Characteristics of Humic Acids Extracted from Weathered Coal and Tropical Peat with Aqueous Ammonia Solution

Abstract

Basic chracteristics of humic acids extracted from weathered coal (China) and tropical peat (Indonesia) were compared. The comparison was also made between the extraction of humic acid by conventional method (NaOH, NaOH/Na₄P₂O₇) and a new process using NH₄OH as an extractant. Regardless of the extractant, humic acid extracted from tropical peat has about four times as large average molecular weight as that from weathered coal. As for the functional groups, humic acid extracted from weathered coal has higher quantity of carboxyl group, but lower quantity of phenolic hydroxyl group.Humic acid extracted from weathered coal contains much aromatics in the structure.
The yield of the humic acid with NaOH was the highest among the three extractants. The humic acid extracted with NH₄OH contained a smaller amount of ash but a larger amount of ammoniacal nitrogen than with NaOH or NaOH/Na₄P₂O₇.
The cation exchange reactions of humic acid were accelerated by the higher electric charge of metal ions, the higher carboxyl group content and the lower molecular weight of the humate.