我国垃圾焚烧飞灰性质及其重金属浸出特性分析

调查分析了我国12个垃圾焚烧飞灰样品的性质和重金属浸出规律.结果表明,飞灰的主要组成元素有Si、Ca、Al、Fe、K、Na、Cl 等,除1个样品外,飞灰样品中的重金属元素含量均在0 .5%～3 .0%范围内.由此可见焚烧飞灰具有较大的环境风险,必须按危险废物进行安全管理.应用单批次浸出程序检测结果表明,美国EPA的毒性浸出程序（TCLP）和我国固体废物浸出毒性鉴别程序（GB 5086 .1-1997）对焚烧飞灰中的重金属浸出率偏低,且二者对飞灰危险性评估的差异较大,这主要是受二者不同的浸出液最终的pH值所影响.常规酸中和容量（GANC）浸出试验结果表明,飞灰中重金属的浸出主要受浸出液的最终pH值影响,而该pH值取决于飞灰中碱性物质与浸取剂酸度二者间的相互作用.通过对不同类别程序的浸出过程分析发现,在相同浸取液作用下,单批次式浸出程序的静态平衡终点与连续过流式浸出程序的平衡终点存在较大差异,有必要结合我国飞灰特点和实际处置场景,建立适用于焚烧飞灰的单批次式毒性浸出试验程序,避免对飞灰危险性识别的不足和管理的失控.

Characterization and Heavy Metals Leaching Toxicity of Fly Ash from Municipal Solid Waste Incinerators in China

The characteristics and leaching behavior of heavy metals in fly ash, sampled from 12 MSWI plants in China, were investigated. The results indicated that the main elements of fly ash were Si, Ca, Al, Fe, K, Na, Cl, and the total fraction of heavy metals was in the range of 0.5 % - 3.0% with the exception of one sample. Therefore MSWI fly ash must be controlled as hazardous materials because of its potential environmental risk. The leaching ratios of heavy metals in fly ash were low to some extent according to the results of batch tests such as Toxicity Characteristic Leaching Procedure (TCLP) of U. S. EPA and GB 5086.1-1997. The notable variance of TCLP and GB 5086 evaluating the same sample was due to the obvious difference of pH values in leachate. The result of general acidity neutralization capacity (GANC) showed that the leaching behavior of heavy metals in fly ash were controlled by the final pH of leachate, which was determined by the inter-reaction of alkaline in fly ash and acidity of leachant. The end points of equilibrium in batch test and flow-through test had great difference based on the analysis of these procedures. It is of significant meaning to build a batch procedure basing on the disposal scenarios and characteristics of fly ash for the purpose of adequate risk assessment and management.