The floatability of solid particles on the water surface governs many natural phenomena and industrial processes including film flotation and froth flotation separation of coal and valuable minerals. For many years, the contact angle (CA) has been postulated as the key factor in determining the particle floatability. Indeed, the maximum force (tenacity) supporting the flotation of fine spheres was conjectured to occur when the apical angle of the contact circle is equal to the contact angle. In this paper, the model predictions are reviewed and compared with experimental results. It is shown that CA can be affected by many physical and chemical factors such as surface roughness and chemical heterogeneity and can have a range of values known as the CA hysteresis. This multiple-valued CA invalidates the available theories on the floatability of spheres. Even the intuitive replacement of CA by the advancing (maximum) CA in the classical theories can be wrong. A few new examples are also reviewed and analyzed to demonstrate the significance of CA variation in controlling the particle floatability. They include the pinning of the contact line at the sharp edge, known as the Gibbs inequality condition, and the nearby interaction among floating particles, known as lateral inter-particle interaction. It is concluded that our quantitative understanding of the floatability of real particles being irregular and heterogeneous both morphologically and chemically is still far from being satisfactory.

固体颗粒在水表面的漂浮性决定着许多自然现象和工业过程，包括煤和贵重矿物的膜浮选和泡沫浮选分离。多年来，已经假定接触角（CA）是确定颗粒漂浮性的关键因素。确实，当接触圆的顶角等于接触角时，会推测会出现支持微球浮起的最大力（强度）。本文对模型的预测进行了回顾，并与实验结果进行了比较。结果表明，CA可能受到许多物理和化学因素（例如表面粗糙度和化学异质性）的影响，并且可能具有一系列称为CA磁滞的值。此多值CA使关于球的可漂浮性的可用理论无效。甚至用经典理论中先进的（最大）CA对CA的直观替换也可能是错误的。还审查和分析了一些新的示例，以证明CA变化在控制颗粒漂浮性方面的重要性。它们包括将接触线钉扎在尖锐的边缘（称为吉布斯不等式条件）和浮动颗粒之间的邻近相互作用（称为横向颗粒间相互作用）。结论是，我们对真实颗粒在形态和化学上都是不规则和异质的漂浮性的定量理解仍然远远不能令人满意。还审查和分析了一些新的示例，以证明CA变化在控制颗粒漂浮性方面的重要性。它们包括将接触线钉扎在尖锐的边缘（称为吉布斯不等式条件）和浮动颗粒之间的邻近相互作用（称为横向颗粒间相互作用）。结论是，我们对真实颗粒在形态和化学上都是不规则和异质的漂浮性的定量理解仍然远远不能令人满意。还回顾并分析了一些新的示例，以证明CA变化在控制颗粒漂浮性方面的重要性。它们包括将接触线钉扎在尖锐的边缘（称为吉布斯不等式条件）和浮动颗粒之间的邻近相互作用（称为横向颗粒间相互作用）。结论是，我们对真实颗粒在形态和化学上都是不规则和异质的漂浮性的定量理解仍然远远不能令人满意。被称为横向粒子间相互作用。结论是，我们对真实颗粒在形态和化学上都是不规则和异质的漂浮性的定量理解仍然远远不能令人满意。被称为横向粒子间相互作用。结论是，我们对真实颗粒在形态和化学上都是不规则和异质的漂浮性的定量理解仍然远远不能令人满意。