Adsorption and seepage properties of permeable reaction barrier construction materials for underground coal gasification
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摘要: 煤炭地下气化(UCG)带来的地下水污染风险是限制其推广发展的主要问题之一。渗透反应墙(PRB)修复技术是地下水原位修复的主要研究热点，而PRB材料特性是影响其正常运行的关键。本文首先探究了砂、有机膨润土、活性炭对UCG特征有机污染物苯酚的吸附特性，在此基础上，采用自建的渗流实验系统研究了砂、有机膨润土、活性炭及其混合物的吸附和渗透特性对净化污染水的综合影响效果。结果表明：①有机膨润土对溶液中苯酚的吸附速率较快，可在10 min之内达到吸附平衡，但吸附容量较小(1.98 mg/g)；活性炭对溶液中苯酚的吸附速率较慢，但吸附容量较大(2.22 mg/g)。②有机膨润土对苯酚的等温吸附可用Freundlich模型描述，模型参数kF = 0.040，n = 1.207；活性炭对苯酚的等温吸附可用Langmuir模型描述，模型参数Smax = 2.44 mg/g，kL = 0.125 L/mg。③砂和活性炭的渗透系数分别为1.006×10-3 m/s和4.761×10-2 m/s，砂与活性炭或有机膨润土混合可有效调节混合材料的渗透性，当砂与有机膨润土质量比由1∶1增大到3∶1时，其混合材料的渗透系数由2.624×10-6增大至3.468×10-5 m/s；而砂与活性炭质量比由1∶1增大到3∶1时，其混合材料的渗透系数由1.379×10-3减小至1.301×10-4 m/s。Abstract: Groundwater pollution induced by Underground Coal Gasification(UCG)seriously hinders its development.Permeable Reactive Barrier(PRB)remediation therefore stands out as a major research focus for in-situ groundwater remediation, where the characteristics of PRB material is crucial to their effective operation.This study thus examines the adsorption properties of sand, organic bentonite, and activated carbon on phenol, a characteristic organic pollutant associated with UCG.A self-constructed permeation experimental system is employed to study the adsorption and permeation characteristics of sand, organic bentonite, activated carbon, mixtures of sand and organic bentonite, as well as sand and activated carbon to investigate their comprehensive impact in purifying contaminated water.The results indicate that: ①Organic bentonite exhibits a rapid adsorption rate for phenol in solution, reaching adsorption equilibrium within 10 minutes, despite a relatively low adsorption capacity(1.98 mg/g). Activated carbon, on the other hand, demonstrates a slower adsorption rate yet a higher adsorption capacity(2.22 mg/g).②The adsorption of phenol by organic bentonite conforms to the Freundlich isotherm model, with parameters kF = 0.040 and n = 1.207.Activated carbon follows the Langmuir isotherm model, with parameters Smax = 2.44 mg/g and kL= 0.125 L/mg.③The permeability coefficients of sand and activated carbon are 1.006×10-3 m/s and 4.761×10-2 m/s, respectively.The mixture of sand with activated carbon or organic bentonite could effectively moderate the permeability of the mixed material.When the mass ratio of sand to organic bentonite increases from 1∶1 to 3∶1, the permeability coefficient of the mixed material increases from 2.624×10-6 to 3.468×10-5 m/s.Conversely, when the ratio of sand to activated carbon increases from 1∶1 to 3∶1, the permeability coefficient of the mixed material decreases from 1.379×10-3 to 1.301×10-4 m/s.
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图 6 有机膨润土等温吸附模型拟合曲线
Figure 6. Isothermal adsorption model fitting curve of organic bentonite
图 7 活性炭等温吸附模型拟合曲线
Figure 7. Isothermal adsorption model fitting curve of activated carbon
图 8 砂和活性炭的渗流实验结果
Figure 8. Results of seepage experiments of sand and activated carbon
图 9 不同质量比砂与有机膨润土混合材料渗流实验结果
Figure 9. Results of seepage experiments of sand mixed with organic bentonite with different mass ratios
图 10 不同质量比砂与活性炭混合材料渗流实验结果
Figure 10. Results of seepage experiments of sand mixed with activated carbon with different mass ratios
表 1 渗流实验所用材料参数
Table 1. Parameters of materials used in seepage experiments
物料 粒级/mm 密度/(g·cm-3) 砂 -0.100 2.50 有机膨润土 -0.075 2.00 活性炭 1~2 1.25 
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表 2 活性炭吸附苯酚溶液一级动力学参数
Table 2. First-order kinetic parameters of activated carbon adsorption of phenol solution
质量/g k/min-1 ζ1/(mg·L-1) ζ2/(mg·L-1) 10 3.043×10-3 71.68 28.96 20 4.105×10-3 82.14 19.22 30 5.621×10-3 84.67 13.67
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表 3 有机膨润土对苯酚的等温吸附实验结果
Table 3. Results of isothermal adsorption experiments of phenol by organic bentonite
序号 原液浓度/(mg·L-1) 平衡浓度/(mg·L-1) 吸附量/(mg·g-1) 1 5 1.49 0.05 2 10 2.32 0.12 3 20 4.18 0.24 4 40 7.32 0.49 5 60 12.06 0.72 6 70 13.73 0.84 7 100 17.83 1.23
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表 4 有机膨润土对苯酚等温吸附模型拟合参数
Table 4. Parameters of fitting the isothermal adsorption model of phenol by organic bentonite
等温吸附模型 公式 参数 R2 线性 S=kdC kd=0.068 L/g 0.978 0 Langmuir $S=\frac{S_{\max } k_{\mathrm{L}} C}{1+\mathrm{k}_{\mathrm{L}} C}$ Smax = -3.042 mg/g
kL =- 0.017×10-3 L/mg0.993 0 Freundlich S=kFCn kF = 0.040
n = 1.2070.990 1 注：kd为线性等温吸附分配系数；Smax为最大吸附容量；kL为Langmuir等温吸附常数；kF为Freundlich等温吸附常数；n为Freundlich等温吸附指数。
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表 5 活性炭对苯酚的等温吸附实验结果
Table 5. Results of isothermal adsorption experiments of phenol by activated carbon
序号 原液浓度/(mg·L-1) 平衡浓度/(mg·L-1) 吸附量/(mg·g-1) 1 2 0.19 0.03 2 8 0.50 0.12 3 20 1.47 0.30 4 45 2.43 0.64 5 60 4.98 0.81 6 85 6.43 1.17 7 95 9.83 1.28 8 105 10.20 1.44 9 115 12.44 1.55 10 125 15.04 1.64 11 135 19.80 1.73 12 145 24.51 1.78
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表 6 活性炭对苯酚等温吸附模型拟合参数
Table 6. Parameters of fitting the isothermal adsorption model of phenol by activated carbon
等温吸附模型 公式 参数 R2 Langmuir $S=\frac{S_{\max } k_{\mathrm{L}} C}{1+k_{\mathrm{L}} C}$ Smax =2.440 mg/g
kL =0.125 L/mg0.988 2 Freundlich S=kFCn kF =0.393
n =0.5070.954 6
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表 7 砂与有机膨润土混合材料
Table 7. Mixed materials of sand and organic bentonite
砂∶膨润土 混合材料孔隙率 装填量/g 渗透系数/(m·s-1) 1∶1 0.29 301.12 2.624×10-6 2∶1 0.38 273.07 1.908×10-5 3∶1 0.47 238.00 3.468×10-5
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表 8 砂与活性炭混合材料
Table 8. Mixed materials of sand and activated carbon
砂∶活性炭 混合材料孔隙率 装填量/g 渗透系数/(m·s-1) 1∶1 0.50 159.04 1.379×10-3 2∶1 0.42 207.55 5.056×10-4 3∶1 0.34 251.92 1.301×10-4
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