Production of metals offers both a problem and a solution for the heavy use of fossil fuels to provide energy in an increasingly ravenous world. Zinc, predominantly refined by electrolysis, is an energy hungry metal, even before considering the extent to which digging it out of the ground, shipping it to initial processing and sorting and waste disposal are already consuming energy usually provided by fossil fuels.

Factors For Consideration

When considering the context of carbon emissions on a site, there are a few key factors to consider. Firstly, what is a site doing? Is it a mine with high ore grades and minimal waste? Or a low-grade concentrate refiner? Purpose determines expectations of need for power and waste, and thus carbon footprint.

Secondly, does a site provide its own power, draw from a public power grid, or some mixture of both? And from whence does the public grid draw its power in turn? This is usually less of a mystery with metals commodities than with oil or gas sites, but integrated power circuits are not unknown.

Thirdly, equipment and technology. Does the company or site push the envelope, and attempt to integrate battery-driven gear, or do they remain with proven diesel driven vehicles and equipment? The choice between the two has come to define carbon emissions action around the world.

Finally, more modern technologies are generally more efficient, and often innovation offers superior environmental performance as well as production. Other factors exist, but the consideration of these factors will allow an understanding of the causes of carbon emissions.

Primary zinc production is not the most carbon-intense metal production process (that award goes to aluminium). However, the two most common steps can be laid out as follows; mining & processing to produce concentrate, then either the pyrometallurgical process of roasting, leaching, purification, electrolysis and then melting to shape into slab form; or the hydrometallurgical process of sintering, retorting and casting.

Almost every step in both methods requires significant energy input, usually as electricity or fossil fuel, but electrolytic and pyrolytic processes are particular energy hogs. A great deal of production, therefore, will need a great deal of energy; and consequently, careful consideration of the carbon costs may be needed for the savvy producer or investor.

The Cost of Doing Business

The chart below shows an aggregated series of the carbon cost of zinc per tonne produced. It attempts to review different estimates of carbon footprints in different nations and the different estimated assignations of carbon footprint weight to the mining or smelting or transportation sectors of the production process.

Without a clear framework with which to standardise measures, but also which particular sites are selected for study will heavily influence any given measure. A study that selects sites that are hydro-power or solar-power supported will have considerably lower CO₂-equivalent emission rates than one forced to use fossil fuel generation.

Who’s Making a Mess?

The major producers of the zinc world are not created equal. For some, like Scandinavian Boliden, carbon emissions are a problem with a set of powerful economies already behind them and only small logistical leaps to be made at a time. For others, like Vedanta’s Indian branch Hindustan Zinc, metals production comes with a heavy energy cost with more limited governmental support.

For those unfamiliar, Scope 1 refers to carbon emissions directly sourced from a site or process – for example, the burning of fossil fuels such as combustion engines. Scope 2 refers to indirect emissions – power generation elsewhere (such as a coal-fired power plant) that is then used on that site, or in that vehicle.

Scope 3 is unfortunately rather more poorly defined, nominally including ‘additional indirect emissions. What ‘extra’ emissions, exactly, seems to vary from place to place. Some suggest that it is any future carbon emissions form your product, more a concern for coal producers than zinc. Others, any emissions required to produce the tools you intend to use as a part of production. For this reason, at this stage Scope 3 is outside our current scope.

Vedanta, who via their subsidiary Hindustan Zinc are one of the world’s largest zinc producers, report their Scope 1 and Scope 2 carbon emissions as part of their sustainability responsibilities to their investors. Vedanta reported their Zinc India business as having Scope 1 Emissions of 4.48Mt of carbon dioxide equivalent for the 2019-2020 financial year. With their production of 870kt of zinc and lead in the year, a rough carbon intensity of 5.15 tonne CO₂-equivalent per tonne of metal produced (tCO₂e/t) is found for Scope 1. Vedanta’s Zinc India finds a Scope 2 intensity of 0.29tCO₂e/t.

In contrast, the Scope 1 intensity for Vedanta’s Zinc International business wing is 0.78 tCO₂e/t and Scope 2 is 2.07tCO₂e/t. Primarily this is due to a difference in power sources and mining methods – the Zinc International sector has solar power access via its connections in Africa, and it uses them effectively to minimize their own emissions.

Vedanta’s international zinc products primarily come from Black Mountain and Gamsberg – supported by the South African town of Aggeneys and its new associated solar power grid, the need for primary fossil fuel power generation on the site is much more limited and restricted. As a result, the site’s carbon intensities are mostly associated with Scope 2 – and Scope 2 tends to be more efficient carbon per unit of power to boot.

Hindustan Zinc’s operations, on the other hand, though investing in renewable power sources, directly operate coal-based power plants totaling 474MW. AME has assumed that this power plant is captured under Scope 1 emissions as it is a captured plant operated by the company.

Similarly, Korea Zinc’s 2019 carbon intensity can be calculated at 4.52 tCO₂e/t, based on reported tCO₂-eq emissions and production levels for the year. Korea Zinc predominantly draws its power from coal-fired power in Australia or captive combined cycle LNG power stations in Korea. The two power environments are noticeably different, but both are ultimately still sourced from fossil fuels. Alas, a business must make do with what it has cost-efficient access to. It’s also important to note that as Korea Zinc’s power generation is captive, it is regarded as Scope 1 rather than Scope 2. Korea Zinc’s Scope 2 is unreported but is likely to be negligible regardless due to their captive energy.

Unfortunately, zinc companies do not offer great clarity when distinguishing between mining and smelting. While models for mining estimate similar carbon emission returns to copper, at between 0.6 and 1.2 tCO₂e/t for most sites, the highly energy-intensive electrolytic and pyrolytic processes needed for the smelting of zinc are not so faithfully matched.

Smelting energy processes tend to be the first targets for companies looking to reduce their CO₂ footprint. Nexa Resources, another of the world’s largest refined zinc producers, claims a 1.32tCO₂e/t carbon intensity, and has already undertaken steps to reduce their carbon output.

The largest steps are always to move away from polluting fossil fuels towards lower carbon cost options. Nexa has committed to reduction of greenhouse gases by replacing the energy source of its smelters, whether by changing out petroleum-derived fuel for biomass or natural gas, or implementation of new systems that will utilize waste energy.

Boliden, another major zinc producer, whose operations are concentrated in Scandinavia, where climate change and carbon emissions have been treated as a public issue with the ensuing government funding aimed at addressing the perceived problem. Boliden Group’s Scope One carbon intensity for its metals production has been calculated by the company at 0.37tCO₂/t product, and Scope Two at 0.24tCO₂/t product.

It is worth noting that Boliden does not publicly distinguish between metals, and metals such as copper that have a lower energy electrolytic refining process, or gold that does not require electrolysis, will lower the ‘prospective’ CO₂ equivalent emissions used to measure zinc. Even so, however, the very low carbon intensities found in Boliden’s portfolio attests to the effectiveness of the national renewable power grids. Hydropower and wind power are significant contributors to the energy grid in Sweden and Norway.

What’s It Matter?

Carbon intensity is a crucial part of the push to net-zero and the implementation green energy. When set in isolation, intensity can make it very easy to look at a company and say ‘they’re not doing enough for climate change’. Unfortunately, life is rarely so simple. One of the most significant factors in zinc’s carbon intensity, and metals production more generally, is simply where you can find it and process it, and what tools the individuals, teams, companies and governments have to do so efficiently.

Renewable energy supply is perhaps the most important, as can be seen above. The enabling of major power sources from renewables can enormously reduce the impact of miners and refiners have on their carbon costs.

There is also one other, crucial factor that is looming in the back: standardisation of measure. Not just of Scope 3’s incredibly dubious definitions, but even of Scope 1 and 2. After all, not all energy sources are created equal.