玉米秸秆活性炭的制备及其吸附动力学研究

以玉米秸秆为原材料,采用ZnCl2活化法制备玉米秸秆活性炭,吸附次甲基蓝染料废水,进行动力学分析。本实验用Langmuir和Freundlich模型对吸附等温线进行拟合,结果表明,玉米秸秆活性炭对次甲基蓝的吸附与Langmuir方程拟合良好,R2=0.9857。采用Lagergren准一级速率模型、Lagergren准二级速率模型、Bangham动力学方程和Elovich动力学方程分别对秸秆活性炭吸附次甲基蓝溶液进行吸附动力学拟合,通过分析得出吸附过程与Lagergren准二级速率模型拟合最好,R2=0.9979。秸秆活性炭对次甲基蓝的最大吸附量达到909.09 mg/g,具有很高的吸附能力。     

酸改性泥炭对含亚甲基蓝废水的吸附净化作用

采用稀硝酸对泥炭进行改性处理获得酸改性泥炭,并将其用于处理亚甲基蓝废水。考察初始溶液pH、接触时间、酸改性泥炭投加量和亚甲基蓝溶液初始浓度等因素对酸改性泥炭吸附效果影响。结果表明,初始溶液pH、接触时间、酸改性泥炭投加量和亚甲基蓝溶液初始浓度对酸改性泥炭吸附性能都有一定的影响。在最佳的反应条件下(接触时间为60 min,反应温度为35℃,初始溶液pH为7.12,酸改性泥炭投加量为2 g),亚甲基蓝去除率可达90.88%,其吸附较好地符合Freundlich和Langmuir等温方程,拟合相关系数均大于0.9。通过热力学计算发现,ΔG<0、ΔS>0,表明该吸附反应是自发的、吸热反应。且该吸附过程符合准二级动力学方程(R2=0.98)。     

Adsorption of chlorpyrifos,penconazole and metalaxyl from aqueous solution by modified clays

Sorption of three pesticides (chlorpyrifos, metalaxyl and penconazole) has been measured on a commercial clay montmorillonite and on the same mineral modified with either of two cationic-surfactant micelles. Both micelle–clay complexes, commercial names Cloisite 20A and Cloisite 30B, showed a good capacity to sorb all three pesticides from water, whereas their sorption on the natural montmorillonite was not described by an isotherm. Modelling sorption on both micelle–clay complexes showed that the Freundlich sorption constant (K _F) was higher for chlorpyrifos on Cloisite 20A (K _F = 7.76) than on Cloisite 30B (K _F = 5.91), whereas the sorption of metalaxyl was stronger on Cloisite 30B (K _F = 1.07) than on Cloisite 20A (K _F = 0.57). Moreover the micelle–clay complex Cloisite 20A also showed a good affinity for penconazole, the maximum quantity adsorbed (q _m) of 6.33 mg g^?1 being 45% more than that on Cloisite 30B. Single-batch adsorption of each pesticide onto both micelle–clay complexes was studied using the Freundlich isotherm for chlorpyrifos and metalaxyl and the Langmuir isotherm for penconazole. The Cloisite 20A micelle–clay complex was predicted to require 23% less adsorbent to treat certain volumes of wastewater containing 30 mg L^?1 chlorpyrifos, 43% more to treat metalaxyl similarly and 57% less to treat penconazole compared with Cloisite 30B.     

Sorption–desorption of imidacloprid onto a lacustrine Egyptian soil and its clay and humic acid fractions

Sorption–desorption of the insecticide imidacloprid 1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine onto a lacustrine sandy clay loam Egyptian soil and its clay and humic acid (HA) fractions was investigated in 24-h batch equilibrium experiments. Imidacloprid (IMDA) sorption–desorption isotherms onto the three sorbents were found to belong to a non-linear L-type and were best described by the Freundlich model. The value of the IMDA adsorption distribution coefficient, Kd_ads, varied according to its initial concentration and was ranged 40–84 for HA, 14–58 for clay and 1.85–4.15 for bulk soil. Freundlich sorption coefficient, Kf_ads, values were 63.0, 39.7 and 4.0 for HA, clay and bulk soil, respectively. The normalized soil Koc value for imidacloprid sorption was ～800 indicating its slight mobility in soils. Nonlinear sorption isotherms were indicated by 1/n_ads values <1 for all sorbents. Values of the hysteresis index (H) were <1, indicating the irreversibility of imidacloprid sorption process with all tested sorbents. Gibbs free energy (ΔG) values indicated a spontaneous and physicosorption process for IMDA and a more favorable sorption to HA than clay and soil. In conclusion, although the humic acid fraction showed the highest capacity and affinity for imidacloprid sorption, the clay fraction contributed to approximately 95% of soil-sorbed insecticide. Clay and humic acid fractions were found to be the major two factors controlling IMDA sorption in soils. The slight mobility of IMDA in soils and the hysteresis phenomenon associated with the irreversibility of its sorption onto, mainly, clay and organic matter of soils make its leachability unlikely to occur.     

The electron density distribution in pyridinium and bipyridylium compounds and its relevance to their adsorption by expanding lattice clays

Abstract

Charge distributions in 1, 1'‐ethylene‐2, 2'‐bipyridylium (diquat), 1,1'‐dimethyl‐4,4'‐bipyridylium (paraquat) and 1‐methylpyridinium organocations were calculated by a Complete Neglect of Differential Overlap semi‐empirical quantum mechanical procedure. The data show that the positive charges in the organocations are distributed around the molecules and are greatest in the positions ortho and para to the heterocyclic nitrogen atoms. Earlier interpretations of the mechanisms of adsorption of paraquat and diquat by soils and clays assumed that the charges were located in the heterocyclic nitrogen atoms. Here some consideration is given to the influence of the charge delocalizations on the processes of adsorption by montmorillonite and vermiculite clay preparations.     

变压吸附技术的应用及其发展简述

文章分析了变压吸附技术存在的问题,并提出解决措施。通过对变压吸附技术应用现状的总结,对该技术未来的发展方向进行预测与评价。指出变压吸附技术能够经济高效地实现物质的分离,有望成为分离技术未来的发展方向,为环保和工业生产做出更大贡献。     

树脂固定床吸附含酚废水预测模型研究

针对应用于实际工业化的树脂固定床吸附研究较少,而与之相关的固定床吸附穿透曲线可以用来确定固定床吸附操作参数,为固定床的设计和实际操作提供指导。通过对恒定波振荡理论和吸附等温方程的联合,来预测固定床吸附穿透曲线;并研究了不同操作条件对大孔弱碱树脂吸附对硝基酚穿透曲线预测模型的影响。以期望为树脂固定床的设计和实际工业应用产生指导意义。     

Pathways to urban sustainability

The concept of sustainable development has become very much in vogue in the past decade. We have also observed a shift in the interpretation of this concept from a global perspective to a meso perspective—that is, at a local, regional or sectoral level. This paper aims at highlighting the urban dimension of environmental issues. After a sketch of urban pollution problems and of tools for economic analysis, the notion of urban sustainability will be advocated as a meaningful analytical and policy concept. Next, the main focus of this paper will be on a typological approach to urban sustainability issues on the basis of three characteristic angles, viz. strong and weak sustainability, absolute and relative decoupling and the spatial ecological footprint. Various methodological issues will also be discussed, while the paper will conclude with some perspectives on policy issues. Copyright © 2001 John Wiley & Sons, Ltd.     

Adsorption of glyphosate on Brazilian subtropical soils rich in iron and aluminum oxides

Abstract

We investigated the adsorption of glyphosate onto five subtropical soils of Paraná and São Paulo states, Brazil, a region of intense agricultural activities, aiming at the determination of kinetic and isotherm adsorption parameters which enable the evaluation of the potential leaching of the herbicide. The adsorption was fast, being described by the pseudo-second order and intraparticle diffusion models, thus suggesting that mixed mechanisms are involved. The Oxisol containing the highest concentrations of metal oxides (209.5?g kg^?1 Fe₂O₃ and 160.2?g kg^?1 Al₂O₃) was the sample with the highest rate constant, indicating the adsorption sites are readily available. All the soils are rich in aluminum and iron oxides, explaining the Freundlich coefficients (K_F) between 642 and 1360?mg^1-1/n kg^?1 L^1/n, which are higher than most of the coefficients described for other soils around the world. The maximum desorption (15% of the adsorbed amount) was observed for the Oxisol. For the other soils, desorption ranged from 2 to 7%. These results suggest that the leaching of free glyphosate to nearby surface and groundwaters is unlikely unless excessive doses are used. The adsorption parameters are useful for managing the right doses applied to the crops, thus avoiding contamination of adjacent areas.     

改性多壁碳纳米管对水中Cd~（2＋）的去除

为了增加多壁碳纳米管（multiwall carbon nanotubers,MWNTs）对水中Cd2＋的吸附量,使用混酸对多壁碳纳米管进行氧化处理,采用红外光谱进行结果表征,并探讨了吸附时间、pH值和MWNTs的使用量、Cd2＋的浓度及干扰离子对镉离子吸附的影响。结果表明,吸附时间为1.5 h、pH为5.3、吸附效果最佳,随MWNTs量的增加Cd2＋去除量增加,共存的阳离子会降低对Cd2＋的吸附效果,对Cd2＋的吸附符合Longmuir吸附定律。研究同时表明,pH小于2时Cd2＋能容易从碳纳米管上解吸。初步探讨了Cd2＋吸附机制。