Basic Research On Rich-Oxygen Leaching Of Sphalerite

Consumption of high-quality zinc sulfide makes it inevitable to exploit low-level polymetallic sphalerite resources.Effective leaching of zinc sulphide concentrate is the key step to the hydrometallurgy process of zinc extraction.Compared with the traditional one,oxygen pressure leaching of sphalerite enjoys unparalleled advantages on recovery of valuable element,adaptation to complex raw minerals,relatively straightforward procedure and little pollution.In order to get valuable metals extracted/recovered as much as possible,it's necessary to take exhaustive research on the strengthening leaching,the role and kinetics mechanisms of the valuable metallic elements,and the behavior of bubbles during the leaching process systematically.Therefore,it is significant to study deeply and systematically on mechanical activation,different catalytic leaching system and behavior Rules of oxygen bubbles in order to provide scientific basis for the high-pressure leaching process of Zinc concentrate and its practical application in this paper.The main research work was as followed.Firstly,the sphalerite was mechanically activated by a high performance ball and subsequently researched for the physical and chemical properties and roasting kinetics.The effect of the variation in crystalline structure,morphology,panicle size and specific surface area of the non-activated and mechanically activated sphalerite concentrates were characterized by X-ray diffraction,scanning electron microscope,thermal analysis,particle size analyzer and volumetric adsorption analyzer,respectively.The roasting macrokinetics of unactivated and mechanically activated were investigated using differential thermal analysis?DTA?in oxygen.The results show that the physicochemical properties of sphalerite was changed changed obviously by mechanically activated.In the roasting process,the oxidation rate of sphalerite activated was much faster than that of non-activated sphalerite.Reaction activity of sphalerite was significantly improved by mechanical activation.When sphalerite is mechanically activated for 30 min and 120 min,the apparent activation energy decreases from 239.78 kJ/mol of non-activated sphalerite to 171.25 and 57.17 kJ/mol.Pressure leaching kinetics of the mechanically activated sphalerite was investigated,the activation energy of sphalerite decreased from 69.96 to 45.91,45.11,and 44.44 kJ/mol as activation time increased from 30,60 to 120 min,respectively.The reaction orders for H₂SO₄ solution were respectively 1.832,1.247,1.214 and 1.085,which indicated that dependency of H₂SO₄ on sphalerite leaching process could be reduced by means of mechanical activation.Secondly,the kinetics of oxygen pressure acid leaching of sphalerite was studied in the low temperature region?383-413 K?.The effects of agitation rate,particle size,temperature,H₂SO₄ concentration,and oxygen partial pressure on the conversion of sulfur(S^2-?S⁰)were investigated.The results showed that the conversion ratio increased with increasing agitation rate,temperature,and oxygen partial pressure,and with decreasing particle size and H₂SO₄ concentration.Moreover,the results demonstrated that sulfur conversion was controlled by an interfacial chemical reaction,with apparent activation energy of 51.17 kJ/mol.The calculated reaction orders of sulfuric acid and oxygen were-0.48 and 1.01,respectively.The leaching reaction followed an unreacted shrinking core model.A model kinetic equation was established for sulfur conversion.Orthogonal experiments regarding the acid balance(S⁰?SO₄^2-)of the oxygen pressure leaching residue were carried out.Variance analysis showed that temperature had the largest influence on this,so the effect of the temperature region?383?443 K?on acid balance was further investigated.When the temperature exceeded 443 K,the increase in the sulfur oxidation ratio was too large,which tended to increase the acidity of the system.The kinetics of oxygen pressure acid leaching sphalerite with high indium content was studied.The effects of particle size,agitation rate,temperature,H₂SO₄ concentration and oxygen partial pressure on the leaching rate of indium were investigated.The results show that when the agitation rate was above 600 r/min,its influence on indium leaching ratio was insignificant.It was determined that the leaching ratios increased with increasing sulfuric acid concentration,temperature,partial oxygen pressure and decreasing particle size.Moreover,the results demonstrate that the process of indium leaching was controlled by interface chemical reaction,with apparent activation energy of 65.7 kJ/mol.The apparent reaction orders of sulfuric acid and oxygen partial pressure were determined to be 0.75 and 1.26 respectively.The leaching reaction process followed shrinking unreacted core model.The kinetics model equation was established for indium leaching.Thirdly,compared to pure sphalerite,changes in relative potential change of artificial iron sphalerite on rich-oxygen leaching was more intense,this shown that the self-precipitated Iron catalyzed of synthesized sphalerite effectively promote the leaching process.Leaching rate and kinetics under various catalytic systems and leaching conditions were calculated along with electric potential analysis for the leaching process.It denoted that as the mass fraction of iron increased,oxygen pressure leaching efficiency of sphalerite was continuously enhanced.When mass fraction of iron were 0,5.75,15.2,25.7,the activation energies of artificial sphalerite in oxygen pressure acid leaching were 32.31,29.02,26.30 and 21.88 kJ/mol,respectively.The kinetic controlling step was transformed from interfacial oxidation reaction of H₂S to the diffusion of the acid agent H+ through the surface H₂S gas film.The reaction orders for H₂SO₄ solution were respectively 1.36,1.27,1.26 and 1.10,the reaction orders for partial oxygen pressure were respectively 1.29,1.60,1.62 and 1.41.A model kinetic equation was established for the oxygen pressure leaching with different iron content of sphalerite.Fourthly,compared with leaching process of sphalerite with no addition,key step of the Mn⁴⁺/Mn²⁺ redox catalytic systeI would be converted to the chemical reaction of Mn²⁺?MnO₂,however,some catalytic effect could be observed.For the expected lattice substitution and sedimentation of Cu²⁺,nevertheless,reaction to achieve the so called lattice substitution to cupric sulphide should take place quite slowly and the sedimentation generated at the mineral surface could not be furtherly oxidized,which,to some extent,inhibit the later leaching process.Whereas for Ag⁺,once the Ag₂S was rapidly produced to accelerate the earlier reaction,it seemed unfeasible to get the covered sedimentation shelled to recover Ag⁺,as a consequence,sequential action couldn't arose,neither the Cu2+ nor Ag⁺could promise the desired kinetic process.Finally,dynamic behaviors of relative elements were thoroughly discussed based on the process potential and SEM of the leach tailings.Fifthly,the transparent quartz autoclave and high speed camera were used to investigate the mixture condition of the gas-liquid phase and the behavior of bubbles in the solution under high temperature and high pressure conditions.The results shown that the variation laws of gas holdup with three straight blades agitator-Runoff type,three blades push type agitator-Axial-flow type,six blades disc turbine type agitator-Mixed flow type and self-priming type agitator were the same.With the stirring speed and temperature increased,the gas holdup was increasing,with the oxygen partial pressure,the gas holdup decreased gradually.The contrasting results of various paddle types illustrate that application of self-priming agitator could significantly enhancethe gas holdup in solution.For the self-priming agitator,the similar criteria relationship is established by Homogeneous Principle and Buckingham's theorem.Comprehensively,empirical equation of gas holdup was deduced on basis of experimental data and similarity theory,where the criterion equation was determined.Lastly,the effects of various types of paddle on the rich-oxygen leaching were investigated.It denoted that the leaching rate of sphalerite using self-priming type agitator was much faster than that of other agitator,so the oxygen pressure leaching efficiency of sphalerite was enhanced.Pressure leaching kinetics of the various paddle types were investigated,the activation energy of sphalerite were 53.23,56.30,59.76 and 67.58 kJ/mol by using three straight blades agitator-Runoff type,three blades push type agitator-Axial-flow type,six blades disc turbine type agitator-Mixed flow type and self-priming type agitator,respectively.The reaction orders for H₂SO₄ solution were respectively 1.39,1.43,1.47 and 1.48;the reaction orders for partial oxygen pressure were respectively 1.80,1.74,1.84 and 1.61.A model kinetic equation was established for the oxygen pressure leaching using various types of paddle.