Decarbonizing copper smelting: a reliable method for carbon footprint comparison between different technologies

According to the International Energy Association (IEA) forecasts,the demand of copper can reach even 30 Mtpa in 2030, which translates to a +25% increase to today’s level. This is a tall order since the existing operations can only produce so much and developing new supply capacity takes time. As a result, we can expect copper price to increase, and this will drive new investments respectively.

At the same time as we need to increase the production of copper to support the boom in electrification, we need to put continuous effort into reducing the emissions that processing of copper and other necessary minerals and metals produce. In general, copper is not the most energy intensive metal to produce, but as new deposits are becoming much harder to mine and typically contain less copper in ton of ore than some 20 years ago, more processing is needed. Also, higher amounts of impurities, such as arsenic, are becoming the rule, not an exception.

Until now, there hasn't been reliable comparison of emissions produced with different copper smelting technologies. Our experts Christina Alexander, Hannu Johto, Mari Lindgren, Lauri Pesonen, and Antti Roine took the challenge and developed a systematic method for this, continuing the LCA pioneer work of Professor Reuter in 2015.

The findings of the team were recently published at ScienceDirect, the world's leading source for scientific, technical, and medical research.

Emission sources and calculation methods

When you extract ore from the ground, you need to process it much more than years ago to produce a sufficient concentrate grade with acceptable impurity levels, and later metallic copper. All this obviously requires extra energy - and the big question is where the energy comes from and in which form.

The overall carbon footprint can be calculated as follows:

• how much you directly release in your own operations (so-called Scope 1)
• how much did the supplier of electricity, steam, heat and cooling generate (Scope 2)
• how much your other value chains emit (Scope 3).

For copper, all these amount to about 4.5 tonnes CO2-eq per tonne of copper in average, largely depending on the source of electricity. From the total emitted 30 billion tonnes of CO2-eq, this represents about 0.31%. Not a totally insignificant share.

Approximately 80% of the carbon emissions generated in copper production originate from copper concentrate production, while the share of concentrate treatment to metallic copper is about 20%. Both process steps can be optimized by selecting the right type of technology for the best energy efficiency and minimized carbon dioxide emissions.

In terms of mining and metallurgy of copper, the question is primarily about the share of renewables in energy production, and secondarily, about the use of carbon containing direct consumables such as coal, natural gas, and diesel. Our task in technology development is to help our clients to minimize the overall energy used and shift completely away from fossil sources to carbon neutral ones. However, this is nothing new to us at Metso Outotec - we have been working on these technologies close to one hundred years already, but now it has become more critical than ever. In copper smelting, Metso Outotec’s energy efficient Flash Smelting has been used for more than 70 years, and our Ausmelt® furnace technology is known as an effective option for the treatment of impure concentrates. 

Creating a reliable life cycle impacts assessment

As mentioned, Metso Outotec has over the years done a lot of research and development on how to calculate copper smelting’s life cycle impacts. Instead of comparing different real-life operations with various technologies and own reporting methods to each other, we decided to deep dive into this issue by creating comprehensive mass and energy models for each process unit in our HSC SIM simulation software.

This allowed us to compare apples to apples, so to say. When the foundation is there and the first baselines have been created, we are able to calculate the energy use of each process route on a very detailed level by feeding in the concentrate assay and desired capacity. In addition to energy use, the simulation also provides data on operational costs and life-cycle assessment over the course of the plant. This is very valuable information for the customers and their project financiers.

So far, the evaluation has been made for copper smelting. According to the evaluation, the Flash Smelting (FSF) – Peirce-Smith Converting (PSC) process produces the lowest level of direct and indirect CO2 emissions in the base case. As this methodology has now been proven to be suitable for the life-cycle assessment, the process area in focus can be expanded. With this methodology, it is also possible to compare not only the technology selection, but also the impact of process changes to the environmental performance of the plant.

The main finding is that it makes a big difference which technology you use when smelting copper concentrates. In economic terms, the difference grows even more significant when you put a price tag on emitted carbon tonne. The methodology helps us to focus our development actions to the factors that have a significant impact on reducing CO2 emissions. Various initiatives can also be prioritized.

In copper smelting, the major source of the carbon emissions is the production of the electricity used in the process. By decarbonizing electricity production, emissions can be lowered with all production technologies. However, technology selection makes a difference on how much carbon emissions can be reduced. Once you know where the pain points are, how they originated, and what is the optimal situation, it is possible to devise a solution and a roadmap on how to get there – and Metso Outotec is happy to support in this quest.

Find out more about the assessment at Comparison of environmental performance of modern copper smelting technologies - ScienceDirect article