The surface chemistry of phosphate mineral flotation with alcohol solutions of octyl hydroxamic acid.

Based on recent research developments at the University of Utah water-insoluble alcohol solutions of octyl hydroxamic acid collectors have been shown to be particularly effective in the flotation of coarse phosphate feed material. The surface chemistry associated with this phosphate flotation is not clear. Therefore, it is important to explore this flotation chemistry in greater detail to understand the nature of the interaction between the insoluble collector and selected minerals. To achieve this objective, the nature of the new collector and its effectiveness in the flotation of phosphate was studied by wetting/spreading analysis of collector drops, surface spectroscopy techniques including FTIR and SFG spectroscopy, and the measurement of interaction forces using the AFM colloidal probe technique. The results showed that wetting of the collector drop occurred at the apatite surface whereas such wetting did not occur at the quartz surface. The dynamic wetting behavior of the collector drops was described based on molecular kinetic theory. Further the organization of hydroxamic acid at model surfaces (CaF 2 and fused silica) was established by vibration spectroscopy study. Of particular significance were the results from SFG studies which showed that a hydroxamic acid monolayer adsorbs from the alcohol solution at a CaF 2 surface with the same structure and conformation as observed for an LB film of the hydroxamic acid transferred to the surface of fused silica. The hydroxamic acid molecules are adsorbed at the CaF 2 surface and form a monolayer. The alcohol molecules are oriented at the hydroxamic acid monolayer as a second layer with their hydrocarbon tail and terminal CH 3 group oriented to face the hydroxamic acid monolayer. Finally interaction forces between colloidal probes and the alcohol hydroxamic acid solution droplet were measured using the AFM colloidal probe technique. The results indicate that the spreading of the alcohol hydroxamic acid solution is energetically favored at the apatite surface, whereas the silica sphere was repelled from the alcohol solution droplet surface. Information regarding adsorption/conformation of hydroxamic acid has been established that appears to account for the selective attachment and wetting of the water insoluble hydroxamic acid droplet at the surface of apatite minerals.