Fundamental Study On Selective Flocculation-flotation Of Ultrafine Molybdenite Particles

Molybdenum mine is a featured mineral resource in China,with abundant reserves.However,molybdenum ore with grade less than 0.1%accounts for more than 65%.With the continuous increase in the demand for molybdenum in the society and depletion of rich ore resources,the large-scale development of low-grade molybdenite ore will result in problems such as low process efficiency and low recovery.Thus,this project takes quartz and kaolinite,the main gangue minerals from the molybdenum ore,and target mineral molybdenite as the research object,focuses on flocculation-flotation of molybdenite.The study takes selective flocculation,flocculation selectivity enhancement and selective flocculation-flotation separation as the main research line,and combines analysis and testing,molecular dynamics simulationwithexperimentalverificationtoexploretheselective flocculation-floatation mechanism of molybdenite using polyethylene oxide.In this paper,the adsorption mechanism of minerals with flocculants was analyzed.The flocculation behaviors of molybdenite,quartz and kaolinite using three flocculants were investigated considering the hydrophobic interaction between particle and macromolecule.Molecular dynamics simulations,quantum chemical calculation,adsorption measurements,and molecular hydrodynamic radius analysis of polyethylene oxide were used to reveal the selective flocculation mechanism of molybdenite.The effect of metal ions and sodium hexametaphosphate on flocculation behavior of quartz and kaolinite in polyethylene oxide solution was investigated.Through interparticle force tests,floc fractal dimension analysis,and particle flocculation,dispersion,and re-flocculation behavior analysis,the flocculation selectivity enhancement of micro-fine molybdenite was studied by fluid.Flotation tests of micro-fine molybdenite in polyethylene oxide solution were carried out and the interface interaction was analyzed.Finally flocculation-flotation of mixed ore was investigated.Firstly,the flocculating behaviors of molybdenite,quartz and kaolinite using polyethylene oxide were studied.The adsorbing behavior of polyethylene oxide on molybdenite,quartz and kaolinite crystal faces was analyzed using molecular dynamics simulations and quantum chemical calculations.The effect of different factors on the adsorption of polyethylene oxide on mineral surfaces and conformation change analysis of polyethylene oxide macromolecules was also investigated.Then the selective flocculation mechanism of molybdenite by polyethylene oxide was revealed.Polyethylene oxide exhibited better flocculation selectivity on molybdenite.The adsorption energy of polyethylene on molybdenite crystal surface was obviously higher than that of quartz and kaolinite.The key role of adsorption of polyethylene oxide on surface of quartz and kaolinite was mainly hydrogen bonding,while in addition to hydrophobic interaction between?001?surface of molybdenite with polyethylene oxide molecules,there was characteristic adsorption of oxygen atoms of polyethylene oxide with Mo atoms of?010?surface of molybdenite.The flocculation effect of molybdenite,quartz,and kaolinite depended on the amount of polyethylene oxide adsorbed and stretching state of macromolecules in solution.As pH value increased,adsorption amount of polyethylene oxide on the surfaces of quartz and kaolinite was significantly reduced,but the effect on molybdenite was less.Polyethylene oxide collapsed in solution in acidic conditions,which was not conducive to flocculation.As the pH value increased,polyethylene oxide macromolecules gradually stretched,which was beneficial to flocs formation.The effect of metal ions on the flocculation behavior of quartz and kaolinite in polyethylene oxide solution was investigated.And flocculating behavior of quartz and kaolinite using polyethylene oxide with the action of sodium hexametaphosphate was studied.The activation and inhibition mechanism of metal ions and sodium hexametaphosphate were clearly identified in the flocculation of quartz and kaolinite using polyethylene oxide.Ca²⁺,Cu²⁺and Fe³⁺had a certain activation effect on flocculation of quartz and kaolinite,and the activation ability was affected by pH.Under the same ion concentration,the activation ability of metal ions on flocculation of quartz and kaolinite was Fe³⁺>Cu²⁺>Ca²⁺.The addition of sodium hexametaphosphate inhibited activation of quartz and kaolinite by metal ions to some extent.Threre was mainly H₂PO₄^-at pH 5.0 in the sodium hexametaphosphate solution system,which formed a complex with metal ions.And compression of double-layers of mineral surface by metal ions was reduced.Based on the interparticle force tests,analysis of flocculating behavior and floc fractal dimension of molybdenite and kaolinite under fluid flow,a selectivity enhancement mechanism for molybdenite flocculation was proposed using intensive turbulence.In the 2 mg/L polyethylene oxide solution,attraction forces between molybdenite particle and molybdenite plate increased significantly from 32.12 nN to62.22 nN,while the attraction forces between kaolinite particle and molybdenite plate increased from 3.46 nN to 5.11 nN,and attraction forces between quartz particle and molybdenite plate increased from 1.05 nN to 3.68 nN.At the same time,the addition of polyethylene oxide increased the distance of attraction force appeared between particles,which was beneficial to flocculation of particles.The formed molybdenite flocs had stronger stability with different stirring intensity and could resist high-strength shearing fluid,and after destruction,the flocs had a certain re-flocculating ability.While for kaolinite,the flocs were instability with higher stirring intensity,and it was difficult to form effective flocs.Re-flocculating ability was also much weaker after destruction than that of molybdenite.The interfacial function of polyethylene oxide in the flotation process of ultrafine molybdenite were studied.The flotation intensification mechanism of ultrafine molybdenite by polyethylene oxide was proposed.At the concentration of 2 mg/L polyethylene oxide solution,the surface hydrophobicity of molybdenite was significantly improved,the induction time between particles and bubbles decreased from 18 ms to 12 ms.The size of molybdenite particles increased to 100?m with 20g/t polyethylene oxide addition.The collision probability of molybdenite particles with bubbles increased from 0.14%to 8.80%.It was assumed that polyethylene oxide only changed particle size and did not change hydrophobicity of molybdenite.The adhesion probability between�edges�and bubbles was only 3.25%.With the addition of polyethylene oxide,the contact angle of�edge�increased to about 50�,and adhesion probability between�edges�and bubbles increased to 44.66%,while hydrophobicity of�faces�of molybdenite was not affected,and adhesion probability between�faces�and bubbles was 73.87%.Selective flocculation-flotation tests of mixed ore were carried out.Through the addition of sodium hexametaphosphate and adjusting stirring speed in flocculation process,the recovery rate of molybdenite was significantly increased from 56.53%to over 80%with less lower grade for concentrate compared to conventional flotation.The selective flocculation-flotation method of ultrafine molybdenite proposed in this study has good feasibility and can provide technical reference for recovery of low-grade molybdenum resources.