基于LaCl_(3)熔盐La直接脱除钛废料中固溶氧研究

Direct Removal of Oxygen from Titanium Scrap using La in LaCl_(3) Flux

随着我国社会经济的快速发展,国防及民用领域对钛及钛合金的需求日益旺盛,钛废料也与日俱增。直接回炉重熔是回收钛废料最经济、最有效的途径,但由于钛废料中氧含量较高,加之重熔过程无法脱氧,导致其无法直接回炉重熔。因此,如何在重熔前有效脱除有害元素氧是目前钛行业发展亟待解决的关键问题。针对现有钛废料脱氧方法存在效率低、金属/熔盐分离困难等问题,结合中国稀土资源丰富的特点,本研究提出了在LaCl_(3)熔盐中,采用La直接脱除钛废料中固溶氧的新方法。热力学计算结果表明:1300 K下,La/La_(2)O_(3)和La/LaOCl/LaCl_(3)平衡的理论脱氧极限分别为5400×10^(-6)O和84×10^(-6)O。基于热力学分析,开展了La/La_(2)O_(3)和La/LaOCl/LaCl_(3)热力学平衡脱氧实验,结果表明:在1300 K下,La/La_(2)O_(3)平衡脱氧极限为3400×10^(-6)O,并且随着La_(2)O_(3)含量的降低,脱氧极限降低;在1300 K下,La/LaOCl/LaCl_(3)平衡条件下的脱氧极限为66×10^(-6)O,结果证实了LaOCl的生成(O(inβ-Ti,1%)+2/3La(l)+1/3 LaCl_(3)(s)=LaOCl(s))促进了La深度脱氧,有效降低了钛中氧含量,并且随着LaOCl含量的降低,脱氧极限降低。本研究通过将理论和实验相结合,证明了LaCl_(3)熔盐中采用La作脱氧剂可有效脱除钛废料中的固溶氧,且效果显著。该方法的建立将有助于实现钛废料的清洁、高效回收利用和低氧钛粉的生产,最终有助于钛产品的大规模使用。

Metal titanium is an excellent structural and functional material,which is widely used in many fields such as aerospace,national defense and military industry.At present,Kroll process is the primary method for producing sponge titanium.This method has the disadvantages of long process and high energy consumption,so the production cost of titanium and titanium alloys is relatively high.In addition,10%~20%of sponge titanium scrap is produced in the sponge titanium production process.Furthermore,as much as 60%~90%of titanium becomes waste scrap during the deep processing of titanium because titanium has a strong affinity with oxygen.With the rapid development of Chinese society and economy,the demand for titanium and titanium alloys in the defense and civil fields has gradually increased,and the amount of titanium scrap produced has also increased day by day.Developing a clean and effi⁃cient method for recycling of titanium scrap is the only way to ensure the sustainable development of the titanium industry in China and the world.At present,it is the most economical and effective way to recycle titanium waste by directly returning to the furnace for re⁃melting.However,the oxygen content of the titanium waste is much higher than that of sponge of titanium,and there is no deoxidation ability during the remelting process.As a result,the titanium scrap cannot be directly returned to the furnace for remelting.Therefore,how to effectively remove the harmful element oxygen before remelting is a key problem that needs to be solved urgently.To face with the problems of low efficiency and difficulty in separation of metal/molten salt in the existing titanium scrap deoxidation methods,com⁃bining the rich content and types of rare earth resources in China should be adopted.This research proposed a new method in which La was used in LaCl_(3)molten salt to directly remove dissolved oxygen in the titanium scrap.First,thermodynamic calculations were carried out.The results showed that the theoretical deoxidation limits of La/La_(2)O_(3)and La/LaOCl/LaCl_(3)equilibrium were 5400×10^(-6)O and 84×10^(-6)O,respectively,at a temperature of 1300 K.The equilibrium deoxidation limit of La/LaOCl/LaCl_(3)was lower than the deoxidation limit of Ca/CaO(570×10^(-6)O)equilibrium,indicating that in LaCl_(3)molten salt,the use of rare earth metal La as a deoxidizer had a good deoxidation effect.At the same time,the thermodynamic results showed that the deoxidation limit of La/LaOCl/LaCl_(3)and La/La_(2)O_(3)equilibrium could be effectively reduced under low temperature conditions.In addition,the equilibrium deoxidation limit of La/LaOCl/LaCl_(3)also decreased with the decrease of activity of LaOCl.The thermodynamic results of this study showed that it was feasible to deoxidize titanium using rare earth metal La as a deoxidizer in LaCl_(3)molten salt.Based on thermodynamic analysis,a thermodynam⁃ic equilibrium deoxidation experiment of La/La_(2)O_(3)and La/LaOCl/LaCl_(3)was carried out.The results showed that at a temperature of 1300 K,the deoxidation limit of La/La_(2)O_(3)equilibrium was 3400×10^(-6)O.In addition,when the numerical value of xLa_(2)O_(3)(mole fraction of La_(2)O_(3))increased from 0 to 0.6,the oxygen content of the titanium sample increased from 3017×10^(-6)O to 3652×10^(-6)O.This indicat⁃ed that the deoxidation limit gradually decreased with the decrease of La_(2)O_(3)content.At 1300 K,the deoxidation limit under the equi⁃librium condition of La/LaOCl/LaCl_(3)was 66×10^(-6)O,confirming that the formation of LaOCl(inβ-Ti,1%)+2/3La(l)+1/3 LaCl_(3)(s)=LaOCl(s))effectively reduced the oxygen content in titanium.When xLaOCl numerical value increased from 0 to 0.8,oxygen content of the titanium sample after deoxidation treatment increased from 45×10^(-6)O to 88×10^(-6)O,indicating that the deoxidation limit decreased with the decrease of LaOCl content.In addition,although the O2-concentration increased in the system(LaOCl content increased),La/LaOCl/LaCl_(3)equilibrium deoxidation limit was still at a relatively low level,indicating that La as a deoxidizer in LaCl_(3)molten salt could handle a large amount of high oxygen content titanium scrap.This study combined theory and experiment to prove that the use of La was deoxidizer in LaCl_(3)molten salt could effectively remove solid dissolved oxygen in titanium scrap,and the effect was significant.On this basis,this research proposed a new green and efficient deoxidation process,which could not only deoxidize titanium scrap,but also could be used to deoxidize high-oxygen titanium powder to obtain low-oxygen titanium with O content of less than 100×10^(-6)O.The efficiency was high,and the molten salt such as LaCl_(3)remaining on the titanium surface after deoxidation could be cleanly re⁃moved by vacuum distillation,and no waste water produced.In addition,the deoxidation byproduct of LaOCl could generate La and LaCl_(3)by electrolysis,which could be reused for thermodynamic equilibrium deoxidation and help to realize the recycling of byprod⁃ucts.There was no rare earth consumption in the entire deoxidation process.The establishment of this method would help to achieve clean,efficient recycling of titanium scrap and the production of low-oxygen titanium powder,so ultimately would help the large-scale use of titanium products.