The preparation of active carbons from nitrogen-enriched lignites was previously described by the authors. This study is carried on with the aim of investigating the role played by the mineral matters of lignites on the process and on the properties of the resulting active carbons. First, the effect of demineralisation by strong acids on the surface chemical properties of the lignite sample was studied. The XRD and FT-IR analysis showed that carbonates (calcite, dolomite) are totally removed, and the main remaining mineral matter constituents are well crystallized quartz besides a small amount of sulphates (bassanite). The changes in the surface chemistry properties were investigated by FT-IR spectroscopy, Boehm's titration method and LSER modelling. All these methods pointed out the increase of the acidic character of the surface of the lignite after de mineralisation. (C) 2003 Elsevier Ltd. All rights reserved.