Investigation of Humate Extraction from Lignites

Abstract

The present study investigated the extraction of humate from low-quality lignite samples acquired from Malkara and Yatagan coal deposits in Turkey. The experiments were conducted on finely ground representative coal samples at atmospheric pressure and room temperature. The samples were first leached with concentrated nitric acid for up to 72 hours and undissolved solids were removed by filtration. Potassium hydroxide was added to the leachate for alkalization in order to produce nitro-humic acid solution at different pH levels. Humic matter precipitation was achieved by addition of diluted nitric acid. The extraction products were investigated by proximate, Fourier Transform Infrared Spectroscopy (FTIR), and elemental analyses. The most important factors affecting humate extraction were found to be the consumption of nitric acid dosage for coal leaching, pH value of the leachate after potassium hydroxide addition, and mixing time. The promising results with over 80% humate extraction were achieved for the Yatagan lignites when the acid-coal consumption ratio was less than 1 mL concentrated nitric acid per 1 gram coal at a pH of 9 with mixing for 48 hours, while Malkara lignites reached 70% humate extraction with 72 hours of mixing under the same conditions.