Study on distribution and enrichment of heavy metal elements in fly ash and slag from fuel coal

In order to study the distribution and enrichment of heavy metal elements in fly ash and slag from fuel coal, the coal, fly ash and slag samples from coal-fired boilers of thermal power plants,heat and power plants and chemical enterprises in Shanghai were collected. The mercury, arsenic, chromium, cadmium and lead content in the samples were tested. The study on the relationship between the content of heavy metals in the coal, fly ash and slag was carried out,and their distribution mechanism was discussed. The results show that mercury content in fly ash is 2～5 times higher than that in the coal. The mercury content in the slag is low. The mercury in coal is enriched in the fly ash during combustion. The arsenic content in the fly ash can reach about 10 times to that in the coal. Arsenic has a significant enrichment in fly ash during combustion. The arsenic content in slag is equivalent to that in coal, indicating that the arsenic has not been enriched in slag. The chromium content in fly ash can reach up to about 8 times of that in coal. The chromium content in the slag is higher than that in the fly ash. During the combustion process, the chromium element in the coal has a significant enrichment in both fly ash and slag. The cadmium content in fly ash can reach up to about 8 times to that in the coal, and the cadmium content in the slag can reach more than 10 times of that in the coal. The lead content in fly ash and slag is significantly higher than that in coal, indicating the obvious enrichment. In addition, the annual amount and proportion of heavy metals in coal, fly ash and slag from coal-fired enterprises in Shanghai were also calculated. The results show that there are 50.0% and 61.7% of the mercury and arsenic from the coal presented in the fly ash after combustion, respectively. There are obvious enrichments of mercury and arsenic in the fly ash, but rare distributions in the slag. The enrichments of chromium, cadmium and lead are observed in both fly ash and slag. The chromium, cadmium and lead in coal are mainly discharged with fly ash. There are 76.7%, 74.4% and 75.1% of the chromium, cadmium and lead in coal discharged with fly ash, respectively. Fly ash and slag are the major ways to discharge heavy metals in the coal.