ABSTRACT
The physical nature of the phenomena governing flotation was not well understood in the early days. Initial flotation processes were the result of patient trial and error despite the phenomena associated with dewetting, hydrophobicity and hydrophilicity being well known at the time. Young [ 1] in a famous paper of 1805 developed the theory of wetting and contact angle, which is an important criterion in flotation, and described the dependence of the contact angle on the specific surface energies. This dependence was derived quantitatively by Laplace [2] one year later but is usually referred to as the Young equation (We still have no satisfactory theory of contact angles). In 1869 Dupre [3] applied thermodynamics to the problem of wetting and dewetting of solid surfaces by fluids and obtained the celebrated Dupre equation describing the work of adhesion. If we follow historically the route of colloid science from the time of Young, Laplace, Poisson, Maxwell, Gibbs, and others, we observe that the physicochemical phenomena occurring at solid-liquid interfaces were the scientific focus at the time of early flotation investigations.
