Adsorption capacity of coal-based activated carbon in advanced treatment of drinking water
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摘要: 活性炭是臭氧-生物活性炭(O3-BAC)饮用水深度净化工艺中的核心材料,准确评价活性炭的吸附性能是活性炭选型的基础。本研究采制我国4种典型商品煤基活性炭样品,同时选取一种木质炭作为对比,测定炭样的碘值、亚甲蓝值、焦糖脱色率等常规吸附性能指标以及对丹宁酸(TA)和腐殖酸(HA)的静态吸附容量;用快速小柱实验(RSSCT)测定活性炭吸附含TA和HA水样的穿透曲线以评价活性炭动态吸附性能。此外,分别利用物理吸附仪和扫描电镜联用能谱仪表征活性炭孔结构和表面微观形貌,采用弗兰克尔-哈尔西-希尔方法计算分形维数以表征活性炭表面粗糙度。结果表明,碘值、亚甲蓝值、焦糖脱色率以及TA和HA吸附量与活性炭的孔发育程度明显相关;在RSSCT评价中无烟煤基活性炭具有最佳的动态吸附性能,表明活性炭动态吸附性能与活性炭孔结构相关性较小,而与表面粗糙度具有一定的关联。利用活性炭表面粗糙度指标初步筛选、再经HA的RSSCT穿透实验优选,可选出性能优良的饮用水深度处理用活性炭。Abstract: Activated carbon is the core material in the process of advanced treatment of drinking water. Evaluating the adsorption capacity of activated carbon accurately is the basis of its selection in practical applications. In this study, four typical commercial coal-based activated carbon samples were collected, and a wood-based activated carbon was selected as a comparison. The conventional adsorption performance indexes such as iodine value, methylene blue value, caramel decolorization rate and static adsorption capacity of tannic acid (TA) and humic acid (HA) were determined. Rapid Small-Scale Column Tests (RSSCT) was used to determine the breakthrough curves of activated carbon adsorption on water samples containing TA and HA to evaluate the dynamic adsorption performance of it. The pore structure and surface micro-topography of activated carbons were characterized by N2 adsorption isotherms and scanning electron microscopy energy dispersive X ray analysis (SEM-EDS). Frenkel-Halsey-Hill model was used to calculate the fractal of activate carbons. The results show that the iodine value, methylene blue value, caramel decolorization rate, tannin acid isothermal adsorption capacity and humic acid isothermal adsorption capacity are obviously correlated with the pore development degree of activated carbon. The anthracite-based activated carbon had the best dynamic adsorption performance in the RSSCT, indicating that the dynamic adsorption performance of activated carbon was less correlated with the pore structure of activated carbon and more correlated with the surface roughness. Therefore, the activated carbon samples can be initially selected by the surface roughness. And then the RSSCT result of the HA is used to select an activated carbon with optimized adsorption capacity under the practical conditions of advanced drinking water treatment.
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表 1 活性炭对TA和HA吸附实验用小柱尺寸及实验参数
Table 1. Parameters of column test for TA and HA adsorption
小柱尺寸 实验条件参数 TA HA 直径/cm 0.50 流速/(m·h-1) 10.95 2.74 炭层高度/cm 8.33 活性炭粒径/mm 0.21 0.21 柱长/cm 14.00 空床接触时间/min 0.46 1.83 进水口直径/cm 0.30 进水浓度/(mg·L-1) 9 5 表 2 活性炭样品的吸附性能指标
Table 2. Adsorption capacity of activated carbon samples
活性炭编号(原料) AC-1(长焰煤) AC-2(长焰煤) AC-3(无烟煤) AC-4(褐煤) AC-5(椰壳) 碘值 1 062 899 979 1 001 1 131 亚甲蓝值 220 166 198 206 204 焦糖脱色率/% 66.55 33.65 15.04 68.49 4.72 表 3 活性炭样品TA和HA吸附等温线Langmuir和Freundlich方程拟合参数
Table 3. Langmuir and Freundlich adsorption isotherms fitting parameters for activated carbon samples on TA and HA
样品 TA HA KL R2 RL KF RF2 n KL R2 RL KF RF2 n AC-1 0.057 1 0.990 0 0.02~0.30 24.723 9 0.952 7 3.001 0 0.003 3 0.942 6 0.37~0.94 1.769 2 0.993 3 1.414 9 AC-2 0.031 9 0.996 4 0.03~0.44 12.532 9 0.987 0 3.189 3 0.004 5 0.974 3 0.31~0.92 1.456 7 0.986 4 1.526 3 AC-3 0.130 9 0.999 1 0.01~0.16 12.823 8 0.808 0 5.308 4 0.004 1 0.924 3 0.33~0.92 1.573 3 0.975 7 1.597 4 AC-4 0.054 0 0.993 5 0.02~0.32 21.618 7 0.979 2 3.425 7 0.001 1 0.753 7 0.64~0.98 0.632 9 0.991 6 1.147 4 AC-5 0.030 5 0.995 6 0.04~0.45 10.506 7 0.918 5 3.628 2 0.005 5 0.971 9 0.27~0.90 2.076 7 0.987 6 1.721 9 注:RL=1/(1 +KLC0) 表 4 活性炭对TA和HA快速小柱实验结果
Table 4. RSSCT results of activated carbon samples on TA and HA adsorption
活性炭 TA HA 穿透时间/min 吸附容量/(mg·g-1) 利用率/% 穿透时间/min 吸附容量/(mg·g-1) 利用率/% AC-1 10 5.3 1.4 16 0.187 10.3 AC-2 14 6.7 2.3 14 0.122 22.6 AC-3 17 4.6 2.5 39 0.453 6.0 AC-4 10 1.9 2.9 18 0.299 4.2 AC-5 3 1.4 1.0 12 0.100 16.7 表 5 活性炭样品的分形维数
Table 5. Fractal dimension of activated carbon samples
活性炭编号 AC-1 AC-2 AC-3 AC-4 AC-5 分形维数D 2.829 2.920 2.939 2.829 2.818 -
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