basalt, Vietnam and find suitable isotherm models. 2. Content 2.1. Theoretical background and experiment Theoretical background of thermodynamics, isothermal kinetic study of ad- sorption were presented in reference [3]. Materials and experiments were also shown in reference [3]. 2.2. Results and discussion 2.2.1. Experimental results Basalt samples were quantitatively analysed by XRF method (in the Institute of Nuclear Engineering). The results showed that Phuoc Long basalt contains Al: 49.68%, Fe: 18.23%, Mg: 5.21%, Si: 3.98%, Ti: 16.00%, remaining V, Cr, Mn, Zn, Rb, Sr, Pb and K, Ca. It is in agreement of the results analysed qualitatively by XR (in the Institute of Materials Sciences), with crystals: Aluminium oxide (Ca3Al2O6), Coalignite (Mg10Fe2OH24CO3) and Gibbsite [Al(OH)3]. a. Results of determination of Zn 2+ adsorption capacity of basalt and powder activated carbon (PAC, for comparison) Table 1. Result of Zn 2+ adsorption capacity of basalt and PAC Position in the Initial Ce Multiplier of last Adsorption capacity Multiplier of qe Adsorption capacity Multiplier of qe graph (mM) Cevalue qe (mg/g) of basalt * value of basalt qe (mg/g) of PAC value of PAC 6 50 2 37.881 6.3 15.438 2.8 5 25 2 5.999 0.7 5.536 1.5 4 12.5 2 8.003 2.2 3.787 1.8 3 6.25 2 3.648 1.9 2.121 2.0 2 3.125 2 1.933 1.8 1.061 2.1 1 1.563 - 1.051 - 0.505 - (* qe was determined after 48 hours) Results of Zn 2+ adsorption capacity of basalt and PAC are shown in Table 1. From these results, the relationship between Zn 2+ adsorption capacity of basalt and concentration was established (Figure 1a). When concentration of Zn 2+ increased from 1.5625 mM to 3.125 mM (2 times), Zn 2+ adsorption capacity of basalt increased from 0.7 to 6.3 times. For basalt, point 4 was 2.2, then point 5 went down 0.7. Next, point 6 increased to 6.3 (Figure 1a). It is inferred that the curve rose from starting point to point 3, then plateaued at point 4. After that, it decreased at point 5 and 74 The first result of study on Zn2+ adsorption on Phuoc Long basalt, Vietnam went up at point 6. Thus, the first plateau line could be around the point 4 and the second one could be over point 6. Therefore, Zn 2+ adsorption capacity of basalt obeys 2 rules : concentration Ce (Zn 2+ ) is in the range of 1.563 mM  12.5 mM, it is obeyed the first rule (from qe = 1.051 mg/g to qe = 8.003 mg/g); and another one (from qe = 1.051 mg/g to qe = 37.881 mg/g), when Ce of Zn 2+ is in the range of 1.563 mM - 50 mM. (a) (b) Figure 1. The plots of Zn 2+ adsorption capacity of (a) basalt, (b) PAC against concentration of Zn 2+ Figure 1b shows relationship between Zn 2+ adsorption capacity of basalt and the Zn 2+ concentration. It shows that when Zn 2+ concentration doubled, adsorption capacity of PAC went up from 1.5 to 2.8 times. At point 3, it reached to 2.0, then it went down at point 4 and point 5. After that, it rose at point 6. Therefore, it can be inferred that the curve increased from beginning point to point 3 and nearly plateau value at point 4. Then, it went up at point 5 and rose at point. Thus, the first plateau line could be around the point 4 and the second one could be over point 6. It shows that Zn 2+ adsorption capacity of basalt obeys 2 rules: the first one is in the range of qe = 0.505 mg/g  3.787 mg/g, when the Zn 2+ concentration is from 1.563 mM to 12.5 mM; and another one (from qe = 0.505 mg/g to qe = 15.438 mg/g), when Ce of Zn 2+ is in the range of 1.563 mM - 50 mM. b. Zn 2+ adsorption of basalt in comparison with that of PAC From the data of adsorption capacity in Table 1, it shows that adsorption ability of basalt is better than that of PAC at low and at high concentration as well. At concentration of 12.5 mM : qebasalt/qePAC = 2.11 At concentration of 50 mM : qebasalt/qePAC = 2.45 c. Determination of Langmuir and Freundlich adsorption con- stants for Zn 2+ adsorption by basalt and PAC (for 6 points) * Freundlich: In order to determine the Freundrich constant, the dependence of logqe and logCe was plotted (Figure 2a). 75 Nguyen Duc Chuy and Nguyen Trung Minh (a) (b) Figure 2. The plots of log(qe) versies log(Ce) for (a) basalt and (b) PAC From adsorption capacity in Table 1, 2 and from Figure 2a, 2b, Freundlich constant was calculated (Table 2). * Langmuir: According to data of adsorption capacity in Table 1 and the Figures which describe the linear type of the Langmuir equation, it is found that results given from Langmuir-2 equation type is suitable for both basalt and PAC (Table 2). (a) (b) Figure 3. Curve for Langmuir-2 equation of (a) basalt and (b) PAC Comment: - For PAC, the most suitable Langmuir equation is Langmuir-2 (with correlative coefficient R 2 = 0.9977). - For basalt, the most suitable Langmuir equation also is Langmuir-2 (with correlative coefficient R 2 = 0.9771). Table 2. Results of calculating Langmuir and Freundlich constants for 6 points PAC Basalt Freundlich Freundlich 1/n Kf R 2 1/n Kf R 2 0.929 0.00977 0.983 0.852 0.0360 0.7992 Langmuir-2 Langmuir-2 qm Ka R 2 qm Ka R 2 71.43 0.000097 0.9977 17.73 0.00118 0.9771 76 The first result of study on Zn2+ adsorption on Phuoc Long basalt, Vietnam d. Results for determining Zn 2+ adsorption capacity of basalt and PAC (for 4 points). * Freundlich: (a) (b) Figure 4. Relationship of log(qe) and log(Ce) for (a) basalt and (b) PAC From the comment (in section 2.2.1) on the rule of adsorption: there was a plateau at point 4 in the curves of basalt and PAC. According to Langmuir equation, however, the best results are finely received when the concentration is low. Thus, the curves were replotted for 4 points (Ce = 1.563 mM ÷ 12.5 mM), Langmuir and Freundlich constants were also recalculated (Figure 4a and 4b). * Langmuir : Similarly, the results from Langmuir-2 were the most suitable for both basalt and PAC (Table 3). (a) (b) Figure 5. Curve for Langmuir-2 equation of (a) basalt and (b) PAC 77 Nguyen Duc Chuy and Nguyen Trung Minh Comment: - For PAC, the most suitable Langmuir equation was Langmuir-2 (correlative coefficient R 2 = 0.9988 was higher than the result calculated from 6 points). - For basalt, the most suitable Langmuir equation was also Langmuir-2 (cor- relative coefficient R 2 = 0.9893 was higher than the result calculated from 6 points). Table 3: Results of calculating Langmuir and Freundlich constants for 4 points PAC Basalt Freundlich Freundlich 1/n Kf R 2 1/n Kf R 2 0.978 0.00774 0.997 0.9595 0.021913 0.9834 Langmuir-2 Langmuir-2 qm Ka R 2 qm Ka R 2 76.92 0.0000887 0.998 19.42 0.001071 0.9893 Similarly to the calculation for 6 points, qe of basalt at 50 mM given by practice (37.881 mg/g) was higher than qm obtained by theory (19.42 mg/g). However, qe of PAC calculated by practice (15.438 mg/g) was lower than qm given by theory (76.92 mg/g). Practical results shows that if it is polluted by Zn 2+ with concentration of ≤ 12.5 mM, both basalt and PAC can adsorb better than with concentration > 12.5 mM only for Zn 2+ concentration ≤ 12.5 mM. 2.2.2. Time dependent of basalt's Zn 2+ adsorption capacity a. Zn 2+ adsorption capacity of basalt on time Table 4. Zn 2+ adsorption capacity of basalt on time Time (min) Initial Ce (mM) Multiplier of last Co value Adsorption capacity qt (mg/g) Multiplier of last qe value 1 6.25 1.102 5 6.25 1 1.684 1.528 10 6.25 1 1.129 0.670 30 6.25 1 1.393 1.234 60 6.25 1 1.684 0.885 300 6.25 1 1.902 0.885 600 6.25 1 2.266 0.839 1440 6.25 1 3.648 1.670 From Table 4, we built the relationship between adsorption capacity (qe) of Zn 2+ and time (t) at constant temperature for basalt: 78 The first result of study on Zn2+ adsorption on Phuoc Long basalt, Vietnam Figure 6. Relationship between qt and t of Zn 2+ adsorption for basalt *Comment: Generally, for 1 - 30 minutes., adsorbed amounts increased gradually, then it nearly reached the plateau value for 60 - 600 minutes. After 1,440 minutes, adsorp- tion capacity went up conspicuously. b. Result for determining the order of reaction In order to determine the order of reaction, the graph based on Lagergren was plotted. - If the order of reaction is the first, the plot of log (qe - qt)νs.time will be linear (Figure 7a). (a) (b) Figure 7. Lagergren (a) pseudo-first-orde and (b) pseudo-second-order 79 Nguyen Duc Chuy and Nguyen Trung Minh - If the order of reaction is the second, the plot of log (qe - qt)νs.time will be linear (Figure 7b). From Figure 7a and 7b, the Lagergren pseudo-first-order gave R 2 = 0.9431, and the Lagergren pseudo-second-order gave R 2 = 0.9333. Therefore, the reaction of Zn 2+ adsorption for basalt can be the first order or as well as the second which is similar to the reaction of Zn 2+ adsorption for photphate rock [1]. 3. Conclusion 1- The adsorption of Zn 2+ from aqueous solution onto basalt and PAC was investigated in aqueous solutions of pH: 4.51÷ 4.67, at temperature of 31 ±0.50C. Experimental values indicated that the first plateau is at 12.5 mM concentration of Zn 2+ and the second at 50 mM. The linear Langmuir 2 and Freundlich models were applied to describe equilibrium isotherm and both models fitted well. 2- At the concentration 12.5 mM of Zn 2+ , the adsorption capacity (qe) of basalt and PAC was equal 8.003 mg/g and 3.787 mg/g, respectively. The monolayer Langmuir adsorption capacity of basalt and PAC was found 19.42 mg/g and 76.92 mg/g; R 2 : 0.9893 and 0.998; respectively. 3- At the concentration 50 mM of Zn 2+ the adsorption capacity (qe) of basalt and PAC was equal 37.881 mg/g and 15.438 mg/g, respectively. 4- The Lagergren pseudo-first-order; pseudo-second-order were used to de- scribe kinetics data of basalt. The experimental data fitted well to the pseudo-first- order and pseudo-second-order kinetic with parameters R 2 = 0.9431 and 0.9333. REFERENCES [1] M. Prasad, H. Xu, S. Saxena, 2008. 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