The environment can be protected by ensuring that the mining area is able to recover after the mine is closed. Photo: Teemu Karlsson, GTK

Environmental impact plays a key part in the lifecycle of mining operations

Text: Sami Lehtinen

Mining has various impacts on nature and the environment. This is why it is vital to supervise and ensure that operations remain under control throughout the lifecycle of a mine.

The environment can be protected, for example, by using all mining-related extractive waste and by ensuring that the mining area is able to recover after the mine is closed.

Use of extractive waste increasing

In excess of 99 per cent of all material extracted from a mine can end up as waste or forms waste material, and most of the waste volume comes from metallic mineral mines. In total, Finnish mines produce 90 million tons of waste rock and tailings per year. Waste rock is produced when rock material is removed from around ore. Valuable metals are separated from the ore using physical and chemical processes, and the remaining material is called tailings.

− The downside of tailings is its difficult storage. Final disposal may be expensive and cause adverse environmental impacts. However, the use of tailings has been studied and it has undisputed potential. It is very important that the potential use of tailings is already addressed when establishing a mine, says Soili Solismaa, geologist at the Geological Survey of Finland (GTK).

The potential to use waste rock and processing tailings is ultimately affected by a number of factors, such as their composition and quality, the location of the mine relative to applications of further processing and use, the costs of logistics, the legislation, as well as research and innovation. Extractive waste have normally been regarded as extra material, but the mindset is about to change.

− This change in attitudes results from greater environmental awareness, feedback obtained from the general public and also from various national and international directives, standards and regulations. Research plays a massive part. For example, GTK has for a long time surveyed the potential of using mining extractive waste. Currently, more and more mines have a utilisation plan, says Akseli Torppa, geologist at GTK.

Early characterisation of waste rock pays off

Waste rock is one of the most significant mining extractive waste. It comprises rock removed from around minerals. Tens of millions of tons of waste rock are generated in Finnish mines every year. In some cases, it can be used in construction, for example. However, the mining infrastructure is the most important application for waste rock. High-quality waste rock can also be sold as infrastructure material outside mines, but this must be separately indicated in mining permits.

Waste rock may also cause adverse impact on the environment. It may discharge hazardous, acidic and metal-containing seepage water. Even if waste rock does not cause any metal-containing seepage, waste rock piles are often sources of nitrogen emissions that cause eutrophication. Nitrogen originates from residues of explosives that are inevitably carried to waste rock piles. Nutrient emissions are particularly problematic in regions low in nutrients, where eutrophication is emphasised.

− Currently, the aim is to control the adverse impact caused by seepage water by dumping hazardous waste rock on a waterproof base, from where seepage water can be collected and forwarded for processing. It is important to characterise any waste rock resulting from mining operations as early as possible before any mining is started by using drill core samples taken in the mineral exploration phase. In this way, the structure of waste areas, water treatment solutions and the use of waste rock can be planned better, says Teemu Karlsson, geologist at GTK.

Closing a mine on the environment’s terms

In the end, mines are simply temporary work environments. Once all the minerals required have been recovered, it is time to stop mining and close the mine.  When closing a mine, it is important to ensure that the extractive waste facilities are closed properly and the mining area is remediated to the original state. This ensures that the environmental impact of the mine is as low as possible, and there can be no unnecessary adverse impact.

Closing a mine is a complicated process consisting of many stages. To facilitate this process, GTK has continuously developed tools and methods for sustainable mine closure by creating a mine closure handbook and a digital mine closure technologies resource. Currently GTK is leading an EIT RM funded project in which an advanced digital planning and management tool for continuous mine closure is developed together with domestic and European partners

Pöyry invests in the comprehensive management of mining waste

Pöyry operates in all fields of mining waste management. Pöyry specialises, for example, in defining the properties of seepage water, identifying storage requirements, designing waste area structures, surveying the building capacity of the ground and planning the closure of mining waste areas. The results of all work stages and reasons for each solution used are always entered in a mining waste management plan.

– The storage of mining waste has a significant impact on land use, which is why social and financial impacts on local communities need to be identified. The management of mining waste is part of the financial optimisation of projects. The disposal of financially valuable elements and usable materials that can be separated should be prevented. The circular economy has for long been part of mining waste management, and mining waste will be used in more diverse ways in the near future, says Päivi Picken, senior environmental consultant at Pöyry.

Picken points out that Finland has significant expertise in mining waste management, even though the field can be fragmented at times. Interaction between technical design, financial estimates and environmental surveys should be developed. Pöyry also aims to spread globally recognised and accepted operating methods, as they communicate sustainable operations and help to obtain financial support.