Using laterite nickel ore and electric furnace to produce ferronickel technology
Due to the advancement of steel-making technology, steel mills that used pure nickel raw materials to smelt alloy steel and stainless steel have switched to non-pure nickel from an economic point of view. Therefore, pyrometallurgical smelting has developed rapidly. There are two smelting methods for pyrometallurgical smelting of laterite nickel ore. One method is to produce nickel in a blast furnace, and the other is to obtain ferronickel by reducing smelting in an electric furnace.
Since blast furnace smelting is one of the earliest nickel smelting methods, this method has been gradually eliminated with the expansion of production scale, advancement in smelting technology, increased requirements for nickel-based raw materials in steel plants, and increased environmental protection requirements. Using an electric furnace for smelting:
(1) The temperature of the molten pool is easy to control, can reach a higher temperature, and can handle raw materials containing more refractory substances. The slag is prone to overheat, which is beneficial to the reduction of ferroferric oxide, and the slag contains less valuable metals;
(2) The amount of furnace gas is less, and the dust content is lower;
(3) The production is easy to control, easy to operate, and easy to realize mechanization and automation. Therefore, electric furnace smelting is a development trend. Since the melting point of laterite nickel ore is between 1600 and 1700K, the stability of the mineral oxides that make up laterite nickel ore is in order: CaO>SiO2>Fe203>NiO. The stability of the oxide determines the reduction of the element.
Therefore, laterite nickel The reduction sequence of oxides in the ore in a reducing atmosphere is NiO>Fe203>SiO2>CaO. In order to improve the quality of ferronickel products, electric furnace ferronickel smelting adopts the principle of selective reduction, that is, carbon-deficiency operation: in the process of electric furnace reduction smelting, almost all nickel oxides are reduced to metal, and iron does not have to be completely reduced to metallic iron.
The degree of iron reduction is adjusted by the amount of coke as a reducing agent. The proportion of nickel is relatively large, which will easily cause corrosion or burn through of the furnace wall and bottom during production (the production cycle is less than 1 month), and electrode accidents Frequently, the product contains low nickel. Therefore, the key technologies of electric furnace ferronickel smelting are:
(1) Extend furnace life,
(2) Reduce electrode accidents,
(3) Increase the nickel content of the product and the nickel recovery rate.
Electric furnace ferronickel smelting technical measures
1) The furnace is built with magnesia materials, and the adhesive should be equipped and the dosage should be controlled during the furnace building; when ramming, the thickness of each layer of the material is 40-60mm, and rammed tightly with a pneumatic pick. Only after the wool is spread can the next layer be rammed; the moisture should be dried in the oven process.
2) Use carbon bricks to build the furnace, change the carbon bricks to be placed horizontally to vertically, and drill holes in the middle of the carbon bricks to connect them into a whole with a small graphite electrode.
3) When the furnace is built, there must be a certain height difference between the two tap holes. The high tap hole is used in the early stage of production, and the low tap hole is used when the furnace bottom is corroded to a certain extent.
4) Control the amount of carbon and increase the voltage of the secondary furnace, control the depth of the electrode insertion, and prevent the corrosion of the furnace bottom.
5) Control the slag type, especially the FeO content in the slag, which not only affects the conductivity of the slag, but also affects the melting point of the slag, and ultimately affects the recovery rate of nickel.
6) The nickel ore needs to be dried and dehydrated before the furnace. The carbon content and moisture are controlled during drying and preheating, which is beneficial to reduce the occurrence of slag-turning accidents, and it is also conducive to electrode accidents caused by slag-turning.
7) When the electrode is pressed and released, it should be placed frequently and less frequently; if conditions permit, carbon electrodes or graphite electrodes can also be used.
8) Strengthen smelting operations, observe frequently, and adjust frequently.