菱镁矿与白云石表面水润湿过程及机理

Wetting mechanism of water on magnesite and dolomite surfaces

摘要

浮选是分离菱镁矿与白云石的主要方法，其分离效率受矿物表面水化特性的影响. 为揭示其微观机理，本文采用Materials Studio 软件，结合密度泛函理论（DFT）与分子动力学（MD）模拟，构建了优化的菱镁矿与白云石晶体及捕收剂十六烷基磷酸酯（CP）分子模型，并系统分析前线轨道能、润湿行为及界面作用能. 结果表明：前线轨道揭示 CP 分子与菱镁矿的轨道能量差（2.643 eV）小于白云石体系（2.670 eV），即 CP 分子最高占据轨道（HOMO）电子优先向菱镁矿最低未占轨道（LUMO）转移；润湿模拟显示，白云石接触角（7.5°）小于菱镁矿（9.2°），表明白云石表面固有的水分子亲和力更强，CP 分子吸附后菱镁矿表面水分子扩散系数高于白云石表面，疏水性显著增强；界面相互作用能分析进一步证实，CP 分子在菱镁矿表面的吸附能（−406.8 kJ·mol⁻¹）及形变能（166.7 kJ·mol⁻¹）均显著优于白云石体系（分别为−95.6 kJ·mol⁻¹ 和 161.9 kJ·mol⁻¹）. 综上，本研究从分子层面揭示了 CP 分子对菱镁矿的选择性作用机制，为钙镁碳酸盐矿物表面水化调控及浮选分离提供理论依据.

Abstract

In nature, magnesite is frequently intergrown with dolomite and other carbonate minerals, forming complex ores that require efficient separation. The flotation separation of magnesite from dolomite remains a significant challenge in mineral processing owing to their similar crystal structures and solution chemistry, which result in comparable surface hydration properties and flotation behavior. Precise regulation of surface wettability is central to achieving selectivity. Previous research has predominantly focused on developing novel flotation reagents, particularly collectors and depressants, with emphasis on their interaction mechanisms at mineral surfaces. Recent studies employing ab initio molecular dynamics (MD) have provided fundamental insights, indicating that although both minerals favor molecular water adsorption, magnesite exhibits a slightly stronger affinity for water than dolomite, thereby affecting subsequent interfacial processes. Molecular simulation can effectively elucidate such intricate microscopic interactions at mineral–water–collector interfaces. To elucidate the atomic-scale mechanism governing the selective adsorption of collectors, this study integrates density functional theory and MD simulations using Materials Studio software. Structurally optimized surface models of magnesite (104) and dolomite (104), together with a typical anionic collector CP (e.g., a phosphoric acid ester), are constructed to systematically investigate frontier molecular orbital energetics, surface wettability dynamics, and interfacial adsorption energies. Frontier molecular orbital analysis reveals a narrower energy gap between CP and magnesite (2.643 eV) than in the dolomite system (2.670 eV), suggesting that electron transfer from the highest occupied molecular orbital of CP to the LUMO of magnesite is thermodynamically more favorable, thereby promoting selective adsorption on magnesite surfaces. MD simulations of wettability behavior indicate that dolomite exhibits a lower water contact angle (7.5°) than magnesite (9.2°), reflecting its intrinsically stronger hydrophilicity. After CP adsorption, the diffusion coefficient of water molecules on the magnesite surface increases significantly and exceeds that on dolomite, demonstrating that CP adsorption effectively disrupts the hydration layer and enhances the hydrophobicity of magnesite. This enhanced hydrophobicity is expected to facilitate bubble attachment more effectively on magnesite than on dolomite. Interfacial interaction energy analysis further confirms that CP exhibits significantly stronger adsorption energy (−406.8 kJ·mol⁻¹) on magnesite than on dolomite (−95.6 kJ·mol⁻¹), along with higher deformation energy (166.7 kJ·mol⁻¹ vs. 161.9 kJ·mol⁻¹), indicating superior adsorption stability and interfacial compatibility on the magnesite surface. This study elucidates the multidimensional selective mechanism of the CP collector toward magnesite from electronic, dynamic, and energetic perspectives, providing a theoretical foundation for reagent design. To translate these molecular-level insights into practical separation strategies and address the complexity of industrial flotation systems, several aspects warrant further investigation. Future studies should focus on (1) investigating the combined effects of surface pretreatment (e.g., acid etching to modulate roughness and active sites) and CP adsorption; (2) examining the influence of solution chemistry (e.g., dissolved ionic species and pH) on the established adsorption model; and (3) extending simulations to the gas-liquid interface to evaluate the potential role of CP in bubble surface modification and its effect on overall flotation kinetics. These investigations will help bridge the gap between molecular-scale insights and the optimization of macroscopic flotation performance.

关键词

分子动力学模拟 / 浮选分离 / 润湿性 / 密度泛函理论 / 菱镁矿

Key words

molecular-dynamics simulation / flotation separation / wettability / density functional theory / magnesite

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基金资助

国家自然科学基金项目(52104263)

湖北省技术创新计划重点研发专项(2023BCB079)

武汉工程大学研究生创新基金(CX2025199)

武汉工程大学研究生创新基金(CX2024049)