Spectroscopic Analysis of the Effects of Alkaline Extractants on Humic Acids Isolated from Herbaceous Peat

Abstract

To study the effect of various extractants on the structure of peat humic acid, peat humic acid was extracted using NH3·H2O, Na2CO3, NaHCO3, and Na2SO3 via alkali-extraction and acid-precipitation methods. The extracted peat humic acid was characterized using ultraviolet−visible (UV-vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and fluorescence (FL) spectroscopy. The results showed that the extractants had negligible effects on the content of peat humic acids. Na2CO3 was found to be the most effective extractant for isolating humic acids from peat, with the highest content of 66.20% and a yield of 32.67%. Moreover, among the extractants used, NH3·H2O resulted in humic acids with the highest aromaticity, and Na2SO3 yielded humic acids with higher number of hydroxyl groups. NaHCO3 yielded humic acids with the most aliphatic ether and lowest aromaticity. Na2CO3 was the best extractant for isolating humic acids from peat, having the highest content, lowest degree of aromatic polymerization, and highest number of carboxylic acids.