Submerged Arc Furnace Ferronickel Smelting Process

Submerged arc furnace ferronickel smelting process is one of the mainstream pyrometallurgical technologies for producing ferronickel alloys from laterite nickel ore, particularly widely used in China and Southeast Asia.

This process is typically the core component of the RKEF (Rotary Kiln-Fused Arc Furnace) process, offering advantages such as mature technology and stable product quality.

The following systematically introduces the SAF smelting ferronickel from the perspectives of principle, process, equipment, raw material requirements, advantages etc.

I. Basic Principles of the Submerged Arc Furnace

A ferronickel furnaces is a metallurgical device that uses electrical energy to generate a high-temperature electric arc and resistance heat through graphite electrodes. Under a reducing atmosphere, it reduces nickel and iron oxides in laterite nickel ore to their metallic state, forming ferronickel alloy (FeNi) with silicon, carbon, and other elements.

Main Reduction Reactions (Simplified):

• NiO + C → Ni + CO

• FeO + C → Fe + CO

Reducing Agent: Usually coke or semi-coke.

Temperature: The temperature inside the electric furnace can reach 1450–1600°C, sufficient to melt the metal and allow it to settle to the bottom, forming an alloy phase, with slag on top.

Note: "Immersion" refers to the electrodes operating deep beneath the charge layer, with the arc covered by the charge, reducing heat loss, improving thermal efficiency, and protecting the furnace lining—this is the standard operating mode for SAF, not an independent process.

II. Ferronickel Smelting Process (Taking RKEF as an Example)

RKEF = Rotary Kiln – Electric Furnace

1. Raw Material Preparation

Lawrence nickel ore (usually limonite type, Ni 1.5–2.5%, Fe 30–50%, high MgO and SiO₂ content)

Add reducing agent (coke/semi-coke), flux (limestone, dolomite, etc. to regulate the slag system)

2. Drying & Pre-reduction (Rotary Kiln)

The ore is roasted in a rotary kiln at 800–1000°C to remove crystal water, and some Fe/Ni oxides are initially reduced.

The produced "hot calcine" is directly fed hot into the submerged arc furnace, resulting in significant energy savings.

3. Smelting & Reduction (Submerged Arc Furnaces)

Hot calcine + reducing agent + flux are added to the ferronickel furnaces.

Deep reduction is achieved under a strong reducing atmosphere, producing:

• Lower layer: Nickel-iron alloy (containing 10-30% Ni, the remainder mainly Fe, with small amounts of C, Si, S, and P)

• Upper layer: Slag (mainly composed of CaO–SiO₂–MgO–Al₂O₃ system)

4. Iron Tapping & Refining

Iron is tapped periodically. The molten nickel-iron can be cast into ingots or sent to a refining furnace (such as AOD) for desulfurization and composition adjustment.

The slag is water-quenched or used in building materials.

III. Key Equipment: Submerged Arc Furnace

• Structure: Circular or rectangular furnace body, 3 self-baking electrodes (Søderberg) or combined electrodes.

• Power: Large ferronickel SAF can reach 30–72 MVA.

• Operating Characteristics:

Electrodes are "immersed" in the charge (hence the name Submerged Arc)

Continuous feeding, intermittent iron tapping

Automatic control of electrode position, power, and charge level

IV. Raw Material Requirements

The core of submerged arc furnace ferronickel smelting process (especially the RKEF process) lies in the efficient reduction of nickel-iron oxides using electrical energy. Despite the challenges of high energy consumption and high carbon emissions, it remains highly competitive in regions with low-cost power resources (such as hydropower and self-owned power plants). 

Its characteristics include not relying on refractory linings and using copper water jacket cooling, improving furnace lifespan and operational stability. Compared to traditional methods, the submerged design can more fully utilize electrical energy, increasing nickel-iron yield and representing an important development direction for current green and low-carbon smelting technologies.

For any questions or needs regarding SAF, ferronickel furnaces, and other metal smelting equipment, please feel free to contact Sanrui Electric Furnace for one-stop service and turnkey projects.