Adsorption characteristics of modified lignite for Cr（Ⅵ） in acid mine drainage

doi:10.19965/j.cnki.iwt.2021-0788

Abstract

Abstract:

In order to solve the problem of limited adsorption saturation of Cr（Ⅵ） in acid mine drainage by lignite，it was modified by high temperature roasting and ultrasonic assisted Al₂（SO₄）₃. The characteristics and mechanism of Cr（Ⅵ） adsorption on aluminum salt modified lignite were studied by means of adsorption isotherm and adsorption kinetic principle，and the microstructure changes of lignite before and after modification were characterized by SEM，BET，XRD and FTIR. The results showed that the lignite modified by aluminum salt and calcined at 500 ℃ had good adsorption effect on Cr（Ⅵ）. The adsorption rate of Cr（Ⅵ） on modified lignite was 62.24% higher than that of original lignite，and the saturated adsorption capacity of Cr（Ⅵ） was 1.04 mg/g. Through the results of SEM，BET and XRD，after Al₂（SO₄）₃ ultrasonic vibration and high-temperature roasting，the original microcrystalline structure of lignite had not been damaged. However， the surface of the modified lignite had become very rough，some small pore structures with uneven distribution appeared，and the adsorption active sites increased. The FTIR results showed that the —CH，—CH₃ of cyclane and aliphatic hydrocarbon combined with the oxygen atoms adsorbed on the surface of lignite to form phenolic hydroxyl group and carboxyl groups. The alkane and olefin branches in the lignite structure，the C $̿$ C skeleton in the aromatic ring and the —OH of alcohols and phenols were reduced to form small molecular organics of hydroxyl and carboxyl groups. The evaporation of free water and bound water in lignite structure made fine pores appear on the surface. The increase of hydroxyl，carboxyl and other oxygen-containing functional groups on the surface of modified lignite provided more adsorption sites for the adsorption process，so as to improve the adsorption capacity of lignite.

Key words: lignite, modified lignite, acid mine drainage, Cr（Ⅵ）, adsorption

摘要：

为解决褐煤对酸性矿山废水中Cr（Ⅵ）吸附饱和量有限的问题，采用超声波辅助Al₂（SO₄）₃及高温焙烧改性褐煤。通过吸附等温线、吸附动力学原理等方法研究铝盐改性褐煤吸附Cr（Ⅵ）的特性和机理，并且利用SEM、BET、XRD以及FTIR表征褐煤改性前后的微观结构变化。结果表明：超声波辅助Al₂（SO₄）₃改性并经过500 ℃高温焙烧后的褐煤对Cr（Ⅵ）的吸附效果好。改性褐煤对Cr（Ⅵ）的吸附率比原褐煤提升了62.24%，对Cr（Ⅵ）的饱和吸附容量为1.04 mg/g。通过SEM、BET和XRD测试可知，褐煤在经过Al₂（SO₄）₃超声震荡和高温焙烧后，原有的微晶结构并未被破坏，但改性褐煤表面变得十分粗糙，出现一些分布不均匀的细小孔状结构，平均孔径有所增加。通过FTIR测试可知，褐煤分子结构中的—CH，环烷烃、脂肪烃中的—CH₃与附着在褐煤表面的氧原子结合，生成含羧基化合物和酚羟基。褐煤结构中的烷烃和烯烃支链、C $̿$ O、芳环中C $̿$ C骨架以及醇类—OH均有所减少，生成较小的羟基类、羧基类的小分子有机物。褐煤结构中的自由水和结合水蒸发使表面出现细小孔隙。改性褐煤表面的羟基、羧基等含氧官能团的增加为吸附过程提供了更多的吸附位点，从而提高褐煤的吸附能力。

关键词: 褐煤, 改性褐煤, 酸性矿山废水, Cr（Ⅵ）, 吸附

CLC Number:

X703.1

Junzhen DI, Ruiqi YANG, Yanrong DONG, Sihang BAO, Xianjun WANG. Adsorption characteristics of modified lignite for Cr（Ⅵ） in acid mine drainage[J]. Industrial Water Treatment, 2022, 42(5): 103-109.

狄军贞, 杨瑞琪, 董艳荣, 鲍斯航, 王显军. 改性褐煤对酸性矿山废水中Cr（Ⅵ）的吸附性能研究[J]. 工业水处理, 2022, 42(5): 103-109.

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URL: https://www.iwt.cn/EN/10.19965/j.cnki.iwt.2021-0788

https://www.iwt.cn/EN/Y2022/V42/I5/103

Figures/Tables 12

Table 1 Adsorption rate and capacity of Cr（Ⅵ） on modified lignite calcined at different temperatures

成分	原褐煤	200 ℃-PAC	300 ℃-PAC	400 ℃-PAC	500 ℃-PAC	600 ℃-PAC
Cr（Ⅵ）吸附率/%	36.80	80.00	71.42	74.28	99.04	86.66
Cr（Ⅵ）吸附量/（mg·g^-1）	0.42	0.84	0.75	0.78	1.04	0.91

Fig.1 SEM images of lignite before and after modification

Table 2 Pore volume，pore size and specific surface area of lignite and modified lignite

样品	比表面积/（m²·g^-1）	总孔容积/（cm³·g^-1）	平均孔径/nm
原褐煤	27.536 6	0.049 9	6.856 1
改性褐煤	20.317 1	0.040 9	8.069 0

Fig.2 XRD spectrum of lignite before and after modification

Fig.3 FTIR spectra of lignite before and after modification

Fig.4 Influence of dosage of modified lignite on Cr（Ⅵ） adsorption

Fig.5 Influence of adsorption time on Cr（Ⅵ） adsorption

Fig.6 Influence of initial concentration of Cr（Ⅵ） on adsorption

Fig.7 Isotherm adsorption curve

Table 3 Fitting characteristic parameters of Langmuir and Freundlich models

Langmuir模型			Freundlich模型
q_e/（mg·g^-1）	k ₁	R ²	1/n	k ₂	R ²
2.430 3	0.080 1	0.989 9	0.299 6	0.576 4	0.969 4

Fig.8 Quasi first and second order kinetics fitting of Cr（Ⅵ） adsorption by modified lignite

Table 4 Kinetic parameters of Cr（Ⅵ） adsorption by modified lignite

参数	q _e/（mg·g^-1）	k	R ²
准一级动力学	1.083 4	0.028 2	0.996 3
准二级动力学	1.204 0	0.036 7	0.998 3

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