Enhancement Of Kaolinite Selective Flocculation In Coal Flotation By Polyaluminum Chloride

The pollution of fine-grained gangue minerals in coal flotation on flotation clean coal is currently an important issue that restricts the quality of clean coal products.Many studies have shown that gangue minerals will enter the foam layer of flotation clean coal through fine mud cover,water entrainment and other ways,thus increasing the ash content of clean coal.In metal ore flotation,inhibitors are added to selectively flocculate gangue minerals,thereby reducing water entrainment of gangue and improving concentrate grade.In coal flotation,it is difficult to selectively flocculate gangue minerals.The research shows that polyaluminum chloride（PAC）can realize the agglomeration of kaolinite in coal flotation,and then reduce the ash content of flotation clean coal.However,due to the unclear distribution of Al species in polyaluminum chloride in existing studies,the selective flocculation mechanism of kaolinite is not perfect.The distribution of Al species in PAC was studied by hourly complexation colorimetry,and the influence of PAC on the settlement characteristics of kaolinite and the properties of kaolinite/coal flocs in different solution environments was systematically studied.Finally,the strengthening mechanism of selective flocculation of kaolinite was clarified.The main research conclusions of the thesis are as follows:The thesis first synthesized PAC with different alkalinity by alkali addition titration method,and determined the distribution of three Al forms in PAC,namely single nuclear aluminum ion Al_a,multi nuclear hydroxylated aluminum ion Al_b,and colloidal sediment Al_c,based on the difference in hourly complexation reaction rate between different Al forms and Ferron reagents.The study on the sedimentation characteristics of kaolinite shows that under the neutral condition and the electrolyte concentration of 0.1 mmol/L,with the increase of PAC base degree,the sedimentation rate of kaolinite slows down and the turbidity of supernatant increases.Under neutral condition and electrolyte concentration of100mmol/L,with the increase of PAC basicity,the sedimentation rate of kaolinite becomes faster,and the turbidity of supernatant decreases first and then increases.This shows that the adsorption bridging effect of Al_a and Al_b is the main mechanism of kaolinite flocculation at low electrolyte concentration,while the precipitation net trapping effect of Al_c is the main mechanism of kaolinite flocculation at high electrolyte concentration.Under acidic conditions,kaolinite settles faster and the turbidity of wsupernatant is lower;Under alkaline condition,PAC disperses kaolinite suspension without obvious sedimentation,and the turbidity of supernatant increases.The influence of PAC with different basicity on the floc chord length of kaolinite/coal at different electrolyte concentration and p H was studied by focusing beam reflectometry（FBRM）;The real-time online particle observation system（PVM）was used to take real-time pictures of flocs and calculate the fractal dimension of flocs.The results showed that under neutral condition and electrolyte concentration of1mmol/L,the average chord length of kaolinite floc first increased and then decreased with the increase of PAC concentration.At 2ppm,the average chord length of kaolinite floc was the largest.With the increase of PAC basicity,the average chord length of kaolinite gradually decreased,and the fractal dimension of kaolinite floc first increased6of kaolinite does not change significantly,and the fractal dimension of kaolinite is smaller than the fractal dimension of 1mmol/L electrolyte concentration.Under acidic conditions,the flocculation effect of kaolinite is better than that under neutral conditions.Especially,PAC₀ and PAC_1.0 significantly increase the chord length of kaolinite floc,while PAC_1.5and PAC industry will cause the secondary flocculation of kaolinite after a long time of stirring.This is due to the high content of alc in PAC1.5and PAC industry.The hydrolysis and polymerization of monomer and polymer in PAC under a long time of stirring lead to the formation of Al（OH）₃,which is precipitated on the particle surface,The chord length of kaolinite floc increases again due to precipitation net trapping.Under alkaline condition,kaolinite basically does not flocculate.The chord length of coal did not show significant changes at different electrolyte concentrations and p H levels.The analysis of zeta potential of kaolinite/coal shows that under neutral conditions,the zeta potential of kaolinite increases gradually with the increase of PAC concentration.When the concentration of PAC_1.0 and PAC_1.5 is 2ppm,the zeta potential of kaolinite is positive,while when the industrial concentration of PAC₀ and PAC is2ppm,the zeta potential of kaolinite is negative.At this time,kaolinite does not reach the neutral state,but the average chord length of kaolinite is the largest.When the concentration of PAC_1.0 and PAC_1.5 is 2.8 ppm,the zeta potential of kaolinite is positive,while when the industrial concentration of PAC₀ and PAC is 2.8 ppm,the zeta potential of kaolinite is close to 0.However,the average chord length of kaolinite is smaller than that when the concentration of PAC is 2 ppm,so in this system,electric neutralization is not the main mechanism of kaolinite flocculation.Under acidic conditions,the electronegativity of kaolinite is enhanced.Under the action of PAC with different basicity,the zeta potential of kaolinite is still negative.Under alkaline condition,the zeta potential of kaolinite has no obvious fluctuation.The narrow scanning results of O1s peak obtained by XPS test on kaolinite show that the content of Al-OH bond and Si-OH bond on the surface of kaolinite decreases and the content of Al-O and Si-O bond increases after the interaction with PAC,which indicates that the cation in PAC polymerizes with the Al-OH bond and Si-OH bond on the surface of kaolinite,and Al-O bond and Si-O bond are formed.The pollution of fine-grained gangue minerals in coal flotation on flotation clean coal is currently an important issue that restricts the quality of clean coal products.Many studies have shown that gangue minerals will enter the foam layer of flotation clean coal through mechanical entrainment,water flow entrainment and other ways,thus increasing the ash content of clean coal.In metal ore flotation,inhibitors are added to selectively flocculate gangue minerals,thereby reducing water entrainment of gangue and improving concentrate grade.In coal flotation,it is difficult to selectively flocculate gangue minerals.The research shows that polyaluminum chloride（PAC）can realize the agglomeration of kaolinite in coal flotation,and then reduce the ash content of flotation clean coal.However,due to the unclear distribution of Al species in polyaluminum chloride,the selective flocculation mechanism of kaolinite is not perfect,and the selective flocculation effect is also relatively limited.In this thesis,PAC with different basicity was synthesized in the laboratory and the distribution of Al species in PAC was analyzed.The settling characteristics of kaolinite and the flocs of kaolinite and coal were studied respectively,and the flocculation mechanism of kaolinite was explained.The thesis first synthesized PAC with different alkalinity levels using alkali titration method and calculated the morphology distribution of various Al forms in PAC through UV spectrophotometry.In this thesis,PAC with different basicity under neutral conditions,with the increase of basicity,the sedimentation rate of kaolinite slows down,and the turbidity of supernatant increases.Under different electrolyte concentrations,low electrolyte concentration is conducive to the agglomeration of kaolinite,the sedimentation rate of kaolinite is faster,and the turbidity of supernatant is lower.Under acidic conditions,kaolinite settles faster and the turbidity of supernatant is lower;Under alkaline condition,PAC disperses kaolinite suspension without obvious sedimentation,and the turbidity of supernatant increases.The influence of PAC with different basicity on the floc chord length of kaolinite/coal at different electrolyte concentration and p H was studied by focusing beam reflectometry（FBRM）;The real-time online particle observation system（PVM）was used to take real-time pictures of flocs and calculate the fractal dimension of flocs.Under neutral conditions,with the increase of PAC concentration,the average chord length of kaolinite floc first increases and then decreases.At 2ppm,the average chord length of kaolinite floc is the largest.With the increase of salinity,the average chord length of kaolinite floc decreases.At high electrolyte concentration,kaolinite has no obvious chord length change.Under acidic conditions,the agglomeration effect of kaolinite is enhanced,and the chord length of kaolinite floc is increased.Under the action of PAC₀ and PAC_1.0,the chord length of kaolinite floc is increased.PAC_1.5 and PAC industry have the phenomenon of precipitation net trapping.In PAC_1.5 and PAC industry,the content of Al_cis high.The hydrolysis and polymerization of monomer and polymer in PAC under long-term stirring lead to the generation of Al（OH）₃,which precipitates on the surface of particles and accumulates,promoting the agglomeration of kaolin particles and dispersed particles,making the chord length of kaolinite floc increase again.Under alkaline condition,kaolinite does not agglomerate with kaolinite.There is no obvious flocculent phenomenon of coal particles at different electrolyte concentrations and p H,and there is no significant change in chord length.The analysis of zeta potential of kaolinite/coal shows that under neutral conditions,the surface potential of kaolinite increases with the increase of PAC dosage.When the dosage concentration is 2ppm,the surface of kaolinite is positive when PAC_1.0and PAC_1.5are added,and the surface of kaolinite is negative when PAC₀ and PAC are added.At this time,the surface potential of kaolinite is not at the zero point,and the average chord length of kaolinite is the largest;At 2.8ppm,the surface of kaolinite is positive at PAC_1.0 and PAC_1.5.When PAC₀ and PAC are added to the industry,the surface of kaolinite is near the zero point.At this time,the average chord length of kaolinite is smaller than the average chord length when the concentration is 2ppm,so in this system,the electric neutralization does not play a leading role in the flocculation process of kaolinite.Under acidic conditions,the adsorption rate of PAC on kaolinite surface becomes faster,and the surface potential of kaolinite is still negative under the action of PAC with different basicity.Under alkaline condition,the surface potential of kaolinite has no obvious fluctuation.At high electrolyte concentration,the absolute value of kaolinite potential decreases,and kaolinite agglomeration is inhibited.High Na Cl concentration will reduce the size and scope of action of the electric double layer force between kaolinite particles.kaolinite agglomeration should be enhanced,but it is inconsistent with the actual agglomeration effect,indicating that there are other reasons for kaolinite agglomeration to weaken with the increase of electrolyte concentration.The analysis of XPS oxygen peak on the change of tube energy group content on the surface of kaolinite shows that the content of Al-OH bond and Si-OH bond on the surface of kaolinite decreases,and the cation in PAC has Al-OH bond and Si-OH bond,forming Al-O bond and Si-O bond.The thesis has 56 figures,5 tables,and 93 references.