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Dual Ecosystem Enhancement: In-Situ Pitlake Remediation by Slag-Silicate Addition
Primary Issue Addressed: Acid Drainage/Water Treatment
Secondary Issue Addressed: Pit Lakes
Project Site: Montana Tech
Collaborating Entities: Montana Tech
Cost Share: None
Project Description
This project will investigate the potential for treating acid rock drainage using smelter slag from various inactive smelter sites in Montana. Thermodynamic calculations show that the silicates within basic smelter slags will increase the pH and, thereby, induce precipitation reactions. However, the level of remediation is dependent on the slag-silicates that are used. Because of their different compositions, three smelter slags in particular will be examined: the fayalite slag from the Anaconda Copper Company in Anaconda; the pseudowallastonite/ rankinite slag from Stauffer Chemical near Ramsey; and the olivine slag from ASARCO in East Helena. The initial overall objectives of this research project will be to collect representative slag samples from the three sources, experimentally verify that slag-silicates can be used to remediate acid rock drainage, and determine if the resulting equilibrium pH concurs with the free energy calculations. Kinetics of the reactions need to be relatively fast to be effective.
Status
Optimization work has been performed to determine slag concentrations and mesh size, as well as attainable solution pH for each of the three slags. After 12 hours of contact with Berkeley Pit water, it was found that the Stauffer pseudowallastonite/rankinite slag yielded the highest equilibrium pH (6.0 to 7.8) of the three slags. The Stauffer slag contains the most calcium of the three slags and is relatively iron free. Equilibrium pH of the Anaconda fayalite slag after 12 hours contact with Berkeley Pit water ranged from 3.4 to 4.5. For the ASARCO olivine slag, equilibrium pH ranged from 4.1 to 5.4 after 12 hours contact with Berkeley Pit water. The low end of the pH ranges corresponded to slag concentrations of 100 g/L and a particle size of 48 mesh, or approximately 300 µm diameter particles. The mid-range pH values corresponded to a slag concentration of 100 g/L and a particle size of 270 mesh, or approximately 50 µm diameter particles. The high range pH values correspond to a slag concentration of 300 g/L and a particle size of 270 mesh.