Experimental Research Of Low Rank Coal Flotation Based On The Magnetized Effects

With the increasing shortage of high quality coal resources in China,low rank coal resources with abundant reserves are becoming the focus of development and utilization,and low rank coal flotation is one of the key points of research.The low rank coal has weak hydrophobicity and poor floatability due to the abundant presence of oxygencontaining functional groups on the surface,which results in a low flotation efficency.Therefore,a novel method is urgently required to enhance low rank coal flotation.In this paper,Jiaya coal slime from a low rank coal preparation plant of Shenhua Shendong was studied.The fundmental properties of coal sample are comprehensively analyzed.Then,the magnetization technology was applied to improve the low rank coal flotation.The effects of magnetized water and magnetized reagents on low rank coal flotation were deeply explored.The ash content of coal sample used in this study 34.59 % and the dominant particle size is-0.045 mm fraction with the yield of 35.86 %.There is a large content in 1.6-1.8 g/cm3 density fraction.The main gangue minerals in coal sample are quartz and kaolinite.In addition,a large amount of oxygen-containing functional groups such as C-O,C=O and O=C-O are presented on coal surface.The coal sample has developed surface porosity with the specific surface area of 13.37 m2/g and the pore volume of 0.025 cm3/g.So,a high consumption of flotation reagent is required during the flotation process.The effects of magnetic pretreatment of water used in flotation tests on low rank coal flotation was investigated.The results showed that with the increase of magnetized time and magnetic field intensity,the ash content of clean coal barely changed,but the combustible recovery increased by approximately 7 %.The rate constant of the flotation test was improved after the magnetization pretreatment of water,and the flotation rate constant when using magnetized water was 0.08 min-1 higher than that of using untreated water.The properties of the water after magnetization pretreatment were analyzed.The results showed that the p H value increased by 0.31 and the interfacial tension reduced by 4 m N/m after the water was magnetized.The effects of magnetic pretreatment of flotation reagents on low rank coal flotation were investigated.The results indicated that the combustible recovery increased by 9.22 % and 4.51 % respectively after the diesel oil and 2-octanol was subject to magnetic pretreatment,but the ash content of clean coal remained almost unchanged.The combustible recovery increased by 9.62 % both using magnetized diesel oil and magnetized 2-octanol.The basic properties of magnetized reagents were analyzed.The results showed that the interfacial tension and viscosity of diesel decreased by 0.97 m N/m and 0.32 m Pa·s respectively and the interfacial tension of 2-octanol decreased by 0.42 m N/m after magnetic pretreatment.This is due to the fact that when the fluid is placed in the magnetic field,its intermolecular force will be weakened by the magnetic field,leading to the change of its basic properties,such as interfacial tension and viscosity.After conditioning with magnetized diesel oil,the contact angle of coal sample increased by 6 degrees and the surface roughness of coal particles was reduced.The interfacial tension of the pulp decreased by 4.56 m N/m and 7.28 m N/m respectively after conditioning with magnetized diesel oil and magnetized 2-octanol.The effects of magnetized water and magnetized reagents on the flotation of low rank coal pure minerals(coal and gangue)were explored.The results demonstrated that the recovery of coal and gangue increased by 8.43% and 3.69% respectively when using magnetized water in flotation.The use of magnetized diesel oil in flotation could increase the coal recovery coal by 9.13 %,and could increase the gangue recovery by 4.33 %.The Zeta potential of coal and gangue decreased by 3.70 m V and 2.34 m V,respectively after the water was pretreated at the magnetic field intensity of 0.15 T for 20 min.The effects of magnetized water and magnetized collector on the mixture of coal and gangue flotation were also investigated.The results showed that the combustible recovery of clean coal increased by 5.96 % and 5.69 % respectively after the water and diesel oil was subject to magnetic pretreatment.However,the concentrate ash did not change significantly under different test conditions.Therefore,the magnetization pretreatment of floatation water and collector only improved the yield of clean coal but has little effect on the selectivity of flotation.