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| 褐煤基材料对Cd2+的吸附机制 |
| Thermodynamics and Kinetics of Cadmium Ion Adsorption onto Lignite-derived Amendments |
| 投稿时间：2017-05-20 |
| DOI：10.13254/j.jare.2017.0136 |
| 中文关键词: 褐煤基材料，吸附剂，镉，吸附热力学，吸附动力学，红外光谱 |
| 英文关键词: materials derived from lignite, adsorbents, cadmium, adsorption thermodynamics, adsorption kinetics, FTIR |
| 基金项目:国家自然科学基金（41371311，41271471） |
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| 中文摘要: |
| 为筛选稳定、高效、环境友好的重金属污染修复材料，利用批吸附试验研究了不同温度下褐煤、腐植酸、活性炭对镉（Cd2+）的吸附特征，采用非线性χ2检验辅助决定系数判断等温线模型拟合度，用红外光谱对材料功能团进行了识别。结果表明，Temkin模型能最好拟合3种材料对Cd2+的等温吸附过程，Langmuir和Freundlich模型也能较好拟合但与温度有关。吸附热力学参数表明，3种材料对Cd2+的吸附为优惠发生的物理吸附，并且是自发的吸热过程，3种材料与Cd2+之间均有较强的作用力。在温度294.55~313.15 K时腐植酸、褐煤和活性炭对Cd2+的最大吸附量分别为36.14~44.09、29.63~38.20 mg·g-1和21.04~30.34 mg·g-1，吸附量随温度升高而升高，吸附自由能随着温度升高而降低，说明升温吸附更容易发生。准二级动力学拟合数据最好，表明3种材料对Cd2+的吸附存在着化学过程。褐煤基活性炭和褐煤基腐植酸具有丰富的孔隙结构。红外光谱图表明腐植酸和褐煤较大的吸附量与其含氧功能团种类较多以及在波数2 360 cm-1和2 342 cm-1附近吸收峰有关。因此，褐煤基3种材料对Cd2+的吸附是自发的吸热过程，腐植酸对Cd2+的最大吸附量和吸附能力最大，用Temkin等温方程和准二级动力学曲线能最适宜描述褐煤基材料对Cd2+的吸附特征。 |
| 英文摘要: |
| Adsorption kinetics and thermodynamics of cadmium onto lignite-derived humic acid and lignite-derived active carbon were investigated by batch experiments under different temperatures. The adsorption thermodynamic isotherms were fitted using Langmuir, Freundlich and Temkin models, the adsorption kinetics were fitted to pseudo-first-order, pseudo-second-order, Elovich, fractional power and intraparticle diffusion models. Thermodynamic studies showed that Temkin model displayed the most suitable model to describe adsorption of cadmium onto raw lignite, extracted humic acid and active carbon. Thermodynamic parameters indicated the adsorption process were spontaneous, favourable, and endothermic physical adsorption in nature. The equilibrium adsorption capacity of cadmium obtained from the Langmiur model for humic acid, lignite and active carbon was 36.14~44.09, 29.63~38.20 mg·g-1 and 21.04~30.34 mg·g-1 respectively in the temperature range of 294.55~313.15 K, adsorption capacity magnitudes increased with a rise of temperature, indicating more feasible adsorption at high temperature. Adsorption kinetics parameters showed that the pseudo-second-order model was better than the pseudo-first-order, Elovich, fractional power and the intraparticle diffusion models, this indicated that cadmium adsorption might be a physisorption associated with chemisorption process. According to the adsorption characteristics of kinetics, thermodynamics parameters such as change in free energy(△G), change in enthalpy(△H), and change in entropy(△S), it was concluded that the adsorption process of cadmium onto these different adsorbents were spontaneous, endothermic, simultaneous physisorption and accompanied by chemisorption or alternatively physicochemical process. Adsorbents of humic acid had the great adsorption capacity and adsorption intensity. Temkin isotherm model and pseudo-second-order model could be the suitable models with good fitting for describing the adsorption properties of cadmium onto these adsorbents. Infrared spectra analysis showed that oxygen containing functional groups and unknown absorbance peaks at approximately 2 360, 2 342 cm-1 had important impact on Cd2+ adsorption. |
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