Application of low-field NMR in the study of flocculant-aided filtration process of coal tailings

Preconditioning of coal tailings with flocculants is a useful technology to improve filtration performance. In this study, anionic and cationic polyacrylamides were used for the pretreatment coal tailings before filtration. Nondestructive and rapid measurement of the filter cakes of coal tailings at different filtration stages was conducted using a nuclear magnetic resonance (NMR). The transverse relaxation time (T-2) results of NMR provided the information concerned the state of water in filter cake, showing that free water entrapped in larger pores was removed mainly during coal tailings filtration, and the pressure in this study cannot remove the inherent moisture of filter cake of coal tailings. The significant increase in the amplitude of T-2 value between 0.1 and 1.0 ms revealed that the flocs collapsed into smaller ones with water entrapped in them during filtration. Comparing the NMR results with different flocculants shows that anionic polyacrylamide of 800 g/Mg produced a larger structure in the initial stage of filter cake formation. The final filter cake entrapped more water. The NMR results well validated the filtration experiments.