Adsorption of ammonia nitrogen and phosphorus by magnesium impregnated biochar: preparation optimization and adsorption mechanism

doi:10.11949/0438-1157.20190802

Abstract

Abstract:

Magnesium-loaded biochar adsorbent was prepared from waste cassava stalks. The effects of modification of different magnesium salts, MgCl₂ concentration, carbonization temperature, solid-liquid ratio and carbonization time on the adsorption of ammonia-nitrogen and phosphorus were studied using the controlled variable method. Samples of magnesium-loaded cassava stalk-based biochar (Mg-BC) using the process with the best adsorption performance were prepared and batch adsorption experiments for ammonia-nitrogen and phosphorus were carried out. The adsorption characteristics were studied using isothermal models (Langmuir and Freundlich model) and kinetic models (quasi-first-order kinetics, quasi-second-order kinetics and intra-particle diffusion model). The adsorption mechanism was also studied using FTIR, XRD, SEM-EDS and XPS. The results show that the adsorption process of ammonia-nitrogen and phosphorus by Mg-BC conforms to the Freundlich model and quasi-second-order kinetic model, and is multilayer chemisorption. The theoretical saturated adsorption capacities were 43.48 mg·g^-1 and 96.00 mg·g^-1for ammonia-nitrogen and phosphorus respectively. Combined with the characterization results, it is speculated that magnesium-titanium-based biochar (Mg-BC) adsorbs ammonia nitrogen and phosphorus mainly through functional groups, complex precipitation and ion exchange and other processes.

Key words: Mg-loading, biochar, cassava straw, adsorption, sorbent, adsorption mechanism

摘要：

利用废弃的木薯杆制备了载镁的生物炭吸附剂。以氨氮、磷为目标污染物，采用控制变量法研究了不同镁盐改性、MgCl₂浓度、碳化温度、固液比和碳化时间对氨氮、磷吸附性能的影响，制备最具吸附性能的载镁木薯秆基生物炭（Mg-BC），进行批量吸附氨氮和磷实验。利用等温模型（Langmuir和Freundlich模型）和动力学模型（准一级动力学、准二级动力学和颗粒内扩散模型）探究其吸附特性，在其吸附特性研究的基础上，运用FTIR、XRD、SEM-EDS、XPS等表征手段对其吸附机理进行探讨。结果表明，Mg-BC对氨氮和磷的吸附过程均符合Freundlich模型和准二级动力学模型，为多分子层的化学吸附，理论饱和吸附量分别为43.48 mg·g^-1和96.00 mg·g^-1。结合表征结果推测，Mg-BC吸附氨氮、磷主要通过官能团作用、络合沉淀和离子交换等多过程协同完成。

关键词: 负载镁, 生物炭, 木薯秸秆, 吸附, 吸附剂, 吸附机制

CLC Number:

X 53

Anyu LI, Shuangli LI, Bige YU, Aiying MA, Xinlan ZHOU, Jianhui XIE, Yanhong JIANG, Hua DENG. Adsorption of ammonia nitrogen and phosphorus by magnesium impregnated biochar: preparation optimization and adsorption mechanism[J]. CIESC Journal, 2020, 71(4): 1683-1695.

李安玉, 李双莉, 余碧戈, 马爱英, 周鑫兰, 谢建慧, 蒋艳红, 邓华. 镁浸渍生物炭吸附氨氮和磷：制备优化和吸附机理[J]. 化工学报, 2020, 71(4): 1683-1695.

Figures/Tables 15

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Mg-BC	Quasi-first-order kinetic			Quasi-second-order kinetic			Intraparticle diffusion
Mg-BC	Q_e/(mg·g^-1)	K₁/min^-1	R²	K₂/(g·(mg·min)^-1)	Q_e/(mg·g^-1)	R²	C/(mg·g^-1)	K₃/(mg·g^-1·min^-0.5)	R²
氨氮	53.89	0.2806	0.9572	0.0022	44.84	0.9979	13.22	2.14	0.8111
磷	19.71	0.0229	0.7174	0.0009	68.97	0.9887	13.02	3.88	0.7537

Mg-BC	Quasi-first-order kinetic			Quasi-second-order kinetic			Intraparticle diffusion
Mg-BC	Q_e/(mg·g^-1)	K₁/min^-1	R²	K₂/(g·(mg·min)^-1)	Q_e/(mg·g^-1)	R²	C/(mg·g^-1)	K₃/(mg·g^-1·min^-0.5)	R²
氨氮	53.89	0.2806	0.9572	0.0022	44.84	0.9979	13.22	2.14	0.8111
磷	19.71	0.0229	0.7174	0.0009	68.97	0.9887	13.02	3.88	0.7537

Biochar	BET/(m²·g^-1)	Total pore volume/(cm³·g^-1)	Average aperture/nm	Biochar magnesium content /(g·kg^-1)
Mg-BC	10.33	0.0406	15.71	113.21
BC	4.10	0.0196	9.60	—
Biochar	C/%	H/%	N/%	O/%
Mg-BC	47.13	7.81	0.66	22.41
BC	57.55	8.29	0.24	28.24
Biochar	O/C	H/C	(O+N)/C	(O+H)/C
Mg-BC	0.48	0.17	0.49	0.64
BC	0.49	0.14	0.50	0.63

Biochar	BET/(m²·g^-1)	Total pore volume/(cm³·g^-1)	Average aperture/nm	Biochar magnesium content /(g·kg^-1)
Mg-BC	10.33	0.0406	15.71	113.21
BC	4.10	0.0196	9.60	—
Biochar	C/%	H/%	N/%	O/%
Mg-BC	47.13	7.81	0.66	22.41
BC	57.55	8.29	0.24	28.24
Biochar	O/C	H/C	(O+N)/C	(O+H)/C
Mg-BC	0.48	0.17	0.49	0.64
BC	0.49	0.14	0.50	0.63

Sample	Atomic/%
Sample	P 2p	C 1s	N 1s	O 1s	Mg 1s
Mg-BC	0.35	73.05	1.68	20.72	4.21
Mg-BC+N/P	1.05	78.82	2.28	16.48	1.37