Study on the microscopic aggregation behavior of lignite molecules in water

Abstract

Molecular simulation is a reliable tool for studying the self-aggregation behavior of lignite molecules in a solution. To explore how the molecular structure of lignite influences its aggregation behavior, 13C NMR analysis was first performed to construct its molecular structure. Molecular simulation results show that the extreme regions of the electrostatic potential on the lignite surface mainly appear near the polar functional groups. In a solution, the hydrogen bonding and van der Waals interactions between lignite and water molecules will hinder the self-aggregation of the former ones. The self-aggregation process of lignite molecules can be divided into three stages: Brownian (random) motion, agglomeration, and structural adjustment. Driven by the Lennard-Jones and electrostatic potentials, the lignite molecules gradually aggregate to form a cluster. This process will destroy the hydration film on the lignite surface, ultimately decreasing the number of hydrogen bonds and changing the orientation of the water molecules. Increasing the number of lignite molecules will help their spontaneous aggregation. This work reveals the self-aggregation process of lignite molecules and helps to understand their aggregation behavior in solution. This work provides theoretical guidance for solving the flocculation settlement of slime water.