Fluid handling – Processes – Affecting flow by the addition of material or energy
Patent
1986-02-24
1987-08-25
Cohan, Alan
Fluid handling
Processes
Affecting flow by the addition of material or energy
406197, F17D 116
Patent
active
046885889
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an improved means of controlling the viscosity of slurries.
Solid in liquid dispersions in which the solid particles usually exceed colloidal dimensions are referred to as suspension concentrates and have been the subject of an extensive review [TADROS Th. F "Physical Stability of Suspension Concentrates", Advanced Colloid Interfaced Science, Vol. 12, p 141, (1980)]. In this review, the author deals mainly with pharmaceutical and pesticidal preparations, but mentions a number of other industrial applications such as paints, dye-stuffs, pigments, paper coatings and printing inks. The main distinction between suspension conecentrates and colloidal dispersions is that the particles in the former tend to settle to the bottom of a container, whereas in the latter the particles are kept dispersed by a mild mixing produced by ambient thermal fluctuations and/or Brownian motion. This settling out tendency, together with the general flow properties, is a cause of major concern to those involved with such coarse suspension concentrates, particularly at higher concentrations.
Another major industrial application of coarse suspension concentrate technology is in mining operations, including operations applicable to the disposal of waste products or tailings. These operations frequently entail the handling, as slurries, of fine powders composed largely of silica and other components. These other components obviously depend on the particular mining operation, but usually include ferric oxide, alumina and, to a lesser extent, other metallic oxides. The handling of such products, particularly in the case of waste products, is usually effected by mechanical pumping of the materials mixed with water as a thick slurry, and transporting by pipeline to processing plant, settling ponds or worked out areas of the mine. The efficiency of the handling will in such case depend on pumping power requirements, which will in turn depend on the concentration, viscosity and yield stress of the slurry.
It is known that the flow of material in the form of suitable fine solids (generally referred to as "fines") may be facilitated by mixing the fines with water, or adjusting the fines/water ratio, and adding an inorganic dispersant to form a flowable slurry. It has been shown that flowable slurries can be so obtained with a water and fines mixture containing between 55 to 70% by weight of fines and 0.1 to 0.25% by weight of inorganic dispersant, such as a sodium phosphate (orthophosphate, pyrophosphate, hexametaphosphate or tripolyphosphate).
Attainment of a flowable slurry can greatly facilitate the handling of fines in many applications such, as indicated, in the mineral processing industry. However, the power requirements in pumping slurries through pipelines are critical in terms of pumping efficiency, and more importantly, overall cost-benefit considerations. In many instances, particularly those involving disposal of mine tailings, the economics are quite marginal and economically viable operation is possible only if power requirements and the cost of dispersant can be minimised. That is, the level of dispersant used to achieve a flowable slurry must be such that the flow characteristics of the slurry permit the efficient pumping at an aggregate cost for power and dispersant which enables economically viable operation. Even at levels of 0.1 to 0.25% by weight of a sodium phosphate dispersant, costing from $1,500 to $2,000 Australian per tonne, such operation can be rendered uneconomic.
It has now been discovered, by conducting rheological measurements on concentrated silica slurries in which are present increasing amounts of inorganic oxide, hereinafter referred to as "impurity"or "impurities", that viscosity increases markedly when only small amounts of certain impurities (up to 10% by mass of total silica) are present in the slurry. In addition to this viscosity increase, the departure from Newtonian behaviour is also increased, whereas pure siliceous slurries closely approximate Newtonian behaviour. Further
REFERENCES:
patent: 4522628 (1985-06-01), Savins
patent: 4526584 (1985-07-01), Funk
patent: 4605329 (1986-08-01), Duffy
Horsley Richard R.
Jones Robert L.
Snow Robert J.
Cohan Alan
Royal Melbourne Institute of Technology Limited
Western Australian Institute of Technology
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