Mechanism and Application Research on Removal of Pb and Cd from Coal Fly Ash by Chlorinating Calcination

Abstract

This is an essay in the field of metallurgical engineering. Calcium chloride was used as chlorination agent to conduct the heavy metals removal experiments for coal fly ash, investigating the effects of calcination temperature, calcination time and amount of CaCl2 on the removal rate of heavy metals. The results of calcination experiments and thermodynamic calculation demonstrate the mechanism of heavy metals removal in fly ash by using chlorinating volatilization method; further, the kinetic model of chlorinating process was discussed. Moreover, the coal fly ash, as raw material, was used to produce soil conditioner which was studied to discover its fertilizing effect by pot experiments. Studies found that the remaining contents of Pb and Cd in mixture were 10.22 g/t and 0.54 g/t, respectively, which meant 89.26% of Pb and 76.88% of Cd were decreased after addition of CaCl2 at high calcination temperature for 40 min. The mineral of mullite, quartz, alumina and disodium oxide in fly ash contributed to the decomposition of CaCl2. PbO and CdO mainly reacted with HCl formed by the decomposition of CaCl2 to form volatile chloride, meaning the oxides do not directly react with CaCl2. thermodynamic models fitting implied that the chlorination of Pb and Cd were controlled by the chemical reaction, and the apparent activation energy of reactions was 84.54 and 44.96 kJ/mol, respectively. Further, the pot experiments showed that the synthesized soil conditioner can improve the condition of the soil, promote nutrient absorption of chives, and improve the quality of chives. The effective calcium content of soil conditional product was increased after the reduction of heavy metals by adding CaCl2. This research provides a method for comprehensive utilization of fly ash.

Keywords

• metallurgical engineering
• coal fly ash
• chlorinating calcination
• heavy metal removal
• soil conditioner