Extraction And Separation Of Molybdenum And Sulfur Resources Through Decomposing Molybdenite By Oxygen Pressure Leaching In Water

China is a major country in molybdenum resources and its reserves of molybdenum ranks the first in the world.Molybdenite is the most valuable and widely distributed molybdenum mineral in nature,and is also a primary raw material for the preparation of molybdenum and molybdenum compounds.The well-known disadvantages of pyrometallurgical roasting process of molybdenite are the low metal recovery ratio,high cost of recovering low concentration sulfur dioxide emissions,And for hydrometallurgical method such as acid or alkaline leaching under oxygen pressure,the existing problems are the large consumption of leaching medium,the difficulty in recovery the molybdenum in the liquid phase,which makes it difficult to be applied in the current industrial process.The research project 'Comprehensive Utilization of Molybdenum and Sulfur Resources through Decomposing Molybdenite by Oxygen Pressure Leaching in Water' was proposed to realize comprehensive utilization of molybdenum resources and sulfur resources in molybdenite.Oxidation decomposition of molybdenite in H2O-O2 system and separation of molybdenum from leach solution by ion exchange method constituted the two main lines of the study.The study focused on thermodynamics,decomposition law and kinetics of the decomposition of molybdenite in the H2O-O2 system.The distribution of oxidation products in solid and liquid two phase and the existence form of molybdenum in acidic leaching solution were analyzed.Based on the existence form of molybdenum,direct adsorption of Mo(?)by ion exchange resin in acidic leach solution of molybdenite was proposed.The comprehensive utilization of sulphuric acid resources in the leaching solution was also explored.The following achievements and progress were exhibited:(1)The thermodynamic calculation of the oxidation decomposition of molybdenite in the H2O-O2 system was carried out.By analyzing the thermodynamic trend and the heat change of the main components of molybdenite,such as MoS2 and FeS2,Cu2S and other impurities in H2O-O2 system,the possible phases and reaction paths of Mo and S were ascertained.(2)The oxidation process and kinetics of molybdenite in the H2O-O2 system were studied.The recommended optimal reaction conditions were:an LTS ratio of 6:1,oxygen partial pressure of 1 MPa,stirring speed of 600 rpm,particle size below 250 mesh and leaching temperature of 200?.Under these conditions,conversion rate of molybdenum could reach 99%after 120 min leaching.The kinetic investigation results revealed that the rate-controlling step was the chemical reaction.Copper and aluminum in molybdenite were easier to leach in the process of oxidative decomposition.The leaching rate of magnesium was 41.7%?57.4%during the decomposition process.(3)The mechanism of oxygen pressure leaching in water was analyzed.The leaching process was mainly composed of the decomposition of molybdenite and the dissolution of the product.During decomposition,Mo was oxidized into MoO3 2H20 and stayed in slag phase with Mg3Si4O10(OH)2,and S was oxidized into S042-and HSO4-dissolved into the liquid phase.The amount and form of Mo in the leaching solution were related to the acidity of the leaching solution:with the increase of acidity,the Mo ion in the solution changed from M0O42-and H2MO7O244-to MoO22+and Mo36O1128-;The amount of the dissolved Mo exhibited a parabolic trend with the increase of the acid concentration.The kinetic conditions,such as temperature,oxygen partial pressure,stirring rate,and mineral grain size,only affected the rate of distribution,but not affect the amount of solid liquid distribution.However,the ratio of liquid to solid affects both the rate and amount of distribution.(4)The process conditions and kinetics of the recovery of molybdenum in acidic leaching solution by ion exchange method were discussed.The loading capacity of D301R for molybdenum from high acidic leach solution was up to 499,6 mg/g.The adsorption process was controlled by the particle diffusion,and the activation energy decreased from 25.47 to 20.38 kJ/mol,with the resin particles sizes reducing from 0.9-1.2 mm to 0.6-0.9 mm.Continuous column experiments verified direct extraction of molybdenum from acidic leach solutions by ion exchange resin D301R and the upstream flow improved absorption from 142.83 mg/g to 285.66 mg/g.Elution conditions were used to determine elution conditions,providing the theoretical basis for the large-scale continuous production.(5)The cyclic leaching method was used to reduce the water consumption and optimize the process.Washing water of the oxidized residue had less molybdenum content,less acid and was stable at composition,which can make the cyclic leaching rate over 96%.The content of impurity Cu,A1 and Mg in oxygen pressure water leaching residue was low.The concentration of ammonium molybdate solution was 300?350 g/L with little impurity and could be directly used in the preparation of molybdate ammonium.Ammonia leaching residue was nontoxic and harmless and could be directly discharged.(6)Comprehensive utilization of sulphuric acid resources in the leaching solution was explored.Combined leaching of chalcopyrite and molybdenite,pyrolusite(manganese dioxide)and molybdenite in H2O-O2 system were explored.Using acidic leaching solution as a leaching agent for copper oxide ore was proposed,providing a new way for comprehensive utilization of sulfur resources in molybdenite.