| Molybdenite is one of the most important sulfide molybdenum ore,because over 99%of the production of metal molybdenum is from molybdenite mineral.Molybdenite shows comprehensive paragenesis with other minerals,especially with copper mineral generating porphyry copper mine owning the most commercial value.It is difficult to separate molybdenite from chalcopyrite and the recovery of molybdenum is not high enough in copper recovery precessing because of the similar floatability of molybdenite and chalcopyrite and the fine disseminated grain size of molybdenite.Bulk copper-molybdenum flotation followed by copper-molybdenum separation is the widely used,so the depression effect of chalcopyrite depressant is vitally important to copper-molybdenum separation.Chalcopyrite is a typical sulfide mineral,and its flotation theory research has always been a hot spot in local and international area.The existing research are mostly focusing on collectors of chalcopyrite,and reports about depression theory is very rare.Moreover,routine tests and analysis methods are considerably limited because of the complicated adsorption mechanism between depressants and mineral surface,so there are many deficiencies about atomic configuration of chalcopyrite surface,electron transision of depressant-mineral adsorption.Therefore,it is important and valuable in atomoc scale and based on quantum chemistry theory to research the mechanism between depressans of different structures and chalcopyrite.Based on widely reviewing relevant references,2,3-disulfanylbutanedioic acid(DMSA),mercaptosuccinic acid(TMA),3-mercaptopropionic acid(MPA),cysteine(CYS)and chitosan(CTS)were chosen to test their depression effect in single mineral,mixed mineral and molybdenum bearing copper concentrate flotation,respectively,and the flotation results were also compared with what using sodium sulfide.Based on the flotation results,Zeta potential,adsorption density,IR,ToF-SIMS,etc.were applied to study the adsorption michenism between depressants and chalcopyrite surface.Depression parameter of depressants were calculated and compared for auxiliary analysis.Eletron structure of chalcopyrite crystal,property of relaxation surface,electron transision during coordination reaction were investigated using DFT theory to verify more detail michenism.The flotation results showed that DMSA,TMA,MPA,CYS and CTS exhibit strong depression effect on chalcopyrite,while very weak effect on molybdenite.Compared with sodium sulfide,the dosage of the five depressants are only from 1/62 to 1/8 of sodium sulfide at the analogous depression effect point.Zeta portential results show that DMSA,TMA,MPA and CYS adsorped on chalcopyrite surface via chemical and electrostatic adsorption,but on molybdenite surface only via electrostatic adsorption.CTS adsorption was found on both chalcopyrite and molybdenite via chemical and electrostatic adsorption,and the adsorption strength of CTS on chalcopyrite was stronger than that on molybdenite what was also poved by ToF-SIMS test.Adsorption density results showed that the adsorption amount of the four sulfydryl style depressants on chalcopyrite were more than that on molybdenite,obviously.CTS showed nearly the same affinity to both chalcopyrite and molybdenite,while the collector preadsorption hindered the CTS adsorbing on molybdenite which inceased the selectivity.IR analysis illustrated that CTS adsorbed on chalcopyrite via both amine Ⅲ(N-H)and protonated amino group(NH2+),while on molybdenite simply via amine Ⅲ.Depression performance index(DPI)results showed that introducing the second thiol group or a site amino group substitution increased the eletronegativity,i and dipole moment what enhanced the depression property of DMSA and CYS.The theoretical results showed that the frontier orbital was not change when the second thiol group was introduced,but the two thiol groups can generate chelation reaction with metal ions increasing reaction energy.The a site amino group substitution hindered the carboxyl group drawing electron from thiol group,meantime,deduced the LUMO energy,band gap AE3 of CYS,which enhanced its activity.Mulliken charge analysis illustrated S of thiol group and N of amino group trainsferred electron to Cu2+ and Fe2+ generating coordinate bond.Charge migration decomposition analysis showed that Cu2+ and Fe2+ also transferred charge to S and N via feedback bond,and charge feedback ability order was Fe2+>Cu2+.The Generation of feedback bond reduced the reaction energy,which was adverse for depressants.The calculation results of chalcopyrite crystal property showed that the band gap of chalcopyrite was 0.3 eV indicating it was type p semiconductor.The spin direction of atoms Fe in neighboring layers were different,and their spin density of states were not symmetrical causing weak magnetic property left in chalcopyrite.Surface reconstitution was found on relaxtion(0 0 1)surface of chalcopyrite.The neighbouring S atoms in the first layer of the S-(0 0 1)surface produced disulphur dipolymer by compearing between every two S atoms.Rich sulphur surface M-(001)was formed through that the metal atoms in the first layer sank down while the atom S in the second layer ascended.The theoretical results showed that the four sulfydryl style and one azyl type depressants adsorped on chalcopyrite surface via atom S and N,respectively.The two S atoms in DMSA reactived with Cu and Fe atoms in chalcopyrite surface via bridge site adsorption,while the one S or N atom in TMA,MPA,CYS and CTS via top site adsorption.N of amino groups and S of thiol groups in depressant transferred p electrons to Cu or Fe via coordinate bond,meanwhile,metal atoms transferred partial electrons to atom S or N generating feedback bond.The coordinate bond or feedback bond eletrons prefer to transfer to the orbital s of receptor.Five depressants were chosed to study comparatively the effect of strcture on the depression and michenism using flotation separation,adsorption density,Zeta portential,IR,ToF-SIMS and DFT theory.Neodoxy,that dithiol chelation and α site amino group substitutionin depressan molecule could improve the depression effect,and that feedback bond was disadvantageous for reaction between depressant and metal ions was found. |
