水热炭吸附Cr(Ⅵ)热-动力学行为及水热裂解时间的影响

摘要/Abstract

摘要：

以花生壳为原材料,通过水热炭化法在200 ℃下以不同的水热裂解时间(1 h、5 h、10 h)制备出水热炭,开展去除水中Cr(Ⅵ)的实验研究。通过水热炭样品红外光谱FTIR表征、元素含量分析、扫描电镜SEM表征等对比分析,表明水热炭化法可以制备出多孔的碳材料,且随着水热裂解时间的增加,水热炭的产率逐渐降低、芳香性逐渐增强、极性官能团逐渐减少,这些性质的改变会影响其吸附能力。通过批实验进行水热炭对水中Cr(Ⅵ)的吸附研究,结果表明准二级动力学模型适用于该吸附过程,热力学Freundlich模型可以更好地描述吸附等温线。由热力学参数计算可知,水热炭吸附Cr(Ⅵ)属于优惠吸附(容易进行)和自发性、物理吸附,且为吸热过程。实验结果表明随着花生壳水热裂解时间的增加,水热炭吸附Cr(Ⅵ)的能力逐渐增强。因此,水热炭可以作为经济型吸附剂应用于水污染修复,相关成果对于综合利用农业废弃物具有重要实践价值。

关键词: 生物质, 水热炭, 水热裂解时间, 吸附, Cr(Ⅵ)

Abstract:

The agricultural wastes of peanut shells were used as carbonaceous material precursors, which were heated under the hydrothermal temperature of 200 ℃ and kept for the desired time duration of 1 h, 5 h or 10 h to prepare the hydrochars for the removal of Cr(Ⅵ) from aqueous solution. According to FT-IR spectrum, elemental analysis and SEM characterization of hydrochar samples, the results showed that hydrothermal carbonization method is feasible for porous carbon-based hydrochars, and the aromaticity increases with hydrothermal time, while the yield and the polar functional groups decrease.These properties would affect the adsorption performance of hydrochars. The batch experiments showed that the adsorption kinetics of Cr(Ⅵ) on hydrochars followed the pseudo-second-order model and the Freundlich model well fitted the isothermal adsorption. According to thermodynamic study, such sorption behavior belongs to a preferential easy process, which is also a spontaneous, endothermic and physical adsorption. The adsorption capacity of Cr(Ⅵ) on hydrochars were enhanced with the hydrothermal time on biomass of peanut shells. Therefore, hydrochars could be applied as an economic adsorbent in water remediation. The present study could also provide an important practical value for the comprehensive utilization of agricultural wastes.

Key words: biomass, hydrochar, hydrothermal time, adsorption, Cr(Ⅵ)

中图分类号:

P595
X142

刘雨嫣, 周景尧, 马少强, 陈家玮. 水热炭吸附Cr(Ⅵ)热-动力学行为及水热裂解时间的影响[J]. 现代地质, 2017, 31(05): 1039-1045.

LIU Yuyan, ZHOU Jingyao, MA Shaoqiang, CHEN Jiawei. Thermodynamic and Kinetic Adsorption of Cr(Ⅵ) on Hydrochars and the Effect of Hydrothermal Time[J]. Geoscience, 2017, 31(05): 1039-1045.

图/表 9

图1 水热炭产率及形貌表征 (A) 水热时间对产率的影响;(B) 水热炭HC(5 h)扫描电镜图

Fig.1 Product yield and morphology of hydrochars (A) Effect of hydrothermal time on the yield; (B) SEM image of the sample HC(5 h)

图2 花生壳原材料及水热炭元素分析 (A)元素含量组成;(B) H/C-O/C比值

Fig.2 Elements analysis of peanut hull biomass and hydrochars (A) Elemental composition;(B) H/C-O/C atomic ratio

图3 样品红外光谱表征 (A) 原材料和水热炭;(B) 水热炭HC(5 h)吸附Cr(Ⅵ)前后对比

Fig.3 FTIR characterization of samples (A) Biomass and hydrochars; (B) HC(5 h) before and after adsorption of Cr(Ⅵ)

图4 水热炭吸附Cr(Ⅵ)动力学 (A)准一级动力学模型;(B)准二级动力学模型

Fig.4 Sorption kinetics of Cr(Ⅵ) on hydrochars (A)Pseudo-first-order model; (B) Pseudo-second-order model

表1 水热炭吸附Cr(Ⅵ)准一级和准二级动力学模型拟合参数

Table 1 Pseudo-first-order and pseudo-second-order kinetic parameters for the sorption of Cr(Ⅵ) on hydrochars

水热炭	平衡吸附量	准一级动力学方程					准二级动力学方程
水热炭	平衡吸附量	q_e	k₁		R²		q_e	k₂	R²
HC(1 h)	4.14	3.827		0.280		0.818	4.61	0.037	0.981
HC(5 h)	9.42	8.411		0.757		0.847	9.90	0.03	0.992
HC(10 h)	10.35	8.835		0.962		0.838	10.00	0.031	0.992

图5 水热炭吸附Cr(Ⅵ)热力学 (A)Freundlich模型;(B)Langmuir模型

Fig.5 Isothermal adsorption of Cr(Ⅵ) on hydrochars (A) Freundlich model; (B) Langmuir model

表2 水热炭吸附Cr(Ⅵ)等温吸附模型拟合参数

Table 2 Model parameters of isothermal adsorption of Cr(Ⅵ) on hydrochars

水热炭	Freundlich				Langmuir
水热炭	k_f	n	R²		q_m		b		R²
HC(1 h)	1.420	0.496	0.980	54.632		0.002 87		0.923
HC(5 h)	2.379	0.429	0.980	50.46		0.004 64		0.904
HC(10 h)	4.789	0.343	0.946	51.21		0.008 07		0.873

图6 不同温度条件下水热炭HC(5 h)对Cr(Ⅵ) 吸附等温线

Fig.6 Isothermal adsorption of Cr(Ⅵ) on sample HC(5 h) at different temperatures

表3 水热炭HC(5 h)吸附Cr(Ⅵ)热力学参数

Table 3 Thermodynamic parameters for adsorption of Cr(Ⅵ) on sample HC(5 h)

ΔG⁰				ΔH⁰	ΔS⁰
290 K	300 K	310 K		25.98	0.1
-2.12	-2.17	-4.05		25.98	0.1

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