Research On Particle Size Effect And Interface Interaction In Low Rank Coal Reverse Flotation

Coal is one kind of important energy.Low rank coal occupies an important position in China's reserved coal resources.With the increasing scarcity of coking coal resources in the world,it is of great significance to improve the utilization rate of low rank coal.The existing methods of improving the utilization of fine low rank coal basically are enhanced flotation,among which there are a lot of problems,such as high consumption of collector,low separation efficiency,etc.It is urgent to look for new technology to separate low rank coal.In this study,reverse flotation was used to separate low rank coal to reduce the ash content and improve the quality,which could transform the disadvantage of low rank coal into advantage.The particle size effect in subbituminous coal reverse flotation was explored.The action mechanism of reagents on the mineral particle surface was studied.The selective flocculation-reverse flotation method for low rank coal deashing was proposed.Firstly,the surface physical and chemical properties of low rank coal(subbituminous coal)were studied using XPS,FTIR,SEM,etc.The results showed that content of water and surface oxygen functional groups of subbituminous coal were very high.The presence of these hydrophilic functional groups would reduce the hydrophobicity of subbituminous coal.The space structure of subbituminous coal was very loose and there are also some holes and ravins,which will result in high porosity and large specific surface area,and increase the flotation difficulty.At the same time,it was found that the isoelectric point of subbituminous coal(pH 3)was close to that of silica(pH 2)and kaolinite(pH 1.8),the main gangue minerals in coal sample.So when the cationic ammonium salt Lilaflot D817 M was used as collector,the addition of depressant is very necessary.The comparison of traditional flotation and reverse flotation result of subbituminous coal showed that when subbituminous coal was separated by traditional flotation method,the consumption of reagent was high and the flotation efficiency was poor.In the conditional optimization experiment of subbituminous coal reverse flotation,clean coal product with 8.23% ash content could be obtained under appropriate condions when the dosage of collector Lilaflot D817 M was 2kg/t.The combustible matter recovery was 86.87%,and the separation efficiency was 71.45%.Therefore,better separation could be gained by using reverse flotation than forward flotation with lower dosage collector.The particle size effect was explored from three perspectives.It was found that only when artificial feed is composed with coarse or medium-size coal and fine quartz,good reverse flotation performance could be obtained.The results showed that the reaction effect of-74 +53?m coal particles on dextrin was the best,and-104 +74?m gangue minerals have the best flotation performance.And also,the presence of ultrafine coal particles reduced the flotation rate and recovery of silica,deteriorating the reverse flotation separation efficiency.Total Organic Carbon analyzer(TOC)was used to measure the total amount of carbon/nitrogen in the reagent solution before and after adsorption to calculate the adsorption amount of mineral.Subbituminous coal could adsorb more dextrin than silica.During the Zeta potential analysis test,it was found that the isoelectric point of quartz and subbituminous coal increased after adsorbing dextrin.The wettability change rule of minerlas before and after adsorbing reagents was measured using Washburn dynamic method.It was found that dextrin could enhance the hydrophilicity of subbituminous coal but weaken the hydrophilicity of silica slightly.During the adsorption process of ammonium salt,subbituminous coal could adsorb much more ammonium salt than silica.The cationic ammonium salt Lilaflot D817 M could significantly change the electrical properties of subbituminous coal and quartz surface,making their isoelectric point increase significantly.Ammonium salt Lilaflot D817 M of same concentration could significantly enhance the hydrophobicity of silica but only slightly enhanced the surface hydrophobicity of subbituminous coal,indicating that there is no direct relation between the adsorption amount and the surface wettability change degree.In order to solve the problem that ultra-fine coal could affect the separation efficiency of reverse flotation,selective flocculation-reverse flotation was proposed.PAM could increase the apparent particle size of both subbituminous coal and silica.Subbituminous coal flocs are much larger.However,during the adsorption process on PAM,the adsorption amount of silica is larger than that of subbituminous coal.PAM could enhace the hydrophilicity of the subbituminous coal but weaken the hydrophilicity of silica.After adsorbing PAM,the functional groups on mineral surface have changed.In the selective flocculation-reverse flotation test,appropriate dose of PAM and stiring speed is very necessary.When PAM dosage is 50g/t,clean coal product with 12.50% could be abtained.It is 1.6% lower than routine reverse flotation,and the separation efficiency increased from 58.39% to 66.07%.