Role of fine kaolinite clay in toluene-diluted bitumen/water emulsion

Abstract

The role of suspension pH and added fine kaolinite clays in the emulsification of a toluene-diluted bitumen/water system was investigated. Within five distinct pH ranges of 2.9–3.7, 4.1–5.3, 7.4–7.9, 8.8–9.4 and 10.5–10.8, mixing toluene-diluted bitumen with de-ionized water at a water:diluted bitumen volume ratio of 4:1 resulted in a stable water-in-oil (W/O) emulsion. Over these pH ranges, the mixture was completely emulsified to a homogeneous, gel-like creamed phase. However, a creamed layer of varying volume was separated on the top of an aqueous phase when mixed outside these pH ranges. The creamed layer was found to be mainly an oil-in-water (O/W) emulsion. This zigzag type of change in emulsion-type inversion over these narrow pH ranges is a unique feature of the current system. The removal of the original fine solids in bitumen prior to emulsification resulted in a constant volume of O/W emulsion separated on the top of the aqueous phase over the pH range 1.5–11 studied. The addition of kaolinite clays to the emulsifying water was found to suppress the original zigzag type emulsification characteristics. Consequently, the volume fraction of the emulsion reduced significantly with a corresponding reduction of water content in the emulsion. For a suspension of pH <3 and clay concentration at 4 g l−1, >98% of the added clay was retained in the emulsion. At pH >3, on the other hand, the majority of the added clay remained in the separated aqueous phase. Measurement of water contact angle (θ) on the collected clay showed that the added clay, originally being hydrophilic (θ ≈4°), was rendered hydrophobic (θ >120°) at pH <3, while remained hydrophilic (θ ≈20°) at pH >3. Release of natural surfactants from bitumen into the aqueous phase was confirmed by the conductivity, surface tension and contact angle measurements.