To Örebro University

Green liquor dreg (GLD) is a calcite dominated alkaline byproduct from the pulp and paper industry with high buffering capacity and thixotropic properties, making it suitable for treatment of acidic mining waste. In a comprehensive four-year study, GLD from 16 Swedish mills was characterised through multiple sampling campaigns, analysing elemental composition, buffering capacity, sequential leaching, and interactions with acid rock drainage. This dataset is now a robust foundation for understanding the variability of GLD between mills, offering key insights into which parameters are most critical for different mining waste applications.

Several small and medium sized tests have been performed, with good results, to determine the suitability and possible drawbacks when mixing GLD and acid mining waste. As a final confirmation of the technique approximately 4,500 tonnes of acid mining waste at Gladhammar, Sweden (pH 3.8, 96 mg/L copper and 21 mg/L cobalt) was slurry injected with 100 tonnes of GLD in 2017.

During injection, pH in the drainage from the area increased from 3.5 to around 10 due to excess GLD being washed out. One to two months after injection, pH was around 7.5 and concentrations of copper and cobalt was 38 and 4.9 mg/L, respectively. During 2024, pH was 8 and concentrations of copper and cobalt were 1.1 and 0.95 mg/l, respectively.

The challenge at Gladhammar was to reduce metal loads while allowing the waste rock piles to be accessible for mineral hunters and geoscientific studies in the future. With alkaline injections, areas with cultural, historical and geological values can be treated with low visual impact.

The full-scale reclamation at Gladhammar confirms that GLD can be used for reclamation of historical mining waste as pH increases and trace element concentrations decrease.