臺灣博碩士論文加值系統

在台灣大部分水庫中，磷酸鹽為控制藍綠細菌生長之營養鹽。 本研究利用兩種吸附劑，分別為實驗室合成之針鐵礦及商業用之Phoslock，對磷酸鹽進行吸附動力及平衡吸附之探討。
動力實驗結果顯示，兩種吸附劑在12小時內達到平衡，約在1小時達到平衡吸附量之一半，可以看出吸附速率很快。在pH=7.0及9.0條件下，針鐵礦之吸附量分別為21.2和11.9 mg P/g；而Phoslock分別為9.9和8.9 mg P/g 。在pH = 7.0情況下，針鐵礦之吸附量為 Phoslock兩倍，而在pH=9.0，兩種吸附劑之吸附量相近。平衡實驗顯示出兩種吸附劑對磷酸鹽的吸附量隨著 pH增加而減少。
針鐵礦會隨著pH上升之表面界達電位變成負值，與磷酸鹽離子產生排斥現象。Phoslock受pH影響較少，主要因為pH會影響鑭與磷酸鹽生成沉澱物。在吸附平衡模式部分，Freundlich模式較適合模擬兩種吸附劑對磷酸鹽吸附之等溫吸附實驗結果。
研究中並應用孔隙擴散模式結合Freundlich等溫吸附模式，成功模擬磷酸鹽在兩種吸附劑中之吸附動力實驗數據。在pH=7.0及9.0條件下，針鐵礦最佳化之孔隙擴散係數分別為2.0×10-8 cm2/s和2.5×10-8 cm2/s；而Phoslock為2.0×10-7 cm2/s和7.5×10-8 cm2/s。為了探討在現地吸附磷酸鹽之可行性，將針鐵礦固定於不織布袋子中進行吸附實驗，結果顯示固定化後之針鐵礦吸附量少於粉末狀，主要可能因為粉末阻塞不織布袋子孔隙及許多顆粒集結造成之質傳阻力，造成實驗時間中還沒達到平衡所致。

關鍵字: 吸附、擴散、針鐵礦、Phoslock、磷酸鹽

Phosphate is a limited nutrient for the growth of cyanobacteria in many Taiwan’s reservoirs. In this study, a laboratory-synthesized adsorbent (goethite) and a commercially available adsorbent (Phoslock) were used to remove phosphate from water. Kinetic and equilibrium experiments were carried out to study the adsorption of phosphate onto these two adsorbents.
For both adsorbents, the time to reach equilibrium was all within 12 hours. About half of the capacities were saturated within 1 hour of adsorption, suggesting a relatively rapid kinetics initially. At the two pHs tested, 7.0 and 9.0, the adsorption capacities were 21.2 and 11.9 mg P/g for goethite, respectively, and were 9.9 and 8.9 mg P/g for Phoslock, respectively. At pH = 7.0, the adsorption capacity of goethite was twice higher than that of Phoslock, while at pH=9.0, their adsorption capacity were similar. Experimental data revealed that the phosphate uptake decreased with increasing equilibrium pH. For goethite, this is because the net surface charge turned to negative at higher pH, causing repulsion of the phosphate anions. For Phoslock, the effect is smaller, and is mainly caused by the effect of pH on lanthanum phosphate precipitation.
The equilibrium adsorption data were well fitted with the Freundlich isotherm equation. A pore-diffusion model (PDM) combined with the Freundlich equation was employed to simulate the phosphate adsorption kinetics. The best fitted pore diffusion coefficients (Dp) for goethite was very similar at t two different pH conditions, 2.0×10-8 cm2/s and 2.5×10-8 cm2/s, and was 2.0×10-7 cm2/s and 7.5×10-8 cm2/s for Phoslock. On the application side, goethite immobilized in non-woven fabric bags, was used to study the feasibility of in-situ adsorption of phosphate in water. The results showed the adsorption capacities were slightly lower than those from goethite particles. It may be attributed to mass transfer limitation of the bag fabrics and particles, and the equilibrium may not be established within the experimental time.

Keywords: Adsorption; diffusion; goethite; Phoslock; phosphate

CONTENTS
摘要 I
ABSTRACT II
ACKNOWLEDGEMENT IV
CONTENTS V
TABLE CONTENTS VII
FIGURE CONTENTS VIII
CHAPTER 1 INTRODUCTION 1
1.1 Background 1
1.2 Research Objectives 2
CHAPTER 2 LITERATURE REVIEW 3
2.1 Eutrophication 3
2.1.1 Sources of nutrients 3
2.1.2 Problems of eutrophication 5
2.1.3 Control phosphorus in reservoir 8
2.2 Iron oxides 9
2.3 The surface chemistry of the metal oxide 14
2.4 Phosphate adsorption onto iron oxides 17
2.5 Introduction of Phoslock 19
2.6 Adsorption and adsorption model 21
2.7 Kinetic adsorption model 23
CHAPTER 3 MATERIALS AND METHODS 25
3.1 Chemicals 26
3.2 Adsorbents 26
3.3 Analysis and Apparatus 29
3.3.1 Surface Structure and Properties 29
3.3.2 The stabilities of goethite in acid/base solution 30
3.3.3 The sedimentation velocity of Phoslock 30
3.3.4 Preparation and Analysis o Phosphate Solution 32
3.4 Adsorption Experiments 33
CHAPTER 4 RESULTS AND DISCUSSION 35
4.1 Surface Properties 35
4.1.1 The SEM micrographs 35
4.1.2 Results of X-ray diffractometer 44
4.1.3 Specific surface area 47
4.1.4 Zeta potential 49
4.1.5 The particle size distribution of two adsorbents 51
4.1.6 The stabilities of goethite in acid/base solution 53
4.1.7 The settling velocity of Phoslock 54
4.2 Adsorption experiments 56
4.2.1 Adsorption kinetics 56
4.2.2 Adsorption isotherms 59
4.2.3 Simulation of pore-diffusion model (PDM) for adsorption kinetic data 62
4.3 Adsorption experiment of immobilized goethite 70
4.4 Adsorption experiments of both adsorbents with a background electrolyte 73
CHAPTER 5 CONCLUSIONS AND SUGGESTIONS 79
5.1 Conclusions 79
5.2 Suggestions 80
REFERENCES 81


TABLE CONTENTS
Table 2.1 The water qualities of twenty reservoirs in Taiwan in 2000 to 2008 7
Table 2.2 Iron oxides (Cornell and Schwertmann, 1996) 10
Table 2.3 General properties of the iron oxides 12
Table 2.4 Point of zero charge of the minerals (Sparks, 1995) 16
Table 4.1 The amount of dissolved iron in different pH 53
Table 4.2 Parameters of Freundlich and Langmuir equation 61
Table 4.3 Properties of two adsorbents 63
Table 4.4 Extracted pore diffusion coefficients and average error between the experiment data for two adsorbents 65


FIGURE CONTENTS
Figure 2.1 The phosphorous cycle in the environment (Manahan, 1994) 4
Figure 2.2 The transformation of phosphorous in land and water (Reddy et al., 1999) 5
Figure 2.3 Different species of phosphate under acidic and basic conditions (Bohn et al., 1985) 8
Figure 2.4 Formation and transformation pathway of iron oxides (Cornell and Schwertmann, 1996) 11
Figure 2.5 The cross-section of the surface layer of a metal oxide. (a) unhydrated surface (b) contact with water (c) a hydroxylated surface (Sparks, 1995) 16
Figure 3.1 Experiment procedure 25
Figure 3.2 Non-woven fabric bag 27
Figure 3.3 Goethite immobilized by non-woven fabric bag 28
Figure 3.4 A schematic chart of the column for sedimentation test 31
Figure 3.5 The correlation between Phoslock concentration and turbidity 32
Figure 3.6 The calibration curve of phosphate 33
Figure 4.1 SEM micrograph of goethite (5000 times) 36
Figure 4.2 SEM micrograph of goethite (10000 times) 36
Figure 4.3 SEM micrograph of goethite (20000 times) 37
Figure 4.4 SEM micrograph of goethite (Gotic, 2007) 37
Figure 4.5 The SEM/EDS mapping of goethite before adsorption 38
Figure 4.6 The SEM/EDS mapping of goethite after adsorption 38
Figure 4.7 SEM micrograph of Phoslock (1000 times) 40
Figure 4.8 SEM micrograph of Phoslock (5000 times) 40
Figure 4.9 SEM micrograph of Phoslock (10000 times) 41
Figure 4.10 SEM micrograph of bentonite (Putra et al., 2009) 41
Figure 4.11 The SEM/EDS mapping of Phoslock before adsorption 42
Figure 4.12 The SEM/EDS mapping of Phoslock after adsorption 43
Figure 4.13 XRD pattern of goethite 45
Figure 4.14 XRD pattern of goethite (Lin, Z. and Robert W., 2003) 45
Figure 4.15 XRD pattern of Phoslock 46
Figure 4.16 XRD pattern of bentonite (Dimirkou et al., 2002) 46
Figure 4.17 Nitrogen adsorption and desorption isotherm curves of goethite 48
Figure 4.18 Nitrogen adsorption and desorption isotherm curves of Phoslock 48
Figure 4.19 The Zeta potential of goethite at different pHs 50
Figure 4.20 The Zeta potential of Phoslock at different pHs 50
Figure 4.21 Particle size distribution of goethite 52
Figure 4.22 Change of particle size distribution for Phoslock at different time 52
Figure 4.23 The changing of turbidity at different time of the column test 55
Figure 4.24 The distribution of Phoslock concentration and settling velocity 55
Figure 4.25 Adsorption kinetics of phosphate on goethite at pH 7 and pH 9 (Initial concentration=1 mg P/L) 58
Figure 4.26 Adsorption kinetics of phosphate on Phoslock at pH 7 and pH 9 (Initial concentration=1 mg P/L) 58
Figure 4.27 Experimental data of goethite fitted by Langmuir and Freundlich isotherms 60
Figure 4.28 Experimental data of Phoslock fitted by Langmuir and Freundlich isotherms 61
Figure 4.29 Simulated PDM and experimental data for the adsorption of phosphate onto goethite 64
Figure 4.30 Simulated PDM and experimental data for the adsorption of phosphate onto Phoslock 64
Figure 4.31 (a)-(d) Prediction of the adsorption kinetics for the adsorption of phosphate adsorption onto Phoslock with different volumes 69
Figure 4.32 SEM micrograph of goethite that trapped on the fabric (500 times) 71
Figure 4.33 SEM micrograph of goethite that trapped on the fabric (5000 times) 71
Figure 4.34 Adsorption kinetic of phosphate on the immobilized goethite at pH 7 and pH 9 (Initial concentration=1 mg P/L) 72
Figure 4.35 Adsorption isotherms of phosphate on the immobilized goethite at pH 7 and pH 9 72
Figure 4.36 Adsorption kinetics of phosphate on goethite in 0.01N KNO3 at pH 7 and pH 9 (Initial concentration=1 mg P/L) 74
Figure 4.37 Adsorption kinetics of phosphate on Phoslock in 0.01N KNO3 at pH 7 and pH 9 (Initial concentration=1 mg P/L) 75
Figure 4.38 Adsorption isotherm of phosphate on goethite in different concentration of background electrolyte at pH 7 and pH 9 77
Figure 4.39 Adsorption isotherm of phosphate on Phoslock in different concentration of background electrolyte at pH 7 and pH 9 78

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