Effects of the extraction temperature on the characteristics of a humic fertilizer obtained from lignite

Abstract

Solutions of 0·1 m and 0·25 m potassium hydroxide were employed to extract a humic fertilizer from lignite at 20, 50 and 80°C. The effects of the temperature on the yields of humic and fulvic acids and on the characteristics of the former were investigated. Higher extraction temperatures did not significantly enhance yield in either case, and neither were the ratios between humic and fulvic acids significantly affected. Humic acids released by hot 0·25 M KOH solutions held less N-rich material and exhibited a lower content of functional groups than those obtained at 20°C. When 0·1 M KOH was employed at 50 and 80°C, changes in the molecular structure of humic acids were less apparent but there were fewer functional groups than in the humic acids obtained at 20°C. Increasing extraction temperatures were matched by the larger molecular size of humic acids extracted with both KOH solutions.