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Nickel-iron raw materials generally fall into two categories: All-Union scrap waste ferrous metals and non-ferrous metal recycling All-Union Board Board recovered.
The sapphire recycling department of the Susu ferrous metal recycling bureau usually supplies sputum waste (USSR standard гOCT2785-75) and weighs 1 to 50 kg. Plate cutting heads, metal strips, wires, blocks, tube heads, metal blocks, sculptures, stampings, industrial depreciation waste, etc. are all in this category. A considerable amount is shavings or rolls of shavings that are made into chunks.
The waste of the All-Sugar Non-Ferrous Metals Recycling Bureau refers to various grades of alloy steel containing 3 to 60% of nickel, 15% of chromium , 1.6% to 2.6% of tungsten, and 1.5 to 3.7% of cobalt .
The waste of the All-Sugar Non-Ferrous Metals Recycling Bureau is characterized by a metal alloy that does not contain waste rock, oxygen, sulfur and other impurities. The above situation is of great significance when selecting a processing technology.
Unlike the all-Sue ferrous metal recycling bureau waste, the non-ferrous metal recycling bureau's waste is used to process various salts, electrolytic sludge, catalysts, waste batteries, corundum powder, etc., as well as metal powders and waste materials of various sizes. Among these wastes, the nickel content is less than that of the ferrous metal recycling bureau, but it does not contain impurities such as tungsten and molybdenum . Of course, some scrap contains 5% cobalt.
The total Soviet standard is limited. Nickel iron contains 5% cobalt, 0.2% sulfur, 0.05% phosphorus , and 0.3% copper . It should not contain chromium, tungsten or molybdenum.
Therefore, the process of producing ferronickel from recycled raw materials should consider removing all metals except iron and nickel, as well as removing oxygen, sulfur and other impurities. Experience has shown that the most convenient metallurgical equipment for processing materials containing nickel and iron is an electric furnace.
In order to remove tungsten, molybdenum and cobalt in the smelting, it is oxidized and converted into slag. Oxygen entering the furnace with air is an oxidant in the pyrometallurgical process. The electric furnace smelting should have a reducing environment or a neutral environment to avoid strong oxidation of the electrodes. In this case, the "solid" oxygen in the furnish, i.e., the oxygen in the form of a compound, which, upon smelting, converts the oxygen into a metal of the slag.
MeO+Me'=Me'O+Me (1)
From a thermodynamic point of view, if ΔG° T is less than zero, the reaction proceeds to the right,
lgK level = (Me'O) [Me] / (MeO) [Me'] (2)
Has a positive value. lgK flat larger, the greater the possibility for the reaction to the right, as
△G° T =-RT lgK flat (3)
Oxygen needs to enter the furnace together with the metal that is not doped with the semi-finished nickel-iron, and this metal can only be nickel and iron. Thus, the smelting furnace ingredients should consist of metal scrap and a solid oxidant with nickel and iron oxide.
In companies that have both ferrous metal recycling and non-ferrous metal recycling bureau waste, they can be processed together.
As mentioned above, one of the extensive wastes of the Non-Ferrous Metals Recycling Bureau is the waste battery.
Table 1 Chemical composition of various components of the battery
Battery electrical component | Weight (kg) | iron | nickel | ||||
Total amount | Including metal amount | ||||||
% | kilogram | % of total iron | kilogram | % | kilogram | ||
Top cover | 1.26 | 99.32 | 1.25 | 95 | 1.2 | 0.4 | 0.005 |
Negative pole | |||||||
powder | 2.5 | 66.13 | 1.65 | 22.9 | 0.57 | 0.49 | 0.012 |
Pole piece | 1.37 | 91.66 | 1.25 | 79.8 | 1.10 | 0.12 | 0.001 |
frame | 0.30 | 99.80 | 0.30 | 82.6 | 0.25 | - | - |
total | 4.17 | - | 3.20 | - | 1.92 | - | 0.013 |
average | - | 77.0 | - | 45.9 | - | 0.33 | - |
Positive pole | |||||||
powder | 2.28 | 1.58 | 0.04 | 1.58 | 0.40 | 43.12 | 0.983 |
Pole piece | 1.24 | 97.80 | 1.21 | 97.80 | 1.21 | 1.90 | 0.023 |
frame | 0.41 | 99.48 | 0.41 | 99.47 | 0.40 | 0.23 | 0.001 |
total | 3.93 | - | 1.66 | - | 1.65 | - | 0.007 |
average | - | 42.2 | - | 37.1 | - | 25.7 | - |
Battery filler | 9.36 | 65.44 | 6.12 | 77.8 | 4.77 | 10.96 | 1.02 |
Table 1 lists the chemical composition of the various components of the battery. The calculation of the listed chemical compositions is based on the following ratios of the various batteries used for smelting:
TЖH-250 50%, TЖH-350 35%, TЖH-500 15%, TЖH-300B 10%.
In the battery (by weight): 12% of the top cover, 47% of the positive electrode, and 41% of the negative electrode. In the electrode (including positive and negative) (by weight): frame 7%, plate 25%, powder 65%.
Listed below are data on nickel content in waste batteries:
Battery type TЖH-250 TЖH-350 TЖH-500 TЖH-300B
Nickel content (% of battery weight) 9.6 9.2 10.3 8.5
Nickel content (% of battery weight) 9.6 9.2 10.3 8.5
According to the content of nickel, the most significant one is the positive electrode. The chemical composition is: 22 to 25% of nickel, 32 to 37% of iron, 8 to 10% of carbon, 0.04 to 0.07% of sulfur, 0.01 to 0.02% of phosphorus, 0.04 to 0.06% of copper, and 0.11 to 0.15% of tin . The negative electrode contained 0.31% of nickel, 78% of iron, 1.96% of carbon, 0.03% of sulfur, 0.01% of phosphorus, and 0.06% of copper. [next]
Originally, smelting ferronickel used only the positive electrode, and now the negative electrode is also used as a charge.
The metal casing is packaged and sent to a recycled ferrous metallurgical enterprise. In the battery block, nickel exists in the form of Ni(OH) 2 Ni(OH) 3 , iron exists in the form of Fe(OH) 3 , and also has a small amount of sodium (Na 2 CO 3 ), alkali (NaOH) and carbon. The metal hydroxide is combined with the metal scrap to simultaneously decompose and subsequently vent the water vapor. The high valence hydroxide is not very stable. The most stable are hydroxides of alkali metals and alkaline earth metals.
As the water in the hydroxide decreases, the pressure of decomposition decreases, and the reaction process is slower. Excluding the last water molecule requires a higher temperature. If the physical decomposition of hydrogen hydroxide begins at a relatively low temperature (200-250 ° C), the temperature at which the decomposition is completed should be above 500-700 ° C. The sodium carbonate in the charge also decomposes and the reaction begins at 1027 ° C and ends at 1500 ° C.
Among the various metal oxides, Na 2 O is the most stable and can be smelted without decomposition, and can actually be completely transferred into the slag. The presence of Na 2 O in the slag is desirable because it reduces the melting temperature of the slag. For example, the melting temperature of 2Na 2 O·SiO 2 is 1080 ° C, and the oxide of nickel is very unstable.
The properties of the metal oxide in the reducing environment can be judged by the data in Fig. 1.
Figure 1 Comparison of various metal oxide reduction curves
In the smelting, not only carbon and carbon monoxide can be used as a reducing agent, but also iron and nickel, and a metal having a large affinity with oxygen can also be used as a reducing agent.
As the affinity for oxygen increases, the metal sequence in the charge is: copper, nickel, cobalt, molybdenum, iron, tungsten and chromium, ie, during smelting, the displacement reaction will be intense:
3NiO+2Cr=Cr 2 O 3 +3Ni3NiO+Mo=MoO 3 +3NiO, 3FeO+W=WO 3 +3Fe, NiO+Fe=FeO+Ni
In the presence of excess ferrous iron oxide, a tungsten compound FeWO 4 can be formed. The melting temperature of WO 3 is 1370 ° C, and above 800 ° C, the sublimation phenomenon is remarkable. The saturated vapor pressure can be expressed by the following equation as a function of temperature:
| ||||||||||
The MoO 3 melting temperature was 795 ° C, and at 650 to 700 ° C, the sublimation was remarkable. The vapor pressure of the oxide of liquid molybdenum can be expressed by the following formula: Â
P= | - | 1158360 | - 690lgT + 2988 | ( 5 ) |
T |
The oxidation of chromium is a fairly stable compound with a melting point of 2265 °C. When entering the slag, it combines with CaO to cause a compound having a relatively low melting point, and can also form a compound with SiO 2 . The state diagram of the Cr 2 O 3 -SiO 2 system is shown in Fig. 2.
Figure 2 Cr 2 O 3 -SiO 2 system state diagram
Since tungsten, chromium and molybdenum are very active at high temperatures, the oxidation of the surface is possible only by the oxygen in the gas phase, regardless of the reductive nature of the smelting (by the air entering the furnace). In individual cases, it is also possible to refine the metal by blowing oxygen through the molten pool or by charging the furnace with solid oxides (Fe 2 O 3 , NiO).
The use of iron-rich ore, iron oxide pellets and nickel oxide as solid oxidants has been verified in the relevant units. The possibility of selective oxidation of impurities by the following reactions is also confirmed:
3Fe 2 O 3 +2Cr=Cr 2 O 3 +6FeO ↘
3FeO+2Cr=Cr 2 O 3 +3Fe (6)
Fe 2 O 3 +Fe=3FeO
Fe 2 O 3 +W=WO 3 +2Fe ↗
In order to prevent oxidation of tungsten, a quartz flux can be added to the charge, which can form the olivine iron oxide to form the olivine and increase the activity of the tungsten oxide in the slag. After the chromium is introduced into the slag by means of the divalent nickel oxide, the tungsten is first oxidized, and then the iron is initially oxidized at a high alloy content. In the alloy, when the content of iron drops to 25 to 28%, molybdenum begins to oxidize. Molybdenum alloy refining requires the addition of divalent nickel oxide and flux. In order to obtain a water-soluble slag, it is recommended to use a sodium-containing material (2Na 2 O·SiO 2 ) as a flux.
Molybdenum should be a metal that is difficult to remove during smelting. Cobalt and copper are actually completely left in the ferronickel.
In the case of finished metal, the content of sulfur and phosphorus is limited. Removing these impurities is also very complicated. In practice, the original charge is supplied in such a way as to ensure that the content of sulfur and phosphorus in the nickel-iron is optimal, otherwise calcium slag will appear. In this case, sulfur and phosphorus may be transferred to the slag in the form of CaS and 4CaO·P 2 O 5 .
In the practice of producing ferronickel from raw biomass, an off-furnace desulfurization method is employed. This method is carried out in a ladle. In this case, the prepared dedicated melt (alkaline) is added to the ladle in a single small electric furnace, and then the ferronickel is discharged directly from the furnace into the ladle. This produces a desulfurization reaction:
Na 2 O+MeS=Na 2 S+MeO (7)
In order to remove a large amount of phosphorus, liquid nickel iron must be blown in a converter equipped with an alkali lining, in which case the experience of primary metallurgy is beneficial.
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