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Among the methods that have been studied for the treatment of nickel- containing scraps, the substantial disadvantage is that only nickel and iron and a small amount of cobalt can be recovered from the middle, and the cobalt transferred into the ferronickel is worthless, and it is not required in ferronickel. . Impurities such as tungsten and molybdenum enter the slag during smelting. They are not very concentrated in the slag, so recovering them from them is not economically economical. However, these two metals are now scarce reserves in the earth's crust is very limited.
The process for treating nickel scrap containing tungsten and molybdenum should take into account its storage in complex alloys or recovery in commercial products.
In the first case, a complex alloy steel having similar chemical compositions is processed into an alloy steel containing a proportionately added insufficient metal.
In primary or recycled non-ferrous metallurgical enterprises, only the lowest grade waste should be received. In this case, it is necessary to treat these wastes together with all valuable components that are beneficial to the national economy.
There are many ways to recover tungsten and molybdenum. The relevant unit proposed a method of melting waste materials containing tungsten and molybdenum, adding sodium carbonate in an electric furnace or blasting in a converter. The smelting products are nickel iron and slag, in which chromium , tungsten and molybdenum are enriched. The addition of sodium carbonate to the charge ensures the preparation of the water-soluble compounds Na 2 WO 4 and Na 2 MoO 4 . These two compounds can be separated by a hydrometallurgical process.
Through industrial tests, the following deficiencies of this method can be revealed: the furnace lining is rapidly depleted, sodium carbonate is dispersed in the atmosphere when oxygen is oxidized, and local overheating during oxidation causes a large amount of burning of the metal.
The Americans have proposed a method of treating melt oxidized impurities by placing iron oxide in an electric furnace and blowing oxygen to oxidize the impurities.
The melt is treated multiple times (8 to 10 times) with a mixture of iron ore, calcium oxide and silicon to ensure that the molybdenum is transferred to the slag. The use of 2Na 2 O·SiO 2 and 2CaO·SiO 2 instead of sodium carbonate eliminates the dispersion of dust into the atmosphere.
The recovery of tungsten and molybdenum from the slag can be carried out in accordance with the procedure shown in FIG. The slag is sintered in the furnace at a temperature of 800 to 900 ° C with sodium carbonate, and the consumption of sodium carbonate is about 10% of the weight of the slag. The leaching is carried out from a hot press leaching apparatus at a pressure of 2 MPa, and the sodium carbonate concentration is 200 to 250 g/dm 3 or less at a temperature of 200 to 250 °C. The recovery of tungsten in the semi-finished product is 95 to 96%, and the molybdenum is about 75%.
Figure 1 Slag treatment flow chart
The slag may also be treated by reducing the slag in an electric furnace with coke or silicon to obtain an intermediate alloy. According to the composition of the slag, the intermediate alloy may contain Ni2 to 10%, W10 to 15%, Mo5 to 10%, and the balance is iron.
Oxidation-vulcanization smelting is also a method when dealing with wastes containing high amounts of nickel, cobalt and other metals. The principle of this method is that the ratio of non-ferrous metals to oxygen and sulfur affinity is different. In the vulcanization environment, nickel, cobalt and most of the iron is vulcanized, and transferred to copper matte. Chromium, tungsten and molybdenum are simultaneously oxidized and transferred to the slag. Pyrite or matte may be used as a vulcanizing agent. Smelting is more suitable in an electric arc furnace, using oxygen as an oxidant. [next]
In order to extract tungsten and molybdenum from the slag, the slag must be sintered together with sodium carbonate.
Many researchers have proposed to smelt waste with alkali metal sulfide into ice-copper wall iron and slag. At this time, the metal undergoes oxidation in the following reaction.
3Na 2 SO 4 +2Cr→Na 2 Cr 2 O 4 +2Na 2 O+3SO 2 ↘
3Na 2 SO 4 +W→Na 2 WO 4 +2Na 2 O+3SO 2 (1)
3Na 2 SO 4 +Mo→Na 2 MoO 4 +2Na 2 O+3SO 2 ↗
In addition to these reactions, there are some interactions that can form metal sulfides:
Na 2 SO 4 +Ni+Me→Ni 3 S 2 +Na 2 MeO 4 +Na 2 S ↘ (2)
CaSO 4 +Ni+Me→Ni 3 S 2 +CaMeO 4 +CaS ↗
Wherein Me represents W, Mo and Cr.
Thus, by using sodium sulfate alone or in combination with calcium sulfate, it is possible to selectively convert tungsten and molybdenum into a compound which is soluble in water or dissolved in a weak alkali solution, and nickel and cobalt are transferred to matte. Studies conducted in an electric furnace with a power of 50 kVA have shown that when the waste is treated according to the process under study, the temperature can be below 1500 to 1550 ° C, and the amount of sulfate is 72 to 95% of the weight of the alloy, at 0.7. Within ~1.2 hours, Cr93%, W93%, and Mo79% were oxidized and transferred to the slag. At this time, the nickel matte is actually free of the above metals. The recovery of nickel in matte is about 88.0%.
MB Lukakov and BP Shereblenkov proposed the use of nickel in liquid magnesium to have good solubility characteristics to treat heat-strength steel scrap. As the research shows, molten magnesium can extract nickel well, but in fact, tungsten and molybdenum are not extracted, and iron is not dissolved much.
The extraction of nickel was carried out in an electric furnace at a temperature of 700 °C. The alloy of nickel and magnesium is distilled, magnesium is enriched and returned to the process. The residual solid iron, tungsten and molybdenum are further decomposed. The disadvantage of this process is that the dissolution rate is small (0.4 to 0.2 mm/hr). The material used for treatment should have a greatly expanded surface with a particle size of no more than 3 mm. This method is complicated to apply in industry because it requires a high level of sealing equipment.
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