Understand your nickel emissions

Part 7 of CarbonChain’s ‘High-carbon Commodities’ blog series.

Nickel, valued for its high energy density, resistance to corrosion, and ability to withstand high temperatures, plays a critical role in the energy transition. It’s used in low-carbon technologies from wind turbines and solar panels to carbon capture systems, and perhaps most notably, battery production. 

Compared to other metals like aluminum, steel, and copper, nickel’s contribution to global greenhouse gas (GHG) emissions is small: roughly 0.27%. This is thanks to its current relatively low production levels, but that is poised to change rapidly. 

About 3 million tonnes of primary nickel materials (not from recycled origins) are put into the supply chain each year. However, the IEA anticipates nickel demand to increase by around 65% by the end of this decade.

With increased regulation on nickel emissions and reporting requirements coming into play, industry scrutiny is set to grow at pace with demand. Read on to understand how nickel’s carbon footprint is impacted at each stage of production.

What is nickel’s carbon footprint?

In 2019, nickel mining was responsible for around 120 million tonnes of CO₂e (carbon dioxide equivalent) emissions. 51 million of those tonnes were attributed to Scope 1 and Scope 2, while the remaining 69 million tonnes came from Scope 3 emissions related to freight and downstream production activities.

Producing high-purity class 1 nickel emits around 13 tonnes of CO₂e per tonne of product, while producing ferronickel (class 2) emits about 45 tonnes CO₂e per tonne of nickel content. 

However, nickel’s emissions intensity is highly variable with some estimates ranging from 20–80 tonnes CO₂e per tonne of nickel product depending on the production pathway and purity of the final product. 

For example, the carbon footprint of class 1 nickel (e.g. nickel cathode, used in lithium-ion batteries) can range between around 5–22 tonnes of CO₂e, according to CarbonChain’s analysis.

At the high end, this range is roughly five times as carbon intensive as copper (4.1 tonnes CO₂e per tonne of product) and about 10 times as carbon intensive as steel (1.9 tonnes CO₂e per tonne of product). 

What causes nickel’s emissions?

Emissions factors for class 1 nickel production depend on operations throughout the entire supply chain, with the energy use associated with mining, extracting, and processing being the key factor.

Emissions intensities are further compounded by declining ore grades. High-grade ores are becoming harder to find, while economies of scale are enabling larger volumes of recovery from lower-grade mines. Lower-grade ores are linked to higher emissions intensity due to the additional energy consumed in the mining and processing stages.

There are multiple pathways from which nickel can be produced, and they vary based on the type of ore being processed.

This is one example of what the emissions breakdown for nickel might look like:

However, this breakdown can change significantly depending on the specific supply chain. Supply chains can have assets within several different regions, so decarbonisation pathways need to be evaluated on a case-by-case basis. 

This is why relying on global or even country-level averages can disguise your true carbon hotspots and make reporting inaccurate.

How is class 1 nickel made? 

Mining

Nickel is made from two main types of ore deposits found in the Earth’s crust, each formed in different geological environments: sulfide (located in temperate to sub-Arctic regions) and laterite (located in tropical and sub-tropical areas). 

Both sulfide and laterite ores contain a low concentration of nickel: 0.5%–3% and 1%–2% respectively. The quality and concentration of nickel at this stage will determine the energy intensity required for processing.

The main source of emissions at this stage is from the fuel combustion required to power the mining equipment.

Processing

There are two main methods for processing ore deposits into nickel products. Sulfide ores are usually processed through a conventional ‘mine-smelt-refine’ pathway. Laterite ores require intensive hydrometallurgical processing (such as high pressure acid leaching or HPAL). This is a more carbon-intensive process due to the additional energy and chemicals required.

Method 1: ‘Mine-smelt-refine’

To date, roughly 70% of class 1 nickel is made from sulfide ore deposits that undergo a ‘mine-smelt-refine’ pathway. It involves three main steps: concentrating, smelting, and refining. 

Concentrating:

Sulfide ore is concentrated using a fairly simple electrochemical flotation technique. Froth flotation involves attaching fine nickel-sulfide mineral particles to bubbles and floating them out of a water–ore mixture. Typical recoveries to concentrate are about 82%.

While the froth flotation process itself is not energy-intensive, a lot of mechanical energy is required to first crush sulfide ore into a finely ground powder.

Sulfide ores are typically concentrated on-site for easy transport to the next stage of the process.

Smelting:

Flash smelting, which is powered with energy from coal and electricity (often coal-based), involves feeding dry sulfide ore along with preheated air and pure oxygen or oxygen-enriched air (30%–40% oxygen) to a 1300 °C furnace. The reaction of oxygen with iron and sulfur in the ore supplies a portion of the heat required for smelting.

The resulting liquid matte product is up to 45% nickel. Unwanted compounds, including leftover iron and sulfur, are removed as slag by injecting air or oxygen into the molten bath. 

After slags are drawn off, the matte is left with a concentration of 65%–80% nickel.

Emissions in this stage come mainly from burning fossil fuels to power the high temperatures required for smelting.

Refining:

There are a few processes used to refine nickel matte, though electrorefining and electrowinning are among the most common.

• Electrorefining involves dissolving impure nickel as an anode in an electrolytic solution, allowing the pure nickel ions to migrate and deposit on a cathode. This process typically uses a sulfate or chloride solution within a cell with a diaphragm to prevent impurities from passing from anode to cathode.
• Electrowinning is the process of “winning” dissolved nickel from solution by passing an electric current through a solution containing nickel ions, causing the nickel to deposit on a cathode as a solid metal. Nickel ions are reduced at the cathode while water is oxidized at the anode, generating hydrogen gas as a byproduct.

2Ni²⁺+2H₂O --> 2Ni +4H⁺+O²

Both processes are capable of producing very high purity metals.

The emissions intensity of this stage depends on the energy source used to power the process. Electricity may be generated from renewable sources or fossil fuels, and energy may be generated on-site or purchased from the local grid.

Method 2: HPAL

High-pressure acid leaching (HPAL) is used to produce about 30% of class 1 nickel today.

Unlike sulfide ore, laterite ore must be completely molten or dissolved to enable nickel extraction. Sulfide ore is first crushed into powder, mixed with water, and preheated. This slurry is then fed into an autoclave along with sulfuric acid at temperatures up to 270°C and pressures up to 725 psi to separate the nickel and other byproducts from the ore. 

This produces a mixed sulfide with a concentration of 20%–40% nickel. This mixed sulfide can be exported to a downstream partner, or further refined via hydrogen reduction to produce class 1 electrolytic nickel, briquettes, pellets, or powders.

Does the carbon footprint vary for different nickel production inputs?

High-pressure acid leaching (HPAL) is less carbon-intensive than smelting when using laterite ore. Limonite-laterite ore (the sub-class of laterite ore most suitable for producing class 1 nickel) is currently far more accessible than sulfide ore deposits. Approximately 73% of undeveloped nickel resources globally reside in laterite deposits.

High-pressure acid leaching of limonite-laterite ore is the most common pathway for class 1 nickel production today. However, when producing class 1 nickel products, HPAL is more carbon intensive overall than sulfide projects.

‘Mine-smelt-refine’ is generally more economic and less carbon-intensive than HPAL. However, sulfide ore deposits are becoming more difficult to find.

Reducing the CO₂e emissions of nickel production will depend on reducing the emissions intensity at every step in the value chain.

Where is lower-carbon nickel produced?

How are manufacturers and producers reducing nickel’s carbon footprint?

There are three keys ways to decarbonize nickel production pathways:

1. Implement new technologies: Selecting newer, more efficient and environmentally-friendly methods such as pressure oxidation-electrowinning (POX-EW) can reduce the carbon-intensity of nickel production processes. Vale, one of the largest producers of nickel in the world, uses a POX-EW hydrometallurgical system at its Long Harbour Processing Plant (LHPP).
2. Increase recycling rates: End-of-life recycling of lithium-ion batteries for the automotive industry will have a big role to play in reducing overall carbon-intensity of the nickel industry. Glencore uses a pyro-metallurgical process at its nickel smelting facility, where it achieves very high metal recovery rates.
3. Run on renewables: Reducing emissions intensity of nickel production pathways will require moving away from fossil fuel energy. One key lever to pull will be switching to zero-carbon fuels to power the high-temperature processes required in production. Powering smelters with hydroelectricity rather than diesel, as demonstrated by Vale, can reduce emissions by over a million tonnes of CO₂e each year.

Calculate your nickel emissions

With regulations like the EU Battery Regulation and CBAM (which applies to ferronickel) coming into effect, it has never been more important to understand the emissions factors affecting your nickel products at each step of production.

Nickel emissions can vary drastically. To meet regulatory requirements and demand for lower-carbon products, you must understand the emissions intensity of your commodity. 

CarbonChain’s carbon accounting platform has the granularity of data you need. Unlike most datasets that combine upstream metal processes into one product lifecycle stage, our data represents the real-world assets and product movements along the supply chain. We provide comprehensive data on nickel production emissions across more than 101 assets and 22 countries.

If you need help accurately measuring your nickel emissions, get in touch today.

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CarbonChain’s carbon accounting platform can help you accurately and automatically track your nickel supply chain emissions.