Presented paper

IMWA2019 Students work

Introducing a New Approach for the Stowage of Waste Brines from Potash Mines of the Werra District in Germany as a Measure to Ensure the Safe and Sustainable Continuation of Potash Extraction and Processing

Pinkse, Tobias (1); Quensel, Robert (1); Lack, Dittmar (1); Zimmermann, Reiner (1); Fliss, Thomas (1); Scherzberg, Heinz (1); Marx, Heiner (1); Niessing, Silvia (2); Deppe, Stephan (2); Eichholtz, Martin (2); Waldmann, Ludger (2)
1: K-UTEC AG Salt Technologies, Germany; 2: K+S AG, Germany

The importance of global potash extraction and processing has been significant for well over a century. Potash based fertilisers will, considering the growing world population, continue to be a vital resource for intensive agricultural land use. The German potash deposits of the Werra District, high in sulphatic and magnesium containing minerals, are unique in their ability to provide resources for the production of special fertilisers, i.e. potassium sulphate and magnesium sulphate. Globally the production of potash fertilisers is however not without controversy due to waste brine discharges into surface and ground water.

To ensure a responsible and sustainable continuation of potash extraction and processing in the Werra District, K-UTEC AG Salt Technologies, in collaboration with K+S AG, has proposed a new approach which can gradually decrease, and in future even eliminate, the discharge of waste brines from the production of fertilisers in rivers and/or their injection in deep aquifers. This approach entails the conditioning of waste brines and subsequent stowage in former potash mines in the Werra District.

The chemical composition of the waste brines in relation to the host minerals in the mines of the Werra District must be adequately considered since the stowage process can potentially initiate dissolution processes weakening the mines’ pillars consequently leading to surface subsidence and/or seismic events.

In the newly developed approach waste brines are conditioned by increasing the concentration of magnesium chloride. A stowage brine with a chemical composition that approximates the chemical equilibrium point in the quinary system of oceanic salts, i.e. the so-called Q-Point with ca. 320 g/l MgCl2, is largely indifferent to the host minerals in the mines of the Werra District enabling a safer and more sustainable stowing practice. The stowage of a high density, indifferent brine can also potentially be used to mitigate water inflows.

This new approach will, after successful implementation, gradually reduce and eventually eliminate the discharge of approximately 3 million m³ waste process brine in the Werra-district into surface water and/or injection of waste brines into deep aquifers.