Research On The Particle Size Effect In The Flotation Of Carbonate-Containing Hematite Ores

There are abundant poor,finely disseminated,and low grade iron ores in China,resulting in fine grinding is required to achieve valuable minerals liberation.Hence,the grindings for flotation are with the feature of wide size fraction and high fine particle contents.In this case,the surface physicochemical properties and particle size characteristics can both influence the flotation performance obviously.The carbonate-containing hematite ore is a typical refractory ore which is fine grain size and complex mineral contents.Meanwhile,the presence of carbonate minerals adversely influences the separation efficiency of hematite and decreases the grade and recovery of concentrate.Therefore,it is necessary to study the surface characteristics and flotation performance of the main minerals(hematite,quartz,siderite,dolomite)contained in carbonate-containing hematite ores,and investigate the particle size effect,namely the effect of inherent particle size distribution and the particle size variation in the slurry,in the flotation of carbonate-containing hematite ores.The above research works have guiding and referencing effects on the efficient utilization of carbonate-containing hematite and complex refractory iron ores.On the basis of studying the crystal structure,surface electrical properties,and wettability of hematite,quartz,siderite,and dolomite,the influence of regulators(calcium ions and starch)on the flotation of four single minerals in sodium oleate system were investigated.The experiment results showed that there are obvious differences between the flotation performance of hematite and quartz whether in the direct or reverse flotation system.The carbonate minerals(siderite and dolomite)could release certain amounts of ions in the slurry,and the dissolution species would adsorb on the surface of hematite and quartz,influencing the interactions between minerals and regents.In the direct flotation system(sodium oleate),dolomite and siderite could depress the hematite flotation and the depressing effects of dolomite were stronger than siderite;in the reverse flotation system(sodium oleate+CaCl2+starch),siderite could significantly inhibit the flotation of quartz,while the inhibition of dolomite was weaker.Hence,the "no-slime" coarse carbonate minerals could also lower the differences between hematite and quartz in flotability and lead to the separation difficulty,which is one of the main reasons resulting in the low flotation efficiency of carbonate-containing hematite ores.Since the grindings of finely disseminated iron ores are with the issues of high fine particle contents,the influence of fine particles on flotation rate and the "self-carrier"function between fine and coarse hematite particles in flotation were investigated.The experiment results demonstrated that the entrainment of fine hematite particles during the flotation process was obvious,and the flotation rate of coarse hematite could be decreased by fine hematite.The recovery of mixtures of fine and coarse hematite was related with the content of fine particles,and the highest flotation recovery was obtained when the fine and coarse hematite were approximately equal in mass,which might attribute to the interaction energies and aggregation tendencies between fine and coarse hematite particles were stronger than that among the fine hematite particles.Meanwhile,the aggregation would weaken when the coarse and fine hematite was mixed at extreme mass ratios of either too much coarse or too much fine hematite particles.Hence,fine hematite has a detrimental effect on the flotation of optimum size(coarse)hematite in most cases.On the issues of grindings of unevently disseminated iron ore are wide size fraction,the effects of particle size distribution on the separation performance between hematite and quartz were investigated in the direct flotation and reverse flotation system,respectively.The results showed that the mixture of coarse(or medium)hematite and quartz with narrow size fraction can be separated efficiently through direct flotation process,which was better than the whole size range mixtures of hematite and quartz.However,the separation efficiency of fine hematite and quartz mixture with narrow size fraction was lower.The reverse flotation results of mixture of hematite and quartz with narrow size fraction(whether coarse or fine particles)were better than that of the whole size range mixtures.Therefore,for mixtures of hematite and quartz,the flotation performance of narrow size fractions was better than the wide size fractions.Since the original and secondary slime in the flotation of carbonate-containing hematite ores would influence the separation performance,the coagulation mechanism and behaviors of fine hematite,siderite,and quartz particles in aqueous suspension were investigated.The results showed that the coagulations of hematite and siderite particles introduced by sodium oleate are obvious,while the sodium oleate cannot interact with the quartz surface and induce the coagulation.When the pH value ranged from 5.0-7.0,there are weak coagulation between hematite and quartz particles in the system of hematite-quartz mixture,the above aggregates could be broken by sodium oleate and new aggregates of hematite particles would generate with the introduced function of sodium oleate;however,for siderite-quartz mixture,the coagulation between siderite and quartz hardly exists and aggregates of siderite particles can be obtained in the presence of sodium oleate;at the same time,sodium oleate can enhance the coagulation between siderite and hematite particles for the system of hematite-siderite mixture.FBRM analysis and E-DVLO theory calculations showed that the hydrophobic forces between mineral surfaces treated by sodium oleate are the dominant force for the coagulation of siderite,hematite,siderite-hematite particles.The suspension of hematite-siderite-quartz mixture slurry can be promoted by citric acid,sodium carboxymethylcellulose(CMC),sodium hexametaphosphate,and the unselective coagulation between fine particles would be weakened.Finally,based on the above research,a classification-dispersion flotation method realized by controlling the particle size and dispersion(or coagulation)status was proposed.The concentrate of Donganshan iron ores with iron grade of 63.30%and iron recovery of 71.32%,and the concentrate of Donganshan mixed magnetic concentrate with iron grade of 66.24%and iron recovery of 79.47%can be obtained,respectively.Compared with the original processes,the recovery and grade of concentrate can be moderately improved through the classification-dispersion flotation method.