22 Dec 2014

Evaluating geochemical and hydrological impacts from a phosphogypsum stack at a tailings management facility

We conducted an in-depth site assessment to help YARA AB determine future environmental protection measures.

The materials left over after separating the valuable from the uneconomic part of phosphate rock are cumulatively known as ‘tailings’. The phosphogypsum stack at the island of Gråen (Sweden) was established in the 1970s as a tailings management facility for the nearby phosphoric acid production plant owned by Hydro Agri (now YARA AB). Over a period of almost 15 years, some 4 million m3 of waste gypsum slurry with very low pH was deposited in the 320,000 m2 tailings disposal site Gipsön. 

After the plant closed down in the 1990s, monitoring of the site continued for two decades. In order to assess future environmental protection measures for the site, YARA AB needed detailed information on the current status of the tailing facility. To help YARA AB, we:

  • set up and performing a detailed sampling programme
  • evaluated the obtained data
  • assessed the current status of the phosphogypsum stack

By combining historical data with the newly obtained data, we were able to assess the current status of Gipsön and predict the development in leaching behaviour based on observed trends. We used site specific monitoring and test data with numerical modelling to predict potential environmental impacts and do a forecast for future operations at the site. Our assessment provided YARA AB with the information needed to reach a qualified decision on the future management of the disposal site.