Study On Hydration Film On Coal Surface And Interaction Force Between Particles Based On AFM

Fine coal has fine particle size and small mass, therefore in the flotation process whose collision probability with bubble is low, which resulting in low recovery capacity, and prone slime cover always affects clean coal quality in the fine coal flotation. To solve this problem in this paper an atomic force microscope(AFM) is used, starting from the basic theory of flotation, and the hydration film on the particle surface and the interaction force between particles are preliminarily studied, which is verified by the fine coal flotation test. The main contents and conclusions are as follows:In this thesis, AFM force curve function principle test for hydration film is explained; Calculation method of hydration film thickness on hydrophilic and hydrophobic mineral particles are proposed. The hydration film on the hydrophobic mineral like coal and hydrophilic mineral like mica are tested separately in the aqueous electrolyte solutions with different CaCl2 concentrations. The results shows that the hydration film on the hydrophobic mineral coal particle surface is thin, Electrolyte CaCl2 can be added to reduce the thickness of the film of hydration weakly; The hydration film on hydrophilic mineral mica particle surface is thicker, with increasing concentrations of CaCl2, the thickness of transition hydration film on mica surface remains unchanged, ordered layer of hydration film thickness keeps increasing, after 0.006mol/L it tends to remain unchanged.AFM was carried out for particles interaction force curve test in different conditions, the test results show that value of pH and electrolyte concentration are important factors affecting the interaction between the particles. Under acidic conditions, the mutual attraction exists between the coal particles, mutual exclusion exists between kaolinite particles, coal particles and kaolinite particles attracts to each other; Under neutral conditions, the mutual attraction exists between the coal particles, but weaker than acidic conditions, the mutual repulsion exists kaolinite particles, and stronger than acidic conditions, the attraction force between coal particles and kaolinite particles disappears and change to mutually exclusive; Under alkaline conditions, attraction force between coal particles disappears and tends to mutually exclusive, the mutually exclusive force between kaolinite particles is stronger than neutral conditions, the mutually exclusive force between kaolinite particles and coal particles is stronger than neutral conditions; CaCl2 added causes the particles attract each other and promote the aggregation of particles, and with increasing CaCl2 concentration, the interaction force between coal particles and between coal and kaolinite particles firstly increases then reduces and in the end keeps constant, and the interaction force between kaolinite particles would keep increasing, and finally tends to remain unchanged. The interaction between the particles is closely related to hydration film on particle surface, the hydration film would hinder close to each other particles, thinning hydration film will promote the mutual attraction force between particles.The effects of pH value of the pulp, Ca2+ concentration on fine coal flotation test results show that: under acidic conditions, recovery of combustibles of the slime and the ash content of clean coal have little change, in pH = 6 or so, recovery of combustibles reach the maximum value of 84.55%; in alkaline conditions, the recovery of combustibles and ash content of clean coal gradually decrease with the pH increase. This slime in neutral or weakly acidic conditions, less than 10% of qualified coal can be got, and also the recovery of combustible body can be ensured; Low ash coal can be obtained under alkaline conditions, but the yield is lower; Ca2+ concentration have great influences on the slime flotation index, after adding CaCl2, the yield and ash of clean coal are significantly increased. When adding 0.001mol/L CaCl2, a good indicator with the clean coal yield of 78.14% and the ash content of 9.96% is got, the coal yield has been improved on the premise of meeting the ash content of clean coal, strengthening the flotation process to a certain extent. After 0.005mol/L, the yield and ash of the clean coal change in the range gradually and finally tend unchanged. This is consistent with conclusions about interactions between particles measured in aqueous solutions of different pH and CaCl2 concentration, attraction between particles easily can improve the recovery of combustibles, while repulsion between particles can improve the clean coal quality.These conclusions above has important theoretical and practical significance to the optimizing flotation technology research,which improve the pulp solution environment, selectively thin or strengthen the hydration film on particle surface, selectively allow mutual aggregation or dispersion between mineral particles and improve mineralization effect and aim to strengthen the flotation process.