【作者】 许醒；

【导师】 高宝玉；

【作者基本信息】 山东大学 ， 环境工程， 2014， 博士

【摘要】 本论文在综述了国内外大量文献的基础上,首先确立了生物质阳离子吸附剂的改性工艺以及最佳的改性条件(吡啶催化法、中间体引入法和乙二胺交联法)；然后通过各种表征手段对不同工艺制备的生物质阳离子吸附剂进行物化特性的表征,探讨了生物质吸附剂的结构特性,以及与各种阴离子之间的构效关系；对比研究了改性生物质阳离子吸附剂在不同吸附条件下(温度、投加量、pH)对硝酸根、磷酸根、高氯酸根、重铬酸根的吸附特性影响,并重点分析了相关的吸附动力学与吸附热力学参数；研究不同过柱条件下(过柱流速、过柱浓度、过柱pH、填柱高度),改性生物质阳离子吸附剂对各种阴离子污染物的过柱穿透参数,并在此基础上研究了过柱条件下饱和吸附柱的化学再生的效果。另外,针对高氯酸根的可生物还原特性,研究了不同条件下富集于生物质吸附剂表面的高氯酸根的微生物还原情况,探讨生物质阳离子吸附剂的微生物再生的可行性。主要结论如下：1,吡啶催化法改性制备阳离子型生物质吸附剂的过程中,吡啶催化的阶段(包括催化时间和催化温度)对整个改性合成实验的影响最为明显。中间体引入法的环氧丙基三乙基氯化铵中间体制备过程中,影响最大的条件为中间体的制备温度；而中间体引入法制备阳离子型生物质吸附剂的过程中,合成过程的温度条件对合成影响最大。乙二胺交联法改性制备阳离子型生物质吸附剂的过程中,乙二胺交联反应的阶段对整个合成实验的影响最为明显。结果表明：最佳条件下乙二胺法制备的阳离子型生物质吸附剂对硝酸根、磷酸根的去除率方面,均要比吡啶催化法以及中间体引入法制备的产品要高5-15%左右。因此,乙二胺法改性后制备的阳离子型生物质吸附剂具有更高的吸附容量。同时,研究发现：各种生物质原料中,麦草秸秆改性后的阳离子型吸附剂对硝酸根以及磷酸根表现出更高的吸附性能。因此,后续的改性、表征以及吸附反应均以麦草秸秆改性后的产物作为研究对象。2.乙二胺交联法制备得到的麦草秸秆阳离子型吸附剂的增重率及产率要高于吡啶催化法以及中间体引入法的产物。因此,乙二胺交联法能够制备更多的吸附剂,具有更高的商业价值。同时,乙二胺交联法改性后,麦草秸秆的N含量变化最为明显,这表明乙二胺交联法引入了更多含氮基官能团。pH为2.0时,未改性麦草秸秆的表面电荷基本为中性(Zeta电位：+2.1mV)；而乙二胺交联法、吡啶改性法以及中间体引入法制备的麦草稻秆吸附剂的Zeta电位分别为+42mV、+39mV和+31mV。改性后的阳离子型麦草秸秆吸附剂的表面引入带正电荷的胺基基团,因此导致其表面电性发生了变化。而乙二胺改性后麦草秸秆表面的电荷较其它改性工艺的产物要高,这说明乙二胺作为交联剂能够引入更多带正电荷的胺基基团。FTIR图谱表明：与未改性的麦草秸秆相比,阳离子型麦草秸秆吸附剂表面引入了大量的胺基官能团与氯代烷,在麦草秸秆表面形成具有吸附功能的吸附结点。拉曼图谱表明：吸附于胺基官能团结点的硝酸根、磷酸根以及高氯酸根,主要是通过静电引力的作用被富集于阳离子型麦草秸秆吸附剂的表面；此时,富集的硝酸根、磷酸根以及高氯酸根仍是以离子形态存在于吸附剂表面,因此,整个吸附过程中基本不存在化学吸附。而阳离子型麦草秸秆吸附剂吸附去除Cr(Ⅵ)的过程中,麦草秸秆吸附剂表面形成了化学键。因此,改性麦草秸秆对Cr(Ⅵ)的去除,除了通过静电吸引作用与吸附剂表面带正电荷的胺基官能团之间的离子交换发生之外,其表面也可能存在其它的化学作用。负载了Cr(Ⅵ)的XPS图显示：575eV处为Cr(Ⅲ)的特征吸收带,这表明,负载于阳离子型麦草秸秆吸附剂表面Cr(Ⅵ)发生了还原反应,生成Cr(Ⅲ)。由于Cr(Ⅲ)为阳离子型金属离子,其与生物质吸附剂表面羧基或羟基官能团反应。从而被附着于吸附剂表面。3.改性阳离子型麦草秸秆吸附剂吸附去除硝酸根、磷酸根、高氯酸根以及Cr(Ⅵ)的速度较快,吸附约10-20min即可以达吸附平衡；吸附过程受溶液pH值影响显著,硝酸根、磷酸根、高氯酸根在pH值为4-9时吸附效果较好,Cr(Ⅵ)在2～4时较高。硝酸根、磷酸根、高氯酸根的吸附体系中pH值大于10之后,吸附效果受到明显抑制。在实验温度范围内,阳离子型麦草秸秆吸附剂去除各种阴离子污染物的吸附等温线符合Langmuir单分子层吸附模型；由此计算出的对硝酸根、磷酸根、高氯酸根以及Cr(Ⅵ)的最大吸附容量Qmax(293K)分别为68.5、65.4、163.5和263.6mg/g。热力学特性研究发现,阳离子型麦草秸秆吸附剂吸附去除硝酸盐、磷酸盐和高氯酸盐的过程中吉布斯自由能变化△G为负值；吸附过程焓变△H和熵变△S分别介于-46.5～-53.54kJ/mol和-0.144～-0.257kJ/(mol·K)。这说明阳离子型麦草秸秆吸附剂吸附去除硝酸盐、磷酸盐和高氯酸盐的过程为放热、自发过程,整个体系的有序性得到了增强。而且降低温度有利于吸附反应的发生。而吸附Cr(Ⅵ)的吉布斯自由能变化△G、焓变△H和熵变△S均为负值。这说明阳离子型麦草秸秆吸附剂吸附去除Cr(Ⅵ)的过程为吸热、自发过程,而且升高温度有利于吸附反应的发生。4.吸附动力学特性研究发现,阳离子型麦草秸秆吸附剂吸附硝酸盐、磷酸盐、高氯酸盐以及Cr(Ⅵ)的过程符合伪二级动力学方程。采用Arrhenius方程计算得到改性麦草秸秆吸附硝酸盐、磷酸盐、高氯酸盐以及Cr(Ⅵ)的活化能介于7.4-27.4kJ/mol,因此判断该吸附属于离子交换吸附,可能是季铵基和阴离子之间由库仑引力形成的离子键作用。阳离子型麦草秸秆吸附剂吸附去除Cr(Ⅵ)过程中各种阴离子的吸附量和C1的解析量具有很好的正相关性。由此判定离子交换是阳离子型麦草秸秆吸附剂去除Cr(Ⅵ)的主要方式。此外,通过吸附溶液中Cr(Ⅳ)浓度的测试及XPS表征分析得到证实,Cr(Ⅵ)在改性麦草秸秆表面吸附后发生了还原反应,生成了Cr(Ⅲ)。5.利用填充了阳离子型麦草秸秆吸附剂的吸附柱对各种阴离子污染物进行过柱吸附研究。结果发现：各种阴离子污染物的过柱吸附特性受过柱的填柱高度、过柱流速、过柱进水阴离子浓度以及过柱pH的影响较大。填柱高度增大,能够吸附更多的阴离子污染物,但是并没有增加吸附剂的吸附效率；过柱流速越大,水力负荷也越大。水力负荷较大时,进水通过吸附柱的时间较短,吸附质与吸附剂之间的接触相对不够充分,导致填充了阳离子型麦草秸秆吸附剂的吸附柱过早被穿透；高浓度进水时,吸附柱内的吸附点位很快被水中大量的阴离子占据,达到饱和吸附,使吸附柱被穿透。因此,选择合适的过柱条件可以有效提高过柱吸附的效率。鉴于此,硝酸盐、磷酸盐以及高氯酸盐的过柱吸附条件为：填料柱高度为2.7cm、进水硝酸盐、磷酸盐以及高氯酸盐的浓度为200mg L-1、进水流速为5mL min-1、调节进水溶液pH为6.0。重铬酸盐的过柱吸附条件为：填料柱高度为2.7cm、进水重铬酸盐浓度为200mg L-1、进水流速为5mL min-1、调节进水溶液pH为3.0。6.过柱条件下的化学再生结果表明：利用0.1M HCl、0.1M NaOH及0.1MNaCl再生后,短时间内解析出大量的阴离子。NaCl和HC1溶液对阴离子进行有效解析的机制在于大量高浓度的C1-与阴离子之间的离子交换作用,从而使阴离子被解析下来。而NaOH的解析机理中不仅包括OH-离子同各种阴离子之间的离子交换作用,而且再生溶液强碱的性质也削弱了阳离子型麦草秸秆吸附剂对各种阴离子污染物的吸附性能,从而加速其解析。阳离子型麦草秸秆吸附剂对硝酸盐、磷酸盐、高氯酸盐的吸附容量受再生的次数影响较小,因此,具有较为稳定的吸附容量及吸附稳定性；但是对重铬酸盐的吸附容量则受再生次数影响较大。富集高氯酸根的微生物还原结果表明：微生物再生虽然能够实现对富集高氯酸根的无害化,但是与化学再生相比,其再生效率明显偏低。还原体系中加入的氯离子及硫酸根离子可以将部分负载于吸附剂表面的高氯酸根通过离子交换的机理置换出来,使其在液相中被微生物菌群还原。与硫酸根离子相比,氯离子更有利于增强负载高氯酸根的还原效率。这是因为氯离子置换出负载的高氯酸根后,改性麦草吸附剂回复至初始形态,即：N+(CH2CH3)3Cl-形式存在。强化微生物再生对吸附剂的二次再生效率虽然低于化学再生的97.6%,但是远高于微生物再生的56.3%。更多还原

【Abstract】 Based on the comprehensive analysis of numerous literatures, three kinds of methods (pyridine catalyst method, two-stage method and ethylenediamine crosslinking method) for modification of biomaterials based adsorbents were first determined in this work. The physicochemical properties and active functional groups of the potential biosorbents were explored and characterised by different techniques. The binding between the adsorbed anions and the functional groups were also evaluated. The adsorption of NO3-,PO43-, C1O4-and Cr(VI) by the biosorbents at different adsorption conditions (temperature, dosage and pH) were conducted; the parameters of adsorption kinetics and thermodynamics were intensively investigated. The adsorption parameters of fixed-bed columns were obtained at different influent conditions (flow rate, pH, influent concentrations and bed heights). Chemical desorption properties were then evaluated based on the column adsorption parameters. In addition, the loaded perchlorate on surface of biosorbents were reduced by the mixed perchlorate-reduction bacteria at different conditions and the reduction discussed in this chapter. The main conclusions were summarized as follows:1. In the pyridine catalyst method, the stage of catalyst (including the conditions of catalyst temperature and catalyst time) was the most important process for the biosorbents preparation. The reaction temperature was the essential factor that controlled the preparation of epoxy propyl triethyl ammonium chloride intermediation in two-stage method. In the ethylenediamine crosslinking method, the ethylenediamine crosslinking process was the control factor for the biosorbents preparation. It was observed that the removal efficiencies of NO3-and PO43-by biosorbents modified from thylenediamine crosslinking method was higher (5-15%) than those obtained from pyridine catalyst method, two-stage method. This indicated that the biosorbents modified from thylenediamine crosslinking method had shown higher adsorption capacities for anions. Result also indicated that the biosorbent originated from wheat stalk showed higher NO3-and PO43-uptake capacity as compared with those originrated from corn stalk, cotton stalk and reed.2. Biosorbents obtained from ethylenediamine crosslinking method showed the highest weight growth rate and yeild as compared with those of pyridine catalyst method and two-stage method. As a result, the ethylenediamine crosslinking method would be more commercial for preparation of biosorbents. Biosorbents obtained from ethylenediamine crosslinking method showed higher nitrogen content; this indicated that more amine functional groups were grafted into the biomaterials. The zeta potentials of the virgin wheat stalk, modified wheat stalks prepared by pyridine catalyst method, two-stage method and ethylenediamine crosslinking method were+2.1,+39,+31and+42mV, respectively. The results illustrated that a large amounts of positive charged amine groups were attached onto the surface of the virgin wheat stalk, so as the zeta potentials were increased. FTIR spectra indicated that the surface of modified wheat stalk was attached with amine groups and chloroalkane, forming the available adsorptive site for anions. Raman spectra indicated that the adsorption of nitrate, phosphate and perchlorate was mainly based on electrostatic attraction between the adsorbed anions and functional amine groups, and no chemical adsorption was involved. However, chemical bond was observed between the attached Cr(Ⅵ) and the biosorbent. As a result, electrostatic attraction, complexation reaction as well as other chemical binding might be involved for the Cr(Ⅵ) uptake by biosorbents.3. The adsorption of NO3-, PO43-, C1O4-and Cr(Ⅵ) by the wheat stalk based biosorbent was a quick adsorption process. The adsorption reached the equilibrium within10-20min. The pH was an essential factor that affected the adsorption process. The optimal adsorption was obtained at4.0-9.0for NO3-, PO43-, and C1O4-and2.0-4.0for Cr(VI). The adsorption isotherms were fit well with Langmuir model, and the maximum adsorption capacities (Qmax) obtained from this model were65.4,54.6,156.3and201.3mg/g for NO3-,PO43-, C1O4-and Cr(Ⅵ), respectively. Parameters of adsorption thermodynamics indicated that the adsorption of NO3-, PO43-, and C1O4-by the wheat stalk based biosorbent was a spontaneous and exothermic adsorption process. A decreased temperature would be in favour of the adsorption process. However, the negative values of△G,△H and△S obtained from Cr(Ⅵ) adsorption illustrated a endothenmic and spontaneous adsorption reaction between the Cr(VI) and the biosorbent. The adsorption was enhanced at higher adsorption temperature.4. The adsorption kinetics indicated that the adsorption of NO3-, PO43-, ClO4-and Cr(VI) by the wheat stalk based biosorbent followed pseudo-second-order kinetics equation. The activation energy calculated from the Arrhenius equation were in range of7.4-24.5kJ/mol, which implied that the adsorption was based on ion exchange. Results also indicated the linear relationship between the amouts of adsorbed anions and eluted C;-; this also confirmed the ion exchange mechanism for the anions adsorption by the biosorbent. A small amount of Cr (Ⅲ) was found in the Cr(Ⅵ) adsorption solution. In addition to this, XPS spectra also detected the Cr (Ⅲ) on surface of the biosorbent, which validated the Cr(VI) reduction reaction occurred on surface of the biosorbent.5. The fixed-bed column adsorption of various anions were controlled by the influent conditions such as influent concentration, flow rate, influent pH and bed depth. It was found that fixed-bed systems achieved a better uptake of NO3-, PO43-, ClO4and Cr(VI) by the biosorbent at a lower concentration, lower feed flow rate and biosorbent bed-depth. The suitable column adsorption conditions would be helpful for improving the efficiency of the column. As a result, the column adsorption conditions for the NO3-, PO43-, and ClO4-were determined as:bed depth2.7cm, influent concentration200mg L-1, feed flow rate5mL min-1and influent pH6.0. The column adsorption conditions for the Cr(VI) followed as:bed depth2.7cm, influent concentration200mg L-1, feed flow rate5mL min-1and influent pH3.0.。6. The chemical regeneration tests were conducted in the fixed-bed column with the0.1M HC1,0.1M NaOH and0.1M NaCl solutions. It was observed that the adsorbed anions could be desorbed in a short time. The desorption mechanism of HC1and NaCl was based on the reverse ion exchange between the high concentration of Cl-and adsorbed anions. After adsorpion of NO3-, PO43-and C1O4-, the spent bisorbent could be reused for several times with less capacity loss. However, the adsorption capacity of the Cr(VI) loaded biosorbent was significantly decreased after four cycles of adsorption-desorption tests. Although the bio-regeneration could reduce the loaded perchlorate to nontoxic chlorate, the biosorbent performance after bio-regeneration with mixed bacteria seemed to be inefficient as compared with the brine desorption technique. The enhanced bio-regeneration method was observed more promising in regeneration of the spent biosorbent as compared with that of direct bio-regeneration method.更多还原