Research On Recovery Of Tungsten-containing Waste And Preparation Of Tungsten Powder

Due to its extremely high melting point(3422?),high hardness,big density,high thermal stability,tungsten play a very important and irreplaceable role in national defense industry,aerospace industry,machinery manufacturing and other fields.Tungsten is known as the strategic reserve metal.The application of tungsten has lasted for more than 100 years,but the extremely limited tungsten resource on the earth is sharply reduced due to long-term mining.Tungsten ore is a kind of non-renewable mineral resources,so recycle and reuse tungsten secondary resource is the only way to achieve the sustainable development of tungsten resource.In this thesis,recycle of tungsten in waste tungsten rod has been studied.We use molten sodium peroxide method,molten alkali method and isothermal oxidation method to recycle waste tungsten rod and studied their recycling effect.In additional,we studied the oxidation behavior of tungsten in the air in this thesis.In this thesis,we studied the preparation of tungsten acid by calcium tungstate's acid decomposition.In this thesis,we use tungsten trioxide as raw materials,and conduct hydrogen reduction at high temperatures,and we studied the effects of reduction temperature and reduction time on the oxygen content of tungsten powder.The experimental results show that the isothermal oxidation method is suitable for recycling waste tungsten rod and held 3 hours at 800? in the air is the optimum oxidation condition of isothermal oxidation method.After oxidation,oxidation product leaching by 2 mol/L boiling sodium hydroxide solution for 20 minutes,and a relatively pure sodium tungstate solution can be obtained.Tungsten could be oxidized by the air at room temperature,and its oxidation results the formation of dense oxide layer consisted of tungsten(VI)trioxide(WO3)and tungsten(IV)oxide(WO2)could block the oxidation.Meanwhile,the oxidation of tungsten became violent at 620?,and the volatilization of tungsten trioxide started around 890?.6 mol/L hydrochloric acid concentration combine with 80? reaction temperature is the optimal preparation conditions of tungsten acid.With the rising of reduction temperature and the increase of heat preservation time,oxygen content of tungsten powder presented down trend and reduce for 60 minutes at the temperature of 850?,the oxygen content of tungsten powder could reach 0.6163%.