铝盐除氟污泥吸附典型重金属研究
文献类型：学位论文
| 作者 | 鞠佳伟 |
| 学位类别 | 硕士 |
| 答辩日期 | 2014-05 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 刘锐平 |
| 关键词 | 氟 镉 砷 吸附 资源化利用 Fluoride Cadmium Arsenic Adsorption Reclamation |
| 其他题名 | Study on adsorption of heavy metals by Al-F hydroxide wastes generated in the process of fluoride removal |
| 学位专业 | 环境工程 |
| 中文摘要 | 我国有7000多万人通过饮用水途径暴露于氟，其中3000多万人表现出氟斑牙等氟中毒症状。饮用水除氟是我国当前饮用水安全保障面临的重要难题。铝盐可与氟发生强烈的络合作用，而铝氧化物、铝氢氧化物对氟有优势去除能力，因此以铝盐或铝氧化物（或铝氢氧化物）为基础的混凝剂、吸附剂大量应用于饮用水除氟中。然而，铝盐混凝或铝氧化物吸附除氟过程中将产生大量的含氟的污泥污泥或含氟氧化铝。如果未对其进行有效处置可能对土壤、地下水和水环境产生不利影响。同时，在饮用水除氟过程中，由于氟平衡浓度较低（1 mg/L），仍有大量活性位点未充分利用即进行吸附剂再生或沉淀去除污泥，而产生的废弃含氟污泥或吸附剂具备资源化综合利用的可行性。因此，如果对除氟水厂产生的废弃含氟污泥或吸附剂进行资源化综合利用，这不仅有利于降低除氟成本，且可在一定程度上避免含氟污泥或吸附剂随意排放而导致的环境污染问题。另一方面，水环境重金属污染仍是我国重要的环境问题，而采用高效、安全、低廉的水处理材料以及操作简单的水处理方法是水体重金属污染综合防治的重要方向。围绕上述问题，本论文对比研究了铝盐吸附除氟污泥（Al(OH)3-Fads）、混凝除氟污泥(Al(OH)3-Fcoag)和氢氧化铝(Al(OH)3)三种吸附剂对阳离子型Cd(II)、非离子型As(III)和阴离子型As(V)等三类典型重金属的吸附行为，并对其吸附机理进行了探讨。 研究显示，Al(OH)3-Fads、Al(OH)3-Fcoag对Cd(II)的吸附可在200 min内达到平衡，且准二级动力学模型能很好地描述其对Cd(II)的吸附动力学过程；Langmuir模型可很好地描述Al(OH)3-Fads,、Al(OH)3-Fcoag对Cd(II)的等温吸附结果，计算而得的最大吸附容量分别达到24.39 mg/g和19.90 mg/g。Al(OH)3-Fads与Al(OH)3-Fcoag对Cd(II)的吸附量随pH升高而增加；在酸性条件下，增大离子强度促进Cd(II)的吸附；在中性和碱性条件下，离子强度升高反而抑制Cd(II)的吸附。Al(OH)3-Fads与Al(OH)3-Fcoag比不含氟的Al(OH)3对Cd(II)的吸附速率慢且吸附容量低，说明氟的引入在一定程度上抑制了对Cd(II)的吸附。Al(OH)3-Fads与Al(OH)3-Fcoag吸附Cd(II)主要包括离子交换、表面络合、表面微沉淀和静电引力四种机制。Al(OH)3-Fads与Al(OH)3-Fcoag应用于吸附除Cd(II)过程中，尽管存在氟的溶出，但氟溶出量有限且浓度在工业废水排放标准以下（<10 mg/L）。Al(OH)3-Fads和Al(OH)3-Fcoag作为处理重金属废水的吸附剂是可行的。 研究发现，Al(OH)3-Fads与Al(OH)3-Fcoag对As(III)和As(V)的吸附动力学均符合准二级动力学模型，而Langmuir模型可较好地描述两种形态砷的吸附行为。进一步由Langmuir模型计算得出Al(OH)3-Fads和Al(OH)3-Fcoag对As(III)的最大吸附容量分别为47.92和 30.99 mg/g，对As(V)的最大吸附容量分别为83.99 和56.29 mg/g；与单纯Al(OH)3相比，对As(III)和As(V)的吸附容量降低了25-50%。XPS与FTIR等表征手段显示，去除As(III)的主要机理为物理吸附和形成As(III)-O络合；Al(OH)3-Fads去除As(V)主要依靠表面氟离子和H2AsO4-和 HAsO42-的离子交换作用，而Al(OH)3-Fcoag去除As(V)主要依靠固体表面和As(V)形成As-O络合。Al(OH)3-Fads和Al(OH)3-Fcoag吸附As(III)和As(V)后释放到溶液中的氟离子最大浓度均低于工业废水排放标准，因此Al(OH)3-Fads与Al(OH)3-Fcoag可作为去除As(III)/As(V)的吸附剂。 进一步研究探索了Al(OH)3-Fads与Al(OH)3-Fcoag制备为颗粒化吸附剂的可行性。考虑到吸附剂造粒过程中往往需要进行热处理，因此进一步将Al(OH)3-Fads、Al(OH)3-Fcoag和Al(OH)3在200℃、600℃和900℃下进行热处理，获得不同温度下的Al(OH)3-Fads、Al(OH)3-Fcoag和Al(OH)3作为吸附剂。结果表明，随着热处理温度的升高，Al(OH)3-Fads、Al(OH)3-Fcoag和Al(OH)3的比表面积减小，表面零电位时的pH值降低。XRD和FTIR分析显示，在加热到600℃时，Al(OH)3-Fads、Al(OH)3-Fcoag和Al(OH)3开始有 Al2O3形成；在加热到900℃时，Al(OH)3-Fads和Al(OH)3-Fcoag有AlF3形成。研究发现，Al(OH)3-Fads、Al(OH)3-Fcoag和Al(OH)3对Cd(II)的吸附容量随热处理温度升高而增加，这主要是由于吸附剂表面零电荷点下降所致；三种材料对As(III)和As(V)的吸附容量随热处理温度的升高而减小，这与吸附剂比表面积下降有关。Al(OH)3-Fads、Al(OH)3-Fcoag和Al(OH)3对Cd(II)的吸附容量随pH的升高而增加，而对As(III)和As(V)的吸附容量随pH的升高而降低。 上述研究显示，Al(OH)3-Fads与Al(OH)3-Fcoag可有效吸附去除阳离子型、非离子型、阴离子型等重金属，且对阴离子型As(V)的吸附容量最高；两种含氟污泥可经简单脱水、风干后作为吸附剂，也可作为颗粒化吸附剂的原料经干燥、造粒等工艺制备成商品化吸附剂。 |
| 英文摘要 | Over 70 million people in China are exposure to fluoride via drinking water and over 30 million among them have symptom of fluorosis. Improvement of defluoridation methods is a crucial problem for security of drinking water. Aluminum (Al) coagulation and Al hydroxide [Al(OH)3] adsorption are widely used for defluoridation due to strong chelating ability of aluminum and fluoride. However, large amounts of Al-F hydroxide solid wastes are generated in both processes. The failure to dispose them effectively will cause challenge to ecological safety due to the release of alumina or fluoride. However, it is possible for reclamation of Al-F hydroxide solid wastes as abundant active sites remain due to the low standard for fluoride. Reclamation of Al-F hydroxide wastes as adsorbents will not only decrease costs for defluoridation, but also avoid the contamination of environment caused by discharge them casually. As a fact, the contamination of heavy metals is a worldwide challenge to human health and exploration of efficient, secure and low-cost adsorbents is significance to the treatment of heavy metal. All around these issues, this study first prepared the Al-F hydroxide precipitates via adsorption and coagulation processes for the removal of fluoride. The resultant solid wastes containing fluoride were denoted as Al(OH)3 flocs with adsorbed fluoride (Al(OH)3-Fads) and Al-F-OH precipitates (Al(OH)3-Fcoag), respectively. After that batch experiments were used to investigate their adsorptive performance for positively-charged ion [Cd(II)], non-ionic As(III), and negatively-charged As(V). Furthermore,adsorption mechanisms were proposed through analysis of characterization by XPS, FTIR, and BET. Results showed adsorption of Cd(II) by Al(OH)3-Fads and Al(OH)3-Fcoag reached equilibrium in 200 min. The pseudo-second-order model was better than both pseudo-first-order and intra-particle diffusion models to describe the adsorption kinetics of Cd(II) onto these adsorbents. Langmuir model was better than Freundlich model to describe the adsorption isotherms. The calculated adsorption capacity of Cd(II) by Al(OH)3-Fads and Al(OH)3-Fcoag was 24.39 and 19.90 mg/g. The adsorption of Cd(II) by them increased with increasing of pH. Ionic strength promoted the adsorption of Cd(II) under acid condition, while inhibited the adsorption of Cd(II) under neutral and alkaline condition. Al(OH)3-Fads and Al(OH)3-Fcoag had a slower adsorption velocity and a lower adsorption capacity of Cd(II) compared to pristine Al(OH)3. The adsorption of Cd(II) was assumed to be mainly controlled by ion-exchange, electrostatic attraction, surface micro-precitation and surface complexation. The maximum concentrations of leached fluoride after the adsorption of Cd(II) by Al(OH)3-Fads and Al(OH)3-Fcoag were below the Chinese Class-I industrial discharge standard for fluoride (< 10 mg/L). Results from this study demonstrated that the solid wastes generated in fluoride removal process could be potential utilized as adsorbents for Cd(II) removal. The adsorption study indicated that As(III)/As(V) adsorption on these Al-based solid wastes followed the pseudo-second-order model and Langmuir model. The calculated adsorption capacity of Al(OH)3-Fads and Al(OH)3-Fcoag for As(III) was 47.92 and 30.99 mg/g, while it was 83.99 and 56.29 mg/g for As(V), respectively. These adsorption capacities were 25-50% lower than those of pristine Al(OH)3. XPS and FTIR analysis indicated As(III) was removed via physical adsorption and formation of complexation of As(III)-O. Anion exchange of fluoride by H2AsO4- and HAsO42- dominated in As(V) removal by Al-Fads while formation of an As-O complex played a more important role in As(V) removal by Al(OH)3-Fcoag. The maximum concentration of released fluoride after the adsorption of As(III) and As(V) by Al(OH)3-Fads and Al(OH)3-Fcoag was below the Chinese Class-II industrial discharge standard for fluoride (<15 mg/L). Results from this study indicated that the aluminum hydroxides generated in the fluoride removal process could be reclaimed as adsorbents for As(III)/As(V) removal. To further investigate the feasibility of reclamation of granular Al(OH)3-Fads and Al(OH)3-Fcoag as adsorbents, they were calcined in 200℃, 600℃ and 900 ℃. After thermal treatment, Al(OH)3-Fads, Al(OH)3-Fcoag, and Al(OH)3 were used as adsorbents for removal of Cd(II)/As(III)/As(V). The results showed SBET and pHpzc of Al(OH)3-Fads, Al(OH)3-Fcoag, and Al(OH)3 decreased with increasing of temperature for thermal treatment. XRD and FTIR analysis confirmed the formation of Al2O3 at 600 ℃ in Al(OH)3-Fads, Al(OH)3-Fcoag, and Al(OH)3 , and AlF3 at 900 ℃ in Al(OH)3-Fads and Al(OH)3-Fcoag. The adsorption capacity of Cd(II) by Al(OH)3-Fads, Al(OH)3-Fcoag, and Al(OH)3 increased with increasing of temperature for thermal treatment due to their decreasing pHpzc. The adsorption capacity of As(III)/As(V) by Al(OH)3-Fads, Al(OH)3-Fcoag, and Al(OH)3 decreased with increasing of temperature for thermal treatment, correlated with their decreasing SBET. Moreover, the adsorption capacity of Cd(II) increased with increasing of pH, while that of As(III)/As(V) decreased with increasing of pH. Above results showed Al(OH)3-Fads and Al(OH)3-Fcoag could be reclaimed as effective adsorbents for cationic, non-ionic and anionic heavy metals and had largest adsorption capacity for As(V). Al(OH)3-Fads and Al(OH)3-Fcoag could be put into use either via simple air-dry or via thermal treatment. |
| 公开日期 | 2015-07-08 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/15707]  |
| 专题 | 生态环境研究中心_环境水质学国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 鞠佳伟. 铝盐除氟污泥吸附典型重金属研究[D]. 北京. 中国科学院研究生院. 2014. |
入库方式： OAI收割
来源：生态环境研究中心
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