Canadian Journal of Chemical Engineering, Vol.97, No.1, 74-83, 2019
Flocculation-assisted dewatering of fluid fine tailings using a volute screw press
A flocculation-assisted process to continuously dewater oil sands fluid fine tailings using a volute screw press was developed. An anionic-cationic flocculant scheme was applied first to flocculate essentially all suspended solids in the fluid fine tailings. The concept of elastic and plastic deformations for metallic solids was extended and successfully applied to describing compression and subsequent water release characteristics of the flocculated sediments. The newly-developed "controlled vertical strain test" (CVST) provided a good measure of the impact of flocculants on the compressive dewaterability of flocculated sediments. A new empirical parameter named "compression dewatering index" (CDI) was obtained from the sediment compression response curve of the CVST. Field tests at Canadian Natural Resources Limited with a prototype volute screw press showed a linear correlation between the CDI and the filter cake dry solids content produced by the volute screw press. Under process conditions in this study, a stackable cake containing 55-60 wt% solids at a 5-7 kg dry solids/h production rate was achieved by applying the volute screw press to the flocculated fluid fine tailings. The novel findings from this study could serve as a useful theoretical framework for future research on flocculation-assisted dewatering of fluid fine tailings by elevated external mechanical forces, as encountered in centrifuge and filtration.