Themodynamics And New Technology Research Of Sheeltie Sodium Hydroxide Roasting

The raw material of tungsten smelting are wolframite and scheelite,as wolframite that easy to smelt increasingly exhausted,scheelite has become the main raw material of tungsten industry.Scheelite smelting in our country mainly adopts high pressure alkali decomposition process,both previous sodium carbonate pressure cooking and now the mainstream of sodium hydroxide pressure cooking must be under the condition of high pressure to achieve scheelite decomposition,the pressure usually at around 6 to 18 kg,often brings security problems;both production are using single reactor intermittent operation,the production efficiency is low,and the slag containing tungsten is 1 2%,the utilization rate of tungsten need to be further improved.Based on equilibrium phase diagram of?CaO?Na₂O-WO₃-H₂ O,we can known that alkali concentration is the main factors influencing the decomposition of tungsten,at the same time,draw lessons from the continuous operation mode of early sodium carbonate roasting decomposition of tungsten,this paper puts forward the ideas of scheelite sodium hydroxide roasting decomposition,and the themodynamics of scheelite sodium hydroxide roasting process and new process were studied.The main contents are as follows:?1?Scheelite under the condition of much sodium hydroxide roasting,after water leaching to extract tungsten,the WO₃ content in slag is unable to meet the needs of industry that need be less than 2%.Drawing lessons from soda sintered method,adding part of silica while decomposing scheelite,the phenomenon of returning to calcium during the process of water leaching has been greatly solved.?2?Doing analysis of scheelite sodium hydroxide roasting product and water leaching residue by XRD,the main components of the calcined products are Na₂WO₄ and Na₂CaSiO₄,the main components of the water leaching residue is CaCO₃.Doing exploration research of water leaching residue by scheelite sodium hydroxide roasting,the research has shown that: CaCO₃ in water leaching residue is generated by Na₂CaSiO₄ react with H₂ O and CO₂ in aqueous solution.?3?According to the reactants and resultants to determine the main equation,and obtain the-T diagram by doing thermodynamics research to the reaction.The gibbs free energy is more and more negative with the temperature increasing,when the temperature at 975 k,the gibbs free energy is-221.58 KJ/mol.And doing research of CaWO₄-SiO₂-CO₂-NaOH system roasting thermodynamics,the study shows that: NaOH and Na₂SiO₃ can decompose the scheelite when temperature is 973 k.?4?This paper researchs the optimum technology conditions of scheelite sodium hydroxide roasting-water leaching extracting tungsten,alkali dosage,silica dosage,roasting temperature,roasting time,water leaching time,leaching temperature,liquid-solid ratio the seven factors were evaluated,the best technology conditions are as follows: the amount of NaOH dosage for theory dosage 1.1 times,silicon calcium ratio of 1:1,calcination temperature 700 ?,roasting time 2 h,water leaching time 4 h,water immersion stirring speed 350 r/min,liquid-solid ratio 3.2:1,the leaching temperature 80 ?.