Performance and mechanism of La-Fe modified vermiculite adsorbent for efficient phosphorus removal
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摘要: 蛭石(VE)作为吸附剂具有很强的吸附性及离子交换能力，价格低廉、丰富易得，对环境无害。近年来，许多关于蛭石吸附的研究获得报道，但由于疏水性弱且缺乏活性位点使其在磷酸盐吸附方面表现不佳。本文制备了Le-Fe双金属改性蛭石提升对磷酸盐的吸附性能。结果表明：La、Fe原子比为1∶2时改性蛭石(La-Fe/VE-2)具有优异的磷吸附能力，最大吸附容量为185.09 mg P/g，且在pH=3~9的范围内能实现高效吸附。La-Fe/VE-2具有较强的抗阴离子干扰性能，在中低浓度磷酸盐溶液(50~100 mg P/L)条件下仍然保持较高的吸附率(>90%)。材料表征结果显示，La和Fe成功负载在蛭石上，静电吸附和配体交换是主要吸附机制。综上所述，双金属改性蛭石对磷酸盐亲和力强，是一种很有前途的除磷吸附剂。Abstract: Vermiculite (VE) as an adsorbent had strong adsorption and the capability of ion exchange, which was inexpensive, abundant, available and environmental friendly. In recent years, many studies on vermiculite adsorption have been reported, but the weak hydrophobicity and lack of active sites made it perform poorly in phosphate adsorption. In this paper, Le-Fe bimetallic modified vermiculite (La-Fe/VE) was prepared to enhance the adsorption performance of phosphate. The results shows that vermiculite at the atomic ratio of La and Fe of 1∶2 (La-Fe/VE-2) has excellent phosphorus adsorption capacity with a maximum adsorption capacity of 185.09 mg P/g and it can achieve highly efficient adsorption in the pH range of 3 to 9. La-Fe/VE-2 has highly resistant to interference from anions, and maintains high adsorption rate (>90%) at low and medium concentrations of phosphates (50-100 mg P/L). Characterization analyses of the materials conclusively establishes the successful deposition of La and Fe onto the vermiculite substrate. The primary adsorption mechanisms are identifies as electrostatic attraction and ligand exchange. In summary, bimetallic-modified vermiculite has a pronounced affinity for phosphate and is a promising adsorbent for phosphorus removal.
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Key words:
- vermiculite /
- lanthanum /
- phosphate /
- adsorption /
- modified materials
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图 1 (a)不同样品的吸附性能；(b) La/Fe原子比为1∶2时改性蛭石(La-Fe/VE-2)剂量对吸附性能的影响
Figure 1. (a) Adsorption capacity of different samples; (b) Effect of vermiculite (VE) at the atomic ratio of La and Fe of 1∶2 (La-Fe/VE-2) dosage on adsorption performance
qe—Equilibrium adsorption amount
图 2 初始溶液(a)、温度(b)、pH值(c)对磷酸盐吸附的影响；(d) La-Fe/VE-2样品的 Zeta 电位分析；(e)磷酸盐在不同pH下的主要形态分布；(f) 共存离子对磷酸盐吸附的影响
Figure 2. Effect of initial solution (a), temperature (b), pH (c) on phosphate adsorption; (d) Zeta potential analysis of La-Fe/VE-2 sample; (e) Distribution of phosphate species at different pH; (f) Effect of co-existing ions on phosphate adsorption
pzc—Point of zero charge
图 3 La-Fe/VE-2在50 mg P/L溶液中5次吸附-解吸的去除率
Figure 3. Removal efficiency of La-Fe/VE-2 in 50 mg P/L solution in five adsorption desorption cycles
图 4 La-Fe/VE-2吸附磷酸盐：(a)拟一级和拟二级模型；(b)粒子内模型
Figure 4. La-Fe/VE-2 adsorption of phosphate: (a) Pseudo-first and second-order model; (b) Introparticle model
图 5 La-Fe/VE-2吸附磷酸盐的Langmuir和Freundlich模型
Figure 5. Langmuir model and Freundlich model for phosphate adsorption by La-Fe/VE-2
Ce—Equilibrium concentration of phosphate
图 6 (a) VE的SEM图像；((b), (c)) La-Fe/VE-2 的SEM图像；(d) La-Fe/VE-2磷酸盐吸附前后的 EDS图谱
Figure 6. (a) SEM image of VE; ((b), (c)) SEM images of La-Fe/VE-2; (d) EDS spectra of La-Fe/VE-2 before and after phosphate adsorption
图 7 La-Fe/VE-2的N2吸附-解吸等温线及其BET分析得出的粒度分布
Figure 7. N2 adsorption-desorption isotherm of La-Fe/VE-2 composite and its particle size distribution derived from BET analysis
STP—Standard temperature and pressure
图 8 (a) VE、Fe-VE、La-Fe/VE-2、La-Fe/VE-2-P的XRD图谱；(b) VE、La-Fe/VE-2、La-Fe/VE-2-P的FTIR图谱；La-Fe/VE-2和La-Fe/VE-2-P的XPS 图谱：(c) 宽扫描；(d) P2p；(e) La3d5/2；(f) O1s
Figure 8. (a) XRD patterns of VE, Fe-VE, La-Fe/VE-2, La-Fe/VE-2-P; (b) FTIR spectra of VE, La-Fe/VE-2, La-Fe/VE-2-P; XPS spectra of La-Fe/VE-2 and La-Fe/VE-2-P: (c) Wide scan; (d) P2p; (e) La3d5/2; (f) O1s
表 1 蛭石化学成分
Table 1. Chemical composition of vermiculite
Oxide SiO2 Al2O3 K2O Na2O Fe2O3 FeO TiO2 MgO CaO MnO P2O5 H2O Content/wt% 37.46 14.19 1.83 0.25 13.07 0.8 1.51 11.42 3.47 0.14 0.043 7.00 
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表 2 La-Fe/VE复合材料的命名
Table 2. Naming of La-Fe/VE composites
Sample Atomic ratio of La and Fe La-Fe/VE-1 1∶1 La-Fe/VE-2 1∶2 La-Fe/VE-3 1∶3 La-Fe/VE-5 1∶4 La-Fe/VE-2-P 1∶2 (After phosphate adsorption)
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表 3 La-Fe/VE-2上磷酸盐吸附的动力学参数
Table 3. Kinetic parameters of phosphate adsorption on La-Fe/VE-2
Kinetic equations qe/(mg·g−1) k1/k2 R2 Pseudo first-order 48.73 0.0668 0.985 Pseudo second-order 56.23 0.0015 0.995 Notes: qe―Phosphate adsorption capacity inequilibrium; k1― Seudo-first-order kinetic con stant (min−1); k2―Pseudo-second-order kinetic constant (g·mg−1·min−1); R2―Determination coefficient.
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表 4 La-Fe/VE-2 粒子内扩散方程参数
Table 4. Parameters of the intra-particle diffusion equation for La-Fe/VE-2
kd1 R2 kd2 R2 kd3 R2 5.01 0.99 3.43 0.98 0.18 0.98 Note: kd1, kd2, kd3―Phase I, phase II, phase III intra-particle diffusion rate constant (mg·min0.5/g).
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表 5 La-Fe/VE-2 的 Langmuir 和 Freundlich 拟合参数
Table 5. Langmuir and Freundlich fitting parameters for La-Fe/VE-2
Langmuir Freundlich qm/(mg·g−1) KL/(L·mg−1) $ R^2$ KF/(L·mg−1) 1/n $R^2 $ 185.09 0.0089 0.977 9.53 0.456 0.907 Notes: qm―Maximum adsorption capacity; KL―Adsorption equilibrium constants of Langmuir; KF―Freundlich Adsorption equilibrium constant; n―Constant related to the adsorption capacity and affinity.
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表 6 制备的 La-Fe/VE-2 与其他材料的性能比较
Table 6. Performance comparison of prepared La-Fe/VE-2 with other materials
Material Adsorption capacity/
(mg·g−1)pH Temperature/℃ Ref. Fe3O4/La-MOF 58.70 5-7 25 [28] Lanthanum modified natural zeolite (LZ)
Lanthanum-modified magnetic zeolite (LMZ)122.70
109.176 25 [29] La/Fe engineered bentonite (LFB) 82.02 2-6 20 [19] NaLa(CO3)2/Fe3O4 composites (MLC) 77.85 4-11 25 [27] La/bi-hydroxyl double salts (HDS) 168.12 2-12 25 [30] La-incorporated ternary (hydr)oxides nanocomposite (MALZ) 80.80 4-10 25 [25] Lanthanum/aluminum engineered bentonite (LAB) 93.61 3-6 25 [31] La(OH)3-modified exfoliated vermiculites 79.60 3-7 25 [32] Le/Fe bimetallic-modified vermiculite (LFV) 185.09 3-9 25 This work
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