Mechanism And Technology Of Ammonia-ammonium Dissolution-activation Flotation In Oxygen-sulfur Mixed Zinc Ore

The reserves of mixed zinc ore containing oxidized minerals and sulfide minerals is very abundant in Yunnan province.Due to its low grade,fine embedding,mixed oxidized-sulfide minerals and large slime content,it is difficult to recover by either a single beneficiation method or a single metallurgical method.It has become a"Key&Core"technical problem for the comprehensive utilization of mixed zinc ore.Especially for the low-grade high calcium magnesium bearing refractory mixed zinc ore with zinc grade less than 10%,due to the lack of novel comprehensive recovery technology,it can onl y be stockpiled.Yunnan Lanping lead-zinc mining company has stockpiled more than 40 million tons,and its efficient development and utilization is imminent.According to the physical characteristics of mixed zinc ore,new mechanism,new process and new technology of combined beneficiation and metallurgy was developed in this dissertation,which can provide theoretical and technical support for the comprehensive recovery and utilization of such kind of resources.Process mineralogy research shows that the z inc grade of raw ore is 7.08%,and the zinc-bearing minerals are mainly smithsonite and sphalerite,in which the zinc content accounts for 53.67%and 42.80%of the total zinc respectively.Smithsonite or inclusion sphalerite,or locked with sphalerite,and it also contains a small amount of refractory minerals such as heteropolar ore and zinc iron spinel.It is a typical low-grade refractory mixed zinc oxidized-sulfide minerals,which is suitable for processing theoretical study on"ammonia-ammonium dissolution-activated flotation".In the leaching system of NH₃-（NH₄）₂SO₄-H₂O,the better conditions are as follows:grinding fineness of 85%-0.074mm,stirring speed of 300 rpm,total ammonia concentration of 3 mol/L,ammonia to ammonium molar concentration ratio of 2:1,leaching time of 45 min,liquid-solid ratio of 4:1,zinc leaching rate of 55.43%（leaching rate of leachable phase of zinc reaches 99.87%）.MLA analysis and comparison show that the continuum of zinc oxide ore and zinc sulfide ore in leaching residue basically disappears;XRD analysis also found that smithsonite could not be detected in the leaching residue,mainly the residual zinc sulfide mineral after ammonia dissolution.After the mixed zinc ore is dissolved and activated by ammonia-ammonium system,not only the zinc oxide ore which is difficult to float is recovered by dissolution,but also the fresh surface of zinc sulfide ore is exposed,which activates the flotation of zinc sulfide ore.FESEM analysis showed that zinc oxide ore and mechanically attached soluble oxides on the surface of sphalerite were dissolved by ammonia-ammonium leaching.Natural sphalerite is used for the research of both ammonia-ammonium dissolution test and flotation mechanism.After the dissolution of ammonia-ammonium system,its floatability has been greatly improved,showing similar or even better floating characteristics as copper ion activated sphalerite,greatly improving the flotation performance and increasing the rec overy by 5.35%～6.33%.The mixed zinc ore is treated by the combined beneficiation and metallurgy process of"ammonia ammonium dissolution-activated flotation",which makes full use of the advantages of ammonia leaching to recover zinc oxide ore and flotation to recover zinc sulfide ore,and has a chieved excellent performance.Through ammonia leaching,the zinc leaching rate of leachable phase in oxidized ore is 99.87%,Through leaching-slag flotation and laboratory closed-circuit test,zinc concentrate with zinc grade of 50.15%and recovery of 96.59%was obtained,and the comprehensive recovery of zinc in the whole process reached 86.78%.Compared with the open-circuit flotation recovery of the conventional flotation process of mixed zinc ore,the recovery of the combined beneficiation and metallur gy process was about 30percentage points higher.AFM analysis of the surface micro area activated by ammonia-ammonium dissolution of sphalerite shows that,compared with natural sphalerite,as part of the zinc containing components on the ore surface are dissolved,depressions are formed on its surface,the surface roughness increases significantly,and the change of roughness increases with the increase of total ammonia concentration.When the total ammonia concentration was 3mol/L,the average surface roughness increased from14.13nm to 60.16nm.At this time,from the TOF-SIMS deep section fragment ion 3D images after the interaction between sphalerite and sodium butyl xanthate,it can be concluded that the xanthate adsorbed on the surface of sphalerite a fter dissolution is more thick,indicating that the ammonia dissolution"activates"sphalerite,enhances the interaction between its surface and C ₄H₉OCS₂^-,and improves its flotation effect.XPS analysis of sphalerite leaching shows that it is difficult fo r N element to exist on the surface of zinc sulfide minerals in the form of NH₃、NH₄⁺and[Zn（NH₃）n]²⁺,indicating that the essence of corrosion activation of ammonia-ammonium system is not the adsorption of zinc ammonia complex ions on the ore surface to increase the adsorption site of xanthate.Further analysis shows that the characteristic peaks of binding energy at 168.8ev and 169.9ev are due to the existence of SO₄^2-group on the surface of sphalerite.After dissolution,it is found that the oxidation characteristic peak of SO₄^2-group on the mineral surface disappeared,and the sulfur atom concentration increases sharply from 24.20%to 32.20%,indicating that dissolution plays a good"cleaning"role on the surface of sphalerite,which accelerates the transfer of inert oxidized zinc components to the solution,destroys the hydrophilic film formed by natural oxidation on the surface of sphalerite,relaxes the surface atoms and reconstructs the sulfur rich surface,creating favorable conditions for the subsequent adsorption of collectors.The Local Electrochemical Impedance Spectroscopy（LEIS）measured by Electrochemical Workstation before and after the dissolution of sphalerite ammonia-ammonium decreased from 3.81³10⁴Ωto 3.06³10⁴Ω,which further confirmed the"cleaning"and"activation"effects of ammonia-ammonium corrosion.After the mixed zinc ore is dissolved by ammonia-ammonium leaching at normal temperature and pressure,it not only recovers the zinc oxide ore that is difficult to float,but also exposes more fresh surfaces of zinc sulfide ore after the zinc oxide ore is dissolved,increases the active sites of flotation reagents adsorption,activates the flotation of sphalerite that is difficult to be activated by conventional methods,greatly improves the flotation performance,and is easier to be industrialized.