The Research On Novel Hydrometallurgy For Molybdenite Concentrate And Its Mechanisms

The roasting method gradually shows its shortcomings. During roasting, many valuable metals are lost due to volatilization and the SO2 generated is a source of environmental pollution. The novel cold atmospheric leaching of molybdenite, the process of extraction and separation of molybdenum and rhenium in the extract, and their mechanism have been investigated, providing theoretical basis for environment-friendly hydrometallurgy of molybdenite.Chlorate and hypochlorite in solution have high electrode potential and strong oxidative property. Thermodynamic calculations of the oxygenolysis process of molybdenite by sodium chlorate and sodium hypochlorite were carried out. The results showed that values of△G°were negative and the absolute values of them were high if sodium chlorate and sodium hypochlorite were used as oxidant in the molybdenite leaching process. In the view of thermodynamic point, MoS2, CuFeS2, FeS2 and ReS2 etc. could be leached by acidic chlorate system and alkaline sodium hypochlorite system theoretically.In this paper, the technology of molybdenum extraction from molybdenite concentrate by using sodium chlorate has been investigated, and a novel hydrometallurgical extraction technology of molybdenite by using sodium chlorate electrolyte was introduced. The optimized leaching conditions are as followed:C(NaCl)=0.71 mol/L, C(H2SO4)=73.3 g/L, NaClO3/MoS2=3.6 (mol/mol), L/S=30, T=70℃, stirring rate is 400 r/min, t=6 h. Under these conditions, leaching yield of molybdenum is 98.62%, leaching yield of copper is 99.77%, leaching yield of iron is 99.28%, leaching yield of rhenium,99.52%; while leaching of molybdenite is completed, Cu, Fe, Re were almost completely leached into the liquid. The acidic sodium chlorate electrolyte by electrochemical synthesis, without purification, crystallization, but just adjust the acidity and was directly used for leaching of molybdenite. The optimized electrosynthesis conditions of sodium chlorate are as followed:cell voltage of 3.0 V, current density of 653.2 A/m2, stirring rate of 100 r/min, concentration of potassium dichromate of 3 g/L, pH=6.7,75℃,35 h. Under this electrosynthesis conditions, sodium chlorate is 290.90 g/L, sodium hypochlorite is 7.08 g/L, leaching yield of molybdenum is 98.51%, and leaching yield of rhenium is 99.56%. It was an efficient and economic wet leaching process that sodium chlorate electrolyte was used for leaching molybdenite, and it can also reduce cost largely. The kinetic study showed that the process of leaching molybdenite using acid sodium chlorate system is represented by shrinking core model, the apparent activation energy (Ea) for the dissolution reaction was calculated as 104.6.6 kJ/mol showed that the chemical reaction is the control step of leaching process.According to the characteristic of electric-oxidation leaching molybdenite, the electro-oxidation technology in CO32--HCO3-buffer system was introduced, molybdenite can be selectively oxidized, and current efficiency increases obviously. Experimental studies showed that when pH=9, the oxidation rate of molybdenite is the fastest. The optimized leaching conditions are as followed:cell voltage of 3.5 V, current density of 653.2 A/m2, liquid-solid ratio of 25:1, stirring rate of 400 r/min, concentration of sodium chloride of 4 mol/L, sodium carbonate of 6 g/L, ammonium acid carbonate of 5 g/L, pH value of buffer system of 8.5-9.5, at room temperature. Under this process conditions, the leaching yield of Mo reaches 99.35%, leaching yield of rhenium is 99.79%after leached 240 min. The current efficiency of buffer system is of 62.75%, but that of unbuffered system is only of 40.44%. In CO32--HCO3- buffer system, it restrained leaching reaction for chalcopyrite, chalcopyrite would not be leached which reduced its electricity consumption, copper content of 10.84% in residue and recovery rate of 97.93%.The application of the buffer system can significantly reduce the energy consumption for electro-oxidation leaching of molybdenite.Anode oxidation and oxidant have been investigated, and dynamic model of leaching process was established. The results showed that molybdenite couldn't be electro-oxidated at the anode directly in the buffer system. The chlorine evolution reaction has played a dominant role in sodium chloride medium. Sodium hypochlorite is the main oxidant of oxidation leaching, which transformed from chloration liberated at the anode. The kinetic study showed that a shrinking core model is presented to describe the dissolution and to analyze the data. It was established that the leaching process is mainly controlled by diffusion through a porous product layer, the apparent activation energy of this dissolution process was found to be 8.56 kJ/mol.The studies on extraction of Mo(Ⅵ), Re(Ⅶ) in the solution and its mechanism by using N235 extractant have been investigated. For extract solution of sodium chlorate, the percentage extraction rates of Mo(Ⅵ) and Re(Ⅶ) under the optimized extraction conditions were about 99.84%and 95.19%; Stripping of molybdenum to aqueous phase was efficient when 17% ammonia liquor were applied, the Mo(Ⅵ) and Re(Ⅶ) stripping efficiencies under the optimized stripping conditions were about 99.90% and 99.73%. For electric-oxidation extract solution, the percentage extraction rates of Mo(Ⅵ) and Re(Ⅶ) under the optimized extraction conditions were about 99.77%and 94.73%; Stripping of molybdenum to aqueous phase was efficient when 17% ammonia liquor were applied, the Mo(Ⅵ) and Re(Ⅶ) stripping efficiencies under the optimized stripping conditions were about 99.89% and 99.54%. The results of equimolar seriers method and infrared spectral analysis indicates that the coordinate reactions in aqueous solution happened while N235 extracted Mo(Ⅵ) and Re(Ⅶ) ions, (R3NH2)[(MoO2)2(SO4)3] and R3NH·Re04 come into being, respectively。The adsorption and separation capability for Mo(Ⅵ) and Re(Ⅶ) ions of D201 resin have been investigated, adsorption kinetics and thermodynamics were revealed by analyzing adsorption data. The results showed that the adsorption capacity of D201 for Mo(Ⅵ) and Re(Ⅶ) ions increases with increase in adsorbing time and the initial ions concentration. For dualistic mixed solution of Mo(Ⅵ) and Re(Ⅶ), the separation capability of D201 for Re(Ⅶ) and Mo(Ⅵ) has been investigated, it indicates that D201 has excellent adsorption selection for Re(Ⅶ) ions, and satisfy the separation demands. For stripping solution of sodium chlorate system, the adsorption rate of Re(Ⅶ) and Mo(Ⅵ) are 92.41%,3.19%,respectively, and separating factor is 190.49,when adsorption condition is 30℃, pH=8, and absorbing time 1 h; For stripping solution of electric-oxidation system, the adsorption rate of Re(Ⅶ) and Mo(Ⅵ) are 92.18%,3.46%, respectively, and separating factor is 169.56,when adsorption condition is 30℃, pH=8, and absorbing time 1 h.The experimental data fit Boyd's diffuse equation of liquid film, indicating that the adsorption is controlled by liquid film diffuse; the isothermal adsorption obeys Langmuir and Freundlich equation, especially the former equation. The saturated adsorption capacity of D201 for Mo(Ⅵ) and Re(Ⅶ) calculated base on simulated results were 4.2633 mmol/g,4.2355 mmol/g, respectively.The results of rough cost and economic analysis for molybdenite of Dexing Copper Mine showed that, compared to conventional roasting process, the overall yield of molybdenum is 99.04%, the overall yield of rhenium is 85.84%, increase the recovery for rhenium by 25%, and more than 97% copper can be recovered, The new-increased income is over 2000 million yuan per annum, the reduced quality of SO2 is 2681 t per annum.