椰纤维生物炭对Cd(Ⅱ)、As(Ⅲ)、Cr(Ⅲ)和Cr(Ⅵ)的吸附

Adsorption of Cd( Ⅱ),As( Ⅲ),Cr( Ⅲ) and Cr( Ⅵ)by coconut fiber-derived biochars

为了研究不同裂解温度制备的椰衣生物炭对Cd(Ⅱ)、As(Ⅲ)、Cr(Ⅲ)和Cr(Ⅵ)的吸附性能差异及其机理,并为制备高效吸附生物炭提供依据,采用Langmuir和Freundlich模型拟合分析了300、500和700℃3个裂解温度下制备的椰衣生物炭对Cd(Ⅱ)、As(Ⅲ)、Cr(Ⅲ)和Cr(Ⅵ)的等温吸附曲线,使用元素分析仪、Boehm滴定法、扫描电子显微镜等研究了不同温度制备的生物炭的组成与理化性质。结果表明,Langmuir模型和Freundlich模型都能较好地拟合生物炭对这些重金属的吸附,提高生物炭的制备温度可增加其对Cd(Ⅱ)和Cr(Ⅲ)的最大吸附量,同时降低其对As(Ⅲ)和Cr(Ⅵ)的最大吸附量;制炭温度升高引起的生物炭C含量、灰分含量、p H、CEC的升高和生物炭表面积增大是导致其对Cd(Ⅱ)和Cr(Ⅲ)的最大吸附量增大的主要原因。而随着制炭温度的上升,O、H元素含量下降引起的碱性官能团的增加,和羟基和酚羟基官能团的减少是生物炭对As(Ⅲ)和Cr(Ⅵ)吸附量下降的主要因素。

Aimed at screening highly efficient heavy metal absorbents,three coconut fiber-derived biochars(YA300,YA500 and YA700) were prepared by pyrolysis of coconut shell fiber at different temperatures(300,500 and 700℃) under a limited oxygen condition to investigate their capacities and mechanisms in absorption of metals including Cd( Ⅱ),As( Ⅲ),Cr( Ⅲ) and Cr( Ⅵ). Langmuir and Freundlich Sorption Isotherm Models were applied to study the metal absorption differences of these biochars. And elemental analyzer,the Boehm titration and the scanning electron microscope mirror methods were employed to study the element and functional group compositions,physical and chemical properties of biochars that influence their capacities in metal adsorption. Results showed that the Langmuir and Freudlich Sorption Isotherm Model well fit the metal absorption curves of these biochars. The maximum absorption capacities of biochars onto Cd( Ⅱ) and Cr( Ⅲ) increased,while the maximum absorption capacities onto As( Ⅲ) and Cr( Ⅵ) decreased,with the pyrolysis temperature increasing from 300℃ to 500 and 700℃. And it was suggested that the main factors leading to the increase in Cd(Ⅱ)and Cr(Ⅲ) absorption were the increase in C and ash content,p H,CEC and surface area of biochar,that increased with the pyrolysis temperature increase. And the reasons causing the decrease in As( Ⅲ) and Cr( Ⅵ)absorption were the increase in base functional groups that increased with the decrease of O and H content,the decrease in hydroxyl and phenolic hydroxyl functional groups with the increase of pyrolysis temperature.