Research On The Effect And Regulation Of Solution Chemical Characteristics On The Mineralization Behavior Between Low Rank Coal And Oily Bubble

Low rank coal has high oxygen content,poor hydrophobicity,developed pores,and is easily muddied by water,which results in lower attachment efficiency and higher reagent consumption in conventional flotation,so it is difficult to be industrialized.Aiming at the problem of low rank coal flotation,oily bubbles flotation technology was adopted to improve the mineralization efficiency of low-rank coal,and the effect of solution chemical characteristics on the mineralization process has attracted the attention of the peer experts.Therefore,Sheng 6 lignite was taken as research object in this paper,starting from the aspect of thermodynamics and taking the surface hydration of low rank coal,the mineralized adhesion energy barrier and the induction time analysis between low rank coal and oily bubbles as principal line,the effect of solution chemical characteristics?pH,ionic species and ion concentration?on the surface properties of low rank coal and oil bubbles and the mineralization process were studied,additionally,oily bubble flotation tests were conducted to verify the effects.Based on these studies,the solution chemical characteristics of flotation were optimized and regulated to improve the effect of low rank coal flotation.The dry base ash content of Sheng 6 lignite used in this paper was 20.35%,which belongs to medium ash.The particle size was fine and easy to slime,and the content of the dominant grade was 53.46%,the oxygen content of the coal sample was high,which was mainly composed with ether and hydroxyl group;and the content was 18.72%.The main mineral impurities in coal sample were quartz,followed by clay minerals,including kaolinite,chlorite,and perlite.Judging by the result of floatation speed test,the natural floatability of coal sample was poor and belongs to the most difficult floating slime.The degree of hydration of coal in different solution chemical environments were calculated by the formula of hydration degree based on Einstein viscosity theory.The results indicated that the hydration of coal surface increased with the increase of pH and decreased with the addition of electrolyte.Moreover,the higher the cation valence state was,the smaller the hydration degree was,and at the same electrolyte concentration?20mmol/L?,the decreasing degree of electrolytes on the surface hydration of coal was:AlCl₃>CaCl₂>NaCl.With the surface potential as the breakthrough point,the influence of solution chemical characteristics on the interaction energy between coal particles and oil bubbles was calculated by DLVO theory.The results indicated that the negative charge of coal surface was stronger than that of the oily bubble,the negative values of surface potential of coal particles and oil bubbles both increased with the increase of pH,and the energy barrier between coal particles and oil bubbles increased as well.On the contrary,both the negative values of surface potential and the interaction energy barrier could be reduced with the addition of electrolyte,and the higher the cation valence state was,the shorter the adsorption equilibrium time was,the stronger the adsorption capacity was,the greater the degree of compressing the electrical double layer was and the smaller the mineralization adhesion barrier was.At the same ion concentration?20 mmol/L?,the energy barrier in the AlCl₃ solution was the smallest,which was 0.037×10^-16J.The results of the induction time showed that the decrease of pH and the increase of NaCl and CaCl₂ concentration could both shorten the induction time.However,with the increase of concentration of AlCl₃,the induction time decreased first and then increased,when the concentration of AlCl₃ electrolyte exceeded 10 mmol/L,the induction time was the lowest,which was 8 ms.The oily bubble flotation results indicated that the change regulation of combustible recovery was basically consistent with regulation of the hydration degree,the interaction potential energy and the induction time varied with the solution chemical characteristics.Based on this,response surface method was used to optimize and regulate the solution environment.The optimal solution conditions for oil bubble flotation were:solution pH of 6,Na⁺concentration of 80 mmol/L,and Ca²⁺concentration of 61.26 mmol/L,and the combustible recovery could reach 59.19%.