| Rhenium is a kind of rare metal and plays an irreplaceable role in the nickel superalloys for the production of turbine engine.Since a low amount of independent rhenium ore deposits exist,most rhenium resource is distributed within the molybdenite ore in the form of ReS2,consequently rhenium is often recovered as a by-product of molybdenum smelting.Up to now,low volatilization rate in roasting process and lacking effective technique to enriching rhenium concentrate in leacheate solution were the important impediments to recovery rhenium involved in molybdenite smelting process.Combining with the common technologies of roasting molybdenum concentrate,the thermodynamic properties of oxidation process for molybdenum and rhenium were systematically analyzed.Moreover,key factors for the volatilization rate of molybdenum concentrate and the concentration of leacheate solution were determined.On this basis,the innovative method for enhancing the volatilization rate of molybdenum concentrate has been proposed.On the other hand,the thermodynamics and kinetics properties of rhenium adsorption process on ion exchange resin was investigated.Aiming at rhenium with low concentration in the leacheate solution by roasting molybdenum concentrate,the direct ion exchange process using weak base resins was proposed to recover rhenium.This paper conquered the technical problems concerning low volatilization rate for rhenium in roasting process and low recovery rate of rhenium in leacheate solution,and the research achievements have been applied in a number of enterprises.Firstly,aiming at the existing problems of common roasting process for molybdenum concentrate,new method was proposed to enhancing the volatilization rate of molybdenum concentrate based on the thermodynamic analysis.The thermodynamic analysis indicated that the rhenium oxide Re2O7 possessed high vapor pressure,which sharply increased with increasing temperature.Hence,the molybdenum concentrate had high volatilization rate unless rhenium is oxidized to high valence state.By investigating the interactions between rhenium compounds and molybdenum compounds,molybdenum element could be oxidized to molybdenum oxide MoO3 with high valence state by rhenium oxide Re2O7,yet the opposite reaction could not be occurred.Therefore,in molybdenum concentrate roasting process,rhenium element could be oxidized to Re2O7 only if molybdenum element was oxidized to MoO3.Among existing roasting technology of the molybdenum concentrate,the volatilization rate of rhenium in the rotary kiln roasting is the lowest,which is only 27.3%because of the existence of molybdenum oxide MoO2 with lower valence state.In multiple hearth furnace roasting process,the volatilization rate of rhenium is 62.4%because the amount of MoO2 is relatively low.The results demonstrated that the oxidation degree of molybdenum calcine determined the volatilization rate of rhenium.In addition,in the bag filter system,a small quantity of 18.3%rhenium diffused into the leacheate solution because the flue gas temperature is only 150?.On the contrary,in electric dust collector system,about 56.6%rhenium diffused into the leacheate solution because the flue gas temperature is 240 ?.Hence,the flue gas temperature is key factor to affect the rhenium concentration in the leacheate solution.Based on the abovementioned analysis,the calcination method of smelting ash and two stage roasting method of molybdenum concentrate were proposed to enhance the volatilization rate of rhenium in molybdenum concentrate roasting process.Secondly,the direct ion exchange process using weak base resins was developed to recovery rhenium with low concentration from the leacheate solution.Different anion exchange resins were applied to investigate the adsorption/desorption properties of rhenium and a suitable weak basic resin was selected.Then,the kinetics and thermodynamic properties of Re adsorption process were systematically studied,and the technological parameters for recovering rhenium were obtained.To verify the process of extracting rhenium in industrial application,the column experiments on adsorption and desorption properties of rhenium in leacheate solution were carried out in industrial scale.Different anion exchange resins were applied to investigate the adsorption/desorption properties of rhenium and ZS70 resins was selected as the research object.The analysis of thermodynamic properties indicated that the Langmuir model excellently fitted the adsorption equilibrium relationship of Re on the resin.Moreover,the values of AG,AH and AS in adsorption process were both less than zero,which indicated that the rhenium adsorption process was a spontaneous,exothermic and decreasing chaos process.The analysis of the kinetics properties demonstrated that the diffusion process of the ReO4-ions in the resin was the limiting step of the adsorption process for Re,and the corresponding apparent activation energy was 4.4 kJ/mol.The existence of impurity ions such as sulfate radical,molybdenum radical and fluoride ions could decrease the equilibrium adsorption capacity and the adsorption rate.In the leacheate solution system,the saturation adsorption capacity for rhenium was 60.42 mg/g,and the saturation adsorption capacity for molybdenum was 9.3 mg/g.The equilibrium adsorption capacity for rhenium increased with decreasing temperature and sulfate radical concentration,and in direct proportion to the initial Re concentration.The adsorbed rhenium could be completely desorbed in 20 min by using 2.5%concentration of aqueous ammonia.Comparing to the leacheate solution,the rhenium concentration enriched 63 times in eluant solution,and the molybdenum rhenium ratio decreased from 6.2 to 0.2.By means of the adsorption and desorption process,the separation of molybdenum and rhenium has been achieved.Finally,to verify the process of recovering rhenium in industrial application,the column experiments in pilot-scale were implemented for recovering rhenium by direct ion exchange method using weak base ion exchange resins.In adsorption process,the adsorption rate of rhenium was larger than 99%when the volume of leacheate solution was 192 BV in 3-4 BV/h flow rate.The flow rate of the eluant solution was 1.5 BV/h and 5 BV aqueous ammonia with 2.5%concentration could completely desorb rhenium from the resins.The majority of Re was eluated in the range of 2-4 BV,which demonstrated that the desorption process of Re possessed rather fast kinetics properties.In the eluant solution,the value of Re was in the range of 4?8 g/L,as well as molybdenum was 0.7?1.2 g/L.The precipitation amount of rhenium was 94.1%when the evaporation amount of eluant solution was less than 93%.The purity of ammonium perrhenate products was larger than 99.98%after secondary recrystallization. |
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