焚烧飞灰螯合效果评价方法优化及新型高分子螯合剂合成

OPTIMIZATION OF THE CHELATION EFFICIENCY EVALUATION METHOD AND ADVANCED SYNTHESIS OF NOVEL MACROMOLECULE CHELATING AGENTS FOR INCINERATION FLY ASH TREATMENT

童立志

11649002

博士

环境科学与工程

胡清

2020-06-03

2020-07-29

哈尔滨工业大学

深圳

近年来，随着垃圾焚烧技术的推广，我国垃圾焚烧飞灰的产生量逐年升高，已跃居世界第一。因此，选择合适的方法处理这些危险废物迫在眉睫。焚烧飞灰具有高盐量和高有毒重金属溶出量等特点，影响其进一步的处理处置。螯合稳定化法具有工艺简单、成本低、不增容等优点，是当前我国处理焚烧飞灰的主要方法之一。然而，由于螯合稳定化法在我国发展时间较短，准确评估其对焚烧飞灰螯合效果，识别螯合飞灰环境稳定性，进而开发高性能螯合剂，是进一步推广使用该技术的关键。本文首先以南方某焚烧厂飞灰为研究对象，统计分析了飞灰重金属含量和浸出浓度的较长时间变化规律，明确了螯合过程需首要关注的重金属；其次，深入分析了传统化学连续提取法(针对土壤和沉积物开发的)对强碱性飞灰中重金属环境风险评价的不确定性，并因此建立了基于螯合物定量提取的飞灰螯合效果的评价方法，讨论了影响螯合飞灰环境稳定性的主要因素；最后，基于以上研究结果，有针对性地开发了两种新型高分子螯合剂，探讨了原料分子量变化等因素对螯合剂螯合性能和环境稳定性的影响，比较了高分子螯合剂和商品螯合剂对飞灰的稳定化效果，并探索了水洗预处理对飞灰螯合工艺的影响。主要结论如下：基于高精度X射线荧光光谱（HDXRF）对焚烧厂飞灰连续6个月快速检测结果，发现飞灰重金属月均含量较稳定（变异系数CV<0.14）但日均含量波动较大（CV>2.54）。飞灰重金属浸出浓度受浸出液终点pH值影响显著。其中，Pb超出《生活垃圾填埋场污染控制标准》（GB16889-2008）中规定限值（0.25 mg/L）的概率最高（68.9%）。通过对比不同酸洗条件下飞灰重金属形态分级结果，发现传统化学连续提取法中的弱酸提取态的操作条件（一次酸洗）仅能去除部分可溶氯盐，不能破坏并提取飞灰中以氢氧化物或碳酸盐等形式存在的重金属。通过开发的基于螯合定量提取的飞灰螯合效果评价方法发现，随着商品螯合剂二硫代氨基甲酸钠添加量增加，飞灰中重金属螯合率增加。尽管在3%的螯合剂添加量条件下，螯合飞灰满足GB16889-2008中的浸出浓度限值，但重金属螯合率不高（如Pb仅为9.7%）。无论是在黑暗密闭或光照空气暴露条件下，螯合飞灰中重金属（Pb、Cd、Zn）浸出浓度在300 d的实验周期内均逐渐升高且超出GB16889-2008中规定的限值（分别为0.25、0.15和100 mg/L）。结合螯合物定量提取和矿物分析发现，重金属螯合物的分解和再分配，以及未被螯合剂捕捉的重金属在环境改变条件下的逐步释放等共同影响螯合飞灰的环境稳定性。通过一系列配水实验和酸碱稳定性实验，以及扫描电镜、红外分析、X射线光电子能谱分析等手段，对合成的新型高分子聚乙烯亚胺螯合剂和可溶改性木质素螯合剂的性质进行了表征。结果发现，合成原料差异在一定程度上影响高分子螯合剂重金属螯合性能及其螯合物环境稳定性。原料分子量增加在降低二硫代羧基中硫原子电负性的同时，可能增强空间位阻效应。其中，以分子量为600的聚乙烯亚胺合成的聚乙烯亚胺螯合剂和以二乙烯三胺为原料合成的可溶改性木质素螯合剂均较商品螯合剂具有更好的选择性去除溶液中Pb2+的能力。基于水洗条件优化及不同螯合剂对飞灰水洗前后螯合稳定化效果对比结果，发现在液固比为1:1，连续水洗4次的条件下，水洗预处理可以基本去除飞灰颗粒外层包裹的可溶氯盐，并实现飞灰减量化（35%以上）。对于飞灰原灰，合成的高分子螯合剂可以在较低用量下（1%）使其满足GB16889-2008中规定的限值。然而，对于水洗飞灰，商品螯合剂或新型高分子螯合剂的添加量至少达5%才可使其满足GB16889-2008中规定的限值。根据重金属螯合物定量提取和矿物形态分析，发现水洗后飞灰中重金属的富集浓缩，以及飞灰颗粒表面的微溶硫酸钙是导致水洗飞灰重金属螯合率降低的主要原因。

While municipal solid waste incineration (MSWI) technology has become increasingly popular in recent years, there is a significant amount of incineration fly ash generated in China, ranking the first in the world. Therefore, it is urgent to employ proper methods to treat this kind of hazardous waste. The characteristics of incineration fly ash, such as high salt content and high potential toxic metal leachability, affect its further treatment and disposal. Chelation stabilization method, which has the advantages of simple operation and low cost, is one of the main technologies currently adopted to treat incineration fly ash in China. However, this technique is at the early stage of development in China. Thus, it is crucial to accurately evaluate the treatment efficiency and environmental durability of this technology, as well as smartly synthesize novel chelating agents to improve the treatment performance. This dissertation firstly analyzed the long-term dynamic changes in the heavy metal contents and leaching concentrations of incineration fly ash that was collected from a MSWI plant in south China and identified the major heavy metals that should be concerned in incineration fly ash. Secondly, the applicability of traditional sequential extraction procedures for the environmental risk assessment of heavy metals in incineration fly ash was assessed, given that the sequential extraction schemes are specifically developed for soil or sediment, and the properties of incineration fly ash differ from soil or sediment. Thirdly, a quantitative extraction of metal chelates in stabilized incineration fly ash was developed, and the possible environmental factors which influence the environmental durability of commercial chelating agent stabilized fly ash were discussed. Finally, based on the results above, two new types of macromolecule chelating agents were synthesized. The stabilization effect of different chelating agents on incineration fly ash was compared, and the influence of washing pretreatment on the fly ash chelation efficiency was explored. According to the rapid quantitative analysis results of heavy metal contents obtained by the high-resolution X-ray fluorescence spectrum (HDXRF), it is found that the monthly average contents of heavy metals remained consistent with coefficient of variation (CV) less than 0.14, while their daily average contents fluctuated significantly with CV over 2.54. The heavy metal leaching concentrations of incineration fly ash are affected by the final pH of the leachate. Among the heavy metals being studied, Pb (shows the highest probability (68.9%) beyond the limit specified in Standard for Pollution Control on the Landfill Site of Municipal Solid Waste (GB 16889-2008). By comparing the metal fractionation results under different acid extraction conditions, it is found that only easily soluble salts, but not the heavy metals in the hydroxides or carbonates was extracted in the traditional sequential extraction procedure with one-time acid washing. Based on the developed chelation efficiency evaluation method that uses ethyl acetate to directly extract metal chelates in stabilized fly ash, the results demonstrate that the chelating efficiency of heavy metal increases with the increasement of SDD addition dosage. Although the heavy metal leaching concentration of stabilized fly ash meets limits stipulated in GB 16889-2008 under the condition of 3% of the commercial chelating agent, the metal chelating efficiency is not high (e.g. 9.7% for Pb). The 300-day environmental durability experiment result shows that the leaching concentration of heavy metals in chelated fly ash gradually increases and exceeds the leaching concentration limit in GB 16889-2008, even under dark and sealed condition. Combined with the quantitative extraction of chelates and mineral analysis, it is found that the environmental durability of chelated fly ash is affected by the decomposition and possible redistribution of metal chelates, as well as the gradual release of non-chelated metals along with the reduction of alkaline substances.Through batch tests, acid stability experiment, scanning electron microscope, Fourier infrared spectrometer, and X-ray photoelectron spectroscopy analysis, the properties of two types of novel macromolecule chelators, including polyethyleneimine chelating agents and soluble modified lignin chelating agents were investigated. The results suggest that the molecular weight change of polyethyleneimine or the change of small-molecule amines can affect the chelating performance of macromolecule chelators. The increasement of molecular weight of raw materials may not only reduce the electronegativity of sulfur atoms in -CSS- functional group, but also enhance the steric hindrance effect. In general, the use of polyethyleneimine with a molecular weight of 600 for polyethyleneimine chelating agent and the use of diethylenetriamine for modified lignin chelating agents can improve the ability to selectively remove Pb2+ from solution compared to the commercial chelating agent.Based on the optimization of water washing pretreatment condition, and the comparison of the chelating efficiency of raw fly ash and water-washed fly ash by different chelating agents, the results illustrate that under the condition of the liquid-solid ratio of 1:1 and continuous washing four times, most of the soluble chlorine salts can be removed and above 35% of mass reduction can be achieved. For raw fly ash, two new macromolecule chelators enable the stabilized fly ash to meet the limits stipulated in GB 16889-2008 at a lower dosage (1%). For the water-washed fly ash, at least 5% of the commercial chelating agent or new polymer chelating agent is required to meet the limits stipulated in GB 16889-2008. According to the quantitative extraction of heavy metal chelates and the analysis of mineral morphology, the decrease of the chelating efficiency of heavy metals can be attributed to the enrichment of heavy metals in the washed fly ash and the formation of calcium sulfate on the fly ash surface with low solubility.

焚烧飞灰 重金属形态 螯合率 环境稳定性 高分子螯合剂

incineration fly ash heavy metal fractionation chelation efficiency environmental durability macromolecule chelating agent

中文

联合培养

南方科技大学

童立志. 焚烧飞灰螯合效果评价方法优化及新型高分子螯合剂合成[D]. 深圳. 哈尔滨工业大学,2020.