Understanding of fundamentals: Key to process modification for tailings reduction

Abstract

The tailings produced during bitumen separation from oil sands have a high water holding capacity attributed to ultrafine (≤ 0.2 μm), aluminosilicate clay fractions. These components readily form gels within which both fine and coarse particles may be embedded. This complex mixture (or “fine tails") shows poor dewatering and consolidation characteristics.

In this work it has been demonstrated that for gel formation to occur an appropriate combination of ultrafines (amount and particle size) and water chemistry is needed. The natural salt concentration in water recycled from the tailings or pore (connate) water is sufficient to cause the ultrafines to form gels in a matter of days. Gel formers are an integral part of oil sands ores which are unavoidably released during processing. However, one way to prevent gel formation is to change the water chemistry in the extraction process where the bitumen is released. This can be achieved by the addition of sodium silicate instead of sodium hydroxide as process aid in the initial oil sands conditioning step.

Key words:

• gel forming propensity
• ultrafine solids