Study On The Flotation Behavior And Mechanism Of The Fluorites With Different Defect Types

As the main source of fluorine in the modern chemical industry,fluorite has been included in the national strategic mineral resources reserve of China.In addition to colorless fluorite,there are also multi colorful fluorites in nature,even in the same fluorite deposit.The pleochroism of fluorite is mainly caused by the lattice defect of mineral.Different colored fluorites possess disparate flotability due to their different surface properties.However,the traditional flotation process of fluorite ignores the difference,performing mixed flotation on the multi colorful fluorites.As a result,the flotation recovery of fluorite concentrate is low,and the dark fluorite is lost to the tailings.In addition,the fluorite concentrate obtained by the mixed flotation loses its application value in the optical industry due to pleochroism,limiting the comprehensive and efficient recovery of fluorite mineral resource and its high value-added applications.Moreover,there are very few reports studying on the physicochemical properties and flotation behavior of different defective fluorites.Therefore,the subject is proposed based on the ideal fluorite（colorless,CF）,and defective fluorites with Y-impurity substitution（green,GF）and fluorine vacancy（purple,PF）produced from the same fluorite deposit in Inner Mongolia,China.Taking the crystal chemical characteristic as a point of penetration,the crystal structure,surface properties and flotation behavior of the three defective fluorites are studied systematically by means of the laser Raman spectroscopy,electron paramagnetic resonance spectroscopy,X-ray photoelectron spectroscopy and quantum chemical calculation,etc.The main findings and results of the paper are as follows:（1）The results of mineral characterization show that the chemical and mineral composition of the three defective fluorites are similar,while their crystal structures are quite different.Lattice defects are the root cause in the coloration of GF and PF,and the main defect types are Y-impurity substitution defect and fluorine vacancy defect,respectively.Meanwhile,the AFM and XPS analyses show that the defect type also affects the surface properties of the three defective fluorites.The surface roughness of CF,GF and PF are 5.13 nm,5.95 nm and 9.15 nm,respectively.And the Ca/F ratio on the surface of CF,GF and PF are 0.52,0.49,and 0.47,respectively.These differences in surface property provide a theoretical basis for studying the flotation behavior of the three defective fluorites.（2）When sodium oleate（NaOL）is used as a collector,the order of the flotation recovery of the three defective fluorites is CF>GF>PF,and all of them show good floatability in a slurry with a pH of 5-10.The large surface roughness and specific surface area make PF possess high adsorption amount to NaOL.Thus,PF could only be flotated under the condition with high NaOL concentration.The oleate anion is the active component of fluorite flotation and acts primarily with the Ca active sites on the fluorite surface.The CF contains more abundant Ca active sites because of its smooth surface and higher Ca/F ratio.Therefore,CF can be floated easily at low NaOL concentration.As a result,the floatability of CF is better than GF and PF in the NaOL system.（3）The alkyl sulfonate surfactants exhibit good collecting performance for fluorite.It is found that the affinity of alkyl sulfonates for fluorite is enhanced with the increase of the alkyl chain length.However,the overlong alkyl chain length makes C16 have low activity due to its limited solubility in pulp,thus having a dissatisfactory collecting performance for fluorite.The introduction of phenyl group in the hydrophobic tails can reduce the energy gap of HOMO-LUMO in C12B,increasing its chemical reactivity and collecting performance for the fluorite.Using C12B as a collector,the order of the flotation recovery of the three defective fluorites is CF>GF>PF,which is consistent with the results of the collector adsorption measurement.In addition,C12B has stronger temperature resistance than NaOL.（4）Due to the existence of mineral crystal habits,fluorite will preferentially cleave or be exposed along the direction of the crystal surface with a small surface energy under crushing and grinding,which makes the fluorites with different particle sizes exhibit distinct surface properties because of thier difference in exposed crystal surfaces.The fluorite（111）surface is the cleavage surface of fluorite and is easier to be exposed in coarse particles,exhibiting a strong affinity for NaOL as a result of having the lowest surface energy and 100%surface Ca┄F broken bonds.In contrast,the exposure of the fluorite（110）surface,when the fluorite is crushed and ground to finer particle size,reduces the adsorption of NaOL because of its hydrophilic surface containing 50%F┄Ca broken bonds.That is why the coarse fluorites possess better flotability than the fine ones.The anisotropy of fluorite is the key factor causing the difference in the floatability of fluorites with different particle sizes.（5）The microscopic analyses reveal all the three defective fluorites are rich in fluid inclusions with different shapes and uneven distribution.The order of the size of fluid inclusions in fluorites is PF>GF>CF.The captured ionized components Ca²⁺,F^-,Cl^-and SO₄^2-,etc.will be released into the slurry,when the fluid inclusions in mineral burst under crushing and grinding,and become one of the sources of inevitable ions in slurry solutions.It is concluded that the release of component in fluid inclusions is the major source of inevitable Ca ions in fluorite flotation slurry solutions.The flotation results show that a proper amount of Ca ions can activate the flotation of fluorite,while the excess Ca ions will preferentially consume the collector,inhibiting the flotation of fluorite.（6）Compared with the mineral bulk phase,lattice defect is more likely to form on the crystal surface of fluorite and directly affect its surface properties.The existence of F-vacancy defect can cause the total density of states of atoms on the fluorite surface to shift towards the lower energy and the Fermi level to move towards the conduction band,reducing the positive charge capacity of the Ca atoms on the fluorite surface.The formation of Y-impurity defect leads to a decrease both in the electronic loss capability of the Ca atoms and the electronic receiving capability of the F atoms on the fluorite surface.Moreover,the contribution to the Fermi level is dominated by the Y impurity.As far as the charge distribution of the surface atoms is concerned,the presence of F-vacancy and Y-impurity defects will inhibit the strength of the anion collector adsorption on the fluorite surface.