Influence of polyaluminum chloride on the preparation of ultra clean coal by selective oil agglomeration

In order to explore the preparation conditions to produce ultra clean coal by selective oil agglomeration,Taixi anthracite was investigated in this study,including the properties of Taixi anthracite coal and the mineral types in coal. The selective oil agglomeration method was used to sort the ultrafine pulverized coal. The effect of the grinding time,kerosene dosage,2-octanol,polyaluminum chloride and aluminum chloride on the ash content and yield of clean coal were discussed. The effects of aluminum chloride,26% polyaluminum chloride and 29% polyaluminum chloride on the sort efficiency were compared. Zeta potentiometer was used to measure the zeta potential of coal samples with different dosages of polyaluminum chloride. The wettabilities of Taixi coal sample and artificial mineral surface at different dosa- ges of polyaluminum chloride were measured by optical contact angle meter. The interaction mechanism between poly- aluminum chloride and heterogeneous mineral particles in coal was revealed by DLVO theoretical calculation. The re- sults show that the ash content of ultra clean coal is 0. 64% and the yield of clean coal is 68. 91% when kerosene con- tent is 1. 19 kg / t,sec-octanol content is 0. 40 kg / t,polyaluminum chloride content is 50 g / t and grinding time is 30 min. At the same dosage a higher clean coal yield was achieved with polyaluminum chloride than that with aluminum chloride. Compared with the separation effect without polyaluminum chloride,the ash content of the clean coal decreases by 0. 18% ,and the clean coal yield increases by 19. 38% . When the dosage of polyaluminum chloride 26% and 29% is 50 g / t,the clean coal yield reaches the maximum of 68. 91% and 75. 00% respectively. The ash contents of clean coal are 0. 64% and 0. 71% respectively. The effect of demineralization with 26% polyaluminum chloride is better than that with 29% polyaluminum chloride. With the increase of polyaluminum chloride,the Zeta potential value of coal increased from -28. 7 mV to -20. 63 mV. The contact angle of coal increased with the addition of polyaluminum chloride,however, the contact angle of artificial minerals decreased. Due to the increase of hydrophobicity of coal and the hydrophilicity of artificial minerals,the difference of surface properties between them was increased. According to DLVO theory,the repul- sion between coal and montmorillonite particles is enhanced by polyaluminum chloride. On the one hand,the agglomera- tion of inorganic minerals in coal increases. On the other hand,the effect of inorganic minerals on the surface cover of coal particles and the entrainment of heterogeneous slime is reduced,resulting in the reduction of ash content in clean coal. Polyaluminum chloride and aluminum chloride can promote the removal of minerals from coal. At low dosage the separation effect is better with polyaluminum chloride than that with aluminum chloride.