Understanding RKEF and HPAL Technologies in Nickel Processing

Nickel is one of the most important minerals used across various industries, ranging from stainless steel production to electric vehicle (EV) battery components. Before it can be widely utilized, nickel must undergo complex processing to extract this high-value metal from its ore.

In this article, we will explore how nickel is processed using two main technologies: RKEF (Rotary Kiln Electric Furnace) and HPAL (High Pressure Acid Leaching). Each method has a different approach, produces different end products, and operates in different processing facilities, namely smelters and refineries.

Understanding Processing Facilities: Smelter vs. Refinery

Before discussing the technologies, there are two key terms in nickel processing that must be understood:

1. Smelter

A smelter is a mineral processing facility that uses a pyrometallurgical approach, meaning it relies on high-temperature heating and melting processes. Its main objective is to produce molten metal products such as Nickel Pig Iron (NPI) or Ferronickel (FeNi).

Key characteristics of a smelter:

• Uses extremely high temperatures (up to >1,300°C)

• Produces alloyed metals (ferroalloys)

• Commonly serves the stainless steel industry

2. Refinery

A refinery is a mineral processing facility that uses a hydrometallurgical approach, meaning it utilizes water-based solutions as the primary medium to extract and purify metals. The final products are typically high-purity nickel chemical compounds such as Mixed Hydroxide Precipitate (MHP) or Nickel Sulfate (NiSO₄).

Key characteristics of a refinery:

• Uses acid, pressure, and controlled temperatures

• Does not produce molten metal

• Commonly serves the battery and chemical industries

RKEF Technology: Processing Nickel Ore in a Smelter

What is RKEF?

RKEF (Rotary Kiln Electric Furnace) is one of the primary methods used in smelters to process laterite nickel ore, particularly saprolite ore, which contains relatively high nickel content. This method falls under pyrometallurgy, meaning it heavily depends on intense heat to transform raw ore into metal products.

Main Stages of the RKEF Process

The processing stages inside a smelter include:

1. Ore Separation

Nickel ore larger than 2 cm is separated at the initial stage.

1. Drying

The ore is dried in a rotary dryer at temperatures between 200–300°C. This reduces its moisture content from around 40% to approximately 20%.

3. Calcination

The ore is further heated in a rotary kiln at temperatures of 700–750°C to remove unwanted elements.

4. Smelting

The heated ore is then melted in an electric furnace at around 1,600°C to separate ferronickel from impurities.

5. Molding

The molten ferronickel is cast into ingots, ready to be shipped to the steel industry.

 

The final products of this process are typically ferroalloys such as Ferronickel (FeNi) or Nickel Pig Iron (NPI), which are used as raw materials in metallurgical industries, particularly stainless steel production.

Smelters using RKEF technology generally operate multiple large production lines continuously to achieve stable and high annual output. Several large-scale RKEF facilities in Indonesia produce thousands of tons of FeNi annually.

Read also: What Is Ferronickel? The Product Behind the Strength of Stainless Steel!

HPAL Technology: Processing Nickel Ore in a Refinery

What is HPAL?

Unlike RKEF, HPAL (High Pressure Acid Leaching) uses an entirely different approach and operates in a refinery. HPAL is a hydrometallurgical method designed to process limonite-type laterite nickel ore, which typically has lower nickel content but contains valuable elements such as cobalt.

Main Stages of the HPAL Process

Processing in a refinery involves the following stages:

1. Ore Washing

Limonite nickel ore is washed and separated from rocks and impurities, forming a slurry.

2. Thickening Process

The slurry is thickened until its solid content reaches approximately 45%.

3. Leaching

The slurry is pumped through pipelines into high-pressure vessels called autoclaves. Inside the autoclave, it is treated with concentrated sulfuric acid at temperatures up to 250°C and pressures of around 50 bar—comparable to the pressure found at a depth of 500 meters underwater. Agitators inside the autoclave continuously mix the material, allowing nickel to dissolve into the acid while other materials settle as residue.

4. Separation

The nickel-rich solution is separated from the slurry residue through seven Counter Current Decantation (CCD) tanks.

5. Purification

The nickel solution is further processed to produce a mixture of nickel and cobalt known as Mixed Hydroxide Precipitate (MHP), after removing aluminum and iron (FeAl removal process).

MHP can be further refined into nickel sulfate and cobalt sulfate. Most recently, Harita Nickel has also produced electrolytic cobalt using Electro Winning technology. These products have various applications, including raw materials for battery manufacturing, electronics, and specialty materials requiring high-purity cobalt.

HPAL technology is known for its higher operational complexity compared to RKEF, as it requires precise control of pressure, temperature, and chemical conditions. However, it enables greater value extraction from lower-grade limonite ore and supports the processing of more complex materials.

Meeting Global Demand from Obi Island

RKEF and HPAL are two distinct nickel ore processing technologies in terms of process, facilities, and final products. RKEF processes saprolite ore in smelters to produce ferroalloys such as FeNi or NPI, while HPAL processes limonite ore in refineries to extract high-purity nickel chemical compounds such as MHP or NiSO₄.

A clear understanding of how these technologies work explains how similar-looking nickel ores at the mine site can result in very different products at processing facilities.

The downstream industrial model on Obi Island demonstrates how RKEF and HPAL can operate side by side within a single industrial ecosystem. Harita Nickel utilizes RKEF to process saprolite ore into ferronickel for the stainless steel industry, and HPAL to process limonite ore into MHP, nickel sulfate, cobalt sulfate, and electrolytic cobalt as raw materials for EV batteries.

This integrated approach addresses two global demands simultaneously: stainless steel demand (through RKEF) and EV battery material demand (through HPAL).

In other words, Harita Nickel does not merely extract nickel it connects Indonesia to the global supply chain of strategic industries, creating broader added value for the national economy.