Development of Metal Recycling Process from Decommissioned Nuclear Power Plants
- PDF / 769,316 Bytes
- 7 Pages / 384.48 x 615.6 pts Page_size
- 60 Downloads / 193 Views
0
mood
-100
Soo -200
,o,
;
t;4
-300
-400
i-
•
i
i00
-500
-Ann3C
1000
1200
1400
1600
1800
2000
Temp.(t) Fig. I Free Energy Change of Metal Oxide Formation reductant:C CO 2
reductant:C O0
slag
m metal
Ind'euctio
E eduction ISt.
1600°C
1600oc
Fig.2 Concept of Oxygen Gab Bubbling Method
1308
Anode (decommissioned metal)
Cathode
ORP (V vs Ag- Iwt%AgC1) Ni2 /Ni : 0.3V
Co2+/Co :0.1V Fe 2'/Fe -0.1V Cr2 /Cr : -0.3V Fig.3 Concept of Molten Salt Electrolysis Method
holders *(MgO crucible)
Fig.4 Schematic Diagram of 0.5kg Scale Apparatus for Oxygen Gas Bubbling Method
1309
S122mm MgO Crucible
Slag • Metal
-4
Ar Gas Outlet
I-• [
• l
Ol
•-
I
I
Graphite CrucibleI•
"' " " ' ".. " i•i: ,": " .....
In du ction
Holder(A120
3
crucible)
Induction Coil
Fig.5 Schematic Diagram of 5kg Scale Apparatus for Oxygen Gas Bubbling Method
100
80
60 rNi
I&Co
0
*Cr
40
20
0 0.0
0.5
1.0
1.5
Amount of 02/Equivalent
Fig.6 Relationship between Oxygen Amount and Residual Ratio of Metals in Molten Metal 1310
used for basic parameter tests and 5.0 kg/cycle scale apparatus were used in order to confirm the performance of this process on larger scale tests. In an oxidation step, metal specimens were melted in magnesia crucibles using an electric or an induction furnace at 1873K with some flux (SiO2,CaO,MgO), then oxygen gas was bubbled into the molten metal (5-10 /mmin). In the next first reduction step, slight amount of carbon was mixed with the slag and melted with some amount of iron metal at 1873K. The cobalt and nickel oxides in the slag were reduced preferentially by the carbon and absorbed into the molten iron metal with the mechanically suspended cobalt and nickel metal. In the second reduction step, more amount of carbon was mixed with the slag and the mixtures were heated up to 1873K. Chromium and iron are reduced and form a metal layer which contains very little amount of nickel and cobalt. Reduction slags can be recycled as an oxidation flux. Molten Salt Electrolysis Method Experiments had been carried out using 1.0kg/cycle LiCI-KCI molten salt containing 1.Owt% iron. Stainless steel or carbon steel rod, which were conditioned with 1.Owt% cobalt in advance, were used as anode. Some diaphragms were tested to prevent the contamination of nickel and cobalt slime into a deposit on a molybdenum cathode. Salt temperature and current density were fixed at 723K and 0.05(A/cm2) respectively. RESULTS Oxygen Gas Bubbling Method Chromium and iron were oxidized preferentially, then separated into the slag from cobalt and nickel remaining in the molten metal. Fig.6 shows the metal residual percentage in the molten melt against the amount of oxygen introduced. The maximum separation ratio was attained at an equivalent oxygen of about 1.2 times of the stoichiometric amount of oxygen oxidizing 100% chromium and 80% iron. Adding 0.2 times carbon with respect to the stoichiometric amount which reduces the cobalt and nickel in the slag, assuming all of them were oxide, led to the maximum separa
Data Loading...
