II The recovery rate of nickel is low. The process of producing nickel iron generally has a nickel recovery rate of less than 90% in the ore. Some factories are still in the primary production stage of producing crude nickel iron and do not have refining workshops for nickel iron. Therefore, this recovery rate differs from the nickel recovery rate seen in foreign literature
III It is coke that consumes high energy and requires a high price. In terms of sintering process, on the basis of the inherent energy waste characteristics of small sintering machines, there is an additional factor of energy waste with high ore return rate. From the perspective of blast furnace process, one of the important reasons for phasing out small blast furnaces is energy waste, and now there is an increase in the factor of large slag volume. Some factories' blast furnace gas and waste heat have not been effectively recycled, wasting valuable energy and polluting the environment
4 The product is not refined and has a high impurity content, which does not meet the standards of international nickel product trade. We require nickel iron to have a high nickel content and low carbon, silicon, sulfur, and phosphorus content. Most of the nickel iron produced by blast furnaces in our country is high carbon, low nickel, and high silicon products, and the phosphorus content is determined by the raw materials. Currently, low phosphorus raw materials are in short supply. The value of nickel element in this semi-finished product is much lower than that of nickel element in qualified nickel iron, and the iron element is basically given to users without value. Five The investment per unit of nickel production is high: the investment in building mechanized material yards, sintering machines, and blast furnaces is higher than the investment in building RKEF processes. Of course, using existing small-scale equipment that is required to be phased out by industry policies to produce nickel iron can save investment. This process has been developed in the context of low-priced laterite nickel ore, extremely high nickel prices, and unfavorable implementation of environmental and energy policies. I believe that the price of laterite nickel ore will continue to rise, and nickel prices will fall back to a reasonable level. National environmental protection and energy conservation policies will be implemented, and this process will automatically exit market competition. The RKE F process of pyrometallurgy was invented in the 1950s with the aim of replacing the blast furnace process for producing nickel iron. This process has opened up a new chapter in the pyrometallurgical smelting of nickel iron. According to incomplete statistics, there are currently 17 nickel iron smelters worldwide that use this process. Basic process flow: preparation of ore processing and reducing agent
— & mdash; Rotary kiln calcination&dash& mdash; Hot charging into mineral thermal furnace smelting&dash& mdash; Off furnace desulfurization of crude nickel iron& mdash; Removing impurities such as silicon, phosphorus, carbon, sulfur, manganese, etc. in the converter& mdash; Refined nickel iron ingots require the construction of workshops for the recovery and utilization of iron and nickel from converter slag. (1) Preparation of ore processing and reducing agents
After the ore is transported to the raw material yard, it is crushed, neutralized, mixed, and mixed with a reducing agent before being sent to the rotary kiln. Some factories also pre dry the furnace materials before entering the rotary kiln, while others add a pelletizing process for the furnace materials. The proportion of furnace materials is important, as it plays a decisive role in preventing ring formation in rotary kilns (where the furnace materials adhere to the furnace lining), controlling the conductivity of the furnace materials, and separating slag and metals (nickel, iron) from the ore thermal furnace
(2) Rotary kiln calcination
The working area of the rotary kiln can be divided into three sections, namely the drying section, the heating section, and the roasting section. In the rotary kiln, the ore is roasted and dehydrated, reducing its weight by about 30%. At the same time, nickel oxide and some iron are reduced by the reducing agent in the furnace charge. A sealed discharge device is installed at the discharge end of the rotary kiln, and nickel slag is sent to the insulation feeding bin of the mineral thermal furnace at a temperature of 600-900 ℃ in an insulated state. Then, it is evenly distributed into the mineral thermal furnace through a sealed tubular material distribution device. According to the different processing methods of furnace materials, rotary kilns have different ratios of diameter to length. The burner structure of the rotary kiln is important for effectively adjusting the length and stiffness of the flame, ensuring that the temperature of the three working zones inside the furnace is within the required range of the process. In addition, it is necessary to fully consider using the flue gas from the rotary kiln to dry the furnace materials, in order to save energy
(3) Hot charging into the ore blast furnace for smelting
After being weighed, the material from the rotary kiln is loaded into the ore furnace in a hot state. The feeding system of the ore blast furnace needs to adapt to the needs of hot charging. Hot packaging is very important. In addition to recovering physical heat, it is also necessary to ensure that the material is not subjected to secondary oxidation during transportation. For environmental protection, industrial hygiene, dust recycling, and gas recycling, the blast furnace is sealed. By arc smelting in a blast furnace, crude nickel iron and electric furnace slag are separated, and a reducing gas containing 75% CO is produced. After purification, the gas is used as fuel for the rotary kiln, accounting for about 30% of the rotary kiln fuel. According to the different raw materials, 1 ton of raw ore can be roasted in a rotary kiln to obtain nickel slag with a concentration of 0.650-700kg. After smelting in a mineral thermal furnace, crude nickel iron with a concentration of 1.10-150kg can be obtained. The nickel content in crude nickel iron is generally between 10% and 18%. (4) Refining of crude nickel iron
· During the process of extracting iron from the ladle in a mineral heat furnace, soda ash is added to the ladle at a ratio of 5-15kg per ton of nickel iron. The sulfur content in the nickel iron can be reduced by 0.5% to 0.08%. It is also possible to inject granular magnesium into the ladle after tapping, which requires a special evaporator to inject the granular magnesium into a depth of about 1.0 m inside the ladle. This process can reduce the sulfur in the molten iron by less than 0.5%
· Remove the slag from the crude nickel iron water and mix it into an acidic converter, where it is oxidized by blowing oxygen silicon. In order to control the temperature of the molten pool from being too high, metal waste or nickel containing waste is added to the furnace
· After desilication, the nickel iron is then mixed into an alkaline converter, where carbon, phosphorus, and some iron are removed from the nickel iron. Add limestone to the converter during the smelting process. Lime can be used instead of limestone when there is sufficient nickel containing waste. The nickel iron produced from the alkaline converter meets the requirements of the commercial nickel iron standard and can be sold as commercial nickel iron. In addition, the two-step refining process for crude nickel iron involves changing the acidic converter to an alkaline converter and adopting a new process to achieve the first conversion
Desilication and desulfurization inside the furnace. The nickel iron from the first converter enters the second alkaline converter for dephosphorization and decarbonization. During the smelting process, lime and limestone are added to the furnace to ensure a suitable smelting temperature. Two step refining can obtain qualified refined nickel iron. 2.3 Process for direct smelting of stainless steel with crude nickel iron (under development) In the two-step refining process mentioned above, the second converter is changed to a refining converter using argon and oxygen, which can directly produce 300 series stainless steel. This process does not require the construction of electric furnaces for melting scrap steel, fully utilizes the heat of silicon oxidation, saves investment and energy, and fully utilizes the iron element in crude nickel iron. This technology has promising prospects, but it is still being explored
The factors that need to be considered in the construction of a nickel iron production plant are based on the strategic goals of comprehensive resource utilization and long-term development planning of the non-ferrous metal industry. It is necessary to choose suitable regions in China to build large-scale nickel iron production bases. However, be careful not to rush forward. The construction of a nickel iron production base should meet the following conditions:& middot; It is necessary to determine the source of the ore: different ores are suitable for different smelting processes. The pyrometallurgical process prioritizes using silicon magnesium nickel ore as raw material, and before deciding to build a nickel iron production plant, it is necessary to determine the source of suitable nickel oxide ore for dry pyrometallurgy. At present, the price increase of nickel ore has become a foregone conclusion, and the source of nickel ore will face difficulties
