Selective attachment and spreading of hydroxamic acid–alcohol collector mixtures in phosphate flotation

Efficient flotation with insoluble-in-water liquid collectors is governed by selective attachment and spreading phenomena at mineral surfaces. This paper investigates the spreading of mixtures of hydroxamic acids and alcohols, recently identified and developed as collectors for the selective flotation of phosphate minerals. The spreading of collector drops on surfaces of apatite and the gangue minerals (dolomite and quartz) immersed in water or surfactant solutions was measured using a high-speed video system and the dynamic contact angle was determined from the transient profiles of the collector drops. Surface and interfacial tensions were measured applying the Du Noüy ring method. The dynamic wetting behavior of collector drops was described using the molecular kinetic theory. This analysis indicates that hydroxamic acids increase the interaction between the alcohol solution and the apatite surface, producing a strong collector attachment. Further information regarding spreading characteristics was obtained from studies at a graphite surface used as a model surface to reveal the nature of the hydrophobic/hydrophobic interaction. The spreading resistance was increased by the hydroxamic acid adsorption resulting in a decrease in the rate of spreading. Both theoretical and experimental results show that at the air–water and alcohol–water interfaces hydroxamic acids exhibit unique interfacial characteristics which account for the selective flotation of apatite from quartz.