Advanced Polymer Flocculants for Solid–Liquid Separation in Oil Sands Tailings

Abstract

volume of tailings is projected to reach two billion cubic meters in 2034 if tailings management procedures remain the same. [3] When fresh tailings consolidate for a few years after their transfer to tailings ponds, gravitational forces cause the coarse components (sands) to settle, releasing a limited amount of the water to the surface. The bottom part of the remaining suspension is called mature fine tailings (MFT). Typically, MFT contains negatively charged clays (≈30-35 wt%), water (≈65 wt%), and residual bitumen (3-5 wt%). [4] Compared to fresh tailings, which still contain coarse particles that consolidate over time, MFT is a gel-like suspension that consolidates extremely slowly. Clays in MFT contain mainly kaolinite, illite, and mixedlayer clays such as interstratified illitesmectite and kaolinite-smectite. [5] Fine clays are mostly responsible for the water retained in MFT due to their high surface area. Additionally, fugitive bitumen binds clay particles, constricting interparticle pathways and trapping water. Colloidal Stability of Tailings and Challenges in DewateringSince MFT contains a mixture of negatively charged clays, it shows strong negative zeta potential that causes colloidal stabilization. Generally, clays contain hydroxyl and oxide functional groups that make their particles negatively charged at neutral pH (pH = 7) and even more negative as pH increases. Thus, the stability of clays in MFT increases with increase in pH. Current bitumen extraction processes use caustic additives to liberate bitumen from oil sands, generating alkaline tailings with pH of approximately 8.5. This alkaline medium increases the electrostatic repulsive forces between clays and significantly increases MFT stability. Surface charges also arise when ions from the neighboring solution adsorb on an initially neutral solid surface. Another source of surface charges is the dissociation of surface groups. The silica surface of clays can react with water to form silicic acid, which can then dissociate to form a silicic anion, as shown below. SiOHO HSiO (HSiO ) H 2 S 2 2 3 S 3 S ( ) ( ) + ↔ ↔ + − +(1) Multifunctional FlocculantsThe generation of tailings as a by product of the bitumen extraction process is one of the largest environmental footprints of oil sands operations. Most of the tailings treatment technologies use polymer flocculants to induce solid-liquid separation. However, due to the complex composition of tailings, conventional flocculants cannot reach the same performance achieved in other wastewater treatments. Over the last couple of decades, the oil sands industry has used acrylamide-based flocculants to treat tailings, achieving major progress in process optimization and integration with mechanical operations, but they still could not reach the required land reclamation targets. Over the last 5 years, the group designed, synthesized, and tested several novel polymer flocculants tailored for oil sands tailings treatment. This feature article communicates recent developments in these innovative polymers. Th...

Evaluation of candidate polymers to maximize geotechnical performance of oil sands tailings

“…The molecular architecture of polymer flocculants, as measured by their molecular weight distributions, chemical composition and/or ionic charge distribution, and branching topology, is expected to affect their flocculation and dewatering performance (Vajihinejad et al 2019;Gumfekar et al 2019). This investigation contrasts the behaviour of four new polymer flocculants, amylopectin-graft-polyacrylamide (AP-g-PAM), hydroxypropyl methylcellulose-graft-7 polyacrylamide (HPMC-g-PAM), poly(vinylbenzyl trimethylammonium chloride)…”

Cellulose Nanocrystals‐Based Polyacrylamide as Flocculating Agent of Mature Fine Tailings

“…The only exception was verified for the neat PAM, in which the CST reduced with increasing the polymer concentration, as commonly reported in the literature. [1,10] Moreover, the CST was not significantly influenced by the polymer composition when a concentration of 2000 ppm of polymer was used to flocculate the MFT.…”

“…As tailings are difficult to treat, they need to be stored in tailing ponds. [1] This situation leads to severe environmental concerns, since approximately 3.3 m 3 of waste are discharged into tailing ponds for each 1.0 m 3 of bitumen extracted. [2] Basically, FFT is composed by water, sands, fine clays, and residual bitumen.…”

“…For that reason, many researchers have been trying to develop a variety of alternative flocculant polymers as an attempt to improve the performance of commercially available PAM-based flocculants that are commonly used in industrial processes. [1,2] Natural polymers, such as starch, [6,7] chitosan, [8][9][10] cellulose, [11][12][13][14][15][16] lignin, [17,18] alginate, [19] and guar gum, [20,21] alone or in combination with synthetic macromolecules, have been tested as an attractive sustainable and eco-friendly alternative to the polymers frequently used as flocculating agents in different processes. Among these biomaterials, cellulose deserves a special attention since this is the most abundant renewable and biodegradable natural polymer existing in the planet.…”

Design of ionic liquids for dewatering stable solid/liquid complex slurries

“…21,25,26 However, based on the high complexity and great variability of the tailings, the performance of these technologies has not been as successful in comparison with their use for other wastewater treatments. 27 Polymers, for example, are designed for the thickening of low solids effluents, and hence, although they are effective for fluid tailings, they do not provide an effective solution for MFT. 27 Also, the presence of bitumen in the tailings tends to impede the action of the polymers, and the solid phase separated using polymers is usually unstable to further stirring, making transfer and handling of those solids during disposal challenging.…”