Effect of ammonia nitrogen and low-molecular-weight organics on the adsorption of additives on coal surface: A combination of experiments and molecular dynamics simulations

Abstract Experiments and molecular dynamics (MD) simulations were conducted to investigate the effect of ammonia nitrogen and low-molecular-weight organics on the adsorption of sodium lignosulfonate (SL) on Shenhua coal. Results of adsorption and adsorption film thickness experiments showed that ammonia nitrogen and low-molecular-weight organics have different effects on the adsorption of SL on coal surface, thus resulting in different adsorption configurations of SL. A ternary system that was composed of water–SL–Shenhua coal was established through MD simulation. The adsorption mechanism of SL on Shenhua coal in different solutions was explored, and the influencing factors were analyzed using a microscopic mechanism. Results showed that the adsorption conformations of SL molecules on coal surface in aqueous and low-molecular-weight organics solutions are single-layer and multi-point adsorption, whereas the adsorption conformations in ammonia nitrogen solutions are double-layer adsorption. The mechanism of the adsorption of SL molecule on Shenhua coal surface by ammonia nitrogen and low-molecular-weight organics was studied in detail. The calculation results of adsorption energy are consistent with the experimental results in thermodynamics. This result demonstrates the feasibility and accuracy of the MD simulation.