In Support of "The Physical Chemistry of the Hot Water Process"
Authors: Wallace Dean , Chow Ross , Takamura Koichi 
Published: March 2010

Comments raised by Jan Czarnecki and Russel Smith on " The Physical Chemistry of the Hot Water Process" reveal the need for the authors of the original paper(l) to explain in more detail their rationale for developing the stability diagram to predict fines stability during extraction.

The first comment relates to the selection of an energy barrier of -400 kT as a reasonable level to differentiate between a stable and coagulated system, In the paper, the authors dearly explained their reasons for adopting the 400 kT level based on a combination of mathematical calculations and batch extraction unit experiments. In view of their explanation, the selection of the transition region from 0 to 400 kT could be regarded as a tit parameter for experimental data rather than a critical level based solely on flocculation kinetics under conditions dominated by Brownian motion.

In recognition of the possible misinterpretations that could be made with respect to the critical energy barrier level, in a subsequent paper(2) in which the same model was used to explain the deterioration in processing behaviour due to aging, the authors described the transition region in the following manner. " To allow for the uncertainties in calculating the net interaction between particles, a transition region of 0 to 400 kT was identified in the batch extraction test. In reality, the transition region represents the uncertainty about whether a significant portion of the particles under consideration are dispersed or coagulated".

If in fact, the selection of 400 kT is the basis upon which the validity of the conclusions in the paper is judged, a single value between say 0 and 20 kT could be defined as being the demarcation between a stable and a coagulated regime. Identification of the position of that single line on the stability diagram covering the range of panicle sizes and types that are found typically in oil sand would regenerate a zone of uncertainty that is similar to the one in the original diagram. However, by doing so, the authors would be ignoring the effect of hydrodynamic forces on coagulation. This leads to the second point raised by Czarnecki and Smith in which they claim that hydrodyarnic forces cannot drive particles together across a 400 kT energy barrier for the s}'stem under examination.

In 1983, Chia and Somasundaran reported enhanced strong agitation between anatase and calcite particles under conditions of intense agitation(3). Rather than interpreting this observation soleIy in terms of increased collision frequency, they related the magnitude of the hydrodynamic forces due to agitation to the net repulsive forces calculated from DLVO theory. The calculations taken from Chia and Somasundaran support our belief that the barrier height to coagulation in our agitated system can exceed the critical level of 20 kT proposed by Czarnecki and Smith. In these calculations, we will cover a range of particle radii from 1 to 10 µm (with a desity of 2.6 g/cm3), conditioning slurry viscosities of 1 to 10 stokes and power inputs (based on BEU measurements) of 10 to 30 N.m/sec.