Elemental mobility in sulfidic mine tailings reclaimed with paper mill by-products as sealing materials

Abstract

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.

Chemical characterization of green liquor dregs from 16 Swedish pulp and paper mills between 2017 and 2019

“…Both pH and electrical conductivity are high (Tables 7 and 8 ). pH is similar to what has been reported by others (Jia et al 2017 ; Nurmesniemi et al 2005 ), indicating equilibrium with solid Ca(OH) 2 generating a pH of 12.45. Even higher pH usually indicates the presence of remaining NaOH in the solid residue, indicating poor washing.…”

“…Prior research has found that GLD is suitable for remediation of acid mining waste and acid rock drainage by means of cover (by itself or as an additive), injection, or co-disposal (Bäckström et al 2010 ; Chtaini et al 2001 ; Jia et al 2013 ; Jia et al 2014 ; Jia et al 2017 ; Jia et al 2019 ; Mäkitalo et al 2014 ; Mäkitalo et al 2015 ; Mäkitalo et al 2016 ; Ragnvaldsson et al 2014 ; Sartz 2010 ; Sartz et al 2010 ; Sartz et al 2018 ). This is due to its low hydraulic conductivity, high pH, high buffering capacity, and ability to stick to the mining waste it is injected into and not being washed out.…”

Stabilization and encapsulation of arsenic-/antimony-bearing mine waste: Overview and outlook of existing techniques

“…The use of dry covers for treating wastes with high contents of (weathered) arsenopyrite has been also investigated (Figure 3). The evaluated dry cover materials include alkaline materials, such as wet limestone (Craw et al, 2002), lime mud, fly ash, and green liquor dregs (Jia et al, 2014(Jia et al, , 2017; organic wastes (biosolids) (Paktunc, 2013); and soil with low organic content (DeSisto et al, 2017). The performance of these materials as surface covers has been evaluated after varying periods from their application by mineralogical studies (mainly by X-ray diffraction (XRD)) and/or geochemical studies using different leaching tests.…”

Amelioration of permeable soil with green liquor dregs for the construction of sealing layers for mine waste storage facilities

“…During the last decade, research on green liquor dregs (GLD), a waste from the pulp and paper industry, indicate they could efficiently reduce the oxygen diffusion in soil that are too permeable. The practice of using GLD is still rather novel and previous studies have focused on the chemical, physical and mineralogical characterization of GLD [14][15][16]], various mixtures containing GLD [16][17][18][19][20] and construction and evaluation of engineered covers containing GLD in field tests and pilot scale studies [22][23].…”