Estimation of Chemical Forms of Heavy Metals in Fly Ash

了解城市生活垃圾焚烧飞灰中重金属的化学形态和浓度，对其解毒回用或阐明其上二恶英的重新合成等复杂反应机理具有重要意义。利用x射线光电子能谱（XPS）、x射线衍射、顺序萃取法和热力学研究等方法对重金属的化学形态进行了估计。测定了粉煤灰中锌、铜、铅、镉的毒性和浓度。应用x射线衍射分析飞灰中重金属的化学形态是无效的。利用XPS法测定了多种粉煤灰中重金属的化学形态，因为重金属集中在其表面，XPS法得到了较高的强度。采用序贯萃取法，研究了重金属与含重金属飞灰组分之间的关系。综合各项分析结果，粉煤灰中主要含锌化合物为2ZnCO_3 3Zn(OH)_2、ZnSO_4 7H_2O和ZnO。测定了PbCl_2、PbCO_3、PbO等多种化合物，但无法确定其主要形式。铜的主要化合物是CuO。干法烟气处理飞灰中镉的化学形态（Cd(OH)_2, CdO）与湿法烟气处理飞灰中镉的化学形态（CdSO_4, CdCl_2）不同。利用XPS法和序贯萃取法可以分别对飞灰中重金属的化学形态进行估算，但两者相结合可以提高估算的准确性。

It is very important to know chemical forms and concentration of heavy metals in fly ash from municipal solid waste incinerator in order to detoxify and reuse it or clarify complex reaction mechanism such as de novo synthesis for dioxin on it. Chemical forms of heavy metals were estimated using X-ray Photoelectron Spectroscopy (XPS), X-ray diffraction, sequential extraction procedure and thermo-dynamics study. Zinc, copper, lead and cadmium were measured for its toxicity and concentration in fly ash.The application of X-ray diffraction analysis for heavy metals in fly ash was not effective to estimate chemical forms. Chemical forms of heavy metals in many kinds of fly ash were estimated by XPS, because heavy metals concentrated onto its surface and higher intensity was obtained for XPS.Sequential extraction procedure was used for the purpose of grasping the relationship between heavy metals and the composition in fly ash keeping heavy metals.Putting the results by each analysis together, the dominant zinc compounds in fly ash were 2ZnCO_3 3Zn(OH)_2, ZnSO_4 7H_2O and ZnO.Many compounds such as PbCl_2, PbCO_3, PbO, etc., were estimated and it is impossible to determine a dominant form in it. The dominant copper compound was CuO.Chemical form of cadmium in fly ash of dry process flue-gas treatment (Cd(OH)_2, CdO) was different from that of wet process flue-gas treatment (CdSO_4, CdCl_2).Estimation of chemical form of heavy metals in fly ash is possible by XPS and sequential extraction procedure respectively, but it is considered to be able to increase the exactitude of estimation by the combination of both methods.