Structure of Molecular Weight Fractions of Bayer Humic Substances. 1. Low-Temperature Products

• Published in: Industrial & engineering chemistry research Vol. 38; no. 12; pp. 4663 - 4674
• Main Authors: Wilson, Michael A, Ellis, Amanda V, Lee, Garry S. H, Rose, Harry R, Lu, Xiaoqiao, Young, Brent R
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 06.12.1999
• Subjects: Analytical chemistry; Applied sciences; Chemical industry and chemicals; Chemistry; Exact sciences and technology; Industrial chemicals; Inorganic industry; Miscellaneous; Differential scanning calorimetry; Pyrolysis; Chemical analysis; Coupled method; Thermogravimetry; Acidity; NMR spectrometry; Experimental study; Infrared spectrometry; Gas chromatography; Bauxite; Ore treatment; Chemical composition; Fulvic acid; Thermal analysis; Alumina; Mass spectrometry; Humic acid; Quantitative analysis
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie9903590

The humic substances in Bayer liquor from a bauxite alumina refinery operating at 145−150 °C have been separated by dialysis into seven fractions of different molecular weight and characterized by acidity, nuclear magnetic resonance (NMR) spectroscopy, infrared spectroscopy, pyrolysis gas chromatography mass spectrometry (py-GC/MS), and thermogravimetric techniques including modulated differential scanning calorimetry. The higher molecular weight fractions contained more aromatic carbon than the lower molecular weight fractions (e.g., >300 000 Da, 56.4%; < 1200 Da, 33.6%). Acidity, NMR, and infrared spectroscopy indicate that carboxylic groups are more prevalent in lower molecular weight fractions (e.g., <1200 Da, 20.1%) than higher molecular weight fractions (e.g., >300 000 Da, 9.8%). Some fractions have particularly interesting structures and properties. For example, lignin-derived humic substances seem to concentrate in the 6000−12 000 Da fraction, as indicated by lignin guaiacyl residues. Involatile polycondensed material concentrates in the molecular weight fraction >300 000 Da. This fraction could be best described as soluble char with unusual properties such as the capacity to hold occluded water above 200 °C.