Investigation on K2Ti4O9 Whisker Absorbent and Applications in Heavy Metal Ions Removal

Abstract The present paper deals with absorption of heavy ions of Pb2+, Cd2+ in water on potassium tetratitanate whisker (PTW). The effects of quantity of PTW, time and pH value on the absorption is studied. The test results show that the absorption efficiency of PTW increases with the quantity of absorbent, time and pH value. The absorption of Pb2+ and Cd2+ ions on PTW follows Freundlich’s Equation. The property of PTW regeneration is also investigated in the present paper. The possibility of using PTW to treat industrial waste water containing heavy metal ions is discussed.

Investigation on K 2 Ti 4 O 9 Whisker Absorbent and Applications in Heavy Metal Ions Removal Shali Tan 1 , Yujun Zhang 2* , Hongyu Gong 2** 1 School of Environmental Science and Engineering Shandong University, Jinan 250061 China (E-mail: shalitan@sdu.edu.cn) 2 School of Materials Science and Engineering Shandong University, Jinan 250061 China (E-mail: * yujunzhangcn@sdu.edu.cn; ** hygong@sdu.edu.cn ) Abstract The present paper deals with absorption of heavy ions of Pb 2+ , Cd 2+ in water on potassium tetratitanate whisker (PTW). The effects of quantity of PTW, time and pH value on the absorption is studied. The test results show that the absorption efficiency of PTW increases with the quantity of absorbent, time and pH value. The absorption of Pb 2+ and Cd 2+ ions on PTW follows Freundlich’s Equation. The property of PTW regeneration is also investigated in the present paper. The possibility of using PTW to treat industrial waste water containing heavy metal ions is discussed. Key words: Potassium tetratitanate, whisker, heavy metal ion, absorption INTRODUCTION Potassium tetratitanate whisker (PTW, formulae K 2 Ti 4 O 9 ) is a white or yellowish needle like crystal [1] . Investigation of PTW in environment protection application started from nuclear wastes treatment. The behavior of ion exchange and absorption of PTW was first studied in the United States. It is found that exchange and absorption capability of radioactive Ba 2+ ions on PTW remains stable even under the neutron radiation strength of 3.85×10 6 n/cm 2 ·s and γ-ray of1.72Gy/h. Researchers in Japan mixed K 2 Ti 4 O 9 whiskers absorbed heavy metal ions with oxides and clays to produce ceramics without radioactivity. Up to now, for the exchange treatment of radioactive heavy ions, PTW is the best selection. In China, researches on PTW as an economic reinforcement material in high performance composites have been carried out [2] . However, investigation on PTW to remove heavy metal ions in industrial waste water by absorption has not been reported. The present paper is a preliminary report of test result of PTW as an absorbent to remove Pb 2+ and Cd 2+ in water. EXPERIMENTAL METHOD Absorption property of PTW is determined by measuring the quantity of Pb 2+ orCd 2+ ions absorbed on PTW. In the test, PTW of different quantity is first put in a 250 ml cone bottle, water containing various Pb 2+ orCd 2+ content(100ml) is added into the bottle, respectively. The bottle with PTW and water containing Pb 2+ orCd 2+ is vibrated at 140 r/m for certain time. After vibration, the water on top of the bottle is separated and content of Pb 2+ and Cd 2+ ions are analyzed using Atomic Absorption Spectrophotometer. - 13 - Journal of Water and Environment Technology, Vol.5, No.1, 2007 RESULTS AND DISCUSSION Absorption behavior of PTW Fig. 1 shows the relationship between the quantity of PTW and the adsorption efficiency of Pb 2+ and Cd 2+ in water. It can be seen from Fig.1 that as the quantity increase, the adsorption efficiency of PTW increases. 012345 40 50 60 70 80 90 adsorption efficiency / % PTW quantity/g Cd 2+ Pb 2+ Fig. 1. The effect of PTW quantity on the adsorption efficiency. 012345 1 2 3 4 5 6 7 8 9 10 11 adsorption capacity/ mg.g -1 PTW quantity/g Cd 2+ Pb 2+ Fig. 2. The effects of PTW quantity on the adsorption capacity Fig. 2 gives the effects of PTW quantity on the adsorption capacity. According to the test result, when PTW is used to treat waste water containing Pb 2+ and Cd 2+ , its absorption rate increases with quantity, so the removal of Pb 2+ and Cd 2+ increases, while the absorption capacity of PTW decreases. This is because that with a given content of the metallic ions in water, as the quantity of absorbent (PTW) increases, the active sites of the absorbent increases, which results in more metallic ions absorbed and less ions remain in water in equilibrium, showing as the removal of metallic more ions. In the mean time, as the ion content in water decreases, the absorption potential of PTW decreases. The removal and absorption rate of Pb 2+ is higher than that of Cd 2+ . This is perhaps due to the difference in the ion size and the separation coefficient of PTW on these two ions [3] . - 14 - Journal of Water and Environment Technology, Vol.5, No.1, 2007 The effect of time on absorption of Pb 2+ and Cd 2+ on PTW is showed in Fig. 3. It can be seen that the absorption of Pb 2+ and Cd 2+ on PTW increases with time. The absorption capacity of PTW increases quickly in the beginning and slows down gradually, and reaches constant at equilibrium. It is because that in the beginning, PTW is fresh and the metallic ion contents are high, so that the absorption potential is high. As time increases, the absorption potential decreases and the absorption capacity approaches to a constant. According to the test results, in 50 min from beginning, the absorption rate of Cd 2+ is slightly higher than that of Pb 2+ , but over 50 min, the absorption capacity of PTW for Cd 2+ is lower than that for Pb 2+ . Absorptions of Pb 2+ and Cd 2+ on PTW both reach equilibrium in about 120 min. 0 20 40 60 80 100 120 140 160 180 200 220 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 adsorption capacity/ mg.g -1 Cd 2+ Pb 2+ tiom / min Fig. 3 The effect of time on the adsorption capacity The effect of pH value on absorption capacity of PTW is showed in Fig. 4. It can be seen that the absorption capacity of Pb 2+ and Cd 2+ on PTW increases with pH value. It suggests that a higher pH value will be preferred by Pb 2+ and Cd 2+ absorption. However, if pH value is too high, it may result in precipitation of metallic hydroxides. So pH value should be controlled in the process. In general, a suitable pH value is 6 − 8. 2345678 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 Cd 2+ Pb 2+ pH adsorption capacity/ mg.g -1 Fig. 4. The effect of pH value on the adsorption capacity. - 15 - Journal of Water and Environment Technology, Vol.5, No.1, 2007 Regeneration of saturated PTW The saturated PTW can be regenerated. The regeneration is done by washing with 5%HNO 3 , then with distilled water completely (until the solution becomes neutral) and drying. The regenerated PTW is tested in the same condition as before. The absorption test results are given in Table 1 It can be seen that the absorption capacity of regenerated PTW is similar to that of fresh PTW. Table 1 The adsorption capacity of regenerated PTW Original content mg/L Absorption on fresh PTW (mg/g) Absorption quantity on regenerated PTW (mg/g) 60 7.0 6.9 80 8.5 8.5 Pb 2+ 100 10 9.8 60 7.5 7.5 80 8.3 8.2 Cd 2+ 100 9 8.8 Absorption mechanism [4] PTW is composed of titanium oxide and potassium oxide. It is fabricated by mixing titanium oxides and potassium oxides in a certain ratio, with a suitable calcination flux, and calcining at 900 – 1100°C. The reaction during calcination is: 4TiO 2 + K 2 O→ K 2 O·4TiO 2 (Stoichiometrically K 2 Ti 4 O 9 ) PTW has a monoclinic structure. The crystal of PTW has lattice constants a = 1.825 nm, b = 0.3791 nm and c = 1.201 nm, β = 106.4º, space group C 2/m , molecular weight of PTW is 413.72. In the crystal, titanium has a complex number of 6 and each titanium atom is surrounded by six oxygen atoms. TiO 6 forms octahedrons and the octahedrons form a layer structure by connecting each other at apexes or edges, parallel to the axis of the crystal whisker. The distance between each layer is 0.85 nm and K + ions stay between the layers, as showed in Fig. 5. 8.5A K 2 Ti 4 O 9 c a β Fig.5. The crystal structure of PTW. - 16 - Journal of Water and Environment Technology, Vol.5, No.1, 2007 Table 2 below gives the ion diameters of some heavy metal ions. It can be seen from the table that the metal ions are much smaller than the layer distance of the PTW crystal [5] . So that the metal ions could rather easily penetrate into the crystal layer and substitute K + ions to form stable metallic/potassium tetratitanates. The metal ions would then be removed from the water. Table2. Diameters of some Element Element Charge Ion diameter （nm） Element Charge Ion diameter（nm） Ac +3 0.222 Ba +2 0.27 Cd +1 +2 0.228 0.194 Co +2 +3 0.148 0.126 Ag +1 +2 0.252 0.194 Ra +2 0.28 Tc +1 +3 0.288 0.190 Tl +1 +3 0.288 0.190 U +3 +4 +5 +6 0.206 0.188 0.174 0.166 Pb +2 0.24 Th +3 +4 0.216 0.198 Sc +3 0.161 Sr +2 0.226 Fig. 6 is the isotherm adsorption curves of Pb 2+ and Cd 2+ on PTW. It shows that Pb 2+ and Cd 2+ absorption on PTW belongs to an L 2 type of Gibbs absorption isotherm curve. Regression of the isotherm absorption curves of Fig. 6 using Freundlich logarithm regression creates the linear logarithm equations, as given in Table 3. It can be seen that the Freudlich logarithm regression and the test result correlate very well. The isotherm absorption constants 1/n of Pb 2+ and Cd 2+ are between 0.1 – 0.5, indicating that these ions absorb on PTW very well [6] . 0 102030405060 1 2 3 4 5 6 7 8 9 10 11 Cd 2+ Pb 2+ balance/ mg.L -1 adsorption capacity/ mg.g -1 Fig. 6 . The adsorption isotherm curves of Pd 2+ and Cd 2+ on PTW. Table 3. Freundlich logarithm regression of the isotherm absorption curves. Regressed equation k 1/n correlative constant Pb 2+ logq e =0.1919+0.4809 logc e 1.5556 0.4809 0.9705 Cd 2+ logq e =0.4050+0.3010 logc e 2.5409 0.3010 0.9600 - 17 - Journal of Water and Environment Technology, Vol.5, No.1, 2007 CONCLUSIONS AND FURTHER CONSIDERATION PTW has a high absorption capability for Pb 2+ and Cd 2+ . The absorption efficiency increases with the quantity of PTW, time and pH value. The isotherm absorption of Pb 2+ and Cd 2+ can be predicted very well by Freundlich logarithm linear Equation. The saturated PTW can be regenerated. The problem with PTW is that, if it would be directly used in waste water treatment, because of the small size of PTW, it is possible to cause secondary contamination of the water, and it is difficult to be collected. To avoid this problem, a possible approach is to fabricate aggregated granules, such as spherule or honeycomb, of PTW by mixing and calcining with a suitable binder material. Research in this area is being done in Shandong University. ACKNOWLEDGMENT This research was founded by The National Natural Science Foundation of China (50542031 ). REFERENCES [1]Ming Wei, Chunbo Wang, Xueying Nai, etc. (2004) Developments of Inorganic whiskers Research: Preparation and Applications of Potassium Titanate Whisker, Journal of Salt Lake Research, Vol.12 , No.4, 58-59 [2]Qinghao Meng, Xiaofeng Li and Zhiqiang Du, etc. (2002) Synthesis and Characterization of Potassium Titanate Whiskers with High Ratio of Length to Diameter ,Chemistry, No.7, 482-484 [3]Weiping Chen, Xin Feng, Changshong Wang, etc.(2004)The Interface Properties of Potassium Titanate Whiskers, Bulletin of Physical Chemistry, Vol.20 No .8, 868-870 [4] inordinately hun sen Chile. (1986 - 8 – 26).Friction Materials inner capillary. Japan publicly concessionaire communique JP 61- 191599. [5] Education Group of Inorganic Chemistry, Tianjin University, China, Inorganic Chemistry, (2002)The High Education Press, Beijing, China,456-457 [6] Jihuan Chen, Danli Xi and Datong Yang,(1990)The Design of Waste Water Treatment Procedure and Example Analyses, The High Education Press, Beijing, China,.120 – 122. - 18 - Journal of Water and Environment Technology, Vol.5, No.1, 2007 . process. In general, a suitable pH value is 6 − 8. 23 456 78 5. 5 6.0 6 .5 7.0 7 .5 8.0 8 .5 9.0 9 .5 10.0 10 .5 Cd 2+ Pb 2+ pH adsorption capacity/ mg.g -1 Fig =0.1919+0.4809 logc e 1 .55 56 0.4809 0.97 05 Cd 2+ logq e =0.4 050 +0.3010 logc e 2 .54 09 0.3010 0.9600 - 17 - Journal of Water and Environment Technology, Vol .5, No.1, 2007