方解石负载羟基磷灰石复合材料去除水中铀离子的PRB活性介质研究

doi:10.13745/j.esf.sf.2021.2.21

摘要/Abstract

摘要：

铀污染地下水分布于世界多国,其危害备受关注。本文基于溶胶-凝胶法制备方解石负载羟基磷灰石复合材料(CLHC),通过静态与动态对比试验,探讨了PRB活性介质对水中铀离子的吸附机理和去除效果。试验结果表明,制备的CLHC表面被羟基磷灰石覆盖,对铀离子具有较强的吸附能力。当U的初浓度为5.0 mg/L、试验周期为2 h、溶液pH值为4、CLHC用量为0.5 g/L时,CLHC可以吸附水中所有的铀离子。CLHC对铀离子的吸附过程可以用Langmuir等温吸附模型、粒子内扩散吸附动力学模型和准二级吸附动力学模型较好地进行描述。石英砂负载羟基磷灰石与CLHC相比,后者具有更强的吸附能力,而且具有更长的使用寿命。CLHC在吸附铀的过程中没有价态变化,其对铀离子的吸附主要为离子交换的化学吸附。本研究的成果可为可渗透反应墙被应用于铀污染地下水修复提供试验依据。

关键词: PRB, 羟基磷灰石, 含水层, 方解石, 铀离子

Abstract:

Through static and dynamic tests, this paper investigated the removal efficiency and mechanism of uranium ion adsorption by calcite-loaded hydroxyapatite composites (CLHC) that was synthesized by the sol-gel method. The experimental results show that the CLHC surface was covered by hydroxyapatite after synthesis and had a strong affinity for uranium ions. The removal rate could reach 100% under the conditions of additive concentration of 0.5 g/L, solution pH of 4, initial uranium concentration of 5.0 mg/L, and experimental period of 2 hours. The adsorption processes of uranium can be described by a langmuir isotherm adsorption model, an intraparticle diffusion-adsorption dynamics model, or a quasi secondary adsorption kinetics model. CLHC has better adsorption ability and longer service life than quartz sand-loaded hydroxyapatite. Uranium ions were always hexavalent during adsorption, mainly by means of chemical adsorption via ion exchange. The results of this study provide a theoretical basis for the application of permeable reactive wall to groundwater remediation.

Key words: PRB, hydroxyapatite, aquifer, calcite, uranium ion

中图分类号:

X523

张卫民, 王振, 钱程, 郭亚丹, 刘海燕. 方解石负载羟基磷灰石复合材料去除水中铀离子的PRB活性介质研究[J]. 地学前缘, 2021, 28(5): 175-185.

ZHANG Weimin, WANG Zhen, QIAN Cheng, GUO Yadan, LIU Haiyan. An activated calcite-loaded hydroxyapatite PRB media for uranium ion removal from aqueous solution[J]. Earth Science Frontiers, 2021, 28(5): 175-185.

图/表 18

表1 静态试验参数

Table 1 Experimental parameters for the static tests

试验条件	单位	取值	方法
CLHC用量	g·L^-1	0.3,0.5,0.7,0.9,1.0	25 ℃恒温气浴,167 r/min震荡,震荡时间为4 h,U初始浓度为5.0 mg·L^-1
溶液pH值		2.0,3.0,4.0,5.5,6.5,7.5
试验周期	min	10,30,60,90,120,180,240
U的初始浓度	mg·L^-1	2,5,7,9,11

图1 动态柱装置图

Fig.1 Diagram of the dynamic column

图2 用量(a)、溶液pH值(b)、试验周期(c)和U的初始浓度(d)对U吸附效果的影响

Fig.2 Effect of dosage (a), pH value (b), experimental period (c), and U content (d) on U adsorption

图3 准一级动力学模型和准二级动力学模型拟合结果

Fig.3 Fitting results of (a) aquasi first order dynamic model (FODM) or (b) a quasi second order dynamic model (SODM)

表2 FODM和SODM拟合特征参数

Table 2 Characteristic fitting parameters using FODM and SODM

浓度	FODM参数				SODM参数
浓度	Q_e/ (mg·g^-1)	a₁/ min^-1	R²		Q_e/ (mg·g^-1)	a₂/ (g·mg^-1·min^-1)	R²
5 mg·L^-1	4.36	0.02	0.96		10.4	0.01	0.99

图4 粒子内扩散动力学模型拟合结果

Fig.4 Fitting results of an intraparticle diffusion dynamics model (PDDM)

表3 LIAM和FIAM拟合特征参数

Table 3 Characteristic fitting parameters using LIAM and FIAM

温度	LIAM				FIAM
温度	q_m/ (mg·g^-1)	K_L/ (L·mg^-1)	R²		K_F/ (L·mg^-1)	1/n	R²
26 ℃	11.7	1.37	0.995		8.52	0.107	0.871

图5 Langmuir等温吸附模型和Freundlich等温吸附模型拟合结果

Fig.5 Fitting results with (a) the langmuir isothermal adsorption model (LIAM) or (b) the freundlich isothermal adsorption model (FIAM)

图6 A、B柱吸附U(Ⅵ)的穿透曲线

Fig.6 Breakthrough curves of Column A and B adsorbing U(Ⅵ)

表4 A、B动态柱试验参数的统计表

Table 4 Statistical table of test parameters for dynamic columns A and B

编号	CLHC	U的初始浓度/ (mg·L^-1)	流量/ (L·h^-1)	pH值	穿透时间点	耗竭时间点	间隔/h
A	方解石	5.0	0.32	4.0	107 h时	624 h时	516
B	石英砂	5.0	0.32	4.0	101 h时	581 h时	482

表5 A柱和B柱的参数表

Table 5 Parameters of Columns A and B

编号	U的初始浓度/ (mg·L^-1)	流速/ (L·h^-1)	总时间/ h	CLHC用量/g	柱吸附U的总量/g	柱饱和单位吸附量/ (mg·g^-1)	柱总流量/L	进液总U 量/g
A	5.0	0.32	627	29.8	0.42	14.3	197	0.99
B	5.0	0.32	557	29.1	0.36	12.5	183	0.91

图7 A柱和B柱的Thomas模型拟合与Yoon-Nelson模型拟合结果

Fig.7 Fitting results using the Thomas or Yoon-Nelson models for columns A and B

图8 方解石吸附前(a)和吸附后(c)及CLHC吸附前(b)和吸附后(d)的扫描电镜图

Fig.8 Results of scanning electron microscopy. (a) Calcite before adsorption; (b) CLHC before adsorption;(c) Calcite after adsorption; (b) CLHC after adsorption.

图9 方解石吸附前(a,b)与吸附后(c,d)的能谱图

Fig.9 EDS spectra and scanning electron micrographs showing the sampling spots for calcite before (a, b) and after (c, d) adsorption

图10 CLHC吸附前(a,b)与吸附后(c,d)的能谱图

Fig.10 EDS spectra and scanning electron micrographs showing the sampling spots for CLHD before (a, b) and after (c, d) adsorption

图11 CLHC的X射线衍射图

Fig.11 X-ray diffraction pattern for CLHC

图12 吸附前后CLHC的宽谱图(a)和窄谱图(b)

Fig.12 Broad (a) and narrow (b) band spectra of CLHC before and after tests

图13 U窄谱峰值拟合图

Fig.13 Uranium narrow band spectrum peak fitting

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