Impact of lime treatment on tailings dewatering and cap water quality under an oil sands end pit lake scenario

Probing Silica-Kaolinite Interactions with Sum Frequency Generation Spectroscopy

“…Recently, one strategy proposed to dewater mature fine tailings from the Athabascan oil sands rich in both silica and kaolinite used lime. 19,37 This work suggested lime could improve dewatering but the mechanism remained unclear, as lime addition both introduced divalent cations known to promote mineral interactions and raised the pH. To gain greater molecular insight into the dependence of clay mineral dispersion chemistry on the nature of the alkaline medium, we conducted SFG measurements on the silica/kaolinite/aqueous interface with 10 wt% kaolinite utilizing Ca(OH)2 or NaOH (Figure 2) to raise the pH from ~7 to 12.4.…”

“…We note that the pH where this lack of water structure is observed (pH 12) correlates well with the optimal pH for dewatering of kaolinite-and silica-rich tailings using Ca(OH)2 and low pressure filtration. 19 This suggests that a lack of water signal in the SFG, attributed to ion-mediated binding of the two oxides, corresponds to conditions where dewatering is promoted. The ability of SFG to predict dewatering conditions based on the absence of ordered water in the SFG signal is a promising application of the technique that could allow for rapid screening of dewatering agents.…”

“…Most interesting was the complete disappearance of the water SF features with lime addition at pH 12 and above, which supports our hypothesis that a lack of ordered watered as seen by SFG is indicative of conditions that promote silica/kaolinite dewatering. 19,37 Furthermore, the SF peak at ~3694 cm -1 assigned to kaolinite increased in magnitude considerably in base titrations at pH 12 with lime and pH 12.4 with NaOH addition, suggesting that high pH promotes silica-clay interactions. However, unlike the lack of ordered interfacial water observed for lime at the silica/kaolinite particle interface, this increase in kaolinite binding in the presence of NaOH was observed with a substantial interfacial water signal.…”

“…2 Hence, there is a great need for more efficient tailings treatment technologies that can yield more water release and a highly consolidated reclaimable material. One promising additive for oil sand tailings dewatering and consolidation is lime (CaO), 19 which has recently been found to facilitate dewatering at high pH when coupled with minimal low-pressure filtration. 19 Employing an analytical technique that can monitor binding of heterogeneous clay minerals with mineral oxides such as silica while giving information on the water structure at the mineral-mineral interface might enable optimization of conditions for mineral heterocoagulation and dewatering in tailings treatment.…”

“…One promising additive for oil sand tailings dewatering and consolidation is lime (CaO), 19 which has recently been found to facilitate dewatering at high pH when coupled with minimal low-pressure filtration. 19 Employing an analytical technique that can monitor binding of heterogeneous clay minerals with mineral oxides such as silica while giving information on the water structure at the mineral-mineral interface might enable optimization of conditions for mineral heterocoagulation and dewatering in tailings treatment. One technique that is well suited for monitoring in situ adsorption processes as well as the interfacial structure of water is vibrational sum frequency generation (SFG) owing to its molecular specificity by resonant enhancement of specific vibrational modes.…”