Biochar supported green nano-iron particles to remove U(VI) from water
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摘要: 铀矿开采与水冶过程产生大量铀废水,对周边生态环境造成污染,因此高效绿色治理是保障核工业可持续发展及生态安全的重要基础。本文以向日葵叶为原料绿色合成生物炭负载纳米铁颗粒(GN-FeNPs/BC),并用于去除水中的U(VI)。利用向日葵叶制备植物提取液,然后将残渣热解制备成生物炭,最后将七水硫酸亚铁溶液、生物炭和植物提取液混合,成功制备出绿色纳米铁复合材料。探究了生物炭碳化温度、铁碳比、pH值、温度、时间和U(VI)浓度对除铀的影响。在298 K、pH=5时,最大吸附量为96.43 mg·g−1,并进行动力学和热力学研究。结果表明,准二级动力学模型和Langmuir等温吸附模型拟合良好。热力学常数表明GN-FeNPs/BC对U(VI)的吸附是一个自发吸热的过程。XPS分析表明去除机制包括吸附作用和还原作用。Abstract: Uranium mining and hydrometallurgy produce a large amount of uranium wastewater, which causes pollution to the surrounding ecological environment. Therefore, efficient and green treatment is an important basis to guarantee the sustainable development and ecological security of nuclear industry. In this study, sunflower leaves were used as raw materials for green synthesis of biochar-loaded nano-iron particles (GN-FeNPs/BC) that used to remove U(VI) in water. Sunflower leaves were used to prepare plant extract, and then the residue was pyrolyzed to prepare biochar. Finally, ferrous sulfate heptahydrate solution, biochar and plant extract were mixed to successfully prepare a green nano-iron composite material. The effects of biochar carbonization temperature, iron-to-carbon ratio, pH value, temperature, time and U(VI) concentration on uranium removal were explored. When the pH is 5 at 298 K, the maximum adsorption capacity is 96.43 mg·g−1. The kinetics and thermodynamics are studied. The results show that the pseudo-second order model and Langmuir model fit well. The thermodynamic constants indicate that the adsorption of U(VI) by GN-FeNPs/BC is a spontaneous endothermic process. XPS analysis shows that the removal mechanism includes adsorption and reduction.
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Key words:
- sunflower leaves /
- biochar /
- nano-iron particles /
- uranium /
- adsorption /
- reduction
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图 3 450℃ BC (a)、GN-FeNPs (b)、GN-FeNPs/BC (c) 和GN-FeNPs/BC吸附铀后 (d) 的SEM图像;GN-FeNPs/BC吸附铀反应前 (e) 和反应后 (f) 的EDS图谱
Figure 3. SEM images of 450℃ BC (a), GN-FeNPs (b), GN-FeNPs/BC (c) and GN-FeNPs/BC-U (d) after uranium adsorption; EDS spectra of GN-FeNPs/BC before uranium adsorption reaction (e) and after reaction (f)
图 5 GN-FeNPs/BC吸附U(Ⅵ)的影响因素及动力学研究:(a) pH值的影响(U(Ⅵ)的初始浓度(C0)=10 mg/L);(b) 时间的影响(pH=5.0、 GN-FeNPs/BC的质量(m)/U(Ⅵ)的体积(V)=0.1 g/L、温度(T)=298 K);(c) 拟一级动力学;(d) 拟二级动力学
Figure 5. Study on influencing factors and kinetics of U(Ⅵ) adsorption by GN-FeNPs/BC: (a) Influence of pH value (Initial concentration of U(Ⅵ) (C0)=10 mg/L); (b) Influence of time (pH=5.0, mass of GN-FeNPs/BC (m)/volume of U(Ⅵ) (V)=0.1 g/L, temperature (T)=298 K); (c) Pseudo-first model; (d) Pseudo-second model
qe—Adsorption capacity at equilibrium; qt—Adsorption capacity at time t; t—Reaction time
图 6 (a) GN-FeNPs/BC的吸附等温线(pH=5、m/V=0.1 g/L);(b) Langmuir等温线;(c) Freundlich等温线;(d) ln(qe/Ce) vs qe线性拟合;(e) lnK0 vs 1/T线性关系图(K0为分配系数);(f) GN-FeNPs/BC吸附-解吸次数对U(Ⅵ)去除率的影响(pH=5、m/V=0.1 g/L、T=298 K、C0=10 mg/L)
Figure 6. (a) Adsorption isotherm of GN-FeNPs/BC (pH=5, m/V=0.1 g/L); (b) Langmuir isotherm; (c) Freundlich isotherm; (d) ln(qe/Ce) ) vs qe linear fitting; (e) lnK0 vs 1/T linear relationship diagram (K0 is the distribution coefficient); (f) Influence of GN-FeNPs/BC adsorption-desorption times on U(Ⅵ) removal rate (pH=5, m/V=0.1 g/L, T=298 K, C0=10 mg/L)
表 1 GN-FeNPs/BC吸附U(Ⅵ)的动力学常数
Table 1. Kinetic constants of U(Ⅵ) adsorption by GN-FeNPs/BC
Adsorbent Pseudo-first order model Pseudo-second order model qe/(mg·g−1) k1/(min−1) R2 qe/(mg·g−1) k2/(g·mg−1·min−1) R2 GN-FeNPs/BC 95.495 0.073 0.869 101.644 0.0011 0.999 Notes: qe—Amount of adsorption at equilibrium; k1—Quasi-first-order kinetic model constant; k2—Quasi-second-order kinetic model constant; R—Correlation coefficient. 表 2 Langmuir和Freundlich等温吸附模型拟合参数
Table 2. Fitting parameters of Langmuir and Freundlich isotherm adsorption models
T/K Langmuir model Freundlich model qm/(mg·g−1) KL/(L·mg−1) R2 n KF/(mg1-n·Ln·g−1) R2 298 214.639 0.093 0.999 1.314 19.562 0.892 308 194.140 0.135 0.984 1.374 24.069 0.929 318 231.252 0.139 0.935 1.299 28.452 0.908 Notes: T—Absolute temperature; qm—Maximum adsorption capacity; KL—Langmuir coefficient related to binding site affinity; KF and n—Constants related to the adsorption strength and adsorption capacity in the Freundlich model. 表 3 GN-FeNPs/BC吸附U(Ⅵ)的热力学参数
Table 3. Thermodynamic parameters of U(Ⅵ) adsorption by GN-FeNPs/BC
T/K ΔG/(kJ·mol−1) ΔH/(kJ·mol−1) ΔS/(J·mol−1·K−1) 298 −2.72 308 −3.04 5.45 27.47 318 −3.27 Notes: ΔH—Enthalpy; ΔS—Entropy; ΔG—Gibbs free energy. -
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