Study On Liberation Law And Flotation Process Of Coking Coal Middlings

The clean coal,containing low ash separated from coking middlings and made full use of it for smelting coke reasonably,is not only conducive to protect the scarce coal resources in China,but also to promote the development of the national economy.Paper on the basis of "different interface separation methods adapt to different particle size",through the conventional flotation and selective flocculation flotation to deal with products of coking middlings after grinding,the re-separation tests were conducted.The screening test showed that the ash content changes a little with the particle size.The coal quality is relatively uniform with average ash content 27.30%.The Gr.I of-3mm coking middlings is just 18.00%,which can not be used without separation.Both of them mean that it has the necessity for re-separation.The float and sink test illustrated that the cumulative rate of +1.40-1.80g/cm~3 density level production is as high as 81.79%,indicating the relationship of mineral and organic components is close.Only through the crush-grinding can achieve effective separation.The mineral characteristics of-3mm coking middlings shows that the main mineral in coking coal is kaolinite,which is secondedly by pyrite,quartz and calcite,etc.Most of clay minerals are disseminated distribution within the cell cavity and matrix at the size of 4 m,which is difficult to achieve full dissociation.Grinding tests illustrated: When grinding time is less than 5min,coarse grinding efficiency is higher,-0.074 mm fraction content has reached 84.59%.When the grinding time increased to 30 min,fine-grinding efficiency is higher,the ground products surpass 96.00% has entered into-0.038 mm fraction,and-0.010 mm fraction content has reached 81.85%.With the increase of grinding time,the ash content in-0.038 mm and-0.010 mm fraction reduced firstly and increased secondly.When grinding time is 2min,both of them reached the minimum values,organic components in coal liberate prioritedly at this time.The float and sink test of grinding productions with liberation degree at-0.074mm54.66%(corresponding to grinding 2min)and-0.010mm86.81%(corresponding to grinding 40min)shows that although the fine particle content increased significantly with the increase of grinding time,but they have the same tendency in washbability curve.Under the provisions of 12.00% in ash content,the increase in separation density just raised 0.033g/cm~3,while its washability property still keeps at extremely difficult separation.The analysis of SEM-EDS test for grinding productions with liberation degree at-0.074mm54.66% and-0.010mm86.81% shows: Clay mineral and organic components still coexist at the way of “locked” particle in +0.2mm fraction,while there are many single particles of coal or rock mineral in-0.010 mm fraction at the dissociation degree of-0.074mm54.66%.When the degree of dissociation is-0.010mm86.81%,the particle size of the fine particles is mostly in the presence of agglomerated particles of 50 m.After ultrasonic dispersion,it can be observed that the mineral particles are completely dissociated from the organic constituent.Contact angle tests indicated the angle of grinding productions increases until dissociation degree of-0.074mm67.32%(corresponding to grinding 3min)reaching its maximum at 83.1°,the hydrophobic on the particles surface is improved.When dissociation degree overpasses-0.010mm81.85%,the contact angle is relatively low and the fluctuation is unconspicuous owing to the attached mineral particles on coal particle surface.Conventional flotation tests indicated: through rough-flotation,even if at the collector 100g/t and frother 50g/t,it still can not obtain the qualified clean coal due to the fine coal pollution.When the-0.074 mm fraction content is 32%-40%,the collectorless flotation process can be used.But due to its inadequate dissociation,the recovery rate is less than 14.00%.The optimal liberation degree for conventional flotation is-0.074mm54.66~67.32%.When the liberation degree is-0.074mm54.66%,through coarse-and-cleaning flotation,the qualified coal with the yield between 35% and 38% can be obtained.Selective flocculation flotation test results illustrated that flocculant and dispersant are both advantageous to the separation,and the flocculant is superior to the dispersant.The liberation degree of-0.010mm81.85~86.81% is suitable for selective flocculation flotation.The clean coal with yield 43.44%,ash 11.93% can be recycled at the liberation degree of-0.010mm86.81%(quantity efficiency at 85.09%).Coarse-grinding and coarse-cleaning flotation process to deal with coking middles,not only has higher separation quality efficiency,but also can greatly reduce the energy consumption of grinding and flotation reagents consumption,at the same time can avoid the froth breaking and weaken the subsequent filtration dehydration interference problem.Test results show that the coarse-grinding and coarse-cleaning flotation process is most appropriate way to recycle coking coal.