Hydrosols from low-rank coals: 1. Preparation and properties

Abstract

The nature of the sodium humates from low-rank coals and the factors that determine their yields are reported in this paper. The sodium humate from Beulah lignite was shown to consist of a colloidal dispersion with a particle distribution in the submicron range, with a Z-average size of 411 nm. Yields for conversion of Beulah lignite to the dispersed humate form (hydrosol) in a sodium hydroxide medium have been increased from 4%, using magnetic stirring to 89%, using a high-speed blender at temperatures less than 45 °C. When carried out in a nitrogen dry bag, the high shear, high mass flow blending gave a 45% conversion of Beulah (North Dakota) lignite to the hydrosol. Other low-rank coals also gave high conversions (Big Brown lignite, 73%; Wyodak, 69%) but bituminous coals gave no conversion to hydrosol. The mineral content of the humic acid resulting from acidification of the Beulah hydrosol was <1%, whereas the residue of material that did not disperse in the basic solution was more concentrated in mineral matter and liptinite macerals. The ash analysis data were consistent with photoacoustic FT-i.r. and 13C n.m.r. spectroscopic studies. These instrumental techniques also substantiated an increase in carboxylic groups in the humic acid products. Significantly lower conversions were observed when bases other than sodium hydroxide and nonaqueous media were used in the blending.