Mineralogical Characteristics And Intensified Separation Mechanism Of A Fine Manganese Ore From Songtao,Guizhou,China

Manganese ore is a major strategic key mineral in short supply in China.The manganese ore in Songtao,Guizhou,China,has the characteristics of"poor,fine and miscellaneous".Effective separation of fine rhodochrosite is the key and difficult point for improving quality and reducing impurity from manganese ore,and also the fundamental way to reduce the emission of electrolytic manganese residue from the source.However,the typical characteristics of fine minerals,including small mass and the huge specific surface area,often result in lower flotation efficiency.Increasing the apparent particle size by selective agglomeration for converting fine flotation to conventional flotation is an effective mean to enhance the flotation separation efficiency of fine minerals.Up to now,many studies on the dispersion,flocculation behavior and action mechanism of reagents for fine rhodochrosite-gangue mineral system have been reported.However,the hydrophobic agglomeration behavior,regulation and intensified separation of fine rhodochrosite have not been studied in depth,the microcosmic mechanism of enhanced separation based on molecular level and micro-nano scale is still unclear.It is of great significance to improve the basic theory of high-efficiency flotation separation of fine manganese ore,promote the efficient utilization of low-grade refractory manganese ore,and reduce the emission of electrolytic manganese residue from the source by studying the mineral characteristics and intensified separation mechanism of fine manganese ore in Songtao,Guizhou,China.In this paper,the manganese ore in Songtao,Guizhou,China is taken as the research object.Firstly,based on optical microscope,X-ray diffraction,X-ray fluorescence spectrometer,automatic quantitative mineral analysis system,inductively coupled plasma mass spectrometer,scanning electron microscope and energy dispersive spectrometer,etc.,mineralogical properties were studied to identify the properties of manganese ore and surface properties of fine rhodochrosite and quartz.Then,by means of laser particle size analysis,single mineral flotation,contact angle test,micro-nano imaging and colloid probe-force spectroscopy measurement of atomic force microscopy,micro wetting heat and other analytical methods combined with EDLVO theoretical calculation,selective agglomeration-flotation behavior of fine rhodochrosite and quartz,the coordinate induction of reagent and shearing,promotion of in-situ CO₂ micro-nanobubbles and emulsified kerosene for rhodochrosite agglomeration were studied.In addition,effect of external magnetic field on the reagent adsorption of rhodochrosite surface and interaction force between fine rhodochrosite particles were investigated.Finally,the regulation mechanism of hydrophobic agglomeration and intensified separation mechanism of fine rhodochrosite under compound force field were revealed.The major findings are as follows.1.The manganese ore are mainly massive,striped and bubble-shaped.The main useful minerals in the ore are rhodochrosite,the main gangue minerals are quartz,tetalite and clay minerals.The main textures of manganese ore include xenomorphic-granular,micro-squama,cryptocrystalline and mud microcrystalline textures.Rhodochrosite in the ore is mostly presented in xenomorphic-granular form,and some of them are aggregated in micrite and microcrystalline structures.The particle size of rhodochrosite monomer is less than 10μm,and the aggregate size is concentrated in the range of 5-60μm.Moreover,rhodochrosite is usually closely associated with or wrapped with quartz and other gangue minerals by microscopic oolitic or microscopic spherulite structures.The content of Mn in the ore is10.70%,mainly occurred in rhodochrosite and tetalite in the form of independent mineral and isomorphism.Content of impurity Si O₂ is 37.55%,mainly distributed in quartz and clay minerals.Content of Al₂O₃ is 9.81%,mainly distributed in sericite and chlorite.Content of Ca O is 9.78%,mainly distributed in tetalite and rhodochrosite.It is difficult to separate rhodochrosite from gangue minerals because of the micro-grained embedding and conjoined wrapping characteristics of rhodochrosite.2.Fatty acids have a selective agglomeration effect on rhodochrosite in the fine rhodochrosite-quartz system.The agglomeration effect of oleic acid is better than that of linoleic acid,α-linolenic acid and stearic acid.In addition,rhodochrosite agglomerates with large size and compact structure can be formed with medium oleic acid concentration(10^-3mol/L),weak acidic environment and moderate shear rate（500 rpm）.The action sequence of reagents has a great influence on the properties of rhodochrosite agglomerates.Compared with the pre-adjustment of p H,the agglomerates formed with pre-adsorption of oleic acid are stable in the range of weakly acidic to weakly alkaline conditions.Rhodochrosite agglomeration can be strengthened and the depolymerization and dispersion effect of alkaline environment on agglomerates can be weakened with low dosage of kerosene（mass ratio of oleic acid to kerosene is 5:1）,emulsified addition of oleic acid and kerosene,and micron-sized oil droplets.The flotation separation efficiency of rhodochrosite and quartz can be significantly improved after the agglomeration induced by fatty acids.Under the synergistic action of oleic acid and low dosage kerosene,the flotation time is shortened obviously,the flotation rate of rhodochrosite increases,and the Mn content and recovery rate of agglomerated flotation concentrate increase with higher values of about 5%and 30%than those in direct flotation,respectively.3.The agglomeration degree of rhodochrosite depends on its surface hydrophobicity and is significantly affected by fatty acid adsorption and fluid shearing.The rhodochrosite hydrophobicity is stronger with fatty acid concentration between premicelle concentration and semimicelle concentration,but it decreases with increasing number of C=C bonds of fatty acid.When the equilibrium concentration of oleic acid is 10^-4 mol/L and the pulp is weak acidic,there is a stronger hydrophobic attraction between rhodochrosite particles inducing their agglomeration.While there is a repulsive force to induce the depolymerization and dispersion of agglomerates with excessive oleic acid and alkaline environment.The critical shear rate for the equilibrium of agglomerate growth and rupture is 500 rpm,and for the significant decrease of particle size and strength is 800 rpm.The rupture of agglomerates is dominated by a mechanism of large-scale fracture.After the recovery from strong shearing to equilibrium shearing,secondary agglomeration of rhodochrosite with 30-45μm grain size as the growth core and-30μm as the branches and coatings can be achieved.The hydrophobic attraction of interparticle induced by fatty acid adsorption is the fundamental driving force for rhodochrosite agglomeration.Shearing provides energy input for interparticle collisions and interactions,ensuring the effective action range of hydrophobic attraction.In conclusion,the hydrophobic agglomeration of rhodochrosite is co-induced by fatty acid and shearing.4.The number,stability and solid-gas contact line of CO₂micro-nanobubbles,generated by acid hydrolysis,are positively correlated with hydrophobicity of rhodochrosite surface pre-adsorbed with oleic acid.Micro-nanobubbles can promote the agglomeration and flotation separation of rhodochrosite through bridging particles and adhering carrier bubbles with capillary force.There is a strong attraction between rhodochrosite and kerosene in oleic acid solution,and the adsorption of oleic acid on rhodochrosite surface induces the rapid spreading of kerosene.Moreover,the hydrophobicity of rhodochrosite is stronger when oleic acid and kerosene were emulsified.With the induction of oleic acid emulsified kerosene,introducing a weak magnetic field can increase the content of 45-100μm fraction in rhodochrosite agglomerates,enhance the flotation separation efficiency of rhodochrosite and quartz,and increase the manganese recovery of flotation concentrate for about 2%.The Lorentz force from the external magnetic field and shear effect increase the collision probability of hydrophobic rhodochrosite interparticle.In addition,the external magnetic field promotes the adsorption and wetting of reagents on rhodochrosite surface,resulting in the stronger hydrophobicity of rhodochrosite.Under the action of external magnetic field and oleic acid emulsified kerosene,the attraction between rhodochrosite particles increases significantly with the increase of magnetic induction intensity.In summary,the composite force field formed by hydrophobic attraction and magnetic attraction drives the agglomeration of rhodochrosite particles to realizes their intensified separation.Furthermore,the contribution of hydrophobic attraction produced by reagent adsorption to the interparticle forces is greater than that of magnetic attraction produced by weak magnetic field.5.In the process of hydrophobic agglomeration and intensified flotation of rhodochrosite,the pre-adsorption of oleic acid on rhodochrosite provides a hydrophobic surface,the adhesion and spreading of kerosene further enhances rhodochrosite hydrophobicity,and the weakly acidic environment provides H⁺to generate in-situ CO₂micro-nanobubbles.So,the gas bridges between CO₂ micro-nanobubbles and the oil bridges between kerosene droplets can be stable established due to hydrophobic surfaces.The kinetic energy and collision opportunities of particles can be imparted by fluid shearing and the reagent adsorption and particle collisions can be enhanced by external magnetic field,further promoting the agglomeration of particles by gas and oil bridges.In addition,fatty acid and fluid shear play the leading roles,the low dosage emulsified kerosene,in situ CO₂micro-nanobubbles and weak external magnetic field play the strengthening roles.In conclusion,the hydrophobic agglomeration and efficient flotation separation of rhodochrosite are achieved by regulating the synergistic effect of fatty acid,kerosene,micro-nanobubbles and shearing.