Forms Of Water In Shengli Lignite And Effect Of Metal Ions On Its Water Absorption Capacity

With the decrease in the amount of high rank coal, low rank coal is beingincreased the use ofin the world The high moisture content of lignite, however,significantly constrained its value. Study of moisture in lignite can provide atheoretical basis for its dehydration technology.In this study, three approaches that were tube furnace dewatering in nitrogenatmosphere combined with Differential Scanning Calorimetry (DSC), acceleratedsolvent extraction dewatering approach, and accelerated solvent extraction dewateringapproach pretreated with microwave were used to determine the forms of water inShengli lignite. Furthermore, some physico-chemical properties including functionalgroups, specific surface area and pore size distribution of all samples were determined.To investigate the effects of cations on equilibrium adsorption water content of lignite,ion-exchange process was characterized by Fourier infrared spectrum (FT-IR) and theash contents. The equilibrium adsorption water contents of all samples weredetermined in a range of relative humidities.Results of these three dewatering approaches show that classification of water inlignite involves: free water, non-freezable water, crystal water, pyrolysis water, closedpore water and bound water including capillary water, inter-particle water,intra-particle water and adhesion water. Effects of these three dewatering approacheson physico-chemical properties change with operating conditions.Study of the effects of cations on equilibrium adsorption water content of lignitehas shown that the extent of ion-exchanged exchange in Shengli coal is in order ofCa2+>Na+>K+>Mg2+. The relative effectiveness of cations in increasing theequilibrium adsorption water content is in order of Mg2+>Ca2+>Na+≈K+. At highrelative humidity, the factor that control equilibrium adsorption water content is freewater molecules interactions. However, at middle relative humidity capillary forcebetween metal cation-carboxyl group complex and capillary is more important. At lowrelative humidity water interactions with sorption sites which are cation-carboxylgroup complex become more important.