Flotation Performance And Adsorption Mechanism Of Oxadiazole-Thione Compounds On Copper Minerals

The molecular structure of oxadiazole-thione compounds contains S and N atoms with strong coordination abilities.The conjugated system of this structure enhances the binding ability of these compounds with metal ions that have empty electron orbitals,thus it can form complex compounds with copper ions.In addition,di-minerophilic molecules are widely used in flotation due to their unique hydrophobic mineral active groups and adsorption abilities.In this article,oxadiazole-thione compounds containing xanthate or dithiocarbamate groups were designed and synthesized as flotation collectors.The flotation separation performances and adsorption mechanisms on chalcopyrite or malachite were investigated.Sodium xanthate and sodium dithiocarbamate were synthesized using alkyl alcohols and alkyl amines as raw materials,respectively.And then it reacted with methyl chloroacetate to obtain the corresponding ester compounds.Using the purified ester compounds,hydrazine hydrate,inorganic alkaline,and carbon disulfide as raw materials to synthesize the oxadiazole-thione compounds containing esterified xanthate or dithiocarbamate groups in one-pot method,including 5-isobutylmethylxanthate-1,3,4-oxadiazole-2-thione（MIXODT）,5-hexylmethyl dithiocarbamate-1,3,4-oxadiazole-2-thione（MHCODT）,5-diethyldithiocarbamate-1,3,4-oxadiazole-2-thione（MDCODT）and 5-octyldithiocarbamate-1,3,4-oxadiazole-2-thione（MOCODT）.The structures of all purified products were determined by nuclear magnetic resonance hydrogen and carbon spectroscopy.MIXODT was used as a flotation collector for chalcopyrite,and its flotation separation behavior and selective adsorption mechanism on the surface of chalcopyrite and galena were studied.Under the conditions of the concentration of 1.0×10^-5 mol·L^-1and p H value of 8.0,MIXODT with a di-minerophilic structure showed better flotation separation effects than 5-heptyl-1,3,4-oxadiazole-2-thione（Hp ODT）,and the flotation recovery of chalcopyrite could achieve 95.4%.Furthermore,compared with traditional flotation processes requiring toxic inhibitors,MIXODT had better flotation selectivity for chalcopyrite and might become an efficient copper-lead selective flotation collector,as well as effectively reducing the use of inhibitors.The adsorption of MIXODT on the surface of chalcopyrite conformed to the pseudo-second-order kinetic equation and Langmuir adsorption model,and it was a spontaneous exothermic and entropy-driven chemical adsorption process.The enthalpy change（ΔH）,entropy change（ΔS）,Gibbs free energy（ΔG）,and activation energy（ΔE）of this process are 56.74 k J·mol^-1,274.70J·mol^-1·K^-1,-23.02 k J·mol^-1（298.15 K）,and 58.68 k J·mol^-1,respectively.Contact angle experiments showed that the hydrophobicity of chalcopyrite surfaces significantly increased after treated with MIXODT under alkaline conditions,but the hydrophilicity of galena did not change significantly,which provided good conditions for the flotation separation of chalcopyrite and galena.Zeta potential results showed that MIXODT could overcome electrostatic repulsion and chemically adsorb on the surface of chalcopyrite.UV spectroscopy showed that MIXODT generated a significant chemical reaction with Cu⁺and Cu²⁺,producing a large number of complex precipitates,while the reaction with Pb²⁺,Fe²⁺,and Fe³⁺was weak.Solid UV spectroscopy showed that MIXODT could chemically adsorb on the surface of chalcopyrite,while there is no significant reaction or surface adsorption phenomenon between MIXODT and galena.Electrochemical experiments showed that MIXODT formed a dense adsorption layer on the surface of chalcopyrite and changed the electrochemical properties.FTIR and XPS showed that MIXODT chemically adsorbed on the surface of chalcopyrite by forming Cu-S and Cu-N bonds,accompanied by partial reduction of Cu（II）to Cu（I）.Finally,DFT calculations compared the reactivity of MIXODT and Hp ODT.That found that MIXODT had a stronger affinity for chalcopyrite.Further research found that the xanthate and oxadiazole-thione groups in MIXODT were both active centers of the reaction,and Cu on the surface of chalcopyrite formed MIXODT-Cu complexes with S and N atoms in MIXODT.MHCODT was further synthesized and used as a flotation collector for malachite from quartz and calcite.In micro-flotation experiments,the effect of stirring time,slurry p H,and collector concentration on the flotation results was investigated.Under the conditions of stirring time of 15 min,p H of 8.1 and concentration of 1.5×10^-4 mol·L^-1,MHCODT achieved better malachite flotation results than octyl hydroxamate（OHA）,with a recovery of 90.5%,while the recovery of quartz and calcite was less than 15.1%.Therefore,MHCODT was expected to be an effective copper-silicon/calcium selective flotation collector.Contact angle experiments showed that the hydrophobicity of malachite surfaces significantly increased after treated with MHCODT under micro-alkaline conditions,but the hydrophilicity of quartz and calcite changed slightly,providing good conditions for the flotation separation of malachite from quartz and calcite.Zeta potential results showed that MHCODT chemically adsorbs on the surface of malachite by overcoming surface electrostatic repulsion.UV spectroscopy showed that MHCODT generated a significant chemical reaction with Cu⁺and Cu²⁺,forming a large number of flocculent precipitates,but almost no reaction occurs with Ca²⁺.Solid UV spectroscopy showed that MHCODT could chemically adsorb on the surface of malachite,while there was no significant reaction and surface adsorption phenomenon between MHCODT and quartz or calcite.FTIR and XPS results showed that MHCODT chemically adsorbed on the surface of turquoise by forming Cu-S and Cu-N bonds with Cu,accompanied by the reduction of Cu（II）to Cu（I）.Finally,DFT calculations found that the dithiocarbamate and oxadiazole-thione groups in MHCODT were active centers of the reaction.Cu on the surface of malachite formed MHCODT-Cu complexes with S and N atoms in MHCODT.