① electrolysis. The enriched sulfide ore is roasted into oxide, reduced to crude nickel with carbon, and then electrolyzed to obtain pure nickel.
② Carbonylation method. Nickel sulfide reacts with carbon monoxide to generate nickel tetracarbonyl, which is decomposed after heating to obtain high-purity metallic nickel.
③ Hydrogen reduction method. Nickel metal can be obtained by reducing nickel oxide with hydrogen.
The smelting and extraction methods of nickel oxide ore can be divided into pyrometallurgical method and wet method. The former can be divided into ferronickel process and sulfur smelting process, while the latter includes reduction roasting-atmospheric ammonia leaching process and pressurized acid leaching process.
1 pyrometallurgical process
Pyrometallurgical process is usually used to treat magnesia. There are mainly two kinds of pyrometallurgy: one is to obtain ferronickel by reduction smelting in blast furnace or electric furnace, also known as ferronickel method; The other is to add vulcanizing agent to produce nickel sulfur by vulcanization and melting, also known as nickel matte process.
Ferronickel process is smelted in an electric furnace, which can reach a higher temperature and the atmosphere in the furnace is easier to control. However, in order to ensure the economy of ore treatment, it is usually required that the ore reach a certain grade, so before smelting, it is necessary to screen the ore to exclude the ore with low weathering degree and low grade. The burden should be dried and dehydrated in a rotary kiln in advance and prebaked at 700 ~ 800℃. The obtained calcine is mixed with volatile coal with particle size of 10 ~ 30 mm, and added to an electric furnace for reduction smelting to produce crude ferronickel. In the reduction smelting process of electric furnace, almost all oxides of nickel and cobalt are reduced to metal, but iron is not necessarily reduced to metal completely. The reduction degree of iron can be adjusted by adding reducing agent. Crude ferronickel is refined to produce finished ferronickel, which is mainly used to produce stainless steel. The principle flow of its production process is shown in Figure XX. The factories producing ferronickel by this method mainly include Donibo smelter in New Caledonia, Ceromotosa smelter in Colombia and Hachihu smelter of Sumitomo Corporation in Japan. Nickel-iron products contain 20-30% nickel, and the recovery rate of the whole process is 90-95%, and cobalt enters the alloy.
In addition, nickel matte can also be obtained by adding a vulcanizing agent to the silicon-magnesium-nickel ore, and gypsum is the most commonly used vulcanizing agent. Matte smelting is generally carried out in blast furnace, or electric furnace. The composition of nickel matte can be adjusted by adding reducing agent (coke powder) and vulcanizing agent (gypsum). The obtained low-nickel matte (usually containing Ni+Co=20~30%) is sent to a converter to be blown into high-nickel matte.
The factories producing high nickel matte mainly include Solo Arco smelter in Sulawesi, Indonesia. High nickel matte products generally contain 79% nickel and 0/9.5% sulfur/kloc. The recovery rate of nickel in the whole process is 70 ~ 85%.
Pyrolysis process is mainly used to treat silicomagnesite, which is suitable for treating nickel content >: 1%, iron content around 30% and low cobalt content. Its biggest feature is simple treatment process and short flow. The disadvantage is that cobalt also enters nickel-iron alloy or nickel matte and loses its due value.
2 Wet smelting process
Limonite-type laterite-nickel ore and low MgO content silicomagnesite-nickel ore are usually treated by hydrometallurgical process. Wet process mainly forms two processes, one is reduction roasting-ammonia leaching process (RRAL for short) and the other is pressure acid leaching process (HPAL for short). In recent years, great progress has been made in hydrometallurgy technology of laterite nickel ore, especially in pressure leaching technology and various solvent extraction technologies.
RRAL method was invented by Professor Caron, also known as Caron method, which is suitable for treating high magnesium content (MgO >；; 10%), the nickel content is about 1%, and the basic process is reduction roasting-ammonia leaching. The purpose of reduction roasting is to reduce nickel silicate and nickel oxide to metal as much as possible, and at the same time control the reduction conditions to reduce Fe to Fe3O4. Nickel and cobalt in calcine are leached by ammonia water, and iron in leaching residue can be recovered by magnetic separation.
Gubanyi Nicaro Smelter is the first smelter to recover nickel and cobalt from low-grade lateritic nickel ore by reduction roasting-ammonia leaching process. The reduction roasting is carried out in a multi-chamber reverberatory furnace, and the process is shown in Figure XX. In order to prevent the wet material from caking in the roasting process, the wet material was dried in a rotary kiln to remove 95% moisture before roasting, and the reduction roasting time was 90min. The reducing gas was supplied by a gas generator, and the reducing atmosphere at the bottom of the furnace was controlled to be 1: 1, and the roasting temperature was 730 ~ 760℃. After being cooled to about 65438 050℃ in reducing atmosphere, the calcined product was quenched in ammonium bicarbonate solution (ACC solution) containing 6.5% NH3, 3.5% CO2 and 65438±0% Ni. The leaching process is carried out in a blast leaching tank, and nickel and cobalt are leached into the solution to form nickel and cobalt ammonia complex ions. After iron removal, ammonia was directly distilled from the liquid to obtain basic nickel carbonate, and the final product NiO was obtained by calcination. The nickel oxide products here contain a lot of cobalt, which does not meet the production requirements of various nickel alloys. The recovery rate of cobalt is very low, only about 40%.
Aiming at the defect that cobalt in Nicaro smelter is not fully utilized, the nickel smelter in townsville, Queensland, Australia and Marinduk smelter in the Philippines have improved the Karon method.
In Towsville Nickel Smelter, the reduction roasting equipment adopts layered Herreschoff reduction roasting furnace, and heavy oil with 4% ore weight is mixed before feeding. The reducing gas in the combustion chamber heats the descending material layer by layer to the roasting temperature of 760℃. After quenching, it was leached in ACC system solution, and the leaching solution was precipitated with H2S to obtain Ni/CoS products (containing about 39% Ni and about 13% Co). The liquid after cobalt precipitation is evaporated by ammonia water, calcined, reduced and roasted by H2 in a belt reduction furnace to obtain nickel powder containing 90% nickel, and finally pressed into nickel blocks at 980℃ in an inert atmosphere. The nickel product obtained by chemical precipitation method has low cobalt content, which is suitable for producing nickel alloy, and cobalt has also been effectively enriched.
Marinduque Smelter is similar to Townsvillen Nickel Smelter, and the main differences are as follows:
( 1)
The reducing agent for reduction roasting is different from cobalt precipitation reagent: the reducing agent used in Marinduk Smelter is gas containing 75% H2 and 25% N2, and the reduction temperature is lower, only 650℃. In the process of separating nickel-cobalt powder from leaching solution, (NH4)2S is considered as the best chemical cobalt precipitation agent.
(2)
The basic nickel carbonate obtained by redissolving and vaporizing ammonia with AAC solution in Marinduk Smelter was partially vaporized to remove impurities, and then reduced with H2 at 165℃ and 3.5MPa to produce nickel powder products.