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SMELTing PROCESS OF NICKEL Introduction Although it is best known for its use in coinage, nickel (Ni) has become much more important for its many industrial applications, which owe its importance to a unique combination of properties. Nickel has a relatively high melting point of 1,453 °C and a face-centered cubic crystal structure, which gives the metal good ductility. Nickel alloys exhibit high resistance to corrosion in a wide variety of media and have the ability to withstand a range of high and low temperatures. In stainless steel, nickel improves the stability of the protective oxide film that provides corrosion resistance. Its major contribution is in conjunction with chromium in austenitic stainless steels, in which nickel enables the austenitic structure to be retained at room temperature.

Modern technology is heavily dependent on these materials, which form a vital part of the chemical, petrochemical, power, and related industries. Nowadays, almost every nickel laterite ore processing in the world uses the pyrometallurgy method where smelting and reduction process is done by using Rotary Kiln – Electric Furnace or with Blast Furnace.

Steps of the Nickel Ore Smelting Process 1. Dewatering/Drying Dewatering or drying is the removal of mechanically entrained water from the concentrate. This process is typically performed in a rotating kiln that is 4 m diameter x 30 m long. The kiln is heated with

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pulverized coal, fuel oil, or natural gas. The moisture of the dried ore is typically about 22%, although in some operations this is significantly lower. The dried material is either sent directly to the calcination kiln or first to a crushing and screening plant and then to a calcination kiln.

ickel laterite ores are always mined from the surface and usually in the tropics. They are almost always wet and sticky and their moisture content varies from the wet season to the dry season. The upgraded ores are also wet and sticky. All the water in the upgraded ore must be removed before it is fed to the electric smelting furnace to avoid explosions in the furnace.

The water is removed in two processing steps: dewatering followed by calcination.

N

The objectives of dewatering are to make a product that has the following properties: • Consistent moisture content of approximately 20% entrained water.

• It does not stick or adhere to conveyor belts, machinery, etc.

• It is not too dusty.

2. Calcination and Reduction Calcination is a removal process of chemically bonded water from the dried ore and reduction is the removal of oxygen from the nickel and

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SME UI Student Chapter iron oxide in the calcine. The calcination kilns are much larger than the dewatering kilns, typically 5 m diameter by 100 m long.

The purpose of the kilns is to produce a bone dry, partially reduced ore. The kiln is heated with pulverized coal, fuel oil or natural gas.

The objectives of the calcination process are such as: • Removing the remainder of the water in the ore (to avoid explosions during subsequent electric furnace smelting).

• Reducing about a quarter of the nickel in the ore to nickel metal.

• Reducing most of the Fe3+ minerals to Fe2+ minerals and about 5% of the iron to metallic iron.

• Adding enough coal in the kiln so that some remains in the ore when it is transferred to the electric furnace for final reduction of nickel and iron.

• Providing the calcine at a temperature of about 900°C to the ferronickel smelting furnace, so that the energy used is minimized.

3. Refining The removal of impurities, such as sulfur and phosphorus, from the molten ferronickel.

Refining is performed in electrically heated ladles in batch mode in four steps: charging, phosphorus removal, sulfur removal and casting. a. Phosphorus Removal Phosphorus is removed from molten ferronickel into molten slag by reacting the ferronickel with lime, CaO and oxygen. b. Sulfur Removal Sulfur is removed from molten ferronickel most commonly by mixing calcium carbide, CaC2, into the molten ferronickel. c. Casting All ferronickel is used for making stainless steel and other ferrous alloys. It is therefore cast into shapes that are convenient for adding it to molten metal in furnaces and ladles.

The removal of phosphorus and sulfur from molten ferronickel is regarded as ladle metallurgy. All removal of phosphorus and sulfur is done in a ladle of freshly tapped ferronickel, which is physically moved through dephosphorization, desulfurization and casting stations.

Simple Diagram of Nickel Ore Smelting Process

Nickel Ore

Rotary Reduction Kiln

1

3

2 Rotary Dryer

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Feronickel Shot

5

4

Electric Furnace

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References Crundwell, F. K., Moats, M. S., Ramachandran, V., Robinson, T. G., & Davenport, W. G. (Eds.). (2011).

Front Matter. In Extractive Metallurgy of Nickel, Cobalt and Platinum Group Metals (p. iii). Elsevier. https://doi.org/https://doi.org/10.1016/B978-0-08096809-4.10039-5 Teknologi Pengolahan dan Pemurnian Nikel.

[Online]. Available from: https://ptpsm.bppt.go.id/ id/program-kerja/teknologi-pengolahan-danpemurnian-nikel/24 [Accessed 18 March 2021] Taylor, J. Campbell and Wise, Edmund Merriman (2013). Nickel processing. [Online]. Encyclopedia Britannica. Available from: https://www.britannica. com/technology/nickel-processing [Accessed 18 March 2021]

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