Another Dimension to Slump

Abstract

Estimating the rheological properties of a paste using convenient methods such as the slump technique are common practice within the industry. However, the universality of comparing slump heights to estimate the flow properties for different paste products has been questioned (Clayton et al., 2003;Paterson, 2002). The dispute relates to the fact that two paste products may in fact exhibit similar slump heights, but may not share the same shear yield strength since their densities may be different. This discrepancy is catered for by the method of Pashias et al. (1996) in which the shear yield stress can be conveniently calculated from the slurry density and the slump height.However, certain paste rheological behaviours are observed which appear puzzling and which cannot be explained on the basis of particle size and slurry density alone. The chemical conditions of pastes (particularly those containing clay minerals) have profound effects on the colloidal interactions of the suspended solids and hence on the rheological behaviour of pastes (Vietti, 2004;Dunn, 2005). This paper demonstrates that different slump heights may be observed for a kimberlite paste containing smectite at one material density, but varying paste chemical conditions. CLAY MINERAL COLLOIDAL PROPERTIESDue to the variety of resources exploited tailings generally contain a kaleidoscope of mineral types.However, in general the fine clay minerals tend to be concentrated within the tailings. Since, the colloidal properties of clay suspensions are highly sensitive to chemical conditions; their behaviour directly affects the operational performance of each aspect of the paste system from thickening to transport to deposition and rehabilitation. As such the clay minerals will be discussed in some detail in the following section. Clay size and structureClays (or phyllosilicates) are typically classified on a size basis as the -2 m fraction within a tailings slurry.However, a distinction must be made between the mineralogy of clay sized particles and true clay minerals (Fourie, 2002). True clays are classified into two major types based on the clay crystal lattice structure, namely 1:1 type clays (composed of a single octahedral layer which is bound to a single silicon tetrahedral layer), and 2:1 type clays (composed of two tetrahedral sheets sandwiching a central octahedral sheet) (Figure 1).

Comprehensive Review on the Interactions of Clay Minerals With Animal Physiology and Production

“…In naturally occurring smectite clays, several tens of layers stack together to form colloidal particles named “tactoids”, which can be leaf-like, needle-like or plate-like in shape. Tactoids display a typical lateral dimension of 100–200 nm, a layer thickness of 10 nm and an interlayer spacing of about 1 nm, and form the basic structure of clays ( 50 – 53 ). Tactoids can gather into different orientations and form clusters (or flocculi) displaying diameters in the sub-micrometer (nanoparticles) to micrometer range, depending on the physical-chemical conditions of the environment in which they are dispersed ( 54 , 55 ).…”

Liquefaction Potential of Surface Deposits of High-Density Thickened Tailings

“…Included on this figure are the particle size distributions for tailings material considered to have a low resistance to liquefaction, according to Ishihara Figure 2 shows the same plot, with particle size distributions of three thickened tailings that are from current operations added. The three sites are Bulyanhulu in Tanzania (Shuttleworth et al, 2005), Peak gold mine in Australia (Pirouz et al, 2005) and the CTP project in South Africa (Vietti, 2001). It is clear from this plot that the possibility exists that some thickened tailings may indeed be potentially susceptible to liquefaction.…”