Process Condition Optimization and Structural Feature Analysis of Humic Acid Extraction from Weathered Lignite.

Area of Science:

• Geochemistry
• Organic Chemistry
• Materials Science

Background:

• Humic acids (HA) are vital organic components in soil and coal.
• Efficient extraction of humic acids from lignite is crucial for their application.
• Understanding the properties of humic acids from different sources is essential.

Purpose of the Study:

• To optimize the process conditions for extracting humic acid (HA) from weathered lignite using response surface methodology (RSM).
• To characterize the extracted humic acids (LSHA and WHHA) using various analytical techniques.
• To compare the properties and biological activity of humic acids from Lishi and Wuhai sources.

Main Methods:

• Response surface methodology (RSM) was employed to optimize extraction parameters (time, NaOH concentration, liquid-solid ratio).
• Analytical techniques included UV-vis spectroscopy, FTIR, XRD, TG-DTG, CP/MAS 13C NMR, XPS, and molecular fluorescence.
• Comparative analysis of chemical properties, aromaticity, molecular weight, functional groups, and biological activity.

Main Results:

• Optimal extraction conditions were determined for Lishi humic acid (LSHA) and Wuhai humic acid (WHHA), yielding results close to model predictions.
• Extraction time significantly impacted LSHA yield, while liquid-solid ratio significantly impacted WHHA yield.
• WHHA exhibited higher aromaticity, while LSHA showed a higher hydrophilic-hydrophobic index, correlating with higher biological activity.

Conclusions:

• The study successfully optimized humic acid extraction from weathered lignite, providing specific conditions for LSHA and WHHA.
• Both humic acids share terrestrial origins and exhibit distinct chemical properties and biological activities.
• The findings offer valuable insights for the future application of humic acids from coal sources.