| Scheelite is one of important strategic sources of tungsten.However,the flotation of fine scheelite(-10μm)still remain a technical challenge for reseachers.Hydrophobic agglomeration flotation technology has been developed for fine scheelite.Although hydrophobic interaction has been proved to be the main driving force in the formation of hydrophobic agglomeration,the formation mechanism of hydrophobic agglomeration at the micro-nano scale is still unclear.A new theoretical perspective for the dispersion and aggregation of fine particle at the micro-nano scale can be provide by inter-particle force。Firstly,the interfacial forces between hydrophilic/hydrophobic scheelite and scheelite/fluorite/calcite were directly measured by atomic force microscope(AFM)colloidal probe technology,and the hydrophobic force was revealed to be the driving force in the formation of scheelite hydrophobic aggregate.The interfacial forces on hydrophilic scheelite-scheelite,scheelite-fluorite varied with pH value.The forces always shown repulsive at natural pH value of ultrapure water and thus attachment was denied.At a higher pH value,The forces shown attraction.The iterface forces always show weakly attraction between hydrophilic scheelite and calcite.The interfacial forces between hydrophobic scheelite and scheelite/fluorite/calcite shown strongly attraction.All of results shown that hydrophobic force promotes the formation of hydrophobic aggregate,which has been proved by optical microscope.The interfacial forces between scheelite and scheelite/fluorite/calcite after sodium hexametaphosphate treating had been confirmed that sodium hexametaphosphate played a role of dispersant and the selective inhibitor of fluorite and calcite.Secondly,the adsorption mechanism of sodium oleate on the surface of fine scheelite had been proved by thermodynamic calculation,AFM imaging technology and XPS.It was indicated that liquid bridging force make a key role by unsoluble oleic acid droplets.The hydrophobic aggregates grown up slowly by the action of hydrophobic force and liquid bridging force.On the basis,a model of fine scheelite hydrophobic agglomeration coated sodium oleate was proposedThe adsorption mechanism of lead ions(Pb2+)on scheelite surface in sodium oleate system had been proved by the contact Angle,ATR-FTIR and ToF-SIMS.When Pb2+ and sodium oleate were orderly added,lead ions increased the active sites for the adsorption of OL-.Lead ions were chemisorbed on scheelite surface in the form of OL--Pb-O-W or OL--Pb-O-W,but ToF-SIMS depth profile of lead ions shown the presence of lead ions could not increase the adsorption thickness of NaOL.When Pb-NaOL complex was added,the thickness of the adsorption layer on surface of scheelite increased significantly,which enhanced the surface hydrophobicity and provided favorable conditions for the formation of scheelite hydrophobic aggregates.On the basis,the adsorption mechanism model of lead ions on scheelite surface in sodium oleate system was proposed.Finally,the characteristics of scheelite leaching residues had been identified by XRF,chemical analysis,optical microscope,particle size analysis,scanning electron microscope(SEM),Electron Probe Micro Analysis(EPMA)and mineral dissociation degree system(MLA).It was proved that cassiterite and scheelite exist as original minerals in scheelite residues after NaOH leaching,and the cassiterite and scheelite quantity were mainly distributed at-10μm grain level;In the process of scheelite leaching,most of the sodium oleate adsorbed on the surface had been resolved,while a large amount of sodium silicate was still adsorbed on the surface.The cassiterite concentrate with Sn grade of 18.65%and Sn recovery rate of 82.94%and was obtained by closed-circuit experiment of centrifugal gravity concentration;Samely,the scheelite concentrate with WO3 grade of 5.82%and recovery of 47.66%was obtained by closed-circuit experiment of hydrophobic aggregate flotation. |
PDF Full Text Request