Article excerpted from the International Nickel Institute.

The main uses of nickel are: stainless steel and other alloys, as well as chemical uses including batteries. Stainless steel is the largest downstream market for nickel, while batteries are the fastest-growing application area.

To meet the global demand for nickel, the industry primarily relies on two sources of production: newly mined ore and recycled materials. Recycling—whether it's stainless steel and nickel alloys or batteries—is a significant component of the nickel value chain. The high recycling rate of nickel is a key aspect of its sustainability profile, but newly produced primary nickel currently takes center stage in the nickel market, with an annual production volume of about 3 million tons entering the supply chain.

Two main types of nickel ore

Nickel is found in two main types of ore:

Red earth ore (oxidized ore), mainly distributed in tropical and subtropical regions;

 Sulfide minerals are mainly distributed in temperate to sub-arctic regions.

The main nickel mining areas are marked on the map - some of which have multiple nickel mining projects, while others have only one project. In terms of the original nickel production of a single country, Indonesia currently contributes more than 50% of the global annual production. Ore is usually processed near the mining area, but there is quite active regional and global trade in laterite nickel ore, as well as a certain amount of trade in sulphide nickel concentrate.

 Red soil nickel mine

Red earth ores occur as surficial deposits and are traditionally divided into two main types: limonite-type red-earth nickel ore (with lower nickel content) and humus-type red-earth nickel ore (with higher nickel content). Limonite usually also contains cobalt as an additional valuable element, while the humus-type ore is mainly used for extracting nickel.

Today, limonite is mainly processed by leaching, which involves reacting the ore with sulfuric acid to dissolve out nickel and cobalt for recovery as nickel-cobalt intermediate products. These intermediates can be refined into nickel metal or directly used in the battery supply chain. This water-based dissolution processing technique is known as hydrometallurgy.

Red soil nickel deposits of the humus type are processed through smelting, which involves drying the ore and using coal and electricity (usually based on coal) for melting to recover nickel in the form of iron-nickel alloy. Iron-nickel alloy is often used directly for stainless steel production. With the growth of battery demand, we have seen a resurgence of an existing process that converts iron-nickel alloy into higher grade materials (nickel matte/high-grade nickel sulfide) through refining. This processing method, based on high-temperature melting, is known as pyrometallurgy.

Sulfide Nickel Ore

Sulfide ore can be close to the surface or buried deep underground and usually contains associated valuable elements in addition to cobalt, such as copper, platinum, and palladium. The total value of these associated elements may exceed that of nickel itself.

The treatment of sulphide ore differs from that of laterite ore. Sulphide ores can almost always be upgraded to a deliverable nickel concentrate at the mine site. The nickel concentrate can then be handled at a central facility, which is typically a nickel smelter where the nickel concentrate is electricity melted and the sulphur it contains is used to produce high-grade matte, and can be further refined, but there are also direct on-site hydrometallurgical methods that use.

Red soil nickel deposits

Red-clay ore bodies are formed by the weathering of parent rocks by water flow, which creates layered structures on the original rocks. Other variants of these deposits may contain aluminum (bauxite) or gold, with their composition determined by the parent rock and the degree of weathering. Red-clay nickel deposits originate from parent rocks with higher magnesium content, where the nickel content in their silicate rocks is lower. During the weathering process, elements are dissolved and transported before recrystallizing. These processes can form red-clay nickel deposits in less than a million years, but some deposits exposed in temperate and northern regions have not yet fully formed after more than a billion years of weathering.

The main processing methods for laterite nickel ore are smelting and high-pressure acid leaching (HPAL). Smelting is mainly used to process humus-type laterite nickel ore to obtain iron-nickel alloy (nickeliferous iron - FeNi, nickel pig iron - NPI), while HPAL is mainly used to process limonite or for the production of higher purity final products.

Red soil nickel mine smelting

At present, the dominant process in the industry is the RKEF (Rotary Kiln Electric Furnace), while the use of blast furnaces/high furnaces is less frequent. The RKEF process comprises three main steps: drying, reduction, and smelting. Laterite-type nickel ore is a conventional charge material, but limonite ore can also be smelted. Most production facilities follow the aforementioned process, although there are exceptions.

RKEF Process

The prepared ore (crushed and mixed as needed) is dried in a rotary dryer, usually heated by coal or natural gas to above 100°C to remove the free moisture from the ore. The goal is to produce material that neither sticks together nor becomes dusty, so it can be processed further.

After drying, the ore is sent into a rotary kiln for further drying and chemical treatment. In the rotary kiln, more heat is added by burning fossil fuels, raising the temperature to about 900°C. High-carbon products such as smokeless coal are also added as chemical reducing agents—to remove oxygen from iron oxide and nickel oxide minerals, thus reducing them to metals.

Limestone addition may also be possible to adjust the metallurgical chemical reaction. Both types of hot rolling drums generate dust that must be captured from the exhaust gases and recovered solids, adding complexity to dust collection and the blending of dust with new furnace charge.

 Simplified RKEF Process

The diameter of rotary dryers is typically 3-5 meters, and the length is 30-50 meters, while the length of rotary kilns can far exceed 100 meters.The hot partially reduced ore is then fed into an electric furnace, where chemical reduction is completed. Through the continuous reaction of electricity input and carbon added in the rotary kiln, as well as the reaction of the gradually consumed carbon electrode, the ore melts at a temperature of about 1500°C. The resulting liquid "metallized" iron-nickel product sinks to the bottom and is removed from there, while the lighter slag floats on top. The molten iron-nickel alloy undergoes refining to remove substances harmful to subsequent steel production processes, and then it is converted into solid form for transportation or, in some recent integrated production projects, directly fed hot into steel production.

These large rotary equipment must maintain continuous high-temperature operation on well-maintained roller systems. Electric furnaces require a very large continuous power supply, with some production facilities needing up to 40 MWh/t Ni of electricity. Most electric furnaces need complex cooling systems to ensure the longevity of the furnace lining.

The smelting process consumes a huge amount of energy, using fossil fuels to provide thermal energy and chemical reduction, as well as for power generation. The air pollution caused by coal combustion is similar to that of power plants, as long as the dust containing metals is properly controlled. The produced slag is relatively stable and can usually be used as construction materials.

 Full Life Cycle Approach

For metals with high recycling rates, such as nickel, the environmental impact of primary production can be depreciated over time, depending on how frequently the metal is recycled after a product cycle ends (e.g., nickel-metal hydride batteries or nickel-containing stainless steel) and reused in other products. The complete "life cycle" of nickel is generally much longer than that of nickel-containing end products.