Research On The Leaching Process Of Coal Fly Ash Assisted By Microwave Irradiation In Hydrochloride Acid Solution

Containing A12O3 and SiO2 as the key component, coal fly ash (CFA) is used as raw materials to prepare aluminum product related with low cost. The development of leaching process in aluminum extracting from CFA is investigated. In order to reduce energy consumption and improve utilization, the microwave heating is introduced into the aluminum extracting process to accelerate the leaching rate of aluminum from CFA. The mechanical activation-HCl leaching process and the roasting-HCl leaching process are discussed in the paper, respectively.The effect of activation time on leaching process of CFA containing Al, Fe, Si in HCl solution is investigated through two activation methods of wet milling and dry milling. It is found that the two kinds of activation method both reduce the particle size of CFA, destroy the crystal structure and promote the activation level, which improves the leaching rate of aluminum from CFA. Furthermore, the influence of the microwave power, leaching temperature, leaching time, concentration of HCl solution and the ratio of liquid/solid on the leaching rate of Al, Fe, Si in activated CFA are explored under the condition of microwave heating. It turns out that the optimal leaching rate is as high as 75% above, when the microwave power is 1080W, the liquid/solid is 20, the concentration of HCl is 20%, the leaching temperature is 200℃and leaching time is 2h. The leaching process of CFA is corresponding to the shrinking core model, which is concluded form the results of dynamic calculation. The apparent activation energy is up to 59.72kJ/mol, even if the diffusion of solid product is controlled. It is concluded that higher temperature and smaller particle size is beneficial to the reaction. Moreover, the results of thermodynamic calculation indicate that the reaction equilibrium constant is decreased with the temperature increased and higher temperature is beneficial to the leaching reaction.The effect of microwave power, concentration of HCl solution and liquid/solid ratio on the leaching rate of Al, Fe and Si extracted from sintering CFA in the non-isothermal leaching process is studied under the condition of roasting with an additive. Compared with the traditional heating leaching process, the microwave heating tremendously increases the leaching rate. The leaching rate of Al is up to 79.51%, when the microwave power is 360W, the concentration of HCl is 20%, the liquid/solid ratio is 5 and the leaching time is 2.5min. In addition, the thermodynamic calculation reveals that the reaction thermodynamic impetus of CFA activated by the additive is more powerful and the reaction is responsive to higher temperature.