薏仁米秸秆生物炭对水中Hg2+的吸附特性及机制

doi:10.16258/j.cnki.1674-5906.2021.05.018

生态环境学报 ›› 2021, Vol. 30 ›› Issue (5): 1051-1059.DOI: 10.16258/j.cnki.1674-5906.2021.05.018

薏仁米秸秆生物炭对水中Hg²⁺的吸附特性及机制

张兵兵(), 杨照, 薛斌, 丁小艳, 娄金分, 王盛, 陈蔚洁, 徐国敏^*()

国家复合改性聚合物材料工程技术研究中心/贵州省材料产业技术研究院/贵州省材料技术创新基地,贵州贵阳 550014

收稿日期:2020-12-10 出版日期:2021-05-18 发布日期:2021-08-06
通讯作者: * 徐国敏,女,研究员。E-mail:410034801@qq.com
作者简介:张兵兵（1992年生）,男（苗族）,助理研究员,硕士,主要从事水体污染治理方向。E-mail:1591505377@qq.com
基金资助:
贵州省科技支撑计划项目([2019]2836);贵州省科技支撑计划项目([2019]2856);贵州省科技支撑计划项目([2020]1Y183);贵州省人才团队项目([2019]5618);贵阳市白云区科技计划项目([2019]17)

Adsorption of Aquatic Hg²⁺ by Biochar Obtained from Coix Straw

ZHANG Bingbing(), YANG Zhao, XUE Bin, DING Xiaoyan, LOU Jinfen, WANG Sheng, CHEN Weijie, XU Guomin^*()

National Engineering Research Center for Compounding and Modification of Polymer Materials/Guizhou Material Industrial Technology Institute/Guizhou Material Technology Innovation Base, Guiyang 550014, China

Received:2020-12-10 Online:2021-05-18 Published:2021-08-06

摘要/Abstract

摘要：

农业废弃物资源化利用和无害化处理是实现农业可持续发展和发展循环经济的有效途径,对薏仁米（Semen Coicis）秸秆制备生物炭吸附剂,实现有机固体废弃物资源化利用,解决重金属废水处理难题,以薏仁米秸秆为原料,采用快速热解法制备生物炭。为探明不同温度下制备的薏仁米秸秆生物炭对重金属Hg²⁺的去除机制及机理,并用扫描电子镜-能谱分析法（SEM-EDS）、傅立叶变换红外光谱法（FT-IR）、氮吸附法（BET）、X射线光电子能谱法（XPS）脱附对制备的生物炭进行了表征,研究其对水中Hg²⁺的吸附特性及机制。通过结果表明,随裂解温度的升高,生物炭的孔径尺寸逐渐增大,表面极性官能团逐渐减少,比表面积、孔隙容积呈现先增加后减小的趋势。薏仁米秸秆生物炭具有丰富的蜂窝状孔结构和-COOH、-OH等表面活性基团。生物炭对质量浓度小于100 mg∙L^-1溶液中Hg²⁺的去除率大于92%,且生物炭对Hg²⁺的去除率主要发生在前1 h吸附时间内,然后趋于平衡;随添加量的增加,生物炭对Hg²⁺去除效率呈现先增加后减小的趋势,含量为2 g∙L^-1时生物炭对水中Hg²⁺的去除效率最高,且700 ℃制备的生物炭对Hg²⁺的去除效率最高,最大吸附量可达235.3 mg∙g^-1。吸附平衡等温线和吸附动力学结果表明,薏仁米秸秆生物炭对Hg²⁺的吸附过程符合Langmuir等温吸附模型和准二级动力学吸附模型,其对Hg²⁺的吸附为单层吸附;结合X射线光电子能谱和立叶变换红外光谱,吸附作用机制主要以共沉淀和表面络合为主,Hg-π非共价相互作用为辅的形式结合机理。

关键词: 薏仁米秸秆, 生物炭, 污水处理, 吸附, Hg(Ⅱ), 去除

Abstract:

It is an urgent need for sustainable agricultural development to catch up with the trend of circular economy development, to which the resourceful utilization and harmless disposal of agricultural wastes could be an effective approach. Coix straw, the leftover remnant from coix seed production, was used as the feedstock for biochar adsorbent by rapid-pyrolysis for Hg(II) removal from aqueous solutions. The abundant availability of the low-cost coix straw waste makes it an ideal sustainable adsorbent for water treatment applications. This study investigated the impact of pyrolysis temperatures on physical characteristics of coix straw biochars (BCs) and their performances for aqueous uptake of Hg(II) ion. Physical and chemical characterizations of the prepared BCs were conducted by Scanning Electron Microscopy (SEM)/Energy Dispersive X-ray (EDX) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) method, and X-ray Photoelectron Spectroscopy (XPS). The results showed the formation of a rich honeycomb-like porous carbon with oxygen-containing functional groups (e.g. -COOH, -OH) on the surface. Furthermore, as the pyrolysis temperature for BCs increased, the pore size increased, the number of surficial functional groups decreased, and both the specific surface area and pore volume firstly increased, then decreased. More than 92% of Hg(II) was removed from aqueous solution in the presence of BCs while the initial concentration of Hg(II) was no more than 100 mg∙L^-1. The Hg(II) removal rate increased rapidly within one hour and then showed a slow increasing trend until the equilibrium was reached. With higher dosage of biochar adsorbent applied, Hg(II) removal rate firstly increased and then decreased. The 2 g∙L^-1 biochar pyrolysed at 700 ℃applied treatment has the maximum removal rate in that case the maximal adsorption capacity of 235.3 mg∙g^-1 can be achieved. Adsorption equilibrium data were analyzed using Langmuir and Freundlich equilibrium models, and former isotherm was appropriate towards explain adsorption characteristics, that suggests the monolayer adsorption was happened on BCs. The pseudo-second order model was relevant to address adsorption behavior. The XPS and FTIR results indicated that the possible mechanisms of Hg(II)/BCs interaction in this process can be divided into coprecipitation and surface complexation supplemented by Hg-π non-covalent weak interactions.

Key words: coix straw, biochar, sewage treatment, adsorption, Hg(Ⅱ), removal

中图分类号:

X703

张兵兵, 杨照, 薛斌, 丁小艳, 娄金分, 王盛, 陈蔚洁, 徐国敏. 薏仁米秸秆生物炭对水中Hg²⁺的吸附特性及机制[J]. 生态环境学报, 2021, 30(5): 1051-1059.

ZHANG Bingbing, YANG Zhao, XUE Bin, DING Xiaoyan, LOU Jinfen, WANG Sheng, CHEN Weijie, XU Guomin. Adsorption of Aquatic Hg²⁺ by Biochar Obtained from Coix Straw[J]. Ecology and Environment, 2021, 30(5): 1051-1059.

图/表 15

图1 所制备生物炭的SEM照片

Fig. 1 SEM images of BCs(a) (b) BC500, (c) (d) BC600, (e) (f) BC700, (g) (h) BC800

表1 不同温度制备生物炭的元素组成

Table 1 Chemical contents of BCs surface

生物炭 Biochar	元素含量 Element content					元素比 Element ratio
生物炭 Biochar	C	O	K	Si	Ca	O/C
BC500	73.59	20.05	4.88	0.18	1.31	0.272
BC600	84.22	9.07	3.40	1.08	‒	0.108
BC700	88.79	8.87	0.80	0.12	0.10	0.100
BC800	88.04	7.23	2.10	0.70	‒	0.082

图2 不同裂解温度制备生物炭的红外曲线

Fig. 2 FTIR spectrum of BCs

表2 不同裂解温度制备生物炭N2吸附-脱附结构参数

Table 2 Structure parameters of BCs

吸附剂 Adsorbent	比表面积 Specific surface area/ (m²∙g^-1)	孔容积 Pore volume/ (cm³∙g^-1)	平均孔径 Average pore size/ nm
BC500	78.127	0.073	15.352
BC600	119.126	0.085	15.405
BC700	293.632	0.119	15.454
BC800	25.262	0.014	15.328

图3 pH对BC吸附Hg2+的影响

Fig. 3 Effect of initial pH on Hg2+ adsorption of BCs

图4 溶液质量浓度对Hg2+去除性能的影响

Fig. 4 Effect of initial concentration on Hg2+ removal

图5 吸附时间对Hg2+去除性能的影响

Fig. 5 Effect of contact time on Hg2+ removal

图6 生物炭添加量对Hg2+去除性能的影响

Fig. 6 Effect of BCs dosage on Hg2+ removal

图7 Hg2+等温吸附曲线及Langmuir和Freundlich等温吸附模型

Fig. 7 Hg2+ isotherm adsorption curves and Langmuir and Freundlich isotherms models

表3 Freundlich 和Langmuir等温吸附模型参数

Table 3 Parameters of Langmuir and Freundlich isotherms models for BCs at 303K

吸附剂 Adsorbent	Freundlich模型 Freundlich model		Langmuir模型 Langmuir model		实际吸附量 Actual adsorption capacity q_a^max/(mg∙g^-1)
吸附剂 Adsorbent	K_f/(mg^1-ⁿ∙Lⁿ∙g^-1)	R²	q₀/(mg∙g^-1)	R²	实际吸附量 Actual adsorption capacity q_a^max/(mg∙g^-1)
BC500	8.05	0.9359	138.13	0.9827	113.1
BC600	8.23	0.9002	167.09	0.9787	171.9
BC700	14.29	0.8323	243.29	0.9570	222.9
BC800	10.18	0.8559	209.27	0.9642	183.7

图8 （a）吸附Hg2+的准一级模型的线性拟合;（b）吸附Hg2+的准二级模型的线性拟合

Fig. 8 Pseudo-first-order (a)and pseudo-second-order (b) kinetics fitting plots for Hg2+ onto BCs at 303 K

表4 准一级动力学及准二级动力学吸附模型参数

Table 4 Quasi-first and Quasi-secondary kinetic adsorption model parameters

吸附剂 Adsorbent	准一级吸附模型 Quasi-first kinetic adsorption model			准二级吸附模型 Quasi- secondary kinetic adsorption model			实际吸附 Actual adsorption q_b^max
吸附剂 Adsorbent	q_t/(mg∙g^-1)	r²	k₁∙10^-3/(min)^-1)	q_t/(mg∙g^-1)	r²	k₂∙10^-3/[g∙(mg·min)^-1]	实际吸附 Actual adsorption q_b^max
BC500	103.46	0.7250	1.39	121.8	0.9883	1.11	121.6
BC600	150.60	0.8484	2.02	170.7	0.9884	1.37	164.7
BC700	189.05	0.7731	2.97	231.54	0.9922	1.81	235.3
BC800	180.53	0.8837	1.19	203.10	0.9834	1.65	196.1

图9 BC700吸附前后XPS谱图（a）全谱扫描图;（b）C1s分峰拟合曲线;（c）Hg4f分峰拟合曲线

Fig. 9 XPS spectra of BC700 before and after treatment(a) wide scan; (b) C 1s; (c) Hg 4f

图10 生物炭在不同pH下的Zeta电位

Fig. 10 Zeta potential measurements of BCs at various pH values

图11 BC吸附机理图

Fig. 11 Schematic diagram of mechanism for Hg2+ adsorption onto BCs

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薏仁米秸秆生物炭对水中Hg²⁺的吸附特性及机制

Adsorption of Aquatic Hg²⁺ by Biochar Obtained from Coix Straw

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