玉米秸秆生物炭对铜的吸附及其影响因素

Adsorption of copper content rate on maize straw biochar and influential factors concerned

为研究Cu(Ⅱ)在生物炭上的吸附特性及影响因素,以玉米秸秆为原材料,在300℃和600℃条件下,采用限氧法制备2种生物炭(BC300和BC600),并用吸附动力学、吸附等温线及热力学相关模型对试验数据进行拟合,探讨热解温度、吸附时间、初始浓度和p H值等因素对生物炭吸附铜的影响,分析其吸附机理。结果表明:两种生物炭对铜的吸附动力学均符合Elovich方程(R2=0.98),表明生物炭对Cu(Ⅱ)吸附过程是非均相的,且升高生物炭制备温度有利于对铜的吸附,即BC600比BC300对铜有更大的吸附能力;Freundlich等温方程能够较好地描述生物炭对Cu(Ⅱ)的吸附过程(R2=0.98),可见玉米秸秆生物炭对Cu(Ⅱ)的吸附为非线性多层吸附,且BC300和BC600对Cu(Ⅱ)的吸附由多种机制共同作用;通过热力学分析发现生物炭对铜的吸附过程是一个吸热熵增的自发过程;BC300和BC600对铜的吸附量随p H值的增加而增加(p H=2~6)。

The objective of this article is to discuss the adsorptive features and the influential factors of Cu( Ⅱ) concerned on the biochar of the maize. And,for the said objective,we have managed to prepare 2 samples of biochar at different temperatures( BC300,BC600) from the maize straw via oxygen-limiting pyrolysis. In the above experiments,we have managed to characterize the physical and chemical features of biochar with a pore and specific surface area analyzer,a scanning electron microscope and a Fourier infrared spectrometer to observe and test the adsorption features and the mechanism of the biochar samples for the copper content in the aqueous solution under the various factors concerned,such as the effects of the pyrolysis temperature,the p H value,the adsorption kinetics,isotherms and thermodynamics on the copper adsorption,in addition to the determination of the pyrolysis temperature of its ash,the elemental composition and its specific surface areas. And,accordingly,we have noticed that,with the increase of the decomposition temperature,both the ash content and the BET specific surface area tend to increase,whereas O/C and H/C tend to decrease. The results of the electron microscope scanning indicate that the surface of BC600 enjoys a rich pore structure,which is conducive to the adsorption of Cu( Ⅱ) . The results of the adsorption kinetics show that the amount of Cu( Ⅱ) adsorbed by the 2 kinds of biochar tends to increase with time prolonging,whereas the adsorption process can be divided into 2 stages. Literarily speaking,the adsorption mechanism of the copper adsorption on the 2 kinds of biochar can well be characterized by the Elovich equation( R2=0. 980),and featured by the surface sorption energy of Cu( Ⅱ)with the biochar heterogeneous. And higher pyrolysis temperature turns out to be favorable for adsorption of copper content,that is,BC600 can have a greater adsorption capacity for copper content than BC300. It also proves that,the isotherm tends to be well consistent with the Freundlich isothermal equation( R2=0. 98). Hence,it can be seen that the adsorption of Cu( Ⅱ) by the corn straw biochar is a non-linear multilayer adsorption,whose adsorption of Cu( Ⅱ) by BC300 and BC600 should be activated by the multiple mechanisms. For instance,the adsorption for copper on the biochar is by nature p H-dependent,and the biochar adsorption of copper tends to increase with the increase of p H( 2-6). Thus,the above mentioned thermodynamic analysis may imply that the adsorption process is actually a spontaneous process of the endothermically increasing entropy.