Utilization of Lime Mud Residue from Kraft Pulp Mills as Akaline Amendment for Oxidized Sulfidic Mine Tailings
Symposium Rouyn-Noranda 2002
Oxidized sulfidic tailings contain significant amounts of accumulated acidity in the form of water-soluble secondary sulfate minerals and thus constitute long-term sources of acid drainage at many metal mining sites. As part of site remediation activities, alkaline amendments are often added to the oxidized tailings to increase the pH and immobilize the metals. This study assessed the advantages and limitations of using lime mud, a byproduct of Kraft pulp mills rich in calcium carbonate (~ 90 wt. %), as alkaline amendment. The inorganic and organic constituents of lime mud samples were quantified, and the performance of lime mud was compared to that of reagent grade quicklime (CaO) and calcite (CaCO3). Tailings treated with lime mud or CaCO3 have strong buffering capacities and remain at neutral pH conditions (pH ~ 6.7) for long times. In contrast, tailings treated with CaO have a low buffering capacity, and their pH decreases with time. Furthermore, lime mud has a finer particle size distribution and thus a greater specific surface area than most forms of commercially available calcite, which results in enhanced solubility. Dissolved metal concentrations are similar in tailings slurries treated with lime mud or CaCO3. This study shows that lime mud is an environmentally and economically attractive alkaline amendment for oxidized tailings.