Correlation Of Surface Oxidation Of Galena,Chalcopyrite And Pyrite With Their Floatability

Throughout the whole flotation process,sulfide minerals are always exposed to water and dissolved oxygen,and only the oxidized surfaces are the real surfaces of sulfide minerals.The surface oxidation is the key factor to influence sulfide mineral floatability.However,the surface oxidation was usually ignored in the flotation fundamental research and theoretical calculation.Notably,there is lack of clear understanding on the correlation of surface oxidation of sulfide minerals with flotation reagents adsorption and their floatability.In this work,by employing the analytical methods of solution chemistry and surface chemistry,under flotation solution environment especially at high alkaline and high calcium medium,we focused on studying the surface oxidation products of galena,chalcopyrite and pyrite and the adsorption of surface oxidation species and flotation reagents on their surfaces.The interaction mechanism of flotation reagents and the fresh and oxidized surfaces was studied in depth,and the relationship between surface oxidation and floatability was established.This work provide reference for further understanding flotation process,regulating flotation behavior of sulfide minerals and developing new technology of effective flotation separation process.The main work and results are summarized as follows:(1)The mechanism of flotation separation of galena and pyrite in high alkaline lime systems was clarified in terms of“adsorption”and“oxidation" The in-situ contact angle and single mineral microflotation tests indicated that sodium diethyl dithiocarbamate(DDTC)collector only worked for galena,but not for pyrite.Ion chromatography(IC)and high-performance liquid chromatography(HPLC)tests showed that the main sulfur oxidation product of galena was sulfur oxyanions(SxOyn-)rather than element sulfur(S0)at pH 12.5.Surface chemistry analysis by time-of-flight secondary ion mass spectrometry(Tof-SIMS)confirmed at pH 12.5,the accumulative normalized intensities of DDTC on galena surface was 3.9 times than that on pyrite surface,while the accumulative normalized intensities of calcium hydroxyl species(CaOH+)on pyrite surface was 3.7 times than that on galena surface.This agreed with the results of in-situ atomic force microscopy imaging and density-functional theory(DFT)calculation.In high alkaline lime systems,the merit floatability of galena could exclude the insignificant contribution of S·.The efficient flotation separation of galena and pyrite in high alkaline lime systems was due to the competitive adsorption of CaOH+ and DDTC.This chapter claried the understanding of the separation mechanism of galena and pyrite in high alkaline systems and the hydrophobic contribution of S0 to galena.(2)In flotation fundamental research,the reactive oxygen species(ROS)during pyrite oxidation is always ignored.The degree of pyrite oxidation was evaluated by the amounts of occurring sulfur species,and pyrite oxidation kinetics in alkaline medium was studied by IC and HPLC.In alkaline solution,we found pyrite oxidation rate increased with pH and the oxidation rate at pH 12.5 was 17.6 times that that at pH 4.5.Meanwhile,ROS produced during pyrite oxidation was investigated by electron paramagnetic resonance(EPR)and it showed that pH influenced the structure of ROS.Combined with electrochemical characterization,pyrite oxidation in alkaline medium still followed the electrochemical mechanism based on the "thiosulfate pathway".This chapter provide new insight on understanding the correlation of pyrite oxidation and floatability and floation solution chemistry.(3)Based on the understanding of pyrite oxidation in alkaline medium,we investigated the influence mechanism of surface oxidation on pyrite flotation.The sulfur oxidation of different degrees of pyrite oxidation was studied by IC/HPLC and the results indicated as the oxidation degree increased,the amounts of sulfoxy species increased and the S0 ratio decreased.X-ray photoelectron spectroscopy(XPS)showedthe surface products were FeOOH and SO42-after sufficient surface oxidation of pyrite.Tof-SIMS tests confirmed that xanthate adsorption had strong selcectivity on FeS2 rather than FeOOH.The computational models of self-consistent-charge density functional tight binding(SCC-DFTB)were established according to the XPS evidence of the surface oxidation species.The SCC-DFTB calculations indicated that xanthate adsorbed on FeS2 but not on FeOOH and Fe2O3,In terms of the coordination chemisty theory,the different electron configurations of Fe led to the selective adsorption of xanthate on FeOOH/Fe2O3 and FeS2.This chapter established an evaluation method including "oxidation law,experimental evidence and computational model".(4)Based on the correlation between the surface oxidation of sulfide minerals and floatability,the effect of surface oxidation degrees of chalcopyrite and galena and medium(Ca and Na system)was studied to provide reference for developing new technology of copper-lead separation.Under high-alkaline Ca(OH)2 systems,the main products of the oxidized chalcopyrite surface were SO32-,SO42-,CuO,Cu(OH)2 and FeOOH,CaOH+ adsorbed preferably on the oxidized chalcopyrite surface and promoted the DX adsorption on chalcopyrite,therefore suppressing chalcopyrite,while galena still flotated well.The separation selectivity of lead and copper was 1.8.Under high-alkaline NaOH systems,the fresh surfaces of chalcopyrite and galena could maintain good floatability,and the DX selectively adsorbed on the fresh surface of galena,therefore suppressing galena.The separation selectivity of copper and lead was 2.6.Under strong H2SO4 systems,the main sulfur species of strongly oxidized chalcopyrite surface was hydrophobic S0 while that of the oxidized galena surface was PbSO4,thus achieving "galena suppression and chalcopyrite flotation".