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Several studies have found that green liquor dregs (GLD) can be a possible remediant for remediation of oxidised sulfidic mine sites. GLD is a heterogeneous alkaline waste from the pulp and paper industry, and as such, broad scale utilization requires environmental properties to be characterized in accordance with Swedish law. Among these properties, water soluble leaching properties of GLD must be examined. In this study samples were collected from 16 mills at five different occasions, approximately 6 months apart, totalling 71 samples. Leaching was performed in sequential steps at a L/S ratio 2 and 8 on wet samples corresponding to 25 g d.w, resulting in a total L/S ratio of 10. The liquid phase was analysed for electrical conductivity, pH, alkalinity, anions and element concentrations, after which correlation calculations and geochemical calculations were performed. Leaching of sodium and potassium was as expected very high while leaching of calcium, magnesium and iron was low. Trace elements leach generally less than ≤ 5%. Na, K, As, Ba, Na, K, Rb and U are present mainly as easily soluble salts that are washed out over time while Ag, Co, Cr, Cu, Ni, Pb, Se, Sr, V and Zn are mainly solubility controlled. Hydroxides are indicated by geochemical calculations to be the solubility controlling phases for Cd, Co, Ni, Zn and in some cases also for lead, while oxides are the suggested controlling phase for cobalt. For copper the results suggested both oxides and hydroxides as controlling phases. In general, most elements of concern had low enough leaching rates that their impact will be moderate as leaching in the study was under optimal conditions and in situ application is expected to lower leching rates further. When comparing the chemistry of leachates from GLD with the chemistry of leachates from acidic mining waste there are environmental benefits to be had from co-disposal even if GLD is not inert. This combined with the fact that both short term and long term buffering capacity is excellent indicates that GLD is suitable for remediation of acidic mining waste.

Sequential leaching was performed on 29 green liquor dreg (GLD) samples from 15 Swedish pulp and paper mills. Results show that element leaching primarily occurred during acidic and reducing conditions with the exception for a few elements present as water soluble salts. Most elements are thus likely associated with carbonates and Fe/Mn-oxyhydroxides, or to a lesser extent associated with stable crystal phases as they have very low leaching. In general, leaching patterns were similar for all samples indicating that all samples likely belong to the same sample population. This study shows that Ag, Cr, Cu and Zn, that have previously been pointed out as elements of potential concern when using GLD as a mine waste remediant, are not a concern when accounting for the geochemical environment. On the other hand, Ba, Cd, Ni and Sr are elements that needs to be monitored when using GLD as they leach significantly with Ba and Cd leaching the most during acidic conditions. They are not necessarily a problem when considering the economic, environmental and practical problems Sweden face in remediating acidic mining waste and GLD disposal as the benefit of using GLD is very high compared to the environmental impact from these four elements. Use of GLD for mining site reclamation is also more consistent with circularity compared to traditional reclamation methods.

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. 

Green liquor dregs (GLD) is an alkaline by-product from the pulp and paper industry with a pH between 10 and 14. Today most of the produced GLD in Sweden is landfilled. As a fine-grained alkaline material, it might be possible to use it for acid-generating mining waste remediation. To increase the utilization, quality characteristics and environmental performance need to be determined. In this study samples were collected 5 times from 16 mills during a period of 2.5 years, and were characterized by analyzing dry matter content, loss on ignition (LOI) 550 °C and LOI 950 °C, elemental analysis, pH, electrical conductivity, and calorific value. The results were then evaluated using multivariate statistics (PCA) as well as being compared to other studies and Swedish till. The results show that even if GLD is heterogenous (both within a mill and between different mills) trends can be seen for samples from most mills. When samples do stand out, it is predominately related to the same four mills. Most of the studied parameters showed characteristics favorable for use as a remediant; however, TOC, sulfur, and some of the elements require further study. In general, this study concludes that GLD can be a viable option for the remediation of small orphaned sulfidic mining sites and thus worthy of further studies on the interaction between GLD and acidic mining waste.Overall, GLD can be a good alternative for cost-effective remediation of smaller orphaned mining sites. It is readily available in large quantities, has the qualities needed for remediation of many orphaned acidic mining sites, and can often be locally sourced near the mining site. The use of GLD for mining site remediation is likely also a more sustainable method compared to traditional remediation methods.

Green liquor dregs (GLD) is an alkaline by-product from the paper and pulp industry with a pH between 10 and 14. Today most of the produced GLD in Sweden are landfilled. In order to increase the utilization, the environmental performance needs to be determined. Samples were collected from 16 mills at 3 different times approximately 6 months apart, totalling 42 samples. Leaching was performed in two sequential steps at an L/S ratio of 2 and 8 on wet samples corresponding to 25 g DM. The liquid phases were analysed for pH, electrical conductivity, alkalinity, anions and element concentrations. Leaching of sodium and potassium were as expected very high but leaching of calcium was low. Chromium, nickel, copper, cadmium and zinc leaches generally less than ≤5% of total concentrations. Sodium and potassium are present in GLD as easily soluble salts that are easily washed out. Calcium leaching is restricted by calcite solubility resulting in little effect on short time buffering capacity, however, in the long term calcium minerals will affect the buffering capacity. For nickel, copper, cadmium and lead there are some soluble salts present in the GLD but most of the elements are probably solubility controlled. Geochemical calculations indicated hydroxides as solubility controlling phases for at least copper and in some cases also for lead. Leaching of zinc is to some extent solubility controlled which is indicated by the fact that the soluble concentrations is similar for both L/S 2 and L/S 8. When comparing the leached concentrations from GLD with concentrations from mining waste there is an environmental benefit even if the GLD is not inert. In conclusion, GLD is well suited to be used for treatment of acidic mining waste instead of being landfilled in non-hazardous and hazardous landfills.

The present study addresses the geotechnical and chemical properties of sealing materials using a paper mill by-product, fly ash, on top of sulfide-bearing mine waste tailings after 5years of field application. From a geotechnical perspective, the low in situ bulk density (1500kg/m(3)) ensured a high degree of water saturation (90.2%) for the field-applied ash. The chemical characteristics and behaviors of the fly ash samples reflected a high long-term leaching capacity (liquid-to-solid ratio of 10cm(3)/g) and high alkalinity (liquid-to-solid ratio of up to 500cm(3)/g). The laboratory leaching results suggested that none of the elements released from the field-applied ash exceeded the EU limits for inert materials, and the concentrations of elements were far below the limits for hazardous materials at landfill sites. Based on the in situ and laboratory characterizations of the field-applied ash, the fly ash sealing material was considered geotechnically stable. However, a number of geotechnical parameters could not be measured due to the cementation of the ash. Moreover, the chemical composition of the field-applied ash exhibited considerable variations when compared with that of the raw ash generated from the same paper mill. Overall, the field-applied ash displayed high alkalinity and effectively buffered the acid generated from sulfidic tailings for long-term sealing purposes.

Sealing layers made of two alkaline paper mill by-products, fly ash and green liquor dregs, were placed on top of 50-year-old sulfide-containing tailings as a full-scale remediation approach. The performance and effectiveness of the sealing layers with high water content for an oxygen barrier and low hydraulic conductivity for a sealing layer in preventing the formation of acid rock drainage were evaluated 5 years after the remediation. The leaching behavior of the covered tailings was studied using batch leaching tests (L/S ratio 10 L/kg). The leaching results revealed that, in general, the dregs- and ash-covered tailings released relatively lower concentrations of many elements contained in acid rock drainage compared to those from the uncovered tailings. A change in the chemical composition and mineralogical state of the tailings was observed for the tailings beneath the covers. The increase in pH caused by the alkaline materials promoted metal precipitation. Geochemical modeling using PHREEQC confirmed most of the geochemical changes of the covered tailings. Both the ash and dregs showed potential to function as sealing materials in terms of their geochemical properties. However, mobilization of Zn and Ni from the lower part of the dregs-covered tailings was observed. The same phenomenon was observed for the lower part of the ash-covered tailings. Ash showed advantages over dregs as a cover material; based on geochemical studies, the ash immobilized more elements than the dregs did. Lysimeters were installed below the sealing layers, and infiltrating water chemistry and hydrology were studied to monitor the amount and quality of the leachate percolating through.