| China is abundant in tungsten resources and has already been ranked the first in tungsten metal production for many years in the world.Scheelite is one of the main exploitable tungsten minerals,and flotation is the most widely used method for its beneficiation.However,scheelite can be easily over-ground due to its fragile property.Additionally,the surfaces of scheelite;as well as its associating minerals such as calcite and fluorite are inevitably contaminated by cast-iron media in grinding.Furthermore,scheelite,calcite,and fluorite are known to have similar floatability,and it is therefore difficult to achieve high flotation separation efficiency when using water glass alone as depressant.Overall,flotation separation of scheelite from calcite and fluorite remains one of the great challenges in mineral processing.In industrial applications,the flotation recovery of scheelite is merely 60-85%,which significantly limits the efficient and comprehensive utilization of scheelite.Hence,this research aimed at improving the floatability of calcium-bearing minerals and enhancing the flotation separation of scheelite from calcite and fluorite via grinding media and metal ion assistant depressants.The main research focus and conclusions of the paper are as follows:(1)Effects and mechanisms of grinding media on the flotation behavior of calcium-bearing minerals.The floatability sequence of scheelite,calcite,and fluorite at four different sizes was+38-75?m>+75-106?m>+15-38?m>-15?m.When the fine particles(-15?m)were mixed with the coarse ones(+38-75?m,+75-106?m,+15-38?m),the fine particles would seriously deteriorate the flotation slurry and reduce the flotation recovery.When the fine and coarse particles were floated separately,the flotation recovery could be improved significantly by increasing the collector concentration of fine particles flotation.When the calcium-bearing minerals were ground by cast-iron media,the zeta potential measurements,SEM-EDS,and XPS analysis indicated that the elemental iron(Fe),ferrous oxide(Fe O),and iron oxyhydroxide(Fe OOH)could adhere to the surfaces of calcium-bearing minerals,which hindered the adsorption of collector sodium oleate.Therefore,the flotation recoveries of calcium-bearing minerals ground by cast-iron media were lower than those ground by ceramic media.Additionally,the DO and ICP-AES tests proved that Fe ions existed in the flotation slurry of calcium-bearing minerals ground by cast-iron media,and the dissolved oxygen contents and Ca ions of the slurry decreased and increased,respectively.(2)Effects and mechanisms of metal ion assistant depressants on the flotation behavior of calcium-bearing minerals.The depression sequence of water glass on scheelite,calcite,and fluorite flotation was fluorite>calcite>scheelite.The zeta potential measurements,FTIR and XPS analysis indicated that water glass could react with the Ca active sites on the surfaces of calcium-bearing minerals to generate calcium silicate,which hindered the adsorption of sodium oleate on their surfaces,and therefore the flotation of calcium-bearing minerals was depressed.When the lead ions were mixed with water glass,there was solid phase generated in the Pb-water glass system.The XRD and FTIR tests indicated that the solid phase was the mixture of lead silicate glasses.The single mineral flotation results showed that the solid phase in the Pb-water glass did not affect the flotation of scheelite,calcite,and fluorite;While the liquid phase in the Pb-water glass could enhance the depression effects of water glass on calcite and fluorite flotation,and slightly activate scheelite flotation.When the zinc ions were mixed with water glass,there was no solid phase generated in the Zn-water glass system.The single mineral flotation results showed that the Zn-water glass had inconspicuous effects on scheelite flotation and strong depression effects on calcite flotation,but relatively weak depression effects on fluorite flotation.However,using the combination of water glass and Zn-water glass as depressant could achieve efficient depression effects on calcite and fluorite flotation,with little depression effects on scheelite flotation.The zeta potential measurements indicated that using the liquid phase in the Pb-water glass or water glass+Zn-water glass as depressant,the negatively charged species in the depressant could significantly adsorb on the surfaces of calcite and fluorite which hindered the subsequent adsorption of collector sodium oleate.While the negatively charged species in the depressant were hardly adsorbed on the scheelite surfaces,sodium oleate could adsorb on its surfaces.The flotation solution chemistry calculations and XPS analysis further indicated that the generated metal-silicate polymers and Si(OH)4 enhanced the depression effects on calcite flotation,while water glass and its hydrolysis components(Si O(OH)3-,Si O2(OH)22-)enhanced the depression effects on fluorite flotation.Under the conditions of p H 10.0,sodium oleate concentration1.0×10-4 mol/L,using water glass(300 mg/L),Pb-water glass(400 mg/L,mass ratio of water glass to lead nitrate 7:1),and water glass(300 mg/L)+Zn-water glass(100 mg/L,mass ratio of water glass to zinc sulfate heptahydrate 3:1)as depressants,respectively,the WO3 grades of flotation concentrates were 43.18%,66.57%,and 60.31%,respectively;and the WO3recoveries were 73.40%,77.70%,and 74.96%,respectively,after flotation separation of artificially mixed minerals.(3)Batch flotation experiments.Batch flotation experiments of scheelite ore in Jiangxi Province suggested that using ceramic media in grinding,separately floating coarse(+15?m)and fine(-15?m)particles,increasing the collector dosage of fine particles flotation,and choosing Pb-water glass or Zn-water glass in cleaning as depressants could effectively improve the flotation index.Under the optimal conditions of sodium carbonate dosage 1500 g/t,water glass dosage4500 g/t,and sodium oleate dosage 500 g/t,using cast-iron and ceramic media as grinding media in parallel,the WO3 grades of roughing concentrates were 3.04%and 3.22%,respectively,and the WO3 recoveries were 88.99%and 90.39%,respectively.When the coarse and fine particles were floated separately,under the conditions of sodium oleate dosage 500 g/t in coarse flotation and 750 g/t in fine flotation,the calculated WO3 grade and recovery of roughing concentrates were 3.35%and 90.38%,respectively.When water glass was used as depressant in roughing,water glass,Pb-water glass,and Zn-water glass were used as depressants,respectively,in cleaning one,after one-roughing,two-scavenging,and two-cleaning,the WO3 grades of concentrates were 3.77%,4.15%,and3.89%,respectively,and the WO3 recoveries were 92.74%,93.78%,and 93.30%,respectively.This research has experimentally studied the flotation separation of scheelite from calcite and fluorite with a focus on the grinding media and metal ion assistant depressants,which contributed to the comprehensive utilization of tungsten resources.Simultaneously,the outcome of this thesis enriched the theoretical system of scheelite flotation,and provided a valuable reference for flotation separation of scheelite from calcium-bearing gangue minerals. |
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