水稻秸秆及其厌氧消化残渣生物炭对Cd(Ⅱ)吸附性能研究

Removal of aqueous Cd(Ⅱ) by biochar derived from rice straw and its anaerobically digested residue

为了寻求水稻秸秆(RS)及其厌氧消化物(DRS)新型的资源化利用途径,采用慢速热解在500℃下制备生物炭(RS500和DRS500)。在对生物炭形貌结构、元素组成、电导率、pH和表面官能团等理化性质及其热稳定性研究的基础上,考察RS500和DRS500去除Cd(Ⅱ)的性能,探讨了潜在的去除机理。结果表明,相比于RS500,经厌氧消化后,DRS500的C、H、O含量下降,而N的含量上升,非极性增大,电导率及比表面积下降,且热重分析显示DRS500热稳定性更好。RS500对Cd(Ⅱ)吸附在12 h达到平衡,而DRS500在48 h仍不能达到平衡。增加pH有利于RS500的吸附,但不利于DRS500的吸附,且吸附过程均为吸热反应。Langmuir模型对Cd(Ⅱ)吸附结果拟合较好,RS500和DRS500对Cd(Ⅱ)吸附符合二级动力学,表明RS500和DRS500主要通过化学作用对Cd(Ⅱ)进行吸附。表面官能团(-OH、C=O、Si-O-Si和C-H等)对Cd(Ⅱ)的吸附起重要作用。

To develop a novel use for rice straw and its anaerobically digested residue, the two resources were carbonized using slow pyrolysis at 500 °C to produce biochar（RS500 and DRS500, respectively）. The thermal stability of the two biochars was compared, as well as their main characteristics, including morphology, elemental composition, electrical conductivity, pH, and surface functional groups. Meanwhile,the adsorption of Cd（Ⅱ）by RS500 and DRS500 were investigated, and potential mechanisms for the observed adsorption as well. DRS500 contained relatively higher levels of C, H, and O, but not N, and possessed relatively lower electrical conductivity and surface area. The thermogravimetric（TG）curves indicated that DRS500 had greater thermal stability. The adsorption equilibrium of RS500 was achieved at 12 h, but the DRS500 was hard to achieve the adsorption equilibrium in 48 h. Increasing the solution pH promoted the adsorption of Cd（Ⅱ）by RS500 but reduced the adsorption of Cd（Ⅱ）by DRS500. The adsorption of Cd（Ⅱ）by RS500 and DRS500 can be regarded as an endothermic process because higher temperatures were beneficial to Cd（Ⅱ）adsorption. The Langmuir adsorption isotherms model was suit-able for describing the adsorption process, and adsorption kinetics could be simulated well by the second-order model, which indicated that Cd（Ⅱ）adsorption was dominated by chemical adsorption, during which surface functional groups, including-OH, C=O, Si-O-Si, and C-H played key roles in Cd（Ⅱ）removal.