High-pressure HCl leaching of coal ash to extract Al into a chloride solution with further use as a coagulant for water treatment

In the present paper a novel process of the coal ash treatment was developed and analyzed: a high-pressure autoclave HCl leaching of the coal bottom and fly ash from an Omsk coal-fired power plant. This process was applied to extract aluminum from the coal ash into a chloride solution, which can further be used as a coagulant for water treatment. The Al extraction efficiency in this process can reach over 90% at certain process parameters discussed in the present study. Kinetics of the leaching process were evaluated using different kinetic (e.g. shrinking core) models. A semi-empirical equation was proposed for description of the kinetics of the leaching process as a function of the HCl concentration, solid-to-liquid ratio and temperature. Different mechanisms of the leaching process were also discussed and proposed. Water treatment by the obtained Al-chloride showed good results compared to an industrial coagulant; the treated water parameters were within the limits recommended by the World Health Organization for drinkable water. •More than 90% of Al extraction achieved by high-pressure HCl leaching of the coal ash.•Kinetics of the heterogeneous leaching process were described by the shrinking core model.•A schematic mechanism of the leaching process was proposed in the paper.•Al-chloride liquor can be used as a coagulant for water treatment.