Metahydrophobicity and orthohydrophilicity tested in flotation of NaCl, KCl, KPF6 in their saturated aqueous solutions

Flotation tests of different size fractions of NaCl, KCl and KPF₆ in their saturated aqueous solutions were performed in a 36 cm in height monobubble Hallimond tube. Also contact angle tests by means of sessile drops of saturated salt solution put on pressed discs of salts were carried out. The obtained sessile drop contact angles were equal to zero, pointing to a complete hydrophilicity (orthophilicity) of the investigated salts. In the case of NaCl and KCl, their orthohydrophilicity was confirmed by flotation tests and flotometric considerations because the entrainment factors, which take into account the maximum size of entrained particles and density of the salt as well as it solution, were similar to those of quartz and magnetite and equal to 0.11 mm. The entrainment factor for KPF₆  was equal to 0.18 mm and was greater than that of NaCl and KCl indicating certain natural flotation of this salt caused by some flotational hydrophobicity called in this paper metahydrophobicity. The metahydrophobicity of KPF₆   was confirmed by flotation results. In the case of KPF₆ the maximum yields of the same size particles were the highest, even though the density of this salt was greater than that of NaCl and KCl. Also, the first order kinetic constants were always the greatest for KPF₆. Further flotometeric calculation based on the balance of forces involved in flotation indicated that the estimated contact angle of KPF₆ was about 8 ^º assuming static flotation, and 7 ^º for dynamic flotation, while for NaCl and KCl was below 5 ^º . It means that during flotation test orthohydrophilic NaCl and KCl are only entrained while for metahydrophobic KPF₆ there is mostly entrainment and some flotation.