| Graphite with a wide range of uses is an emerging strategic resource in the 21 st century.The larger the diameter of the graphite sheet,the higher the application value.As the exploitation of large flake graphite resources tends to be exhausted,fine flake graphite gradually becomes the main resource to be used in the future.The traditional multi-stage grinding and multi-stage flotation process is common methods to recover this kind of graphite resources in current production practice,which has problems such as low recovery efficiency of fine particle graphite,difficult liberation of graphite minerals,poor flake protection effect and too long flotation process.Therefore,the research and development of new mineral processing technology will inevitably play an important role in promoting the efficient utilization of fine flake graphite mineral resources.The study was carried out with fine flake graphite from Luobei area of Heilongjiang Province as a representative sample.The fine flake graphite ore from the area adopts conventional ten-stage grinding and ten-stage flotation technology to realize resource recycling.Based on the study of the technological mineralogical characteristics of the fine flake graphite ore in this area,the causes of graphite mineral liberation and flake damage were clarified,and then the liberation mechanisms of the fine flake graphite ore under different crushing and grinding conditions and the protection mechanisms of the flake mineral in the ore were studied;Developed a short-flow and high-efficiency graphite separation and quality improvement process with nanobubble flotation as the core technology integrating high-pressure grinding roller(HPGR)and stirred mill;On this basis,the hydrophobic agglomeration effect,stability of agglomerates,flotation rate and flotation selectivity characteristics of fine graphite particles in the nanobubble flotation system were studied,and the mechanism of nanobubble enhancing the flotation of fine flake graphite was revealed by the use of Zeta potential and FTIR,XPS,contact angle analysis,adsorption kinetic methods,etc.The main conclusions of the subject research are as follows:(1)Based on the process mineral characteristics of the fine flake graphite ore samples,the difficult liberation mechanisms,graphite flake damage mechanism and the main factors affecting the flotation concentrate index are revealed.Part of the flakes in the raw ore showed a curved shape and the muscovite interspersed between two flakes was the main reason that caused the flakes to be damaged and difficult to liberate during the grinding process.Most of the fine particle graphite in the ore are distributed in the fine particles of-38 ?m,and some gangue minerals such as pyrite and quartz in the ore are distributed among the graphite mineral particles in a disseminated state,which will affect the grade of the graphite concentrate.(2)It reveals the liberation mechanisms of the fine flake graphite and the flake protection mechanisms by the combination of the HPGR and the stirred mill.HPGR promote the cracks generation along the graphite and gangue surfaces,thereby achieving monomer liberation and flake protection.Based on the shearing force grinding mechanism of the stirring mill and the weak impact force of the medium,it is easy to break the bond between muscovite and graphite flakes,and cracks are not easily generated in the graphite flake crystals,thereby further realizing the liberation of graphite minerals and flake protection.(3)Combined with the nanobubble flotation technology,the short flow flotation of fine flake graphite resources is realized.The short-flow flotation process for fine flake graphite resources was determined,which reduced the number of grinding and flotation stages to 3 stages,increased the concentrate grade by 0.2 percentage point,the recovery by 14.73 percentage points,the large flake(+150 ?m)yield by 1.5percentage points,effectively recovered the fine particle graphite and significantly reduced the dosage of flotation reagents in whole process.(4)The hydrophobic agglomeration effect and stability of fine particles of graphite in the nanobubble flotation system are clarified.The hydrophobic agglomeration of graphite in the nanobubble flotation system presents a floc-like structure,which has high stability in the ultrasonic field,thus increasing average apparent size of fine graphite minerals in the pulp to improve the flotation effect.(5)The differences of flotation kinetics and flotation selectivity of nanobubble flotation and conventional flotation were clarified.The nanobubble flotation rate of fine flake graphite is significantly higher than that of conventional flotation,and it effectively recovers the fine particle graphite that cannot be recovered by conventional flotation,thereby improving the recovery rate of graphite concentrate.In addition,the selectivity of fine flake graphite by nanobubble flotation is also better than that of conventional flotation,and the grade of nanobubble flotation concentrate is significantly higher than that of conventional flotation concentrate under the same flotation conditions.(6)From the perspective of electrostatic force,the stability mechanism of graphite hydrophobic agglomerates in the nanobubble system and the enhancement mechanism of hydrophobicity of the graphite surface are revealed.Nanobubbles nucleate and precipitate on the surface of graphite,which reduces the electrostatic repulsion between two graphite particles,promotes and enhances the hydrophobic agglomeration and the agglomerates stability,thereby enhancing flotation effect of conventional bubbles.In addition,surface nanobubbles reduce the electrostatic repulsion between diesel droplets and graphite,enhance the adsorption capacity of diesel on the graphite surface,improve the hydrophobicity of the graphite surface,and improve the collection selectivity of conventional bubbles on fine flake graphite flotation.(7)From the perspective of hydrophobic force,the stability mechanism of the graphite hydrophobic aggregates and the enhancement mechanism of the degree of hydrophobicity of the graphite surface are revealed in the nanobubble system.The nucleation and precipitation of nanobubbles on the graphite surface enhances the hydrophobicity of the graphite surface,improves the hydrophobic attraction of diesel and graphite particles,enhances the adsorption strength of diesel on the graphite surface,thereby improving the graphite again,which enhances selectivity of conventional bubbles to graphite mineral collection.The degree of surface hydrophobization strengthens the selectivity of conventional bubbles in the flotation system for graphite mineral collection.In addition,the secondary improvement of the hydrophobicity of the graphite surface enhances the hydrophobic attraction between the graphite particles,improves the hydrophobic agglomeration effect and stability between the graphite particles,and further strengthens the flotation recovery effect of fine particle graphite.(8)The dynamic mechanism of nanobubbles enhanced fine flake graphite flotation and the characteristics of diesel on the graphite surface in the nanobubble system are clarified.In the nanobubble system,the adsorption rate of diesel oil on the graphite surface is faster compared with conventional flotation system,the hydrophobicity of the graphite surface is rapidly enhanced,thus significantly improving the graphite flotation rate and flotation selectivity;Adsorption rate of diesel on graphite surface can be described by the pseudo-second-order kinetic equation accompanying the diffusion behavior of the liquid film,and the adsorption of diesel on the graphite surface can be described by the Freundlich and Langmuir isotherm adsorption equations,which is considered to be a favorable monolayer physical adsorption. |
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