Study On The Depressive Mechanism Of Metal Citric Acid Complexes On Calcium Gangue Minerals During Scheelite Flotation

Scheelite and calcium gangue minerals such as fluorite and calcite have similar surface-active sites,and have similar surface chemistry and solution chemistry property in slurry environment.They are difficult to separate from each other.Traditional sodium silicate and phosphate inorganic depressants have great disadvantages,such as large consumption of reagents,high energy consumption,low flotation separation efficiency,and difficult tailings treatment.Macromolecular organic depressants such as polysaccharides,celluloses,and natural vegetable gums face the disadvantages of poor selectivity and poor solubility.Therefore,the research of small molecule organic depressants such as citric acid（CA or H₃L）,oxalic acid and tartaric acid has been paid more and more attention.Monocarboxylic acid lactic acid and dicarboxylic acid tartaric acid and oxalic acid have limited hydrophilic functional groups,and their inhibitory ability and ability to coordinate with metal ions are limited.This paper studied the effect of mixed depressants of metal ions and citric acid in the flotation separation of scheelite from fluorite and calcite.The effects of different combinations of metal ions and tricarboxylic acid citric acid,different dosing sequences,and different ratios of mixed depressant on the flotation performance of three minerals were studied.The best combination of metal ion with citric acid,dosing sequence and reagent ratios were selected.A series of mechanism experiments such as mineral surface wettability analysis,zeta potential analysis,infrared spectroscopy analysis（FTIR）,UV spectrophotometer,thermodynamic calculations,solution chemical analysis,X-ray photoelectron spectroscopy（XPS）analysis and atomic force microscopy（AFM）revealed the different selective adsorption mechanisms of the mixed depressant on the surface of the three minerals.Through the characterization of a series of properties of metal complexes in solution,the form and mode of reaction of metal complexes adsorbed on mineral surfaces by the mixed depressant of metal ions and citric acid were proved.Finally,a theoretical system of selective inhibition of calcium-containing gangue minerals by metal ion-organic complexes in scheelite flotation was established.Finally,according to the technological mineralogical characteristics and ore sample properties of scheelite in the flotation tailings of a copper-zinc polymetallic ore in Yunnan,an appropriate flotation reagent system and separation process were selected.The main research contents and results are as follows:（1）Single mineral experiments showed that scheelite,fluorite and calcite all had strong floatability under the NaOL system,and the flotation separation of minerals was difficult.The depressive order of citric acid on the three minerals was fluorite>calcite>scheelite,and the depression of CA on calcite was not good,the recovery of calcite could still reach 55%.The four metal ions Fe³⁺,Al³⁺,Cu²⁺and Ca²⁺lacked selectivity for the inhibition of the three minerals.The mixed depressant of Fe³⁺/CA and Cu²⁺/CA can realize the flotation separation of scheelite from fluorite and fluorite.The best combination of flotation reagent was the mixed depressant of Fe³⁺/CA,and adding Fe³⁺first and then adding CA was better than adding CA first and mixed dosing,and the molar ratio of Fe³⁺to CA was1:5,and the recovery of the three minerals were 81.05%,13.05%and8.95%,respectively.（2）The mechanism experiment of the adsorption of depressant on the mineral surface showed that the difficulty order of CA to produce the hydrophilic product Ca L^-on the surface of the three minerals was fluorite>calcite>scheelite.The mixed depressant of Fe³⁺/CA had a strong chemical co-adsorption on the surface of fluorite and calcite,which can reduce the zeta potential of the surface and enhance the wettability of the surface of fluorite and calcite.The order of CA’s ability to dissolve calcium ions on the surface of the three minerals was fluorite>calcite>scheelite.The reduction of calcium ion active sites on the surface of scheelite was the least,which was most conducive to the adsorption of the collector NaOL.Fe³⁺and CA promoted each other’s adsorption on the surface of fluorite and calcite,and produced a strong selective depression effect on the two gangue minerals of fluorite and calcite.Fe³⁺was mainly adsorbed on the surface of fluorite and calcite in the form of hydroxyl compounds,and CA was mainly adsorbed on the surface of fluorite and calcite that has adsorbed Fe³⁺species.The order of concentration of metal complexes in the slurry is Fe L>Fe OHL^->Fe HL⁺,and the order of adsorption strength of the complexes on the mineral surface is calcite>fluorite>scheelite.（3）UV spectrophotometer and potentiometric titration analysis proved the existence of metal ions organic complexes in the solution,and solution chemistry calculations proved that the order of the conditional stability constants of calcium ions organic complexes was Ca L^->Ca HL>Ca H₂L⁺,and the stable order of iron ion organic complex was Fe L>Fe HL⁺.The main forms of organic complexes of metal ions generated in the slurry solution are Ca L^-and Fe L,iron ion organic complexes Fe L were more stable than calcium ions organic complexes Ca L^-in the solution.Thermodynamic calculations showed that the iron ion organic complexes（Fe L,Fe HL⁺）and calcium ion organic complexes（Ca L^-,Ca HL,Ca H₂L⁺）solution could be generated autonomously in the mixed depressant,and the iron ion organic complexes,especially Fe L,were more easily generated.In different ratios of Fe³⁺and CA mixed depressant solutions,when pH=9.5,the concentration order of the the complexes was Fe L>Fe OHL^->Fe HL⁺,and the complexes mainly existed in the form of Fe L and Fe OHL^-.Atomic force microscopy（AFM）proved that the mixed depressant Fe³⁺/CA had a relatively small change to the adsorption morphology and roughness of the scheelite surface,and it was adsorbed significantly on the surface of fluorite and calcite,forming a sheet-like dense adsorption layer.The height of the adsorption layer was significantly increased,and the surface roughness was also significantly larger on the surface of fluorite and calcite.（4）According to the property of the flotation tailings of a copper-zinc polymetallic mine in Yunnan,and the WO₃ grade of the raw ore is 0.15%.The adjusting reagents were sodium hydroxide（NaOH）and sodium carbonate（Na₂CO₃）（800+1000 g/t）,and the collector was 733（300 g/t）,and the depressants were selected as the mixed depressant Fe³⁺/CA（60+360 g/t）.The final test index obtained by the open circuit test of scheelite normal temperature flotation was that the WO₃ grade in the obtained scheelite crude concentrate was 5.17%,and the WO₃ recovery was 58.25%.The closed-circuit test of the whole process adopted a process of one rougher,three cleaners and two scavengers,and the WO₃ content in the coarse tungsten concentrate was 4.02%,and the WO₃ recovery was82.41%,and a good test index could be obtained.