垃圾焚烧飞灰水洗-酸浸稳定化技术研究

Effects of a water-washing process on heavy metal speciation and leaching efficiency in MSWI fly ash during acid extraction

垃圾焚烧飞灰中富集了浓度较高的重金属,对环境存在潜在威胁,但同时具有一定的回收价值。对水洗-酸浸稳定化技术处理城市垃圾焚烧飞灰的效果进行了实验室研究,分析了垃圾焚烧飞灰的主要化学组成,考察了水洗过程对于飞灰中主要元素和重金属去除的影响、水洗过程中的化学组成变化和飞灰重金属酸浸的效果,评价了水洗飞灰酸浸残渣的稳定性。结果表明:L/S=20时,水洗过程可以浸出60%以上的Cl,47%以上的Na、K、Ca,18%以上的Pb。水洗后,重金属Zn、Pb、Cu含量分别增加76.37%、21.91%和46.16%。与原灰相比,水洗飞灰酸浸过程中的Zn浸出量也有很大提高,而Pb浸出量的增加很小。当HCl浓度<1M时,Pb和Zn的浸出量随着HCl浓度增加迅速增大,这主要是因为重金属的可交换态和碳酸盐结合态对溶液中离子强度和pH变化敏感。对水洗飞灰酸浸残渣进行的连续提取实验表明,重金属以残留态存在为主,其稳定性显著提高。本文的结果表明,水洗-酸浸工艺能够通过增加飞灰的稳定性和减少重金属的浸出性来提高飞灰的环境安全。

Fly ash from municipal waste incinerators form a major environmental problem as they are polluted with heavy metals. But the metal value can be partly removed and recovered by extracting with acid solution. Experiments have been performed to investigate the effect of water washing-acid extraction process （WWAE process） for treatment of MSWI fly ash. The chemical composition of fly ash has been analyzed. The effects of water-washing process on the removal of the major elements and on heavy metals, their speciation in the washing process, the effects of acid extraction have been elucidated and heavy metals stability in the extracted washed ash residuals have been evaluated. The results indicate that more than 60% of the Cl, and more than 47% of the major elements of Na, K, and Ca, as well as more than 18% of the Pb, were found to be leached at L/S=20. The washing process resulted in more concentrated heavy metal content in the washed fly ash. A comparison of the results of acid extraction of raw ash and washed fly ash demonstrated that increment of extracted amount of Zn improved evidently after washing, while Pb improved indistinctively. Leaching with more concentrated acid yielded greater heavy metal content from washed fly ash. The removal of most of the exchangeable and carbonate fractions from the ash, which were sensitive to the change of ion intensity and pH, was thought to be contributing to the rapid extraction of Pb and Zn as the L/S increased within 1M. The results of sequential extraction procedure reveal that the zinc and lead fractions in the extracted washed ash shifted from being mostly bound to the Fe-Mn oxides and carbonate, to being mostly bound to residual form, which is stable in the environment. Results from this work showed WWAE process can increase the environmental safety of fly ash by increasing its stability and decreasing heavy metal leachability.