Surface Wettability Regulation Of Minerals In Flotation Of Calcium-magnesium Phosphate Ore

Apatite is a valuable mineral and carbonate minerals(dolomite and calcite)are the main gangue minerals in low and medium grade calcium magnesium phosphate ores.Flotation is the most effective technology to separate apatite and gangue.The wettability of mineral surface is the key factor to determine its floatability in flotation process.Because apatite,calcite and dolomite are all calcium bearing minerals,their crystal structure and surface physical and chemical properties are similar.The mutual interference in the flotation process leads to difficult flotation separation and complex wettability change mechanism.It is of great significance to further enrich and improve the basic theory of high-efficiency flotation separation of phosphate rock and promote the research and development of high-efficiency flotation separation technology for low-grade phosphate ore by strengthening the research on surface wettability regulation of three calcium bearing minerals in flotation system.In this paper,apatite,dolomite,and calcite are taken as the research objects.By means of contact angle test,pure mineral flotation,micro wetting heat and other analytical methods combined with density functional theory calculation and molecular dynamics simulation,the research idea is"surface property,interface regulation and solid-gas strengthening".Based on the analysis of mineral crystal structure and surface electronic properties,the natural wetting mechanism and hydration layer structures of three mineral surfaces were studied.The effects of roughness on mineral surface wettability and flotation characteristics,effects of flotation reagents on mineral surface wettability and selective flotation separation,characteristics of CO₂ microbubbles released by acidolysis of carbonate minerals and its promoting effect on particle bubble adhesion were studied.The micro mechanism of surface wettability of three minerals in the flotation system of calcium magnesium phosphate ore was revealed.The main conclusions are as follows.1.The main structure of phosphate rock is colloidal aphanitic structure,fine-grained sand chip structure,inclusion structure,fine-grained mesocrystalline structure,microcrystalline structure,etc.The main useful minerals are fluorapatite,the main gangue minerals are dolomite and quartz;phosphorus(P₂O₅)is mainly in the form of independent minerals in fluorapatite,the content is 26.64%,Mg O is mainly in dolomite as an independent mineral,the content is 4.06%.The particle size of fluorapatite is concentrated in the range of 0.01-0.2mm,accounting for 24.1%of the fine particle size of<0.07mm;the particle size of dolomite is between 0.01-0.15mm,and part of the particle size is over 50%in the range of microcrystalline powder crystal(<0.06mm).2.Apatite(001),calcite(104)and dolomite(104)planes are identified as stable cleavage planes by XRD analysis combined with surface fracture bond density and surface energy calculation,which have the smallest surface fracture bond density(19.26 nm^-2,10.00 nm^-2 and 10.81 nm^-2,respectively)and surface energy(1.02 J/m²,0.43 J/m² and 0.68 J/m²,respectively).The surface of the three minerals has a certain polarity,and the electronic properties of metal atoms are similar,but the distribution density of metal active sites on dolomite and calcite is higher than that of apatite.A single water molecule can be strongly adsorbed on the surface of these three minerals.O and H in water molecules interact with Ca or Mg and O on mineral surface respectively to form hydroxylated calcium or magnesium structure and hydrogen bonds with different strength.It is the nature of the three calcium bearing minerals showing natural hydrophilic properties.During the wetting process,apatite,calcite,and dolomite form 2-3 layers of water structure with higher water density than that of bulk phase.The hydration film with the highest density was formed at the distance of 2.625A,2.642Aand 2.473A,respectively.In which,the orientation of water molecules was highly ordered,and the corresponding hydration hydrogen bond density and adsorption energy of dolomite and calcite were higher than that of apatite.3.The effect of roughness on the surface wettability of apatite,calcite and dolomite accords with Wenzel and Cassie surface wetting theory.For the hydrophilic surface,the higher the roughness,the stronger the hydrophilicity;for the hydrophobic surface,the higher the roughness,the stronger the hydrophobicity.The surface roughness has amplification effect on the wettability of mineral surface,which is applicable to both natural mineral surface and the surface regulated by flotation agent.The coarse particles have higher flotation rate and recovery.At the same particle size,the surface roughness of rod milled particles is slightly higher than that of ball milling(about 5%),and the relative flotation rate is higher than that of ball milling.When the wettability of apatite and dolomite/calcite is different,the wettability difference between them can be enlarged by increasing the roughness of particles.4.Oleic acid,linoleic acid and linolenic acid can regulate the hydrophobicity of apatite surface,and the hydrophobic ability of linolenic acid>linoleic acid>oleic acid.The O in the polar group(carboxyl group)can form chemical adsorption with Ca site on apatite surface.In water system,sodium oleate(Na OL)polar group can overcome the effect of hydration layer on mineral surface and form stable adsorption with metal sites on mineral surface,which is the premise of realizing the control of mineral surface wettability.The Na OL monolayer adsorption structure on apatite(001)surface can form a good hydrophobic surface,while the bimolecular layer adsorption can form a hydrophilic surface.The hydrogen bond association between water molecules and Na OL polar groups is the hydrophilic nature of the double-layer adsorption surface.5.The selective regulation of the surface wettability of apatite and carbonate minerals by inhibitor acids is achieved by the interaction of collector adsorption,surface material composition change,particle dissolution roughness increases and CO₂ microbubbles.H₂PO₄^-is the location ion of apatite.In the process of acid reverse flotation of apatite and dolomite,the H₂PO₄^-dissolved on apatite surface or ionized by phosphoric acid can enter apatite's electric double layer by characteristic adsorption.Currently,H₂PO₄^-make the surface of apatite hydrophilic through hydrogen bonding with water molecules.As the amount of acid increases,the surface of apatite becomes more hydrophilic,while dolomite can maintain better hydrophobicity.The effect of acid dissolution on the mineral surface increases the particle roughness,further enhances the hydrophobicity of dolomite particles,and improves the flotation rate.At the same time,the surface of carbonate minerals in the acid pulp will dissolve and produce CO₂ microbubbles.The contact angle of CO₂ bubbles on the surface of hydrophilic particles is almost zero,which conforms to the"isonuclear growth model",and will break or leave the mineral surface after growing up.While on the hydrophobic surface after pre adsorption of collector,CO₂ bubbles have strong surface affinity and maintain large contact angle,and effective contact on the mineral surface during the growth process.Currently,the growth and accumulation of bubbles are conducive to the selective carrying of carbonate mineral particles to achieve pre floating.