Mineralogical Characterization And Flotation Enrichment Of Ultra-Large Flakes Graphite From Inner Mongolia

Graphite mineral is a crystalline form of the element carbon,with a hexagonal structure,and is highly conductive.Graphite particles are frequently found in the shape of flakes or crystalline layers in metamorphic rocks rich in carbon and pegmatites,their diverse properties and high electric conductivity enhance its importance as raw material in the production of lithium batteries,refractories,lubricants,and others.Graphite ores can be classified according to the dimensions of their particles;flakes between 150-850μm in diameter are considered as coarse,while fine flakes are measured in 45-150μm diameter,large flakes in 1000-2000μm diameter,and ultra-large flakes+2000μm with the highest standard as raw material due to their excellent properties.Nowadays,the graphite ores from Inner Mongolia are the most valuable and demanded because of the nature of their flakes and high electric conductivity,hence the mining industries have focused their efforts on the recovery of flakes graphite through innovative efficiency processes to obtain high graphite concentrates products,especially by recovering large and ultra-large particles.Likewise,the mineral processing research centers pay special attention to the study of froth flotation as the best beneficiation process for graphite concentration especially by analyzing the efficiency of the chemical reagents during flotation experiments.In the following project,the characterization of the graphite ore from Inner Mongolia was studied,and the application of active pulsing air classification（APAC）,heavy liquid separation,and froth flotation as experimental processes to recover big flakes was explored.After primary crushing and classification,a particle size distribution was determined 5 ranges,like ultra-large particles（+4 mm）,large particles（-4 mm+2 mm）,coarse particles（-2 mm+1 mm）,fine particles（-1mm+0.5mm）and ultra-fine（–0.5mm）,where 41.63%corresponds to large particles,18.52%coarse,16.13%ultra-fine particles,12.69%fine particles and 11%for ultra-large particles.Moreover,the mineralogical phases were identified and quantified by X-ray diffraction（XRD）and X-ray fluorescence（XRF）.The analyses described calcium carbonate（Ca CO₃）and silicon dioxide（Si O₂）as the main non-graphite mineralogical phases.The XRF results show that the content of Ca O is 55.17%,Si O₂ is 13.44%,and carbon（C）is 4.33%.Furthermore,the scanning electron microscope analysis（SEM）revealed large,flat hexagonal crystal graphite with matrix intercalation on its edge surface in contact with gangue particles,spherical intercalate flakes,and free graphite particles.Also,two groups of samples with different particle sizes were analyzed by Energy Dispersive Spectroscopy（EDS）,the carbon content identified in 1.65 mm and 1.08 mm graphite particles was 36.50%and 78.19%respectively,an oxygen content of 36.27%and 12.50%,while the content of Si O₂was 4.72%and 0.88%,with a proportion for aluminum and chloride relatively low.The active pulse air classification experimental trials aim to improve the separation efficiency of flakes bigger than 1 mm from gangue particles.The air velocity range used in the separation process was established between 140 m³/h-190 m³/h,and pulsate air frequency ranges from 3 Hz and 9 Hz.It was found that under the condition of the same pulsating frequency（5 Hz）,using 190 m³/h and 170 m³/h respectively,the recovery rate and graphite grade of ultra-large flakes in+4 mm,-4 mm+2 mm particle size fractions were low,but the pre-concentrate contains a certain proportion of ultra-large flakes that have been completely dissociated.In contrast,coarse flakes in the-2 mm+1 mm size fraction had a higher recovery rate at 160 m³/h and 7 Hz,but with a low graphite grade and low concentrate,mainly because the particle size of graphite was large and the degree of dissociation was relatively low.In the case of-1 mm+0.5 mm size fraction and-0.5 mm size fraction,the air separation effect was poor due to the fine particles.For the pulsating airflow separation of+1 mm graphite,the grade of graphite concentrate was not high,mainly because the particle size of graphite was large and the degree of dissociation was relatively low.To protect large flakes of graphite,the tail of graphite ore should be discarded by pulsating airflow separation,then large flakes and ultra-large flakes can be recovered as much as possible.Therefore,the final graphite concentrate is obtained by using the pulsating airflow to discard the tail and then by heavy liquid separation.For the graphite with particle sizes of+4 mm,-4mm+2mm,-2mm+1mm,after the experimental study of tail removal by active pulse air classification and heavy liquid separation process was developed using tribromomethane carbon tetrachloride with 4 different densities.The results certified that large and ultra-large flakes of graphite are not floatable in the solution at 1.9g/cm³ of density,so higher densities were used to recover big flakes.For instance,ultra-large flakes（+4 mm）started being recoverable at 2.5 g/cm³ although with a very low dissociation of ultra-large particles.In contrast,the particle fractions of-4 mm+2 mm and-2mm+1 mm in the large graphite had a good separation effect when the density of the f heavy liquid is 2.1 g/cm³,because the dissociation degree of graphite particles of this particle size is high,and the corresponding heavy medium separation recovery rate is also high.Moreover,3samples concentrated by float-sinks were measured in 2.72 mm,2.94 mm,and 4.91 mm in diameter.These graphite particles can be described as flat and spherical amorphous flakes with a total weight of carbon content estimated at 75.23%,79.35%,and 75.57%.The froth flotation was carried out for ultra-fine particles（–0.5mm）and fine particles（-1mm+0.5mm）using a single-cell flotation machine.Reagents such as kerosene（collector）,sodium dodecyl benzene sulfonate（frother）,and sodium silicate（depressant）were selected to evaluate their feasibility by changing the reagent’s dosages and air rate during the recovery of fine particles and ultra-fine particles.The optimal flotation process conditions for a-0.5 mm size fraction are as follows:400 g/t of collector dosage,frother dosage 450 g/t,depressant dosage 200 g/t,and air rate variation 150 L/h.The optimal flotation process conditions for-1 mm+0.5 mm particle size fraction were 300 g/t of collector dosage,frother dosage 450 g/t,depressant dosage 200 g/t,and air rate variation 200 L/h.On the other hand,the optimal flotation process conditions for-1 mm+0.5 mm particle size fraction were 300 g/t of collector dosage,frother dosage 450 g/t,depressant dosage 200 g/t,and air rate variation 200 L/h.By one stage floatation,for particles size of-0.5mm,under the optimum conditions,the recovery rate,and ore grade were 63.58%and 56.99%respectively.For-1mm+0.5mm particles,the recovery rate under the optimal flotation conditions was 70.55%,and the ore grade was 69.39%.In conclusion,the graphite raw ore from Inner Mongolia was processed by APAC,froth flotation,and heavy liquid separation.After the separation process,the graphite had a high recovery rate and grade.Fine particles（-1mm+0.5mm）and ultra-fine（-0.5mm）particles are recoverable by froth flotation using conventional reagents such as kerosene and sodium silicate,also a new frothing agent like sodium dodecyl-benzenesulfonate.On the other hand,ultra-large,large,and coarse flakes can be recovered by active pulse air classification to remove gangue particles,followed by float-sink using tribromo methane in solution with densities higher than2.1 g/cm³.