Solid-Liquid Interface Characteristics Of Collophanite And Dolomite In Phosphate Flotation System

The flotation method is usually used to separate collophanite and dolomite.However,due to the similar physical and chemical properties of the surface of collophanite and dolomite in the flotation system of phosphate rock,it is difficult to separate the two.Flotation is mainly based on the wettability difference of mineral-water interface to achieve mineral separation.The degree of hydration on the surface of mineral particles directly affects the hydrophilicity/hydrophobicity of mineral surface,while the hydration film formed by hydration affects the adsorption of reagent molecules on mineral surface.Therefore,studying the hydration properties of the interface between collophanite and dolomite and regulating its hydration characteristics provide some theoretical guidance for realizing the effective separation of collophanite and dolomite and promoting the selective recovery of medium and low grade phosphate ore.In this paper,a phosphate rock in Guizhou was taken as the research object.Through single mineral flotation test,contact angle test,microcalorimetry test and infrared spectroscopy test,the natural wettability of collophanite and dolomite and the effects of sulfuric acid and sodium oleate on the floatability and wettability of collophanite and dolomite were investigated.The effects of sulfuric acid and fatty acid collectors on the separation of collophanite and gangue minerals were studied by flotation test of calc-magnesian phosphate rock.The thickness of hydration film on the surface of collophanite and dolomite was characterized in situ by atomic force microscopy（AFM）.Based on density functional theory and molecular dynamics simulation（MDS）,the interfacial hydration characteristics of fluorapatite and dolomite were studied.The surface hydration mechanism of collophanite and dolomite was explored from micro-nano scale and atomic and molecular level,and the influence and regulation mechanism of flotation reagents on the interfacial hydration characteristics of collophanite and dolomite were revealed.The main results are as follows:The floating rate of collophanite and dolomite increases with the increase of sodium oleate dosage.When the dosage of sodium oleate is 150 mg/L,collophanite and dolomite have good floatability.When the dosage is more than 150 mg/L,the floating rate of collophanite decreases.After adding sulfuric acid,the floating rate of collophanite decreases,and the floating rate of dolomite remains basically unchanged.Sulfuric acid has a good inhibitory effect on collophanite.When the dosage of GJBW is 700 g/t and the dosage of sulfuric acid is 16 kg/t,a better flotation index can be obtained.The content of P₂O₅ in the phosphate concentrate is 35.15%,the content of Mg O in the concentrate is 0.86%,and the recovery rate of P₂O₅ in the concentrate is 91.01%.The impurities in the calcium magnesium phosphate ore are effectively removed.The moist heat of water and collophanite and dolomite is negative.It is said that the surface of gelatin phosphate rock and dolomite is hydrophilic,and water molecules can spontaneously adsorb on the surface of collophanite and dolomite,resulting in surface hydration.When only sodium oleate acts,sodium oleate will adsorb on the surface of phosphate rock and dolomite to enhance its hydrophobicity.When sulfuric acid and sodium oleate act together,the hydrophilicity of phosphate rock is enhanced by sulfuric acid,and the hydrophobicity of dolomite is enhanced by sodium oleate.Sulfuric acid and sodium oleate can change the wettability of phosphate rock and dolomite and affect their surface hydration.In the aqueous solution system,there is a transition layer between the surface of collophanite and dolomite and water,namely the hydration film.The thickness of hydration film at the interface of collophanite and dolomite in pure water measured by AFM is 9.18 nm and 9.76 nm,respectively,and the difference between the two hydration films is small.In sodium oleate solution,the thickness of hydration film at the interface between collophanite and dolomite is 8.46 nm and 6.98 nm,respectively.In sulfuric acid solution,the thickness of hydration film at the interface between collophanite and dolomite is 9.68 nm and 9.16 nm,respectively.Sodium oleate will weaken the hydration of the surface of collophanite and dolomite,and sulfuric acid slightly strengthens the hydration of the surface of collophanite.In the sulfuric acid and sodium oleate solution system,the thickness of the hydration film at the interface of collophanite and dolomite is 9.87 nm and 6.61 nm,respectively.Under the combined action of the two agents,the hydration film on the surface of collophanite is slightly increased compared with that in the aqueous solution,indicating that the interaction between sulfuric acid and collophanite will hinder the action of sodium oleate.The thickness of the hydration film on the surface of dolomite is close to that of sodium oleate alone,indicating that the interaction between sodium oleate and dolomite is not affected by sulfuric acid.Water molecules form stable adsorption on the surface of fluorapatite and dolomite.O（H₂O）interacts with Ca/Mg sites on the surface to form weak chemical adsorption,and H（H₂O）interacts with O（Surface）to form hydrogen bonds.MDS results show that hydration film can be formed on the surface of both collophanite and dolomite.The relative concentration distribution analysis shows that the hydration film structure on the surface of collophanite and dolomite is divided into ordered layer,transition layer and bulk water.The concentration of water molecules in the ordered layer is larger and the arrangement is more order and dense.The results of MDS analysis show that the thickness of the hydration film on the surface of fluorapatite and dolomite is 0.56 nm and 0.67 nm,respectively.The thickness of the hydration film at the interface between collophanite and dolomite is close to that of AFM test results.The hydrophilic group of oleic acid ion can easily overcome the interfacial hydration of fluorapatite and dolomite,and interact with the Ca/Mg site on the surface of the mineral.The hydrophobic group of oleic acid ion is upward,and the surface of fluorapatite and dolomite will not form a hydration film after adsorbing oleic acid ion.Sodium oleate can greatly weaken the hydration of mineral surface.After SO₄^2-interacts with the Ca site on the surface of fluorapatite,a very small number of oleic acid ions form co-adsorption with SO₄^2-at the surface Ca site.SO₄^2-will occupy the defect vacancies generated by the dissolution of CO₃^2-on the surface of dolomite,and then interact with the Ca site.Oleate ions mainly interact with the exposed Mg sites,and there is also a phenomenon of co-adsorption with SO₄^2-.When sulfuric acid and sodium oleate coexist,a hydration film is formed on the surface of fluorapatite,and an oleic acid ion adsorption layer is formed on the surface of dolomite.The combined action of the two agents can selectively regulate the hydration film on the surface of the particles,resulting in a decrease in the floatability and hydrophobicity of collophanite and an increase in the floatability and hydrophobicity of dolomite.