Study On The Leachability And Treatment Of Trace Elements In The Fly Ash

Coal is the most important energy resource in china. With the development of large amount of coal in use, a large number of by-product from coal combustion leads to significant impacts on the environment, for example, because most of the fly ash was disposed in the open landfill, heavy metals in the fly ash could be leached and enter into the surrounding water. The release of the heavy metals does great harm to the human through the food chain. Therefore, the research of heavy metals in fly ash becomes more and more important.This thesis aims to investigate the leaching behavior of heavy metals and try to find control method in fly ash via laboratory experiments and simulation. The fly ash used was collected in the coal fired power plant from Guizhou Province. The fly ash was classified into three size range. In the experiment, ferrous sulfate (FeSO₄) solution was used to treat fly ash in order to capture hazardous leachable heavy metals. The investigations of experiments indicate that:(1) the leaching rates of heavy metals except Cd are highest in the larger size fly ash with largest surface area; (2) the smaller the solid to liquid ratio, the higher leaching rates of heavy metals; (3) the leaching times of heavy metals are different, which is due to the speciation in the fly ash; (4) the leaching rate obviously gets smaller after the treatment.Visual MINTEQA was used to simulate leaching process. Pb, Cd and Ni were considered in the simulation. From the calculations, the impact of pH values is the key point. The absorption plays an important role in the leaching test when pH values are lower. On the contrary, in the condition of high pH values, the leaching behavior of heavy metals depends on the balance of dissolution-precipitation.