Covering the Hattorf and Wintershall tailings piles

There is no potash mining in the world without residues. At the Werratal potash plants, a large part of the residues is disposed of in tailings piles, as is customary worldwide. Rainfall on the tailings piles generates saline water, which in turn has to be disposed of. K+S sees covering and revegetating the tailings piles as an important contribution to further reducing their impact on people and the environment in the future. The aim is to minimize contact between precipitation and the salt body of the tailings pile and thereby reduce the generation of mineralized tailings pile water. Since the summer of 2022, the plateau areas of the tailings piles in Hattorf and Wintershall have been covered and then landscaped. Beginning in the early 2030s, we intend to progressively cover and revegetate the tailings pile slopes using a system specifically designed to meet the unique requirements of these structures.

The tailings consist of the residues from the production of fertilizers and other valuable mineral products in the surface plants. Rain or snow dissolves salts from the tailings piles. The resulting saline tailings water is collected in trenches around the pile, stored in basins, and then, in accordance with the relevant permits, discharged into the Werra river or used for the prescribed flooding of former mines. K+S and, therefore, Werra Plant aim to reduce the volume of saline tailings water generated by the tailings piles to the lowest technically achievable level through the implementation of a covering system. This is intended, for example, to further reduce discharges into the River Werra. At the same time, the covering system is expected to reduce the impact of the tailings piles on groundwater.

Four reasons form the basis for the measures to cover the tailings piles at the Werra plant:

The K+S Werra plant is aware of the importance of its long-term responsibility for people and the environment in the region. Covering the tailings piles is an expression of this commitment. Through the revegetation of the tailings piles, we aim to contribute to the enhancement of the landscape and the ecological development of these areas. The goal is to create sustainable solutions that address both environmental and social issues. The commitment extends beyond the environment. We work closely with the local communities, listen to their concerns, and work together on solutions that take different interests into account.

As a major employer and provider of training in the Werra Valley region, K+S wants to secure the jobs of the approximately 4,400 employees at the Werra plant in the long term. The continued existence and maintenance of the production sites is only possible if the disposal of production residues is secured. Sustainable management of residues and the covering of tailings piles ensure that K+S is a reliable partner for the people and the economy of the region, not only today, but also in the decades to come.

According to current planning, covering and subsequent revegetation of the tailings piles are intended to progressively reduce the infiltration of rainwater into the salt piles and thereby decrease the generation of tailings water, ultimately reducing it to the lowest technically unavoidable level. Tailings pile covering is intended to contribute to reducing the volume of saline waters generated and thereby support improvements in the ecological condition of rivers. The goal is to create a sustainable future in which industrial production and environmental protection go hand in hand. Reducing salt inputs into rivers is an important step in this direction and forms part of K+S's ongoing efforts to further reduce environmental impacts.

Werra Plant aims to integrate the tailings piles more closely into the surrounding landscape over the long term and support the ecological development of these areas. Through tailings pile covering and subsequent revegetation, we intend to reintegrate the tailings piles into the landscape. Revegetation is expected to create additional habitats for plants and animals while also supporting the re-establishment of native plant species. In this way, additional habitats can be created and biodiversity across the covered areas can be supported.

The implementation of an integrated tailings pile covering system is intended to achieve several key benefits:

1. Reducing the environmental footprint of Werra Plant as a production site, particularly through the reduction of tailings water generation.
2. Restoring the land surface, reintegrating the tailings piles into the surrounding landscape and creating new habitats for plants and wildlife.
3. Supporting the river basin management plan of the Weser River Basin Community (FGG Weser), with the medium- and long-term objective of achieving a good chemical and ecological status of the Werra and Weser rivers.
4. Maintaining the production capacity of Werra Plant and thereby helping to secure jobs in the region for the long term.

The covering of the tailings piles in the Werra Valley consists of two distinct sections: the flat plateau areas and the long, steep slopes. In 2022, we began covering the plateau areas of the tailings piles at our Hattorf and Wintershall sites. The system consists of a durable, tear-resistant synthetic liner that is placed on the prepared surface of the tailings pile. On top of this, a drainage layer and an approximately one-metre-thick soil layer are installed. The soil originates from the preparation of new tailings pile areas and can therefore be reused locally in a sustainable manner. The soil layer provides the foundation for vegetation establishment. The plants subsequently return a large proportion of precipitation directly to the atmosphere through evapotranspiration. The synthetic liner is designed to minimise the infiltration of rainwater into the tailings pile, thereby significantly reducing the generation of saline tailings water. Covering of the Hattorf tailings pile plateau was largely completed by the end of 2024 (approximately 6.8 hectares). Covering of the Wintershall tailings pile plateau is progressing steadily and is expected to be provisionally completed by the end of 2026.

Based on the positive experience gained with the surface covering already established on the tailings pile plateaus, as well as the numerous advantages of this system, plans are in place to extend the covering to the tailings pile slopes in the future. A prerequisite for this is the regrading of the steep slopes to allow the soil layer to be placed permanently and in a stable manner. The required reshaping will be carried out using tailings salt. Existing slope sections will be partially regraded, with the resulting material being selectively reused to reshape and flatten other areas of the tailings pile.

The standardized design of the low-profile covering system and the use of tailings material for slope regrading significantly reduce the need for external construction materials and, consequently, the volume of transport on public roads. Construction times are also shorter compared to other covering systems used on tailings piles, such as soil and demolition waste covers, which require large quantities of material. Overall, this approach reduces impacts on the surrounding environment and minimizes disturbance to local residents. At the same time, the technically sealed system is designed to significantly reduce the formation of contaminated saline seepage water.

This system is ideally suited to both sites, as it requires only a limited amount of material and enables rapid implementation through to completion of the entire slope covering project. Although covering the slopes will result in an increase in the footprint of the tailings piles, the further developed concept enables the implementation of a fully sealed system that, according to current planning, is intended to reduce the generation of saline seepage water in the long term to the lowest technically unavoidable level. To conserve natural resources and support sustainable practices, tailings material from our own production processes, as well as material generated from the selective regrading of existing areas, will be used primarily for reshaping purposes. As part of the permitting process, K+S demonstrates that only suitable and environmentally safe materials are used. As with the plateau areas that have already been covered, the soil applied above the sealing component originates from the surrounding region. In this way, we aim to further reduce the environmental impacts associated with our tailings pile sites. The multi-phase permitting process began in 2023 with the so-called scoping phase, during which the scope of the required investigations was defined. These investigations cover all relevant aspects, ranging from the quality assessment of the materials used and the long-term stability of the covering system to its impacts on people and the environment. A large proportion of the required studies has already been completed. The results are currently being incorporated into the application documents and prepared for submission. We will continue to provide regular updates on the progress of the permitting process and the covering project itself through our News section.

According to current planning, tailings pile covering is intended to contribute in the long term to reducing tailings water generation, improving the integration of the sites into the surrounding landscape, and supporting the development of near-natural vegetation communities on the covered areas.