Ferronickel Smelting with DC Submerged Arc Furnace (DC-SAF)

Ferronickel Smelting with DC Submerged Arc Furnace (DC-SAF)

As global demand for stainless steel and new energy materials continues to grow, nickel—one of the most critical strategic metals—has become increasingly important. Ferronickel, with its stable composition, high metal recovery rate, and compatibility with stainless steel production, has become the dominant nickel source for the stainless steel industry. In the face of changing resource structures, declining ore grades, and rising energy costs, the pursuit of more efficient, economical, and environmentally friendly ferronickel smelting technologies has become a central concern for the industry.

Although the traditional Rotary Kiln–Electric Furnace (RKEF) process is well established, it presents limitations when processing low-grade ores, fine ores, or high-moisture laterite. High energy consumption, elevated electrode consumption, unstable furnace operation, and increasing environmental pressures further highlight these constraints. To improve metallurgical efficiency and expand feedstock compatibility, the DC Submerged Arc Furnace (DC-SAF) has rapidly emerged over the past decades as a new, high-performance solution for ferronickel production.

Leveraging its unique single-electrode DC arc structure, the DC-SAF provides highly concentrated energy, stable furnace operation, and strong ore adaptability. This technology has been widely adopted in ferronickel projects worldwide, particularly where low-grade laterite, fine ores, and large-scale continuous production are required. DC-SAF demonstrates significant economic and technical advantages under these conditions.

Overview of Ferronickel Smelting Process

The primary objective of ferronickel smelting is to efficiently extract nickel and iron from laterite nickel ores, producing a critical feedstock for stainless steel, specialty steels, and certain high-temperature alloys. Compared with sulfide nickel ores, laterite ores present more complex challenges: high moisture content, heterogeneous mineral structures, fluctuating chemical compositions, and generally low nickel grades, often varying significantly by mining region. These characteristics make the metallurgical process more difficult and highly sensitive to temperature, reduction atmosphere, burden structure, and energy distribution within the furnace. Therefore, selecting an appropriate smelting route is essential to minimizing energy consumption, maximizing metal recovery, and ensuring stable production.

Typical characteristics of laterite nickel ore include:

1. High moisture content (20–35%)

2. Complex mineral structures (silicate–magnesium–nickel–iron clays)

3. Large grade fluctuations (commonly 0.9–2.0% Ni)

4. Difficult reduction and low thermal stability

These features impose demanding requirements on the ferronickel smelting process, including:

1. High energy intensity

2. Strong feedstock adaptability

3. Efficient control of reduction reactions

4. Stable furnace management capabilities

   
   

Therefore, the choice of smelting technology directly affects production cost, environmental performance, and metal recovery efficiency.

1. The Two Main Technology Routes for Ferronickel Smelting

Globally, ferronickel production is dominated by two categories of processes: the traditional RKEF route (drying–pre-reduction–smelting) and direct electric furnace smelting via AC-SAF or DC-SAF. Over the past decade, as laterite resources have trended toward lower grades, finer particle sizes, and higher moisture—especially in Southeast Asia—the limitations of the RKEF route have grown more apparent. In contrast, DC-SAF technology, with its stable furnace operation, high energy efficiency, and excellent ore adaptability, is increasingly viewed as a key solution for the future of ferronickel production.

(1) RKEF (Rotary Kiln–Electric Furnace) Process

The RKEF process remains the most widely used ferronickel production method worldwide. Its core flow includes ore drying, rotary kiln pre-reduction, electric furnace smelting, and refining. In this system, the rotary kiln plays a crucial role by partially reducing NiO and FeO into metallic phases using coal or other reductants, reducing the energy demand of the subsequent electric furnace.

RKEF has advantages such as process maturity, high throughput, and suitability for large-scale operations. However, its drawbacks are increasingly prominent:

1. Long, complex process route

2. Strict ore particle size requirements

3. Difficulty processing fine ores and high-moisture ores (requiring pelletizing or prolonged drying)

4. High overall energy and coal consumption

5. Significant electrode consumption and furnace condition fluctuations

6. Reduced efficiency when ore quality is unstable

As ore variability increases, challenges such as kiln temperature instability, kiln lining issues, and pellet disintegration further reduce operational efficiency. These limitations have become a significant barrier to industry upgrading.

(2) AC-SAF (AC Submerged Arc Furnace) Direct Smelting Process

AC-SAF has attracted attention as a shorter, simplified smelting route compared with RKEF. By eliminating the rotary kiln, AC-SAF can directly melt and reduce laterite ores using high-temperature AC arcs. The process enables faster reactions and flexible ore blending.

However, AC-SAF faces inherent challenges:

1. Unstable three-phase arcs

2. Non-uniform temperature distribution

3. Higher risk of electrode breakage

4. Significant grid disturbances and flicker

5. High electrode and maintenance costs

6. These issues limit AC-SAF's deployment in large-scale, modern ferronickel projects.

DC-SAF: A New Generation of Ferronickel Smelting Technology

DC-SAF has thus emerged as a highly competitive solution. The system uses a single top electrode paired with a conductive bottom anode, producing a stable and focused DC arc. Compared with AC arcs, DC arcs offer superior stability, deeper penetration, and more uniform heat distribution—ideal conditions for laterite smelting.

Key advantages of DC-SAF include:

1. Highly stable arc and furnace conditions

2. Lower electrode consumption

3. Strong ability to process fine ores and high-moisture ores without pelletizing

4. High energy utilization efficiency

5. Reduced dust emissions and improved environmental performance

6. Better compatibility with large-scale, continuous operations

7. Lower flicker and reduced impact on the power grid

8. Excellent suitability for automation and digital control

With advances in power electronics, electrode manufacturing, refractory materials, and bottom-anode technology, DC-SAF systems are now more reliable and durable than ever, making them ideal for long-term industrial operation.

Industry Trends in Process Selection

The ferronickel industry is undergoing a noticeable shift in technology selection. As ore grades decline, feedstock becomes finer, and global energy and environmental constraints tighten, the long, energy-intensive RKEF route is becoming less competitive. Many new high-capacity ferronickel projects have already adopted DC-SAF as their primary smelting furnace. Existing RKEF plants are also exploring hybrid flows—such as “rotary kiln + DC-SAF”—to enhance flexibility and energy efficiency.

DC-SAF’s compatibility with automation, digitalization, and intelligent furnace control positions it strongly for the next generation of smart metallurgical plants.

Overall, while RKEF, AC-SAF, and DC-SAF will continue to coexist, DC-SAF is steadily becoming the key technology for the low-grade, variable laterite era. Its stability, adaptability, and high energy efficiency make it a vital solution for industry upgrades, energy savings, and environmental compliance in ferronickel production.