Effect Of Surface Stability On Floatability Of Medium And Low-grade Phosphate Ore

It is very difficult to separate apatite and dolomite in calc-magnesia phosphate ore by flotation because of their similar physical and chemical properties on the surface.Depressant is the key to realize the separation of the two minerals.Under the action of inhibitors,the surface stability of calcium-bearing minerals deteriorates and their physiochemical properties are complex,which has an important influence on flotation separation.In this study,the effects of inorganic depressants（hydrochloric acid,sulfuric acid,phosphoric acid,sodium tripolyphosphate）and organic depressants（citric acid,hydroxyethyl bisphosphonic acid（HEDP））on the flotation behavior of minerals were investigated through single mineral flotation test and artificial mixed ore flotation test.On this basis,the flotation research of calcium magnesium phosphate ore was carried out.The influence of surface stability on the floatability of apatite and dolomite under the action of depressant was analyzed by contact Angle test,Zeta potential test,adsorption capacity test,surface dissolution test combined with photoelectron spectroscopy（XPS）,solution chemical analysis,infrared spectroscopy and atomic force microscopy（AFM）micro-nano morphology observation.The main results are as follows:After the action of sodium oleate,the floatability of apatite and dolomite is enhanced,but the floatability is close to that of sodium oleate.Only the addition of sodium oleate cannot achieve the effective separation of the two minerals,so it is necessary to add depressants in the flotation process.Several depressants promoted the separation effect of apatite and dolomite in the order of HEDP>phosphoric acid>sulfuric acid>hydrochloric acid>citric acid,and sodium tripolyphosphate had no selective inhibition effect.In the range of flotation size,the floatability of apatite and dolomite decreases with the decrease of flotation size.The flotation test of calcium-magnesium phosphate ore indicates that HEDP can cooperate with phosphoric acid to remove magnesium and extract phosphorus.When the dosage of phosphoric acid and HEDP is 5.5 kg/t and 1.5 kg/t,respectively,A phosphorus concentrate with P₂O₅ content of 30.70%,P₂O₅recovery of 88.41%and Mg O content of 1.35%was obtained with 750g/t GJBW.Sulfuric acid,phosphoric acid,hydrochloric acid,citric acid and HEDP can obviously improve the hydrophilicity of the surface of apatite,but the influence of these depressants on the hydrophobicity of the surface of dolomite is relatively weak,and the surface of dolomite still maintains a strong hydrophobicity.Under weak acidic conditions,sulfuric acid and phosphoric acid generate Ca SO₄,Ca HPO₄ and Ca（H₂PO₄）₂on the surface of apatite,respectively,which hinder the adsorption of collector on the surface of apatite,leading to the hydrophilic surface of apatite.The metal active sites on mineral surface determine the adsorption effect of collector.Citric acid reduces the number of active calcium sites on the surface of the mineral through the synergistic effect of adsorption and dissolution on apatite and dolomite.Due to the low solubility of apatite,there is little change in the surface-active sites of calcium.Citric acid adsorbed on the surface of apatite,occupying the metal active sites on the surface of apatite,leading to the difficulty of collecting agent adsorption on the surface of apatite,resulting in hydrophilic surface of apatite.However,dolomite has a higher solubility,a large number of calcium sites on the surface are reduced,and calcium ions consume a large amount of citric acid.However,due to the large calcium density on the surface of dolomite,there are still many active sites on the surface of dolomite,so the collector can be adsorbed on the surface of dolomite,and the dolomite shows hydrophobicity.HEDP chelates with calcium active metal sites on the surface of apatite through two phosphonic groups to form ring chelates,which affect the stability of mineral surface.In addition,hydrogen bonding forces enhance the force between HEDP and apatite surface.These two effects prevent the adsorption of collector and make the surface of apatite show hydrophilic.However,HEDP only has weak hydrogen bonding on the surface of dolomite,so the collector can be adsorbed on the surface of dolomite,leading to better floatability of dolomite.In conclusion,under the action of depressants,the surface stability of apatite and dolomite deteriorates and the surface properties change,resulting in differential adsorption of collectors on mineral surfaces.Inorganic depressants affect surface hydrophobicity mainly through surface transformation.On the surface of apatite,dissolved ions react with inorganic depressants to generate precipitates,which cover the active sites on the surface of apatite and affect the adsorption of collectors,thus making the surface of apatite hydrophilic.The action mode of organic depressants affecting mineral surface stability is related to depressants.Citric acid makes it difficult for collector to adsorb on apatite surface through surface dissolution and adsorption,resulting in hydrophilic apatite surface.HEDP is chemically adsorbed on the surface of apatite,which affects the surface stability and leads to more hydrophilic surface of apatite.