At present, there are roughly three treatment processes for nickel oxide ore in the world, namely, a combination of a fire process, a wet process, and a fire-wet process. Fire process its output may also be divided into the product to produce nickel iron smelting reduction process and a reduction process to produce nickel matte smelting sulfide; wet process can be divided according to the different ammonia leach solution and acid leaching process Leaching The combination of fire and wet process refers to a process in which a nickel oxide ore is subjected to reduction roasting to select a useful product by a beneficiation method.
First, the fire process
(1) Reduction of smelting production of ferronickel
The most used in the world of fire treatment processes is reduction smelting to produce ferronickel. At present, at least 14 plants use reduced smelting to treat nickel oxide ore to produce ferronickel. The annual output of nickel-iron (including nickel) is about 250,000 tons, most of which are smelted in electric furnaces. Only a few smaller factories are smelted in blast furnaces.
The process of producing ferronickel by electric furnace is suitable for treating various types of nickel oxide ore. The production scale can be determined according to the supply of raw materials and the storage capacity of ore. It can be large or small, and the particle size of the furnace charge is not strict. Requirements, powder and larger blocks can be processed directly. The only disadvantage of electric furnace smelting to produce ferronickel is the high energy consumption.
The advantage of blast furnace smelting to produce ferronickel is that it has low investment and low energy consumption, and is suitable for areas with small production scale, difficulty in power supply, and low nickel content in nickel oxide ore. Its shortcomings are poor adaptability to ore, stricter requirements on magnesium content, and the inability to handle fine ore, as well as strict requirements for furnace charge.
(2) Reduction of sulfurized smelting to produce nickel bismuth
The process of reducing nickel sulfide produced by smelting and smelting nickel oxide ore is the earliest treatment of nickel oxide ore. It was applied in the 1920s and 1930s, and it was blast furnace smelting. This process has the same disadvantages as the process of smelting reduction smelting to produce ferronickel. Large-scale factories built after the 1970s have adopted the technology of electric furnace smelting to treat nickel oxides from nickel oxide ore. Currently, several of the largest plants with an annual output of more than 40,000 tons of nickel are in Indonesia and New Caledonia. The amount of nickel produced by nickel oxide ore in the world is about 120,000 tons.
The vulcanizing agent for reducing sulfurized smelting is available in the form of pyrite, gypsum , sulfur and sulfur-containing nickel raw materials. The advantage of using sulfur as a vulcanizing agent is that it is simple and easy, and does not have a negative impact on the smelting process (ie, does not affect the slag composition, does not affect the processing capacity, does not increase the power consumption), but it is more expensive, and the effective utilization rate of sulfur is not High, and there must be a set of facilities for sulfur melting and conveying spray. Sulfur is used as a vulcanizing agent in factories in Indonesia and New Caledonia, which are owned by International Nickel Corporation (INCO). After the sulfur is melted, it is controlled to be sprayed on the calcined roasting in the rotary kiln at a certain temperature to convert iron and nickel into sulfides, and then sent to an electric furnace for smelting to produce low nickel niobium. It is said that the source of its sulfur is natural sulfur in the crater, and its price is lower.
The process of producing nickel ruthenium by reductive smelting treatment of nickel oxide ore, the product of which has high flexibility of nickel bismuth: nickel oxide after desulfurization by calcination can be directly reduced and smelted to produce universal nickel for stainless steel industry; Nickel pellets and nickel powder are produced by the carbonyl-refined nickel raw material; since the high nickel niobium does not contain copper , it can be directly cast into an anode plate to send nickel sulfide electrolytic refining factory to produce cathode nickel. In short, it can be further processed to produce various forms of nickel products and to recover cobalt therefrom.
Second, the wet process
(1) Ammonia leaching method (Caron method)
After the reduction roasting, multi-stage atmospheric ammonia leaching is carried out. The representative factory is the Cuban Nicaro nickel plant constructed in the United States. Ammonia leaching treatment of nickel oxide ore, the product may be nickel salt, ammonia leaching process is not suitable for the treatment of copper and cobalt-containing high-nickel oxide or silicon-magnesium-nickel sintered nickel, nickel powder, nickel block and so on. The type (New Caledonia) nickel oxide ore is only suitable for the treatment of the laterite clay, which greatly limits the development of the ammonia leaching process. In addition, the recovery rate of nickel and cobalt in the ammonia leaching process is low, the recovery rate of nickel in the whole process is only 75-80%, and the cobalt is about 40-50%. So far, only four factories in the world have used ammonia leaching to treat nickel oxide ore, and they were built before the 1970s. For more than 30 years, no new plant has used ammonia leaching.
(2) Acid leaching
At 250 ~ 270 â„ƒ, high temperature and pressure conditions of 4 ~ 5 MPa, with a dilute sulfuric acid of nickel, cobalt and other valuable metals and iron and aluminum minerals dissolved together in the subsequent reaction, the pH value of the control constant conditions, The impurity elements such as iron, aluminum and silicon are hydrolyzed into the slag, and nickel and cobalt are selectively introduced into the solution, and are recovered from the solution by solvent extraction, sulfide precipitation and the like.
The wet process of treating nickel oxide ore began in the 1940s. The earliest use of the ammonia leaching process is that the nickel oxide ore is dried.
The industrial production of nickel oxide ore by the acid leaching process began in the 1950s. The representative factory at that time was the Cuban Ma'ao Nickel Smelter, which was also designed and built by the United States. The acid leaching process is suitable for treating low-magnesium oxide nickel ore. If the magnesium content in the ore is too high, the acid consumption will be increased, the operating cost will be increased, and the process will be affected. If the cobalt content in the ore is high, it is more suitable to adopt the acid leaching process. Not only is the leaching rate of cobalt higher than that of the ammonia leaching process, but since the value of cobalt is higher than that of nickel, the unit production cost of the acid leaching process is greatly reduced. Although the high-pressure acid leaching nickel leaching rate can reach more than 90%, the acid leaching process is also restricted by the ore conditions. At present, there are only three factories in the world that use acid leaching to treat nickel oxide ore, and the equipment is processed due to high temperature and high pressure. Demanding and running are not very normal. Overall, the development of the acid leaching process is not yet mature.
Third, the combination of fire and wet process
The fire-wet process combines the process of treating nickel oxide. Currently, there is only Oyama Smelter of Nippon Yakim in the world. The main process is: pulverized coal mixed with the pulverized ore briquetting, the briquettes dried and high temperature reductive roasting, roasting ore pellet was finely ground mineral ore pulp (reselection and magnetic) was isolated as a nickel-iron alloy product. The biggest feature of this process is the low production cost, 85% of the energy consumption is provided by coal, and 160-180kg of coal consumption per ton. The energy consumption of the fire process electric furnace smelting is more than 80% provided by electric energy, and the electricity consumption per ton of mine is 560-600 kWh. The cost difference between the two energy consumption is very large. According to the current domestic market value, the price difference between the two is 3-4 times. . However, there are still many problems in the process. Although the Dajiangshan smelter has been improved many times, the process technology is still not stable enough. After several decades, its production scale still stays at an annual output of about 10,000 tons of nickel. The technical key of the process is the temperature-controlled mixing of powdered coal and ore in the reduction roasting process. From the perspective of energy saving, low cost and comprehensive utilization (processing of low-grade nickel oxide ore) nickel resources, this process is worthy of further research and promotion. Russian researchers have conducted experimental research on the use of separation and roasting for flotation or magnetic separation in the Ural nickel oxide ore. It is considered to be the only method that can reduce costs, save energy and increase nickel production. It is suitable for processing any type of Nickel oxide ore.
The pyrometallurgical process of producing nickel-iron alloy in nickel oxide ore has the advantages of short process and high efficiency, but the energy consumption is high, and the largest component of its operating cost is energy consumption. For example, electric furnace melting is used, and only electricity consumption accounts for about operating cost. 50%, plus the fuel consumption of the drying and roasting pretreatment process before the smelting of nickel oxide ore, the energy cost in the operation cost may account for more than 65%. The low-grade nickel laterite ore is treated by the fire process due to smelting. The high energy consumption of ore is high, and the smelting cost is high. Therefore, the current fire process mainly deals with high-grade nickel laterite ore. At present, the main method for treating low-grade nickel laterite ore is wet process. Although the cost is lower than that of fire method, the wet process of nickel oxide ore is complicated, the process is long, and the process conditions are high. In summary, solving the problem of high energy consumption in the fire process and developing a new wet process to treat low-grade nickel laterite ore will be the future development direction of nickel smelting.
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