Preparation of Hangjin clay-supported sulfidated zero-valent iron and its performance on phosphate removal
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摘要: 以具有较大比表面积和良好吸附性能的天然杭锦土为载体制备杭锦土负载硫化零价铁（HJ@S-nZVI）。优化铁负载比、硫铁摩尔比（S/Fe）以及陈化时间等制备条件，利用扫描电子显微镜（SEM）、能量色散光谱(energy dispersive spectroscopy，EDS)、X射线光电子能谱（XPS）及比表面积（specific surface area，SSA）等手段对HJ@S-nZVI进行综合表征分析。考察投加量、初始pH以及共存离子等因素对HJ@S-nZVI去除磷酸盐效果的影响，并结合吸附等温线和吸附动力学研究其吸附性能和吸附机理。结果表明：HJ@S-nZVI的优化制备条件为铁负载比为0.25，S/Fe为0.01，陈化时间为10 d；SEM、EDS和元素分布图分析表明，硫化零价铁以球状颗粒形式成功负载于杭锦土表面，XPS表明HJ@S-nZVI表面铁的主要存在形态为FeS和FeOOH等；投加量、初始pH和SiO3 2−共存对HJ@S-nZVI去除磷酸盐的效果影响较大，而SO4 2−、CO3 2−和Cl−共存对磷酸盐的去除效果无明显竞争影响；HJ@S-nZVI对磷酸盐的吸附过程符合Freundlich等温模型（R2=0.992），不同初始浓度下，准二级动力学模型可较好地描述磷酸盐的去除过程（R2>0.995）。Abstract: Natural Hangjin clay with large specific surface area and excellent adsorption properties was used as a carrier to synthesize Hangjin clay-supported sulfidated zero-valent iron (HJ@S-nZVI). Preparation conditions such as the iron loading ratio, the molar ratio of sulfide iron (S/Fe) and the aging time were optimized. Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and specific surface area (SSA) and other methods were utilized to comprehensively characterize and analyze the characteristics of HJ@S-nZVI. The effects of the dosage, initial pH, and co-existing ions on the phosphate removal efficiency were investigated, and the adsorption performance and adsorption mechanism of phosphate removal by HJ@S-nZVI were studied based on the adsorption isotherms and adsorption kinetics. The results showed that the optimized preparation conditions of HJ@S-nZVI were: iron loading ratio was 0.25, S/Fe was 0.01, and aging time was 10 d. SEM, EDS and element distribution map analysis manifested that sulfidated zero-valent iron was successfully loaded on the surface of Hangjin clay in the form of spherical particles. XPS analysis showed that the main existing forms of iron on the surface of HJ@S-nZVI were FeS and FeOOH. The dosage, initial pH and SiO3 2− had a greater influence on phosphate removal, while SO4 2−, CO3 2− and Cl− had no obvious competitive influence. The adsorption process of phosphate by HJ@S-nZVI conformed to Freundlich isotherm model (R2=0.992). Under different initial concentrations, the quasi-second-order kinetic model could better describe the phosphate removal process（R2>0.995）.
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Key words:
- sulfidated zero-valent iron /
- Hangjin clay /
- modification /
- adsorption /
- phosphate
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图 1 铁负载比对HJ@S-nZVI去除磷酸盐效果的影响
Figure 1. Effect of iron loading ratios on the removal of phosphate by HJ@S-nZVI
图 2 S/Fe对HJ@S-nZVI去除磷酸盐效果的影响
Figure 2. Effect of S/Fe on the removal of phosphate by HJ@S-nZVI
图 3 陈化时间对HJ@S-nZVI去除磷酸盐效果的影响
Figure 3. Effect of aging time on the removal of phosphate by HJ@S-nZVI
图 4 改性前后HJ的SEM图、HJ@S-nZVI（S/Fe=0.01）的EDS图和S、Fe元素Mapping图
Figure 4. SEM of Hangjin clay before and after modification, EDS of HJ@S-nZVI（S/Fe=0.01） and Mapping map of S and Fe
图 6 HJ@S-nZVI投加量对去除磷酸盐效果的影响
Figure 6. Effect of HJ@S-nZVI dosage on the removal of phosphate of
图 7 初始pH对去除磷酸盐效果的影响
Figure 7. Effect of initial pH on the removal of phosphate of HJ@S-nZVI
图 9 HJ@S-nZVI去除磷酸盐的等温吸附拟合结果
Figure 9. Langmuir and Freundlich adsorption isotherms for phosphate adsorbed by HJ@S-nZVI
图 10 HJ@S-nZVI去除磷酸盐的吸附动力学模型曲线
Figure 10. Kinetic model curve of adsorption of phosphate by HJ@S-nZVI
图 11 HJ@S-nZVI去除磷酸盐的颗粒内部扩散模型曲线
Figure 11. Curves for the interparticle diffusion models of phosphate adsorbed by HJ@S-nZVI
表 1 HJ矿物组成与阳离子交换量[17]
Table 1. Mineral composition and cation exchange capacity of Hangjin clay
CEC/
(cmol/kg)矿物占比/% 烧失
量/%SiO2 Al2O3 CaO Fe2O3 MgO K2O Na2O TiO2 32.2 50.9 15.2 6.4 5.9 3.6 3.6 0.9 0.6 12.9 
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表 2 HJ及改性材料SSA、微孔体积及平均孔径
Table 2. Specific surface area, pore volume and average pore diameter of Hangjin clay and modified materials
样品 SSA/(m2/g) 微孔体积/(cm3/g) 平均孔径/nm HJ 66.59 0.1153 6.92 HJ@nZVI 42.07 0.0899 8.55 HJ@S-nZVI 47.34 0.0929 7.85
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表 3 HJ@S-nZVI去除磷酸盐的等温吸附模型拟合参数
Table 3. Isotherm parameters for phosphate adsorption by HJ@S-nZVI
Langmuir等温吸附模型 Freundlich等温吸附模型 qm/(mg/g) KL/(L/mg) R2 KF n R2 32.86 2.168 0.9903 22.45 4.926 0.9920
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表 4 HJ@S-nZVI去除磷酸盐的吸附动力学参数
Table 4. Kinetic parameters of phosphate adsorption by HJ@S-nZVI
磷酸盐浓度/
(mg/L)qe,exp/(mg/g) 准一级动力学模型 准二级动力学模型 k1/min−1 qe,cal/(mg/g) R2 k2/min−1 qe,cal/(mg/g) R2 5 9.82 0.055 9.44 0.939 0.012 0 9.89 0.999 10 19.07 0.052 17.78 0.937 0.003 7 19.27 0.999 15 25.25 0.035 22.93 0.909 0.001 6 25.61 0.999 20 29.15 0.012 28.15 0.949 0.000 7 30.08 0.998 25 29.81 0.009 28.54 0.889 0.000 6 30.68 0.995 注：qe,exp为试验得到的吸附平衡时的吸附容量；qe,cal为模型计算得到的吸附平衡时的吸附容量。
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表 5 HJ@S-nZVI去除磷酸盐的Weber-Morris颗粒内扩散模型参数
Table 5. Parameters of the Weber-Morris diffusion model for phosphate removal by HJ@S-nZVI
磷酸盐
浓度/
(mg/L)第一阶段 第二阶段 第三阶段 kid1/〔mg/(g·min−0.5)〕 R2 kid2/〔mg/(g·min−0.5)〕 R2 kid3/〔mg/(g·min−0.5)〕 R2 5 1.39 0.971 0.45 0.935 0.003 8 0.723 10 2.53 0.962 0.74 0.958 0.060 0.840 15 2.89 0.999 0.92 0.969 0.18 0.804 20 2.03 0.965 1.41 0.971 0.30 0.823 25 2.40 0.949 1.16 0.940 0.39 0.870
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