ACID NEUTRALIZATION AND METAL MOBILIZATION IN OIL SANDS FROTH TREATMENT TAILINGS
Date
2024-09-25
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Masters
Abstract
Acid generation and metal(loid) release is an emerging closure consideration for oil sands mines in northern Alberta, Canada. Froth treatment tailings (FTT) generated during bitumen extraction generally exhibit higher sulfide-mineral contents relative to other tailings streams. Recent studies have shown that pyrite oxidation can promote pore-water acidification and metal(loid) release within the unsaturated zone of FTT beach deposits. The corresponding sequence of acid neutralization reactions and their influence on metal(loid) release has not been studied. Laboratory column experiments examined acid neutralization reactions and their influence on metal(loid) mobility in samples collected from a commercial scale FTT beach deposit. Near-surface samples were collected from non-weathered, partially weathered, and highly weathered regions of this sub-aerial deposit, which provided an opportunity to examine the influence of initial weathering extent on acid neutralization and metal(loid) release. The experiments also considered non-solvent-washed (i.e., as received) and solvent-washed sample splits to assess impacts of residual hydrocarbons on these reactions. An acidic solution (i.e., 0.05 M H2SO4; pH ~1.5) solution was continuously pumped through each column and effluent samples were regularly collected for geochemical analysis. Effluent pH decreased from ~7 to 5.5 over the first 5 pore volumes (PVs) for the non-weathered and partially weathered columns. Gradual decreases in effluent pH to ~ 4.5 were observed over time, with subsequent rapid pH decreases to < 3 observed after more than 50 PVs in these columns. Effluent pH was consistently <2.0 for the highly weathered columns. We attribute these effluent pH ranges to the dissolution of Mg-bearing carbonates (pH ~6.5 to 6), Fe-bearing carbonates (pH ~5.6 to 4.5), Al hydroxides (pH ~4.5 to 4.0), and silicates (pH < ~2). These interpretations are supported by pH-dependent increases in effluent concentrations of Fe (< 1 to > 500 mg L−1), Al (<0.1 to >10 mg L−1), Si (<0.1 to >10 mg L−1), and several additional metal(loid)s (e.g., Ni, Zn, V, As) associated with FTT minerals. Cumulative mass release for metal(loids) was typically highest in the non-weathered samples, and generally higher in solvent-washed compared to non-solvent washed sample splits. These results offer important new insight into relationships between acid neutralization and metal(loid) release in FTT deposits that can inform FTT management and reclamation.
Description
Keywords
geochemistry, oil sands, FTT, column experiments, acid neutralization, metal(loid) mobility
Citation
Degree
Master of Science (M.Sc.)
Department
Geological Sciences
Program
Geology