Study On Effect And Mechanism Of The Multivalent Metal Ions On Sodium Oleate Flotation Of Low Rank Coal

The metal ions in the slurry have various complex effects on the flotation of low rank coal,such as affecting the formation and stability of bubbles,the interaction between particles and bubbles,and the aggregation state of particles.The influence of metal ions on the interface properties of low rank coal particles and the adsorption behavior of collectors is not yet clear,especially the mechanism of metal ion synergistic polar collectors at the interface needs to be further studied.In view of this,this thesis studies the effects of three different metal ions(Ca²⁺,Al³⁺,Fe³⁺)on the flotation behavior of low rank coal with sodium oleate,and explores the influence of multivalent metal ions on the flotation behavior of sodium oleate.Through solution chemistry calculations of the metal ion-oleic acid system and characterization of its adsorption behavior on the surface of low rank coal,the activation/inhibition mechanism of metal ions on sodium oleate flotation of low rank coal was revealed.Using molecular simulation to study the complex interactions between the surface of low rank coal particles,ions,and oleic acid,the mechanism of the influence of multivalent metal ions on the flotation effect of polar collectors was clarified,providing reference for the control of low rank coal flotation interface and the practice of brine（seawater）flotation of low rank coal.The research conclusions of this article are as follows:The behavior of sodium oleate in the flotation of low rank coal was studied,and the influence of Ca²⁺,Al³⁺,Fe³⁺on the flotation of low rank coal with sodium oleate was found and summarized.For Shen Dong low rank coal,sodium oleate has better collection performance compared to traditional diesel,and sodium oleate has the best flotation effect in acidic environments（pH about 4）,superior to alkaline conditions;The research on flotation kinetics shows that the flotation behavior of sodium oleate is more in line with classical first-order kinetics.The effect of metal ions and their concentrations on the flotation of low rank coal with sodium oleate is as follows:at low concentrations（around 1 m M）,the addition of three metal ions has no significant effect on the flotation efficiency of low rank coal;When the concentration is about 1 m M,Ca²⁺,Al³⁺,and Fe³⁺all enhance the flotation process of low rank coal,resulting in a significant increase in clean coal yield and quality,and a faster flotation rate;At high salt ion concentrations（5 m M）,Al³⁺and Fe³⁺worsen the flotation effect of sodium oleate on low rank coal,while the effect of Ca²⁺is slightly weaker.The advantageous components of metal sodium oleate flotation solution were clarified,and the possible mechanisms of activation/inhibition of Ca²⁺,Al³⁺,Fe³⁺on sodium oleate flotation of low rank coal were elucidated.After mixing different metal ions with sodium oleate solution,corresponding metal oleate complexes can be spontaneously formed,and these complexes are all dominant components.As the ion concentration increases,the adsorption capacity of oleic acid complexes slightly increases in the presence of Ca²⁺.In the presence of Al³⁺and Fe³⁺,the adsorption capacity reaches its maximum at around 1 m M and then rapidly decreases.At high ion concentrations,the surface properties of low rank coal gradually tend to be positively charged,resulting in ineffective adsorption of oleic acid components and a sudden decrease in the yield of low rank coal.The addition of Ca²⁺,Al³⁺,and Fe³⁺all caused changes in the surface element content of low rank coal,resulting in adsorption on the surface of low rank coal and bonding with O in the oxygen-containing functional groups on the surface of low rank coal.As the concentration of metal ions increases,the possible mechanism of activation and inhibition in sodium oleate flotation of low rank coal is that the inhibitory effect of high concentration metal ions comes from the changes in surface properties of low rank coal caused by metal ions,which worsens the adsorption of positively charged metal oleic acid components;The activation effect of metal ions comes from the adsorption and modification effects of corresponding metal oleic acid complexes.Explored the adsorption mechanisms of metal ions and metal oleic acid complexes at the molecular scale,and revealed the mechanism of metal oleic acid complexes enhancing low order coal flotation.The ions with small ionic radius and high positive charge number have stronger interaction with water molecules,that is,the law of strength is Al³⁺>Fe³⁺>Ca²⁺.The adsorption of hydrated ions on low rank coal and the change of charge density on the surface of low rank coal model follow the same law.The metal oleic acid complex exhibits strong positive charge locally in space,which is advantageous for adsorption at oxygen containing sites in low rank coal compared to anionic oleic acid radicals.The adsorption strength law is Al≈Fe>Ca,and the oleic acid complex formed by trivalent metal ions has stronger adsorption effect.Moreover,as the number of ligands increases,the adsorption effect weakens and the modification effect is stronger.The molecular dynamics simulation results indicate that high valent metal ions forming oleic acid complexes can efficiently locate and adsorb at low rank coal hydrophilic water points,with their hydrophobic carbon chains extending outward and the adsorption configuration leaning towards"vertical"adsorption;At the same time,its diffusion ability on the surface of low rank coal also follows the principle that high valence（trivalent）metal ions are lower than low valence ions.The metal oleic acid complex has strong positional adsorption ability,effectively strengthening the flotation of low rank coal;The high valence of metal ions corresponds to higher adsorption energy,that is,the activation of Al³⁺and Fe³⁺is significantly stronger than that of Ca²⁺,and the influence of ionic radius is less than that of ionic valence.