The dispersion and gelation of clay suspensions have major impact on a number of industries, such as ceramic and composite materials processing, paper making, cement production, and consumer product formulation. To fundamentally understand controlling mechanisms of clay dispersion and gelation, it is necessary to study anisotropic surface charge properties and colloidal interactions of clay particles. In this study, a colloidal probe technique was employed to study the interaction forces between a silica probe and clay basal plane/edge surfaces. A muscovite mica was used as a representative of 2:1 phyllosilicate clay minerals. The muscovite basal plane was prepared by cleavage, while the edge surface was obtained by a microtome cutting technique. Direct force measurements demonstrated the anisotropic surface charge properties of the basal plane and edge surface. For the basal plane, the long-range forces were monotonically repulsive within pH 6-10 and the measured forces were pH-independent, thereby confirming that clay basal planes have permanent surface charge from isomorphic substitution of lattice elements. The measured interaction forces were fitted well with the classical DLVO theory. The surface potentials of muscovite basal plane derived from the measured force profiles were in good agreement with those reported in the literature. In the case of edge surfaces, the measured forces were monotonically repulsive at pH 10, decreasing with pH, and changed to be attractive at pH 5.6, strongly suggesting that the charge on the clay edge surfaces is pH-dependent. The measured force profiles could not be reasonably fitted with the classical DLVO theory, even with very small surface potential values, unless the surface roughness was considered. The surface element integration (SEI) method was used to calculate the DLVO forces to account for the surface roughness. The surface potentials of the muscovite edges were derived by fitting the measured force profiles with the surface element integrated DLVO model. The point of zero charge of the muscovite edge surface was estimated to be pH 7-8.

The roles in the hot waterprocess ofsodium hydroxide, surfac-tants, watersolubleelectrolytesfinesolidsandelectricproper-ties of the bitumenlwater and solidslwater interfaces are examined. Recovery of bitumen from low-to medium-grade oil sands can be increased by ensuring the fine solids remain dis-persed during digestion by adjustment of digestion water salin-ity and pH. Recovery of bitumen from high-grade oil sands appears to be controlled by surfactants which affect bitumen-water interfacial tension and the size of bitumen dropletsformed during the initial separation of the bitumen from sand grains. Processing behaviour of mixtures of oil sands is explained within the framework of these mechanisms. Introduction In the past few years, there has been a renewed effort to under-stand the hot water process which is used by Suncor Inc. and Syn-crude Canada Ltd. to commercially extract bitumen from mined Athabasca oil sand. The process can be considered in terms of two distinct stages; separation of the bitumen from the sand fol-lowed by flotation which encompasses both primary flotation and scavenging. Separation is induced by mixing the oil sand in a conditioning drum with hot water and often a process d ait, usually sodium hydroxide. The conditioned slurry is pumped a primary separation vessel (PSV) where the bitumen froth is skimmed from the surface. The sand tailings which settle in the PSV are removed. The middlings (water) are pumped to a secon-dary recovery vessel where air is introduced through the bottom of the vessel, attaches to some of the suspended bitumen and causes it to float.The amount of sodium hydroxide added to the conditioning stage of the process is the major variable used to maximize recov-ery of bitumen. The addition rate historically has been based on empirical but sometimes imprecise correlations of oil sand grade with processability. Recently Schramm and co-workers proposed that the process could be optimized around the concentration of free surfactants formed due to reactions between sodium hydrox-ide and organic acids in the bitumen, and found in the tailings water(t).Even if the surfactant concentration in the tailings stream of a hot water processing plant could be accurately monitored there would be a delay between the time recovery fell below its opti Current Address: BASF Canada Inc.,Dispersions R&D, Sarnia,Ontario. Keywords: Bitumen recovery, Hot water process, Interfaces, Surfactants, Surfaces. _ mum level and an adjustment to the digestion stage of the process could be made. A model that is used to predict the best operat-ing conditions based upon properties of oil sand that are easily measured either during a coring program or on-line, would be beneficial compared to one which is used in a reactive mode. This paper describes a model for the hot water process based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) and Ionizable Surface Group theories that can be used to predict from concen-trations of inorganic salts in the digestion stage of the process, the conditions for maximizin...

The chemical composition of the aqueous phase in oil sand slurries influences bitumen recovery from oil sands, especially those containing greater than 10% fines. The composition is controlled by a combination of mixing and dilution, ion exchange with clay surfaces and precipitation of divalent ions as carbonate minerals. Elevated levels of soluble potassium in the oil sand, which appear to be a marker for degraded illite or smectitic clays, are associated with depressed bitumen recovery. These clays have a swelling character and can contribute divalent ions to the slurry by ion exchange between the clay mineral surfaces and the process water.

As analytical methodology improves and instrumental methods allow, or often require, the use of smaller and smaller analytical test portions, the error in the sampling operations becomes increasingly significant. Also, heterogeneity of trace components can introduce major sampling problems. Sampling errors cannot be controlled by use of blanks, standards, or reference samples and so are best treated independently.