As shown in Figure 1.
3. Equipment
Self made open electrolytic furnace, ZKLD - 1A single tube furnace, JK-200A vacuum unit, ZG-0.025A vacuum medium frequency induction furnace
2、 Results and discussion
1. Effect of cathode current density on metal yield and electrical efficiency
Fig. 2 D. Effect on Direct Yield and Electric Effect
The effect of 1-D on the direct yield of Y ∈ Os; Effect of 2-D on electric efficiency
In this test, the cathode Y ³+, Mg ²+ The eutectoid method can produce Y-Mg alloy with higher yttrium content. Y in molten salt system at 900~1000 ℃ ³+ And Mg ²+ The difference of standard electrode potential is 0.193~0.202V. Therefore, high cathode current density is adopted to make cathode Y ³+ And Mg ²+ Achieve the goal of eutectoid analysis. The test shows that when Di<15A/cm ² When, Y ³+ The precipitation power is insufficient, and the yttrium content in the alloy is only 61.1%, its gravity is less than that of the molten salt, which causes the metal to float and burn, and the yield decreases; When D Increase in favor of Y ³+ Precipitation, the content of yttrium in Y-Mg alloy increases, the gravity increases, the cohesiveness increases, it is easy to sink, and the separation performance is good; When D>36A/cm ² When the electrolyte is overheated, the solubility of the alloy is too large, resulting in a sharp drop in electrical efficiency. Therefore, we choose 25~30A/cm ² The scope is appropriate.
2. Electrolyte composition selection
Electrolyte composition is an important factor directly related to the normal operation of electrolysis process and the quality of products. This experiment explored the composition of YF3, LiF, BaF2 and MgF2. The content of YF ｜ is too low (<72%), the dissolution of Y ∈ O3 slows down, and the content of Y in molten salt ³+ Precipitation, F generates sparks in the anode and "passivates" the anode, which is not conducive to the long-term use of molten salt components; If the content of YF ｜ is too high (>80%), the melting point of electrolyte and viscosity will increase, which will reduce the electric efficiency; LiF is an important additive to reduce melting point and improve conductivity, but when LiF>20%, electrolyte volatilization is too large, which is not conducive to continuous electrolysis of molten salt; The addition of BaFz can reduce the volatilization loss of molten salt and improve the separation degree between molten salt and alloy, but should not exceed 10%; MgF2 in molten salt can promote the dissolution of rare earth oxide, reduce the content of YF3, and reduce the cost of molten salt. From the test, the addition of MgF2 is beneficial to electrolysis.
3. Feeding speed selection
The test shows that generally, the current intensity is high, the feeding speed is high, and the electrical efficiency is improved. However, the solubility of rare earth oxides in molten salt is limited (Y ∈ O3 3% ～ 6% wt) 37, so it is impossible to increase without limitation. Under the selected test conditions, it should not exceed 5.2g/min; When the feeding speed is less than 3.1g/min, the anode effect is frequently generated and the electrolysis condition is bad.
Fig. 3 Effect of feeding speed on direct yield and electric efficiency
1 - Effect of feeding rate on the yield of Y ∈ O3; 2 - Effect of feeding speed on electric efficiency
4. Vacuum distillation system selection
In this experiment, the stepwise heating vacuum distillation was selected to explore the furnace capacity, heating system and final distillation temperature. In a certain furnace and pumping system, with the furnace load increasing from 250~500g, the Mg removal effect decreases, and the Mg content in sponge metal yttrium changes from 0.7% to 3.05%; In order to achieve high efficiency without reducing the effect of Mg removal, when the distilling furnace capacity is increased to 500g, the final temperature is increased to 1020 ℃, the Mg content in sponge yttrium is less than 0.8%, and the metal recovery is 97.86%
5. Selection of vacuum melting and casting system
The test shows that the content of Mg in yttrium metal is less than 0.001% by controlling certain vacuum degree, temperature and various melting and casting conditions. The key is to control the heating and holding time. The melting and casting time should not be longer than 75min. Otherwise, many sparks will be splashed in the crucible, the metal loss will increase, and the recovery rate will decrease. The better melting and casting time is maintained within 45~50min
3、 Quality of yttrium metal products
The surface of yttrium metal products is black gray, and the fracture surface is silver gray luster. The surface is a little dark after being placed in the air for a long time. The metal is plastic and can not be broken:
Yttrium Analysis Results (Y
Table 1
试样
YzO₃ T REO
RE
Fe"
Ca
Mg
C
Si
Al ·
S
P
0
Y-1
99.508
98.399
0.49
0.014
<0.001
0.030
0.005
0.42
<0.01
<0.001
0.63
Y-1
99.469
98.745
0.27
0.005
<0.001
0.033
0.015
<0.37
<0.01
<0.001
0.55
*In this test, the corundum crucible is used to receive the alloy. The alloy is broken by hand, which is easy to cause high content of Al and Fe in the product and can be completely avoided in mass production.
4、 Conclusion
In this test, yttrium was prepared by molten salt electrolysis vacuum distillation method. The electrolysis process does not produce toxic gas chlorine, and the alloy grade is high. The utilization rate of yttrium oxide obtained by continuous tests is more than 97.66%, and the electrical efficiency is 82.74%; The vacuum distillation has high efficiency, good Mg removal effect, and the metal direct yield is 97.86%; After melting and casting, dense metallic yttrium ingots can be obtained with a direct yield of 97.65%. this
Method provides a new method for producing yttrium metal.
reference
〔1〕 Rare earth compilation group. Rare Earth (Volume II) The first edition, Beijing: Metallurgical Publishing House, 1972
〔2〕 Hunan Metallurgical Research Institute. Preparation of rare earth metals, alloys and their materials September 1973
〔3〕 Du Senlin, Wu Meihuang, etc Solubility of rare earth oxides in molten alkali metal and alkaline earth metal fluoride salts. Rare earth, 1987 (2)
