Study on adsorption effect and mechanism of uranium by hydroxyapatite modified bentonite
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摘要: 伴随我国核能的开发与高效利用,铀已成为我国地表水、地下水和土壤的常见污染物之一,从含铀废水中去除U(VI)已成为亟需解决的环境问题。本工作以膨润土(BTN)、磷酸氢二钠、硝酸钙为原料,采用简单易行的一步水热法成功制备出羟基磷灰石(HAP)改性膨润土复合材料(HAP/BTN)。考察了HAP/BTN对水溶液中铀的吸附性能,利用单因素试验和正交试验探讨了pH、转速、温度、投加量、时间对吸附性能的影响。试验结果表明,在pH=6.0、转速=100 r·min−1、室温(298.15 K)、HAP/BTN投加量1 g·L−1、吸附时间t=30 min时,该吸附材料对10 mg·L−1含铀废水的去除率可达98%,最大吸附量为186.45 mg·g−1。吸附过程更符合Langmuir模型和准二级动力学,热力学参数表明HAP/BTN对铀的吸附是自发吸热的过程,结合XPS及XRD的结果证实了HAP/BTN吸附铀主要归因于络合反应、化学吸附、静电吸附和离子交换作用。Abstract: With the development and efficient utilization of nuclear energy in China, uranium has become one of the common pollutants in surface water, groundwater and soil. The removal of U(VI) from uranium-containing wastewater has become an urgent environmental problem to be solved. Hydroxyapatite modified bentonite composite hydroxyapatite modified bentonite (HAP/BTN) was successfully prepared by a simple one-step hydrothermal method using bentonite, disodium hydrogen phosphate and calcium nitrate as raw materials. The adsorption performance of HAP/BTN on uranium in wastewater was investigated. The effects of pH, rotation speed, temperature, dosage and time on the adsorption performance were discussed by orthogonal test. The results showed that under the conditions of pH=6.0, rotation speed=100 r·min−1, room temperature (298.15 K), HAP/BTN dosage of 1 g·L−1 and adsorption time t=30 min, the removal rate of 10 mg·L−1 uranium-containing wastewater could reach 98%, and the maximum adsorption capacity was 186.45 mg·g−1. The adsorption process was more in line with the Langmuir model and pseudo-second-order kinetics. Thermodynamic parameters show that the adsorption of uranium on HAP/BTN was a spontaneous endothermic process, combined with XPS and XRD results, confirmed that the adsorption of uranium by HAP/BTN was mainly attributed to complexation reaction, chemical adsorption, electrostatic and ion exchange.
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Key words:
- bentonite /
- hydroxyapatite /
- uranium wastewater /
- adsorption /
- U(VI)
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图 13 HAP/BTN吸附铀的动力学研究:准一级动力学 (a)、准二级动力学 (b)、Elovich动力学 (c)、Morrist颗粒内扩散模型 (d)
Figure 13. Kinetic study of uranium adsorption on HAP/BTN: Quasi-first-order kinetics (a), Quasi-second-order kinetics (b), Elovich kinetics (c), Morrist intraparticle diffusion model (d)
qt—Adsorption capacity at time t; qe—Equilibrium adsorption capacity
图 15 HAP/BTN循环试验 (a)、BTN或HAP/BTN吸附铀前/吸附后的Zeta电位值 (b)、吸附时间对HAP/BTN吸附铀稳定性的影响 (c)、不同水样稀释对HAP/BTN吸附铀的影响(pH=6.0、R=100 r·min−1、T=298.15 K、m=1 g·L−1、V=50 mL、t=30 min) (d)
Figure 15. HAP/BTN cycle test (a), Zeta potential values of BTN or HAP/BTN before and after adsorption (b), effect of time on the stability of HAP/BTN (c), effect of different water samples on H (pH=6.0, R=100 r·min−1, T=298.15 K, m=1 g·L−1, V=50 mL, t=30 min) (d)
图 17 ((a), (c)~(e)) HAP/BTN吸附铀前后的XPS分析;(b)铀的精细谱;(f) BTN、HAP、HAP/BTN及HAP/BTN吸附铀后的XRD图谱;(g) HAP/BTN吸附铀的机制
Figure 17. ((a), (c)-(e)) XPS analysis before and after adsorption of uranium; (b) Fine spectrum of uranium; (f) XRD patterns of BTN, HAP, HAP/BTN and after HAP/BTN adsorbs uranium; (g) Adsorption mechanism of HAP/BNT
表 1 HAP/BTN吸附铀的正交试验因素及水平设计
Table 1. Orthogonal test factors and level design of HAP/BTN adsorption of uranium
Factor A B C D E 1 2 0 298.15 0.01 1 2 6 60 308.15 0.02 10 3 11 100 318.15 0.05 30 Notes: A—pH of aqueous solution; B—Revolution speed (r·min−1); C—Temperature (K); D—Addition amount (g); E—Adsorption time (min). 表 2 HAP/BTN吸附铀的正交试验设计方案和结果
Table 2. Orthogonal experimental design and results of HAP/BTN adsorption of uranium
Factor A B C D E S/% 1 2 0 298.15 0.01 1 18.55 2 2 60 308.15 0.02 10 22.32 3 2 100 318.15 0.05 30 24.26 4 6 0 298.15 0.02 10 46.30 5 6 60 308.15 0.05 30 92.05 6 6 100 318.15 0.01 1 71.51 7 11 0 308.15 0.01 30 50.05 8 11 60 318.15 0.02 1 40.76 9 11 100 298.15 0.05 10 70.63 10 2 0 318.15 0.05 10 23.56 11 2 60 298.15 0.01 30 26.78 12 2 100 308.15 0.02 1 20.13 13 6 0 308.15 0.05 1 44.25 14 6 60 318.15 0.01 10 86.12 15 6 100 298.15 0.02 30 99.48 16 11 0 318.15 0.02 30 53.26 17 11 60 298.15 0.05 1 42.14 18 11 100 308.15 0.01 10 74.42 K1 135.6 235.97 303.88 327.43 237.34 — K2 439.71 310.17 303.22 282.25 323.35 — K3 331.26 360.43 299.47 296.89 345.88 — k1 45.20 78.66 101.29 109.14 79.11 — k2 146.57 103.39 101.07 94.08 107.78 — k3 110.42 120.14 99.823 98.96 115.29 — R 101.37 41.48 1.47 15.06 36.18 — Primary and secondary order A>B>E>D>C Notes: Ki—The ith (i=1,2,3) level of the factor is the test index.; ki—Average value of Ki; R—Range. 表 4 HAP/BTN吸附铀的动力学模型参数
Table 4. HAP/BTN kinetic fitting data
Model types Equation qe/
(mg·g−1)R2 Pseudo first-order model ln(qe−qt)=−0.10035t+1.26104 3.53 0.911 Pseudo second-order model t/q=0.09797t+0.14599 9.98 0.997 Elovich model qt=0.87196 lnt+6.80159 — 0.981 Morrist intraparticle diffusion model qt=0.67023t1/2+6.52163 — 0.930 qt=0.62663t1/2+6.50141 — 0.961 qt=0.299508t1/2+7.78542 — 0.956 表 3 HAP/BTN吸附铀的吸附等温线参数
Table 3. Adsorption isotherm parameters of HAP/BTN adsorbing uranium
T Langmuir Freundlich qm/
(mg·g−1)Kc/
(L·mg−1)R2 n−1 Kf
/((mg·g−1)·(mg·L−1)−1/n)R2 273.15 K 186.45 0.04215 0.99992 0.57112 14.29826 0.91888 Notes: qm—Saturated adsorption capacity of monolayer adsorption; Kc—Constant related to adsorption energy; Kf —Constant related to the adsorption capacity; n−1—Measure of the adsorption strength; R2—Correlation coefficient. 表 5 HAP/BTN对铀(VI)的吸附热力学具体参数
Table 5. Thermodynamic parameters of uranium (VI) adsorption on HAP/BTN
T/K ΔHθ/
(KJ·mol−1)ΔSθ/
(J·mol−1·K−1)ΔGθ/
(KJ·mol−1)298.15 45.27 157.58 −1.71 308.15 −3.29 318.15 −4.86 328.15 −6.44 338.15 −8.01 348.15 −9.59 358.15 −11.16 368.15 −12.76 Notes: ΔHθ—Heat of the adsorption; ΔSθ—Standard entropy change; ΔGθ—Gibbs free energy of adsorption. -
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