Study On Attachment Between Coal And Oily Bubbles And The Thinning Characteristics Of Wetting Film Under Various Solution Chemistry Conditions

The flotation of low rank coal is a major technical problem that must be faced and urgently needed to be solved in the field of coal preparation.It is of great theoretical and practical significance to explore the influence of solution chemical environment?p H,ion type and concentration?on flotation.The coal sample used in this paper is Shendong non-stick coal.The content of oxygen-containing functional groups in the coal sample is high,and the dry ash-free oxygen content(O_daf)is as high as 24.55%.Therefore,in view of the rich characteristics of oxygen-containing functional groups on the surface of low-rank coal,this paper starts with surface reactivity and solution chemistry,and analyzes the occurrence of oxygen-containing functional groups and mineral impurities on the surface of low-rank coal by means of XRD,XPS,and FT-IR form.By measuring the Zeta potential of coal particles-oily bubbles,and the induction time of coal particles measured in different solution environments,using the EDLVO theory and Stefan-Reynolds liquid film thinning equation to fit the relationship between the coal particle-oily bubble hydrophobic constant(K₁₃₂)under different solution conditions,and high-speed camera technology is used to observe the process of collision,sliding,adhesion and desorption of low-order coal particles on the surface of the oily bubble,at the same time,the micro-force balance is used to measure the desorption force of the coal sample-oily bubble,and the oily bubble slip angular velocity is calculated.Therefore,the adhesion mineralization and desorption behavior in the flotation process are explored,which provides a theoretical basis for improving the mineralization efficiency and flotation effect of low rank coal.Flotation solution chemistry research shows that the p H value of the solution and Na⁺,Ca²⁺have an important influence on the flotation effect.When p H=2,the recovery rate of combustibles in coal samples is as high as 81.70%.With the increase of p H,the induction time continues to increase,the recovery rate of combustibles decreases,and the ash content of clean coal also decreases.When the p H of the solution is 12,the recovery rate of combustibles is only 17.03%.For ionic solutions,as the Na⁺and Ca²⁺concentrations continue to increase,the induction time decreases,the combustible body recovery rate also increases,and the ash content of clean coal also increases with the increase in ion concentration.Under the same ion concentration condition,the recovery rate and ash content of the combustible body of clean coal after flotation in Ca Cl₂ solution are higher than those in Na Cl solution.The EDLVO theory and Stefan-Reynolds equation were used to analyze and fit the hydrophobic force constant(K₁₃₂)between oily bubble and coal particle under different solution conditions.Studies have shown that as the Na⁺and Ca²⁺concentrations increase,their hydrophobic constants continue to increase.Because as the ion concentration increases,the surface potential between the coal particle and the oily bubbles decreases,the electrostatic potential energy decreases accordingly,and the hydrophobic force increases.The adsorption of Ca²⁺on the surface of coal particle is stronger than that of Na⁺,so the surface potential of coal particles in Ca Cl₂ solution is lower,so the hydrophobic force between coal particles and oily bubbles in Ca²⁺solution is higher than that in Na⁺solution at the same concentration.As the p H increases,its hydrophobic force constant becomes smaller.As the p H increases,its hydrophobic force constant becomes smaller.When the solution is under acidic conditions,the lower the p H,the greater the H⁺concentration,the more H⁺is adsorbed on the surface of the coal particle,the lower the negative charge of the coal sample surface,the smaller the electrostatic repulsion,and the greater the hydrophobic force.When the solution is alkaline,the greater the p H,the more OH^-ions in the solution,the more negatively charged particles on the surface of the low-rank coal particles,which reduces the hydrophobic surface of the coal particles and weakens the hydrophobicity of the coal particles.Using the high-speed dynamic analysis system to study the dynamic process of adhesion between coal particles and oily bubbles shows that as the p H increases,the slip angular velocity decreases continuously.For Na⁺and Ca²⁺ionic solutions,when the concentration of Na Cl and Ca Cl₂ solution increases,the average sliding angular velocity of particles increases,and the sliding velocity of particles in Ca Cl₂ solution is larger than that in Na Cl,but the change range is generally consistent.As the ion concentration increases or the p H decreases,the average sliding angular velocity of coal particles gradually increases.Increasing the sliding angular velocity will increase the particles'ability to overcome the centrifugal force when sliding on the surface of the oily bubble,thereby increasing the probability of coal adhesion on the surface of the oily bubble.The study on the desorption process of coal and oily bubbles by high-speed camera and micro force balance shows that when the ion concentration is greater than10 mmol/L,as the concentration of Na⁺and Ca²⁺ions increases,the desorption force between coal sample and oily bubble increases continuously.But at the same concentration,the desorption force between coal sample and oily bubble is greater than that of Na⁺solution in Ca²⁺solution.As the initial concentration of ions increases,the adsorption of Na⁺and Ca²⁺ions by coal samples and oily bubbles reduces the surface potential.The lower the electrostatic repulsion between coal particles and oil bubbles,the greater the hydrophobic attraction and the greater the desorption force required;In addition,the valence state of Ca²⁺ions is smaller than that of Na⁺.The radius of Ca²⁺ions is smaller.The distance between Ca²⁺ions and coal samples is closer than that of Na⁺.Therefore,the adsorption capacity of coal samples for Ca²⁺is stronger than that for Na⁺.The desorption force between coal sample and oily bubble in the solution is greater.With the continuous increase of p H,the desorption force between coal sample and oily bubble decreases rapidly,and the desorption force in alkaline solution tends to 0,and when p H=2,the desorption force of coal sample and oily bubble is 0.05579 m N.In an acidic solution,as the p H decreases,the absolute value of the negative potential on the surface of the coal particles is smaller,the electrostatic repulsion between the coal particles and the oily bubbles decreases,and the hydrophobic attraction increases,so the adhesion between the coal sample and oily bubble is greater.When the solution is alkaline,the greater the p H,the more OH^-ions in the solution,the more negatively charged particles on the surface of the low-order coal particles,the electrostatic repulsion between the coal sample and the oily bubbles gradually increases,and the hydrophobic attraction becomes smaller.The adhesion between the coal sample and the oily bubble becomes smaller,so in alkaline solution,the particles are prone to desorption on the surface of the oily bubble.