(477k) Increasing Strength of Thickened Oil Sand Tailings with Geopolymers

The government of Alberta recently imposed new regulations requiring that oil sand tailings deposits must reach strength of 5 kPa one year after deposition. However, due to the limitations of gravitational settling and thickener operation, fine oil sand tailings can be thickened only to certain degree, and the strength may not meet the regulatory requirement. CanmetENERGY and Total E&P Canada (TEPCA) have conducted an investigation on the feasibility of using geopolymer additives to improve the strength of the deposit.

 In this project, fly ash (type C) and cement were used as additives. Mature fine tailings (MFT) containing 35 wt% solids and thickened tailings (TT) with solids contents of 50 wt% were used as tailings material. Geopolymer was mixed with tailings and the treated tailings were distributed into 250-mL jars, some of which were closed, while others were left open. The solids content in the closed jars remained constant because no water evaporated, but increased in the open jars as the tailings dried in air at ambient conditions. The tailings strength was measured in each jar after a specified time.

These experiment results indicate that the addition of small amount of geopolymer increased the tailings strength significantly in both open and closed jars under the test conditions. Addition of about 5 wt% fly ash to TT increased the yield stress of the tailings to over 5 kPa after the solids content increased to around 60 wt% under natural drying. Similarly, adding around 5 wt% fly ash to the MFT increased the yield stress to over 5 kPa when the tailings were dried to about 55 wt% solids. Adding 3 wt% Portland cement also increased the yield stress of MFT or TT to more than 5 kPa when the solids concentration increased to 55 wt% for MFT and 65 wt% for TT. By comparison, untreated MFT or TT had to be dried to over 70 wt% and 85 wt%, respectively, in order for the yield stress to reach 5 kPa.