Study On Hydrophobic Aggregation Flotation Of Fine Cassiterite Using Hydroxamic Acids As Collectors

Tin ore from primary deposits is the primary source of tin in China;it has a complex mineral composition and is intergrowth with other minerals as fine particles,resulting in a considerable volume of fine particles during the crushing and grinding processes.Fine cassiterite is typically recovered by flotation after desliming,resulting in the loss of numerous mineral particles in the tailings.To solve this problem,the aggregation and flotation behaviors of fine cassiterite（–37μm）using hydroxamic acids as collectors were studied in this paper.The combination of stirring experiment with laser-based particle size analysis and focused beam reflectance measurement（FBRM）with particle video microscope（PVM）imaging revealed:In the presence of benzhydroxamic acid（BHA）,fine cassiterite particles were unable to form hydrophobic aggregates;however,it formed in the presence of sodium oleate（Na OL）,with scheelite aggregating faster than cassiterite.The EDLVO theory and aggregation dynamics model calculations demonstrated that the high electrostatic interaction energy and the weak hydrophobic interaction energy between particles resulted in a high energy barrier between cassiterite particles which could not be overcome by the kinetic energy provided by intense agitation.Therefore,cassiterite particles were unable to aggregate in the presence of BHA.Due to a larger hydrophobic interaction energy between cassiterite particles in the presence of Na OL,the energy barrier between particles vanished,the particle collision adhesion efficiency reached 1,and particles were able to form hydrophobic aggregates.Five alkyl hydroxamic acids with carbon chain lengths of C₆,C₈,C₁₀,C₁₂,and C₁₄ were synthesized using the hydroxylamine method.The measured surface tension revealed that the increasing carbon chain length of hydroxamic acid increased its surface activity.The density functional theory（DTF）calculations revealed that the anion of one hydroxamate has a greater dipole moment than the molecule.Both the dipole moments of molecule and anion tended to increase as the carbon chain length increased.The effect of carbon chain length of alkyl hydroxamic acid on cassiterite flotation behavior was studied by micro-flotation test,adsorption amount of hydroxamate and contact angle measurements.The results showed that increasing the carbon chain length improved the collecting abilities of hydroxamates for cassiterite,increased the adsorption amount of hydroxamic species on the cassiterite,and increased the contact angle of the cassiterite surface.DFT calculation results indicated that in the absence of H₂O molecules,hydroxamate with a longer carbon chain was more easily absorbed on the Sn O₂ surface.H₂O molecules could spontaneously adsorb on the Sn O₂ surface.Hydroxamates adsorbed on the hydroxylated Sn O₂ surface via hydrogen bonding interaction.X-ray photoelectron spectroscopy（XPS）analysis revealed that hydroxamates adsorbed on cassiterite surface through physical interaction.FBRM and PVM were used to measure the hydrophobic aggregation of fine cassiterite using varying alkyl hydroxamic acid concentrations as collectors.It demonstrated that fine cassiterite particles did not aggregate by adding C₆.The lowest concentrations of C₈,C₁₀,and C₁₂ added to induce hydrophobic aggregation of cassiterite were approximately 1×10^–3,1×10^–4,and 2×10^–5 mol/L,respectively.Due to C₁₄’s poor solubility in water,no hydrophobic aggregates were found in its presence.Flotation results indicated that the metal ions Pb²⁺,Fe³⁺,Fe²⁺,and Zn²⁺could activate the flotation of cassiterite at a specific dosage.The measured zeta potential indicated that metal ions could reduce the surface potential of cassiterite in the presence of hydroxamic acid.EDLVO theoretical calculations indicated that the addition of metal ions decreased the electrostatic repulsion energy and increased the hydrophobic attractive energy of cassiterite particles.Therefore,the addition of metal ions could reduce or eliminate the energy barriers between particles,leading to the formation of hydrophobic aggregates of fine cassiterite particles.The results of FBRM and PVM imaging revealed that the addition of Pb²⁺decreased the concentrations of the alkyl hydroxamic acids required for cassiterite to form aggregates,promoted the formation of hydrophobic cassiterite with shorter carbon chain hydroxamic acids,and increased the apparent particle size of the aggregates.The flotation rate test results indicated that increasing the stirring time and rotating speed was advantageous to improve the recovery of mineral fine minerals.When Pb²⁺was added,the large aggregates could break into smaller ones in the stirring process,however,the content of micron particles did not increase significantly,which did not affect the flotation recovery of fine minerals.The stirring condition and flotation tests of fine cassiterite obtain from the Xintian Concentration Plant of Yunnan Zinc&Indium Stock CO.,LTD.revealed that octyl hydroxamic acid had a stronger collecting ability compared with YT-1.The addition of octyl hydroxamic acid（roughing stage:125g/t）increased the recovery of Sn by 6.68%in comparison to the addition of YT-1（roughing stage:1000g/t）.The distribution of Sn in-10μm particle size of tailing added octyl hydroxamic acid was 7.83%lower than that added YT-1.The addition of octyl hydroxamic acid improved the recovery of fine cassiterite.Strong stirring could reduce the stability of the flotation foam,weaken the capacity of the foam to carry particle,and lower the recovery of concentrate,but improve the concentrate grade.