抄録
In this work, the conversion of heavy metals contained in fly ash into less soluble sulfides was studied. At first, fly ash was mixed with pure water, and with pure water and Na2S solution. The ratio of Na2S/heavy metals content in fly ash was varied from 0.15 to 1.53. Then, the suspension was shaken on vertical shaker for different time with different shaking speed. Finally, the suspension of fly ash and formed heavy metals sulfide was filtered. Both filtrate and filtration cake were analyzed. The effects of Na2S addition, reaction time, and also shaking speed on the formation of heavy metals sulfides were investigated. The efficiency of heavy metals' sulfidation was evaluated by determination of heavy metals in filtrate after reaction with Na2S, through the use of ICP-AES. Heavy metals were not detected in filtrate, when the ratio of Na2S/heavy metals was higher than 0.92. The filtration cake was investigated by XRD and formation of heavy metals sulfides, especially PbS was proved. With the increasing addition of Na2S, also reduction of the PbO peaks is possible to observe, which confirms that not only heavy metals chlorides, but also their oxides can be converted into the sulfides by the reaction with Na2S in solution. Analyses by means of SEM-EDS also have shown similar maps for lead and sulfur. The amount of formed heavy metals sulfides in relation to shaking time was determined by TG analyzer and it was found that, after 24 hours of shaking fly ash with Na2S (ratio 1.53), the amount of formed heavy metal sulfide is almost stable and corresponds to 34.2% heavy metals in fly ash.
