| Zinc oxide ore is an important part of zinc resources. Smithsonite is a typical representative of zinc oxide ore. With an increasingly zinc demand, exploitation and utilization of zinc oxide ore has become inevitable. Smithsonite flotation theory has long been a significant research topic in China and other countries. Smithsonite flotation is a technique to recover zinc through sulphidization with amine or xanthate. As a result of two methods have their shortcomings, therefore, they are not widely used in industrial. Compared with sulphidization-amination flotation, the surface of sulfurized smithsonite requires more completely by sulphidization-xanthate flotation, but, the surface of sulfurized smithsonite is difficult. Therefore, how to effectively the surface of reinforced sulfurized smithsonite, stability of the surface of sulfurized smithsonite becomes the key by sulphidization-xanthate flotation. In view of the successful application of ammonium salt in the oxide copper flotation, ammonium salt is used to reinforce the sulphidizing flotation of smithsonite for the first time in this study. Therefore, the reinforcing effect of ammonium salts on sulphidization requires further investigation.This paper focuses on the study of smithsonite. First, the equilibrium in the chemical reaction between zinc ion and sulfide ion is explored, and the dominant component and distribution of the two types of ion under different pH values are ascertained. Ammonium salt is used to reinforce the sulphidizing flotation of smithsonite for the first time and a good flotation effect is achieved. The samples from the reinforced sulfurized smithsonite are examined via surface analysis through the application of SEM-EDS and XPS. The electronic structure, surface atom, Mulliken population of bonds, and other features of smithsonite are examined through density functional theory (DFT) calculation. Considering the features of the surface atomic structure of smithsonite, we conduct an in-depth study on the mechanism of sulphidization effect of S2- and HS- on smithsonite as well as the reinforced sulphidization effect of ammonium salts on smithsonite through DFT calculation to consolidate the theoretical foundation of the sulphidization mechanism for smithsonite. Finally, we explore the mutual effect of sulfurized smithsonite or reinforced sulfurized smithsonite with sodium isoamylxanthate (IX) through DFT calculation. The results confirm the absorptive effect of the surface of sulfurized smithsonite and reinforced sulfurized smithsonite with IX, on the basis of which a reinforced sulphidizing flotation model is proposed for smithsonite.The existence of form of zinc ion and sulfide ion in the sulfurized smithsonite slurry solution and theirs dominant component depend on the pH value. The suitable pH value for smithsonite flotation is 10-12. Most of the S exists in the form of HS-and some in S2-. The smithsonite will be partially hydroxylated when the pH value ranges from 10 to 12. The zinc in the solution mainly exists in the form of Zn(OH)2, and a small amount in the form of Zn2+, Zn(OH)+, and Zn(OH)3-.Findings from the ammonium salt-based reinforced sulfidization-flotation experiment show that ammonium salt can facilitate the flotation of smithsonite, increasing the floatation recovery by 15 to 25 percentage points. Ammonium chloride exhibits the most ideal effect, followed by ammonium nitrate, ammonium sulfate, and ammonium bicarbonate. The dynamic tracking test of sulfide ion indicates that smithsonite may increase the consumption of sulfide ion. However, ammonium salt may result in rapid consumption of sulfide ion when the system is composed of smithsonite, ammonium salt, and sodium sulfide. The smithsonite solubility test in different conditions indicates that the concentration of zinc ion in the ammonium salt solution nearly doubling that in pure water. When smithsonite is affected by sodium sulfide, the concentration of zinc ion in the solution is lower by one order of magnitude than that in the pure water. When smithsonite is affected by both ammonium salt and sodium sulfide, the concentration of zinc ion in the solution is lower by two orders of magnitude than that in the pure water and lower by one order of magnitude than that in the sodium sulfide solution. The result indicates that the solubility of surface of reinforced sulfurized smithsonite decreased significantly.EDS-based semi-quantitative analysis shows that the concentration of sulfur on the surface of sulfurized and reinforced sulfurized smithsonite is 2.0% and 8.55%, respectivel y.The S content on the mineral surface increases after reinforced sulfurized. The XPS-based analysis of the substances on the smithsonite surface after sulfidization and reinforced sulfidization show that S2- are found on the sulfurized smithsonite surface and reinforced sulfurized smithsonite surface.The area ratio and atomic concentration ratio of sulfur on the surface of reinforced sulfurized smithsonite is 8.99% and 9.12%,respectively.The area ratio and atomic concentration ratio of sulfur on the surface of sulfurized smithsonite is 4.72% and 5.84%,respectively. Smithsonite is easier to be sulfurized by sodium sulfide under the effect of ammonium ion.Research on electronic structure and surface atomic configuration shows that an ideal smithsonite possesses a wide band gap insulator.Smithsonite has a calculated value of 3.529 eV, and its crystal surface is not electrically conductive.The electronic configurationof the optimized zinc atom in the smithsonite is zn 3p0.563d9.994s0.23,and the charge on the zinc atom is+1.22 e.This optimized zinc atom is an electron donor. The electronic configuration of the optimized carbon atom is c 2s0.922p2.44, and the charge on the carbon atom is +0.64 e.The optimized carbon atom is an electron donor. The electronic configuration of the optimized oxygen atom is o 2s1.802p4.82,and the charge on the oxygen atom is -0.62 e.This atom is an electron acceptor.Ionic and covalent bonds co-exist in the smithsonite crystal.Strong mutual effects occur between carbon and oxygen.The DFT calculation of the absorption of sulfur ion,hydrogen sulfide ion and ammonium and sulfide ions on the smithsonite surface indicates that sulfur can be absorbed to the zinc atom on the smithsonite surface,but not to carbon or oxygen atom.However,the absorption of sulfur to the zinc atom is weak.The absorption of hydrogen sulfide ion on the smithsonite surface is stronger than that of sulfur.The absorption of ammonium and sulfide ions on the smithsonite surface is strongest than that of sulfur and hydrogen sulfide ion.The DFT calculation of the mutual effect of IX and sulfurized smithsonite or reinforced sulfurized smithsonite shows that IX can adhere to the non-sulfurized smithsonite surface and the absorption is quite weak.IX can also be absorbed on the surfaces of sulfurized smithsonite and reinforced sulfurized smithsonite. The reinforced sulfurized smithsonite shows the highest absorption strength, followed by hydrogen sulfide radical-based sulfurized smithsonite and direct sulfurized smithsonite. This result indicates that the collection of reinforced sulfurized smithsonite is easier by IX.The findings of this study develop and improve the basic theory forthe sulphidizing flotation and reinforced sulphidizing flotation of smithsonite. The results also reflect a thorough grasp of the essential distinction between sulphidization and reinforced sulphidization of smithsonite as well as their significance and practical value to the flotation of smithsonite. |
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