Zinc Sulfide Concentrates Of High-speed Rail And Multi-metal Complex Sulfide Ore Pressure Leaching Process And Theoretical Studies

In this dissertation the technology and fundamentals of pressure leaching of high iron-zinc sulphide concentrate and polymetallic sulphide ore are studied systematically.The achievements and existing problems of non-ferrous metallurgical industry in our country are summarized and historical evolution of pressure hydrometallurgy is presented with an emphasis on its advantages and important role in non-ferrous metallurgy. The advances in pressure hydrometallurgy and the research achievements and industrial application status of pressure leaching of high iron-zinc sulphide concentrate and polymetallic sulphide ore at home and abroad are briefed, thereby significance and main contents of this research are put forward explicitly.This dissertation can be divided up into two parts: investigation into the fundamentals of oxygen pressure leaching of high iron- zinc sulphide concentrate and research on the technology of oxygen pressure leaching of polymetallic sulphide ore.In the first part, (1)the thermodynamic laws of oxygen pressure leaching of high iron-zinc sulphide concentrate are analysed, theφ-pH diagram of (Zn_0.75Fe_0.25 )S-H₂O system at 298K is constructed, and the superiority of oxygen pressure leaching of high iron-zinc sulphide concentrate is shown from the standpoint of the thermodynamics. The formation of H₂S in the oxygen pressure leaching process is also analysed, the chemical attack of H₂S on titanium-base autoclave is observed and the corrosion mechanism is proposed, and the safe working rules are recommended. And the heat balance of pressure leaching of zinc sulphide concentrate is calculated. The results indicate that reactive heat quantity is not balanced with heat quantity for heating up the slurry to 150°C and require supply exteriorly. The method of preheating temperature of reture spent electrolyte for leaching is proposed. (2)the effects of particle size, agitation rate, temperature, oxygen partial pressure, initial acid concentration, leaching time, additive, iron content in the concentrate and liquid-to-solid ratio on the leaching rates of zinc ,copper and iron are examined from the technological angle. The results show that the effects of temperature, leaching time and acidity are predominant. The reasonable technological conditions obtained by experiment are: the particle size of the sample is -320 mesh, the temperature 140℃to 150℃, the leaching time 2 hours to 2.5 hours, the initial acid concentration 150g/L to 170g/L, the overall pressure 1.2MPa to 1.4MPa, or the oxygen partial pressure 0.9MPa to 1.1Mpa, the liquid-to-solid ratio 5:1 to 6:1, the agitation rate 600r/min to 650 r/min, and the amount of additive 0.8% to 1.0% of the sample amount. Under these experiment conditions, the leaching rate of zinc is greater than 97%, the leaching rate of copper greater than 90%, the leaching rate of iron 30% to 35%, and the output rate of sulphur is 70% to 85%. (3)Under the determined kinetic conditions, the kinetics of oxygen pressure leaching of high iron-zinc sulphide concentrate is studied, the original "kinetic model of shrinking core" for liquid-solid reaction is developed andapplied to the reaction of a solid species with two or more water-soluble species, a mathematical model for this leaching process is obtained, and the reaction mechanism of this leaching process is discussed and analysed. The role of iron in the process of pressure leaching of zinc sulphide concentrate is explained. The kinetic study of oxygen pressure leaching of high iron-zinc sulphide concentrate is emphasis of this part, and the results show that as to zinc the leaching process is controlled by the surface chemical reaction and follows the kinetic law of "shrinking of unreacted core", the reaction activation energy is 55.04kJ/mol, the apparent reaction order with respect to the initial acid concentration is -0.3182; and as to iron, at the initial stage the leaching process is controlled by the chemical reactions and follows the surface chemical reaction-controlled kinetic law of "shrinking of unreacted core", and the reaction activation energy is 26.63kJ/mol.The kinetic mathematical model for leaching process is :α%=100×{1-[1-exp(2.1704-6606.005×1/T+0.779lnP-0.312ln[C] + 142.425[Fe]+27.941[Fe²⁺])t/r₀]³} In the second part, (l)the thermodynamic laws of oxygen pressure leaching of polymetallic sulphide ore, and the relative stability and dissolution order of various sulphides are analysed theoretically. (2)The effects of particle size, agitation rate, temperature, oxygen partial pressure, initial acid concentration, leaching time, additive, and liquid-to-solid ratio on the leaching rates of various metals in the samples are examined from the technological angle. The reasonable technological conditions obtained by experiment are: the particle size of the sample is -320 mesh, the temperature 145℃to 150℃, the overall pressure 1.5MPa, or the oxygen partial pressure 1.1MPa, the initial acid concentration 150g/L, the liquid-to-solid ratio 8:1, the leaching time 2 hours, the agitation rate 600r/min to 650 r/min, and the amount of additive 0.5% to 1.0% of the sample amount. Under these experiment conditions, the leaching rate of zinc is greater than 99%, the leaching rate of copper greater than 91%(the Cu content in the residue is less than 0.5%), the leaching rate of iron greater than 95%, more than 98% of lead and silver are left in the residue, and the output rate of sulphur is about 70%. (3)Reserch on oxygen pressure leaching of low-grade mixed polymetallic sulphide concentrate and polymetallic run-of-mine sulphide ore is conducted, and the reasonable technological conditions are determined. (4)A new technological process of comprehensive utilization of polymetallic sulphide ore and concentrate and recovery of valuable metals is suggested. The leaching liquor is pre-neutralized to precipitate iron and then sent to the neutral leaching section in an existing zinc production plant. The residue is sent to the lead bath smelting section. Thus Zn, Cu, Pb, Ag, In, Cd, and S in the polymetallic sulphide ore can be recovered comprehensively. By comparison with traditional process selective of flotation followed by separate metallurgical treatments, the advantages of the new process are as follows: the overall recovery is higher, the capital costs are lower, and the levels of environmental pollution are abated. The results of up-to-date back-check of literature indicate that the new process is novel one.