加拿大一枝黄花生物炭对Cd2+的吸附特性及机理

Characteristics and mechanism of cadmium adsorption by Solidago canadensis-derived biochar

以外来入侵种加拿大一枝黄花为原料,探究不同成分在不同热解温度下制得的生物炭的基本性质及其对水中Cd^2+的吸附能力、最优吸附工艺条件和吸附机制,以提高其资源化利用效率。结果表明:以茎叶混合作为原料在450℃下热解制得的加拿大一枝黄花生物炭(SCBC450)对Cd^2+吸附能力最优。正交结果显示,3种所选因素对生物炭吸附Cd^2+的影响程度依次为吸附质起始浓度>pH>温度;当pH=6、温度35℃、吸附质起始浓度50 mg·L^-1时,Cd^2+的吸附效率最高,可达(95.6±0.38)%。SCBC450对Cd^2+的吸附过程符合二级动力学模型,以化学吸附为主,且符合Langmuir等温吸附模型,最大理论吸附量达107.03 mg·g^-1。通过对生物炭吸附前后的XPS、FTIR和SEM-EDS分析可知,其对Cd^2+的吸附机制包括离子交换、络合反应、沉淀作用和物理吸附。因此,加拿大一枝黄花生物炭对Cd^2+的吸附具有极大的应用潜力。

Solidago canadensis(Canadian goldenrod)is a herbaceous worldwide invasive plant, which spreads rapidly and poses a serious threat to ecological environments in China. In order to improve the management of this highly problematic alien invasive species and enhance resource utilization efficiency, Solidago canadensis-derived biochar was prepared in the present study. The basic properties of biochar produced at various pyrolysis temperatures were investigated. The optimum conditions for cadmium adsorption by biochar in aqueous solution were studied systematically through batch adsorption experiments. In addition, the adsorption mechanism was explored. The results showed that the SCBC450, which was the Solidago canadensis-derived biochar pyrolyzed at 450 ℃ by stem-leaf mixture as the raw material, out-performed the other prepared biochar. Three factors were selected for orthogonal experiments, and their influence on the adsorption of Cd^2+ by biochar were as follows:initial concentration of adsorbate > pH > temperature. The highest adsorption efficiency Cd^2+ could achieve was(95.6±0.38)% when the initial concentration of adsorbate was 50 mg·L^-1 at 35 ℃ with pH 6. Under these optimal conditions, the adsorption process was better fitted using Langmuir isotherm and pseudo second-order model, which demonstrated that chemical adsorption dominated. The maximum theoretical adsorption capacity could reach 107.03 mg·g^-1. The analysis of biochar by XPS, FTIR, and SEM-EDS analyses showed that ion exchange, complexation, precipitation, and physical adsorption were the main mechanisms of Cd^2+ adsorption by SCBC450. Therefore, the study showed that Solidago canadensis-derived biochar has a great potential for cadmium adsorption in water treatment.