Diluted MFT Settling by Ozonation; A Mechanistic Study

Abstract

The oil sands tailings generated after bitumen extraction are permanently contained in lake-size ponds. Primarily the tailings ponds are used to settle the solid particles so the cap water could be recycle back to the extraction operations, while the tailings with higher concentration of suspended particles, like Mature Fine Tailings (MFT), need to be treated by other means. Different methods have been developed to accelerate the dewatering of MFT, such the use of different polymers and gypsum. Chemical treatments like ozonation could treat diluted MFT to release the trapped water, as a novel method for the settlement of MFT particles and recovery of water. Ozonation of MFT led to a substantial pH change (from 8.4 to ≤ 4.0) that helped the fine particle to be settled. Formation of small organic acids after the oxidation process led to this pH drop. The objective of this research was to study the substantial pH change during the ozonation of diluted MFT, and its possible correlation to MFT particle settlement. During the ozone treatment an increment in the concentration of ions was observed, as well as the formation of carboxylic bonds on the surface of MFT particles, and the release of humic acids to form metal humate complexes. The increment on conductivity, salinity, and ionic strength during the ozone treatment suggested that the drop of the pH could influence the settlement mechanism. Changes on the particle surface properties improve the settlement of particles and led to the release of trapped water. It was concluded that changes in particle conformation and suspension caused by a drop in the pH were major factors in MFT aggregation.