How to realize efficient treatment of coal slime generated by a coal washing operation is an urgent problem to be solved in this industry. The presence of clay minerals, especially highly hydrophilic montmorillonite (MMT), is the key to the poor treatment effect of coal slime. Polyacrylamide (PAM) is very popular as a polymer agent to improve the treatment of coal slime. However, when it is used to treat coal slime with a high content of MMT, the selection of PAM type and the mechanism of action are still lacking. In this study, the effects of different types of PAM on the treatment of coal slime water containing MMT are considered by sedimentation and press filtration tests. The interaction mechanism of PAM on the MMT surface is studied by using ζ-potential, Brunauer–Emmett–Teller (BET) analysis, low-field nuclear magnetic resonance, density functional theory (DFT), and molecular dynamics (MD) simulations. The results show that the three PAM can improve the sedimentation and filtration effect of coal slime water, and the performance is CPAM > NPAM > APAM. The ζ-potential of the MMT (001) surface increases under the action of three PAM, and the effect of CPAM is the most significant. The adsorption of PAM on the MMT (001) surface has the ability to neutralize the surface charge of MMT. The flocculation of MMT particles under PAM results in an increase of particle size and a decrease of specific surface area. Meanwhile, the pore volume of MMT decreases, and the average pore size increases. In addition, PAM mainly removes vicinal water on the MMT surface. The active sites of the MMT surface and PAM are calculated by DFT. The adsorption of three PAM structural units on the MMT Na-001 surface and non-001 surface is nonbonding interaction, and the adsorption energy of CPAM is the largest. And the left shift of ε_p of the O atom on the MMT surface is conducive to the stable adsorption of CPAM. The MD results show that the concentration of water molecules on the surface of MMT Na-001 decreases after PAM is adsorbed on the MMT Na-001 surface, indicating that PAM can keep water molecules away from the surface of MMT, which means that the hydrophobicity of the MMT surface is enhanced. This study has guiding significance for the selection of PAM and the development of new flocculants in the treatment of coal slime with a high content of MMT.

中文翻译：

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PAM对蒙脱石表面疏水性的影响及界面吸附差异的实验与模拟研究

如何实现洗煤作业产生的煤泥的高效处理是该行业亟待解决的问题。粘土矿物尤其是高亲水性蒙脱石(MMT)的存在是煤泥处理效果不佳的关键。聚丙烯酰胺（PAM）作为一种聚合物药剂，在改善煤泥处理方面非常受欢迎。但用于处理高含量MMT煤泥时，PAM类型的选择及作用机理尚缺乏。本研究通过沉降​​和压滤试验考察了不同类型PAM处理含MMT煤泥水的效果。通过使用 z 势、Brunauer-Emmett-Teller (BET) 分析、低场核磁共振、密度泛函理论 (DFT) 和分子动力学 (MD) 模拟，研究了 PAM 在 MMT 表面上的相互作用机制。结果表明，三种PAM均能提高煤泥水的沉降过滤效果，其表现为CPAM>NPAM>APAM。 MMT(001)表面的ζ电位在三种PAM的作用下增加，其中CPAM的效果最显着。 PAM在MMT(001)表面的吸附具有中和MMT表面电荷的能力。 MMT颗粒在PAM作用下的絮凝导致颗粒尺寸增大和比表面积减小。同时，MMT的孔容减小，平均孔径增大。另外，PAM主要去除MMT表面的邻近水。通过DFT计算MMT表面和PAM的活性位点。三个PAM结构单元在MMT Na-001表面和非001表面的吸附均为非键相互作用，且CPAM的吸附能最大。而MMT表面O原子的εp左移有利于CPAM的稳定_吸附。MD结果表明，PAM吸附在MMT Na-001表面后，MMT Na-001表面水分子浓度降低，表明PAM可以使水分子远离MMT表面，这意味着疏水性MMT表面的性能得到增强。本研究对于高MMT含量煤泥处理中PAM的选择和新型絮凝剂的开发具有指导意义。