This paper reported the leaching of Yallourn brown coal fly ash uniquely rich in magnesioferrite (MgFe2O4) using hydrochloric acid, by varying acid concentration, liquid-to-solid (L/S) ratio, temperature, and time, to understand the mechanisms underpinning the extraction of iron and magnesium. Results indicate that Yallourn fly ash is composed of a densely packed, crystalline ash matrix, mainly in the form of MgFe2O4 and maghemite (gamma-Fe2O3). Thermal cleaving at 100 degrees C and above liberates embedded octahedrally coordinated Fe3+, a controlling step for the leaching process. Increments from 100 to 200 degrees C did little to enhance extraction of Fe and Mg in single-stage leaching. Except at 70 degrees C, the thermal decomposition for the elution of both metals was complete within 1 min, while increasing the L/S ratio and acid concentration had negligible influence. The application of two-stage leaching gave protons a larger driving force to access embedded unreacted species. Subsequently, the extraction yields of both Fe and Mg went beyond 80%. The reductive leaching of Fe3+ with the assistance of a small amount of marcasite (FeS2) is the crucial reaction improving the breakage of framework at 100 degrees C and above. Consequently, the concentration of eluted Fe2+ accounted for 60% and up to 90% in 100 and 200 degrees C leachates, respectively.