Suspensions consolidation

The chemical and physical properties of clay suspensions produced during oil production from oil sands are described. With a composition of approximately 70 wt% water (with some unrecovered bitumen) and 30 wt%solids (>90% less than 44 gm in size)9 these clay suspensions consolidate very slowly. Clay aggregate or floe morphology has been shown to be a function of the water chemistry and can be manipulated to produce a tailings suspension that is easier to consolidate and dewater. Commercial oil sands processing has been going on in northeastern Alberta since 1967, and in that time approximately 250 million m3 of this difficult to dewater clay suspension has been produced. The reclamation options for this material (mature fine tailings) on a commercial scale are also outlined. 

In the fabrication route used by Barringer and Bowen (89), powders with controlled characteristics are prepared and consolidated, by colloidal methods, into uniformly packed green bodies (e.g., similar to that shown in Fig. 1.17). An abbreviated flow diagram of the fabrication route is shown in Fig. 1.27b. Powders are prepared by controlled hydrolysis of titanium tetraisopropoxide (denoted powder I) or titanium tetraethoxide (powder II). The powder particles are nearly spherical and almost monosized. After washing, each powder is dispersed in a basic aqueous solution to produce a stable suspension. Consolidation of the suspension is accomplished by gravitational or centrifugal settling. The consolidated body is dried in a vacuum and sintered for —90 min at 800°C (for powder... 

How do interparticle interaction forces influence suspension consolidation ... 

The Dorr agitator (Coulson and Richardson, loc. cit.) consolidates in one unit the principles of the thickener and the Pachuca tank. Resembling a rake-equipped thickener, it differs in that the rake is driven by a hollow shaft through which the solids-liquid suspension is lifted and circulated by an air stream. The rake moves the pulp to the center, where it can be entrained by the air stream. The unit may be operated batchwise or continuously. 

Air injection may sometimes be an alternative to deflocculation. In general, defloccu-lated suspensions flow more readily but they tend to give much more highly consolidated sediments which can be difficult to resuspend on starting up following a shutdown. Furthermore, deflocculants are expensive and may adversely affect the suitability of the solids for subsequent use. 

The solgel process uses a liquid reactive precursor material that is converted to the final product by chemical and thermal means. This precursor is prepared to form a colloidal suspension or solution (sol) which goes through a gelling stage (gel) followed by drying and consolidation. The process requires only moderate temperatures, in many cases less than half the conventional glass or ceramics... 

Most authors who have studied the consolidation process of solids in compression use the basic model of a porous medium having point contacts which yield a general equation of the mass-and-momentum balances. This must be supplemented by a model describing filtration and deformation properties. Probably the best model to date (ca 1996) uses two parameters to define characteristic behavior of suspensions (9). This model can be potentially applied to sedimentation, thickening, cake filtration, and expression. 

The dispersion stability, rheology, and consolidation of numerous aqueous and non-aqueous Si3N4 suspensions have been studied extensively [251-257]. Recently a novel class of dispersants for Si3N4 powders in non-aqueous media has been designed and its interactions with the powder surface have been characterised systematically on the basis of surface chemistry and fundamentals of colloidal stabilisation [255, 258]. 

Now the technique provides the basis for simulating concentrated suspensions at conditions extending from the diffusion-dominated equilibrium state to highly nonequilibrium states produced by shear or external forces. The results to date, e.g., for structure and viscosity, are promising but limited to a relatively small number of particles in two dimensions by the demands of the hydrodynamic calculation. Nonetheless, at least one simplified analytical approximation has emerged [44], As supercomputers increase in power and availability, many important problems—addressing non-Newtonian rheology, consolidation via sedimentation and filtration, phase transitions, and flocculation—should yield to the approach. 

Yang C. Y., Shih W. Y. and Shih W. H., Gelation, consolidation, and rheological properties of boehmite-coated silicon carbide suspensions. J. Am. Ceram. Soc. 83 (2000)pp. 1879-1884. 

The sol-gel process is a versatile solution process for making ceramic and glass materials involving the transition of a system from a colloidal suspension (sol) into a solid phase (gel) ". The resulting porous gel can be chemically purified and consolidated at high temperatures. In the classical sol-gel process, the precursor (e.g. a metal enolate or a metal aUcoxide) is exposed to a series of hydrolysis and polymerization reactions to form... 

Later, Papet [58] presented an alternative process for preparing mbular ceramic cross-fiow filtration membranes. Papet s method consists of the casting of mbular mineral microfiltration membranes with titanium dioxide suspensions. The deposited particles on the porous support were then compressed and finally, the layer was consolidated by firing. 

The pore properties of cast bulk porous material and coating layers from the same suspension become different above sinter temperatures where intermediate stage sintering in the bulk starts (see Section 6.2.5). At lower temperatures pore properties of free casts determined with Hg porosimetry can be used to compare the pore properties of consolidated dispersion coatings. 

In Fig. 6.48 the porosity of free cast layers as a function of the suspension pH is given and in Fig. 6.49 the pore size distributions as determined with Hg porosimetry for free cast layers at pH 3.6 and 8.1 are given. It is shown that the porosity difference between consolidated coatings obtained from stable and coagulated suspensions is only 10% and the median pore diameter decreases from 210 nm to 160 nm going from instable to stable suspensions. The decrease... 

---