Not all energy sources are created equal. Carbon costs are a looming problem for the environmentally conscious miner, and carbon emissions studies are still a relatively young science. The use of fossil fuels, mainstay of global economies for decades, is beginning to suffer from changing attitudes towards carbon emissions, climate change, and environmental pollution.
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.