Kinetics of Iron Extraction from Coal Fly Ash by Hydrochloric Acid Leaching

Iron contained in coal fly ash of the Ekibastuz power station is distributed between magnetite and hematite. XRD data showed that ~80 wt % of iron is contained in magnetite and ~20 wt % in hematite. The leaching of iron from CFA by HCl was studied. It was determined that leaching efficiency increased with the increase in hydrochloric acid concentration and temperature. The maximum iron extraction efficiency was 52%. Aluminum is contained in the mullite and was practically not leached. The maximum aluminum extraction efficiency was 3.7%. The kinetics investigation showed that the process of iron leaching was controlled by chemical reaction and diffusion process steps, with an activation energy of 33.25 kJ·mol−1. The aluminum leaching process is controlled by a diffusion process step with an activation energy of 19.89 kJ·mol−1. The reaction order of hydrochloric acid is determined to be 0.9 and 0.23 for iron and aluminum, respectively.