Demineralization of lignites from Nallihan, Turkey, was investigated using various aqueous acids, such as HCl, HNO3, and H2SO4, which were used at the concentrations of 5 and 10 vol%, hydrofluoric acid (HF) acid solutions of 5, 10, 20, 30, and 40 vol%. The experiments were done at 20, 40, 50, and 60 degrees C temperatures in order to observe the heating effect on the removal yields. The best result was found for the sample being done experimentally with 5% HF. The ash content is decreased from 17.12 to 6.98 wt% and heating value is increased from 16,652 to 23,950 kJ/kg according to the original lignite. The yields are 59.23 and 44%, respectively. Fourier transform infrared and X-ray diffraction were used to observe the leaching effect of the mineral acids on the demineralization degree of Nallihan lignite.