Nickel matte and concentrate: properties and applications

Nickel concentrate and nickel matte are key intermediate products in the technological chain of nickel production. Concentrate is obtained by beneficiation of sulfide copper-nickel ores, and matte is produced by pyrometallurgical smelting of the concentrate. These materials serve as a link between the mining complex and final metallurgical processing, ensuring the production of high-purity nickel, cobalt and associated valuable components. Understanding their composition, properties and processing technologies is necessary for organising efficient supplies and stable operation of metallurgical enterprises.

Chemical Nature and Composition

Sulfide copper-nickel ores typically contain low amounts of nickel, so their direct smelting is economically unviable. Beneficiation allows the metal concentration to be increased tens of times. A typical nickel concentrate from sulfide ores contains approximately 10% nickel, 2% copper, 40% iron and 30% sulfur. Depending on the ore type and beneficiation technology, the nickel content in the concentrate can vary: processing a mixture of rich and cuprous ores yields a concentrate with 14.7–15.6% nickel at a recovery of about 77%. A collective copper-nickel concentrate may contain up to 9% nickel and 2–3% copper.

Nickel matte is an alloy of nickel and iron sulfides in which metals (nickel and iron) are dissolved. The basis of the matte consists of the minerals heazlewoodite Ni₃S₂, chalcocite Cu₂S and a metallic alloy based on nickel, copper and precious metals. Depending on the type of ores processed and the technological process, the matte may consist of nickel and iron sulfides, nickel-iron-copper sulfides, nickel sulfides or nickel-copper sulfides. The nickel content in matte produced by electric smelting is 7–16%, cobalt — 0.3–0.5%, iron — 17–55%. Smelting in shaft furnaces followed by converting yields fine matte containing 78–79.5% nickel, 0.3–0.5% cobalt and 0.2–0.3% iron.

Physicochemical Properties

Nickel mattes possess a number of specific properties that distinguish them from copper and copper-nickel mattes. The region of existence of nickel mattes in the Ni-Fe-S system is limited by the Fe-FeS-Ni₃S₂-Ni quadrilateral, and they do not stratify into sulfide and metallic phases at sulfur contents from 0 to 36%, remaining a homogeneous melt at the corresponding temperature. The density of nickel matte containing 16% nickel and 17% sulfur at 1250 °C is 5.88 g/cm³, and as the temperature rises to 1380 °C it decreases to 5.72 g/cm³. The melting range lies within 800–900 °C. The high aggressiveness of the matte towards refractory lining is determined by the content of metallic iron, which oxidises first due to its higher affinity for oxygen.

Classification and Processing Products

In metallurgy, matte is the name for an alloy of sulfides. Depending on the predominant metal, matte can be nickel, copper or iron. The final product of nickel matte processing is fine matte, containing mainly nickel sulfides and copper impurities. Solidified fine matte consists of two forms: nickel sulfide and metallic nickel, with the share of metallic nickel reaching 20% and depending on the sulfur content in the mass. Typical composition of nickel fine matte: 76–78% nickel, 19–21% sulfur, 0.2–0.4% iron, 0.3–0.5% cobalt and up to 2.0% copper.

For nickel concentrate obtained by flotation separation of fine matte, the nickel content is 67.2%, copper 5.0%, iron 2.7% and sulfur 22.3%. Nickel concentrate from flotation separation of fine matte is smelted in reverberatory furnaces to anodes, which are then subjected to electrolytic refining. The specific gravity of nickel concentrate is 3.97 g/cm³.

Production Technology

Production begins with the extraction of sulfide copper-nickel ores and their beneficiation. The main beneficiation method is flotation: crushed ore is treated with reagents that impart hydrophobic properties to nickel mineral particles, after which they are separated using air bubbles. The beneficiation scheme allows a collective copper-nickel concentrate or selective nickel and copper concentrates to be obtained.

The concentrate is then sent for pyrometallurgical processing. Sulfide concentrates are typically treated by smelting and converting to produce a nickel-rich matte. Smelting can be carried out in reverberatory, shaft, electric or flash furnaces. When smelting sulfide ores to matte in electric furnaces, the liquid products are copper-nickel mattes. Shaft furnace matte is blown in converters to fine matte. When converting nickel mattes in the first period, the main final product is fine matte containing 76–78% nickel, 17–20% sulfur, 0.2–0.45% iron and less than 2% copper.

Fine matte is crushed, ground and subjected to oxidative roasting in fluidised bed furnaces to nickel oxide, or separated by flotation into nickel and copper concentrates. Nickel concentrate is smelted into anodes, which are then subjected to electrolytic refining. High-nickel matte can also be used to produce electrolytic nickel, nickel oxide, ferronickel, nickel-containing alloys and various nickel salts, and after special treatment — directly for steelmaking.

Applications

The main purpose of nickel concentrate and matte is as feedstock for refined nickel production. Electrolytic nickel is obtained from fine matte and used in the production of stainless and alloyed steels, special alloys (nichrome, monel, inconel), electroplating coatings and battery materials. High-nickel matte also serves as feedstock for the production of nickel sulfate — a precursor for lithium-ion battery cathode materials.

Nickel concentrate obtained by flotation separation of fine matte is sent for smelting in reverberatory furnaces to anodes for subsequent electrolytic refining. In addition, concentrates and mattes can be processed by hydrometallurgical methods: oxidative dissolution of nickel matte in dilute sulfuric acid allows up to 90% nickel and 80% cobalt to be extracted. This opens up opportunities for flexible production of various nickel products depending on market conditions.

Safety and Storage

Nickel and its compounds belong to substances of moderate hazard. Dust from concentrates and mattes can cause irritation of the respiratory tract and skin, and prolonged exposure to certain nickel compounds is associated with the risk of sensitisation. When working with dusty materials, personal protective equipment must be used: respirators, safety goggles, gloves and protective clothing. Premises must be equipped with effective ventilation.

Storage of concentrates and mattes is carried out in closed warehouses or on equipped areas with hard surfacing that protect the material from moisture and contamination. When storing in bulk, mixing with other materials must be prevented and moisture content must be controlled, since high humidity can lead to caking and changes in technological properties. Transportation is carried out in bulk in specialised railcars, containers or in ship holds in compliance with the requirements for the transport of dangerous goods.

Market and Trends

The market for nickel concentrate and matte is closely linked to the refined nickel market. In recent years, there has been a shortage of quality sulfide raw materials due to the depletion of rich deposits and an increasing share of complex laterite ores. This stimulates price growth and intensifies competition among smelters for raw materials. Key trends include an increasing share of hydrometallurgical processing schemes, the introduction of digital technologies to optimise beneficiation, and tightening environmental requirements for mining and processing operations. The Asia-Pacific region remains the largest importer of nickel raw materials, while countries with rich resource bases are the main exporters.

Conclusion

Nickel concentrate and matte are critical links in the nickel production chain, ensuring efficient processing of sulfide ores and supplying smelters with quality feedstock. Understanding their composition, production and processing technologies is necessary for organising stable supplies and effective interaction between mining and metallurgical enterprises. Selecting the concentrate or matte grade for specific technological conditions and organising logistics requires an individual approach taking into account nickel content, impurities and logistical constraints.