垃圾焚烧尾气中稀土元素的分异特征及其对周边土壤污染示踪

Incineration disposal has brought a great advantage to garbage reduction, but how to assess the impact of incineration on ambient environment still remains as a difficult problem. Soil has the function as the main incinerarion tail gas receptor. Its pollution levels can be used to explain the influence of incineration tail gas on ambient environment. As one of the typical pollutants, the cost of detection of the dioxin is extremely high. Heavy metals are possible used to assess soil pollution levels. However, heavy metals have variable interference sources, which makes it hard to be precisely analyzed. Rare earth element(RRE),one of the most important tracers in the earth science research,is able to transfer typical differentiation characteristics of the source area. Furthermore, it has stable geochemical properties, easy detection way and less interference sources. Once the functional materials in garbage have been incinerated, the contained REE will migrate to exhaust and form differential characteristic of REE in MSWI fly ash. The research is to find the formation mechanism of the RRE differential characteristics in incineration tail gas. The research also aims to form RRE characteristic indexs which can represent diferent incineration waste sources. Based on previous information, the research will reveal the source tracing effect of RRE within small-scale range. It is known that other pollutants in incineration tail gas settle to the surrounding soil with incineration fume as well as the RRE. Therefore, they have similar spatial distribution in ambent soil enviroment. The relevance between various pollutants and RRE differentiation characteristics will be studied in order to indentify soil pollution leves using RRE as index. The last aim of the research is to develop an effective way using RRE index to assess pollution levels caused by incineration.

如何评估垃圾焚烧给周边环境造成的影响是目前焚烧技术应用中的一大难题。土壤作为焚烧尾气的最大受体，其污染状况可在很大程度上反映周边环境受到的影响，而作为典型污染物，二噁英检测费用极高，重金属则干扰源复杂多变，难以准确解析。稀土元素是一种重要的物源示踪剂，能携带源区特征、性质稳定、易于检测且干扰源项少。垃圾中废弃的功能材料焚烧后部分稀土元素将富集迁移到尾气中形成具有焚烧源属性的稀土分异特征。本项目将首先研究这种分异特征的形成机制，探索代表焚烧源的稀土特性指标，并据此研究稀土元素在小尺度范围内对焚烧污染源的示踪效应；同时，焚烧尾气中的稀土元素与其他污染物一起随烟流沉降，它们将具有十分类似的空间分布规律。本项目拟通过尾气源及土壤中稀土特性指标与各种污染物的关联性规律对土壤污染进行稀土化识别，并建立基于稀土化指标的污染诊断模型，为评估焚烧尾气对周边环境的影响提供有效的手段。

通过四川、重庆、广西、辽宁、浙江、海南等地的多家垃圾焚烧厂及其周边区域进行了实地采样、测试与数据分析工作，解析了稀土元素在垃圾焚烧尾气中的分异特征与形成机制，探索代表焚烧源的稀土特性指标，并对土壤污染进行稀土化识别，建立了基于稀土化指标的污染诊断模型，同时还对垃圾焚烧飞灰的无害化、资源化进行了扩展研究，得到主要结论：.（1）生活焚烧厂尾气捕集物的稀土元素均最终来自于当地土壤，与当地土壤中的稀土分异特征保持高度一致，焚烧过程中使用的添加药剂由于体量太小，不会对最终尾气中的稀土来源造成明显影响。医疗垃圾焚烧厂进炉垃圾源特殊，未体现出类似规律。Ce是城市生活垃圾焚烧厂尾气中含量最高的稀土元素，达11.8-269 mg/kg；其次为Y、Nd、La，所调查样品含量分别为9.83-88.5 mg/kg、4.64-74 mg/kg、10.01-71.8 mg/kg。.（2）四川、重庆、广西、辽宁、浙江、海南六个垃圾焚烧厂尾气及其周边区域土壤中的Cd和Cr的来源较为相似；Zn、Cu和Pb受到相同来源影响。从尾气和土壤中重金属含量的比较来看，Cu、Pb、Zn和Cd的变化趋势相似，可能受到焚烧尾气的影响较大。.（3）通过尾气和土壤中稀土元素的绝对含量、化学性质、配分规律等特性分析发现Ce、La、Nd作为垃圾焚烧尾气标识性元素较为适宜，同时它们还和Pb、Zn、Cu一样体现出与当地风频较为类似的分布特征，表明Ce、La、Nd可作为替代元素来诊断垃圾焚烧的尾气重金属污染状况。.（4）选取浙江某垃圾焚烧厂周边区域土壤为代表，开展了污染诊断模型及环境寿命评估。在稀土元素中Ce与Pb、Zn、Cu体现出最高的相关关系，同时也是含量最高的稀土元素，表明Ce是最适合与该厂污染诊断的标识稀土元素。通过灰色关联与质量守恒关系建立了重金属污染稀土化诊断模型并用于垃圾焚烧厂环境寿命评估。.（5）广西、重庆、四川、海南垃圾焚烧飞灰中的稀土元素具有资源化的潜力，关键元素含量超过30%，Coutl系数介于0.881-1.46之间，而浙江垃圾焚烧飞灰的Coutl系数虽未达到0.7，但其稀土元素总含量达298.96mg/Kg，Ce含量177.94mg/Kg占绝对比例，具有潜在的单一元素资源化价值。