互花米草生物炭的添加对土壤吸附三氯生的影响及其机制研究

互花米草作为入侵物种,在我国沿海分布广泛,对沿海生态造成负面影响.本研究以互花米草资源化利用为出发点,在300℃和600℃下将其热解分别制得BC300和BC600两种生物炭,采用批量平衡法研究了生物炭添加对土壤吸附三氯生(TCS)的影响及其机制.结果表明,BC300内含有未炭化有机质,对TCS的吸附以分配作用为主,有利于对高浓度TCS的吸附;BC600有较大的比表面积,对TCS的吸附以表面吸附为主,有利于对低浓度TCS的吸附.生物炭添加能够促进土壤对TCS的吸附,且吸附量随生物炭添加比例的增加而增加;添加BC300的土壤对TCS的吸附量要显著高于添加BC600的土壤,这主要与生物炭的结构特征及其对土壤p H值的影响有关.因此,添加300℃下制备的互花米草生物炭可以有效地降低土壤中TCS的环境风险,同时也能为护花米草的资源化利用提供一条可行途径.     

山梨酸废水在ABR中的基质降解行为

稳态条件下,采用厌氧折流板反应器(anaerobic baffled reactor,ABR)处理山梨酸废水并进行基质降解动力学研究.实验表明,在污泥负荷为0.54～1.63 kg COD/(kg VSS·d)的范围内,COD去除率随着负荷的增加从85%降到55%.各隔室出水COD沿程递减,前3个隔室承担了去除COD的重要作用,但随着污泥负荷的增加,后部承担的COD去除率比例增大.基于各串联隔室完全混合的假定,推导ABR中山梨酸废水的基质降解动力学方程,并通过实验确定相关动力学参数及相应的动力学方程.实测值与预测值基本吻合.     

水中六氯苯的高级氧化降解机理及其动力学探讨

采用UV、O3、UV/O3高级氧化法对水中六氯苯(HCB)的降解效果及机理进行了研究.结果表明, UV本身对HCB的去除贡献率不大, HCB可被O3、UV/03快速降解,即UV相似文献   

黄棕壤不同粒级组分对镉的吸附动力学与热力学研究

采用一次平衡法研究了黄棕壤不同粒级组分(粘粒≤2 μm、粉粒2～20 μm、细砂粒20～200 μm、粗砂粒200～2000 μm)对镉的吸附动力学与热力学,并采用拉格朗日假一级动力学方程、假二级动力学方程、颗粒内扩散模型对试验数据进行拟合.结果表明,2种温度下各粒级组分对镉的吸附均可分为快反应和慢反应2个阶段,0～15 min内为快反应阶段,吸附量达到饱和吸附量的95%以上,此后为慢反应阶段;随着温度由25℃升高到45℃,各组分对镉的饱和吸附量增加了4.86%～25.3%;各组分对镉的吸附动力学符合拉格朗日假二级动力学方程,吸附过程以化学吸附为主;二级动力学吸附速率常数表明,随着各组分粒级增大,吸附速率降低;在试验温度范围内随着温度升高,吸附速率加快;吸附过程的限速步骤为颗粒间扩散;各粒级组分对镉的吸附为吸热反应,反应能自发进行.     

短程硝化的生化机理及其动力学

短程硝化的生化反应机理和动力学是生物脱氮技术的理论基础,同时也是生物脱氮工艺设计、运行科学化和合理化的重要依据.基于短程硝化的生化机理、氨氧化菌的电子传递(能量产生)模式,从微生物学和化学计量学两个方面详细论述了短程硝化一系列复杂的生化反应过程.由此可知,短程硝化是一个涉及多种酶及多种中间产物,并伴随着电子(能量)传递的复杂生化反应过程,是基质(NH4 -N)利用(产能代谢)和微生物(氨氧化菌)增殖(合成代谢)两类反应的综合,因此,研究氨氮比利用速率和氨氧化菌比增殖速率动力学则是对短程硝化反应的深层次研讨.并建议采用积分法和微分法来确定动力学参数μnmax、KN、vnmax.     

水-土体系中溶解有机质对菲解吸动力学的影响

土壤解吸过程是影响污染物生物有效性和土壤修复的重要因素.采用人工添加方法制备加菲(PHE)老化1个月的土壤.考察水-土体系中溶解有机质(DOM)对PHE解吸动力学的影响和相互关系.结果表明.DOM与PHE的解吸释放浓度表现出相似的先增后减、最后趋于平衡的动力学过程(双尾显著性水平0.000,Spearman 秩相关系数0.778).PHE 解吸动力学常数量级的变化范围在10-5～10-6s-1之间,而且转折变化发生在峰值释放量所对应的时间点(2.5 h 左右).另外,紫外光谱表征参数E4/E6<5说明解吸进入水相的 DOM 主要为胡敏酸,另一参数A254,SUV 的变化趋势与PHE解吸动力学过程相一致.在不同pH条件下,PHE解吸浓度的关系为:碱性>中性>酸性.因酸性条件下溶解释放的胡敏酸(DHA)发生沉淀而无法判定其与PHE释放浓度的相关性;在其它pH条件下DOM、A254,,SUV>都分别与PHE的解吸浓度显著相关.这些结果说明DOM是影响PHE解吸动力学的重要因素.     

Adsorption of mercury on laterite from Guizhou Province, China

The adsorption behaviors of Hg(Ⅱ) on laterite from Guizhou Province,China,were studied and the adsorption mechanism was discussed.The results showed that different mineral compositons in the laterite will cause differences in the adsorption capacity of laterite to Hg(Ⅱ).Illite and non-crystalloids are the main contributors to enhancing the adsorption capacity of laterite to Hg(Ⅱ).The pH of the solution is an important factor affecting the adsorption of Hg(Ⅱ) on laterite.The alkalescent environment (pH 7-9) ...     

Batch studies of adsorption of copper and lead on activated carbon from Eucalyptus camaldulensis Dehn. Bark

Powdered activated carbon (PAC) prepared from Eucalyptus camaldulensis Dehn. bark was tested for its adsorption capacity for Cu(Ⅱ) and Pb(Ⅱ). The experiment was conducted to investigate the effects of pH, contact time, initial metal concentration, and temperature. The best adsorption of both Cu(Ⅱ) and Pb(Ⅱ) occurred at pH 5, where the adsorption reached equilibrium within 45 min for the whole range of initial heavy metal concentrations (0.1-10 mmol/L). The adsorption kinetics was found to follow the pseudo-...     

Effective removal of Cobalt(II) ions from aqueous solutions and nuclear industry wastewater using sulfhydryl and carboxyl functionalised magnetite nanocellulose composite: batch adsorption studies

A new adsorbent sulfhydryl and carboxyl functionalized magnetite nanocellulose composite [(MB-IA)-g-MNCC] was synthesized by graft co-polymerization of itaconic acid onto magnetite nanocellulose (MNCC) using EGDMA as cross linking agent and K₂S₂O₈ as free radical initiator. The adsorption occurs maximum in the pH 6.5. The best fitted kinetic model was found to be pseudo-second-order kinetics. Therefore the mechanism of Co(II) adsorption onto (MB-IA)-g-MNCC follows ion exchange followed by complexation. The Langmuir model was the best fitted isotherm model for the adsorption of Co(II) onto the (MB-IA)-g-MNCC. Simulated nuclear power plant coolant water samples were also treated with (MB-IA)-g-MNCC to demonstrate its efficiency for the removal of Co(II) from aqueous solutions in the presence of other metal ions. To recover the adsorbed Co(II) ions and also to regenerate the adsorbent to its original state 0.1?M HCl was used as suitable desorbing agent. Six cycles of adsorption-desorption experiments were conducted and was found that adsorption capacity of (MB-IA)-g-MNCC has been decreased from 97.5% in the first cycle to 84.7% in the sixth cycle. Recovery of Co(II) using 0.1?M HCl decreased from 93.2% in the first cycle to 79.3% in the sixth cycle.

Abbreviations: T: absolute temperature; q_e: amount adsorbed at equilibrium; q_t: amount adsorbed at time t; CELL: cellulose; Co: cobalt; C_e: concentration at equilibrium; C_HCl: concentration of HCl; C_NaOH: concentration of NaOH; C_A: concentrations of acid; C_B: concentrations of base; W_g: dry weight of composite; W_i: dry weight of MNCC; DS: energy dispersive spectra; EGDMA: ethylene glycol dimethacrylate; Ce: equilibrium concentration; K_L: equilibrium constant; F: Faradays constant; FTIR: Fourier transform infrared spectra; ΔG^o: free energy change; K_F: Freundlich adsorption capacity; 1/n: Freundlich constant; R: gas constant; D: grafting density; EC_o: initial concentration; IA: itaconic acid; IA-g-MNCC: itaconic acid-grafted-magnetite nanocellulose composite; b: Langmuir constant; MNCC: magnetite nanocellulose composite; Q⁰: Maximum adsorption capacity; (MB-IA)-g-MNCC: 2-mercaptobenzamide modified itaconic acid-grafted-magnetite nanocellulose composite; NC: nanocellulose; pH_pzc: Point of zero charge; K₂S₂O₈: potassium peroxy sulphate; k₁: pseudo-first-order rate constant; k₂: pseudo-second-order rate constant; SEM: scanning Electron Microscope; b_s: Sips adsorption capacity; Q_s: Sips maximum adsorption capacity; ΔH°: standard enthalpy change; ΔS°: standard entropy change; A: surface area; σ₀: surface charge density; 1/n_s: surface heterogeneity factor; VSM: vibrating sample magnetometer; V: volume of solution; W: weight of (MB-IA)-g-MNCC; M_composite: weight of the composite; XRD: X-ray diffraction     

Kinetic mechanism and effects of molecular structure on thermal hazards of azo compounds

In this paper, the kinetic mechanism of AIBN, AMBN, and ABVN was proposed, and the effect of molecular structure on their thermal hazards based on the kinetic mechanism was investigated. Calculated by non-isothermal DSC datum, the kinetic mechanism of AIBN, AMBN, and ABVN is revealed by the linear relationship between the integrated form of mechanical function and reaction time. The results indicate that the thermal decomposition process is controlled by the Johnson-Mehl-Avrami equation. Based on the determination of kinetic mechanism function, the reaction rate constants at various heating rates are directly calculated, and the intercept of the best fitting straight line of reaction rate constants with heating rate is approximately equal to the reaction rate constant under isothermal conditions. Besides, theoretical values obtained by multiplying kinetic mechanism function by reaction rate are well consistent with the experimental values, suggesting that the kinetic mechanism obtained is credible. Bond Dissociation Energies (BDE) calculated by quantum chemical equations are employed to evaluate the thermodynamics stability of AIBN, AMBN, and ABVN. Depending on similar molecular structures, the influence of differentiated group structure on the thermodynamic stability represented by BDE and heat release and the kinetic stability characterized by reaction rate constant were revealed. Finally, the results demonstrate that the thermal hazard increases as the volume of substituent group and molecular weight.