Mineral surface wettability and its regulation by the adsorption of collectors have an important influence on the flotation performance. The adsorption behavior of C₁₈ fatty acid with different unsaturation and its effect on rhodochrosite wettability was investigated with surface tension, contact angle, and atomic force microscopy (AFM) measurements. The results indicated that rhodochrosite hydrophobicity increased with the increasing concentration of fatty acid, along with the maximum contact angle (θ_max) between hemimicelle concentration (HMC) and critical micelle concentration (CMC). Oleic acid (OA), linoleic acid (LA), and α-linolenic acid (ALA) had a higher θ_max than stearic acid (SA), but the value decreased with the increase of C=C bond number. Besides, preferential adsorption of unsaturated fatty acids on the liquid-air interface can be attributed to the molecule’s steric hindrance resulting from C=C double bond, and the θ kept almost invariant with a higher value of Γ_LG than Γ_SL until HMC. The oriented monolayer and bilayer structure of fatty acids formed gradually on rhodochrosite surface with increasing concentration. However, the θ_max may not necessarily correspond to the beginning of bilayer formation. Cylindrical monolayer and bilayer micelles of SA molecules were observed on rhodochrosite surface at HMC and CMC, respectively. While bilayer structures of unsaturated fatty acids formed before complete coverage of monolayer on rhodochrosite surface because of surface heterogeneity. This work provided a good understanding on the adsorption mechanism of fatty acid on rhodochrosite for flotation.

中文翻译：

---

菱锰矿表面的吸附行为和润湿性：C18脂肪酸不饱和度的影响

矿物表面的润湿性及其受捕收剂吸附的调节对浮选性能有重要影响。通过表面张力，接触角和原子力显微镜（AFM）测量研究了不同不饱和度的C ₁₈脂肪酸的吸附行为及其对菱锰矿润湿性的影响。结果表明，菱锰矿的疏水性随着脂肪酸浓度的增加以及半胶束浓度（HMC）和临界胶束浓度（CMC）之间的最大接触角（_θmax）而增加。油酸（OA），亚油酸（LA）和α-亚麻酸（ALA）的_θmax较高与硬脂酸（SA）相比，该值随C ＝ C键数的增加而降低。此外，液体-空气界面上的不饱和脂肪酸优先吸附可以归因于分子的从C = C双键导致的空间位阻，和θ保持与Γ的一个较高的值几乎不变的_LG比Γ _SL直到HMC。脂肪酸的定向单层和双层结构随着浓度的增加逐渐在菱锰矿表面形成。但是，_θmax不一定与双层形成的开始相对应。在菱锰矿表面分别在HMC和CMC处观察到SA分子的圆柱单层和双层胶束。而由于表面异质性，不饱和脂肪酸的双层结构在单层完全覆盖菱锰矿表面之前形成。这项工作对脂肪酸在菱锰矿浮选上的吸附机理提供了很好的理解。