Mineralogical characterization of chemically isolated ingredients from biomass

The complex structure of biomass materials can be studied by means of a number of different techniques. Of which, chemical isolation of macromolecular biomass ingredients such as lignin, hemicellulose, and cellulose, and then characterization of each isolated ingredient has been a common practice. However, the isolated individual ingredients have always been regarded as pure materials, and so far potential inorganic impurities resulting from the parent biomass have not been considered. Accordingly, this paper focuses on the determination of inorganics, if any, in the isolated parts of biomass. For this, two different biomass species such as hybrid poplar wood and apricot stones have been subjected to sequential isolation procedures of ASTM D1105, Wise's Chlorite Method, and van Soest's Method. The isolated holocellulose (hemicellulose + cellulose), lignin, and extractives-free bulk were then characterized mineralogically by X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) techniques, and the results were compared with those for the parent biomass species. It was found that the isolated holocelluloses and lignins are not just ash-free and they have ash contents up to 2.2% and 4.0%, respectively. Also, various minerals including potassium chloride, several phosphate minerals, and alumina silicates were found to survive after chemical treatments applied during isolation. In addition, several heavy metals were also detected. These results reveal that minerals cannot be eliminated entirely because of the natures of the chemicals used, and they unavoidably remain in the isolated macromolecules.