Slurry transport in the mining industry is a commonly used technique for moving partially and fully processed materials, and waste.
Often this type of treatment is more economical and rapid than other transportation methods, such as those involving conveyor systems or haulage. Additionally, the materials on a mine-site are often slurried for processing, and pipeline transport is necessary.
However frequently utilised, efficient slurry transport still poses serious engineering problems through the properties of the slurry. These include, but are not limited to, particle settling, attrition, pipe/fitting/impeller wear, degradation of flocculated or friable solids, and the pumpability of the slurry. In addition, the effects of these challenges can be exacerbated, or reduced by process or environmental variables, such as temperature, pH or solids loading.
In-transit particle settling leads to stratified flow, which in turn can cause uneven and excessive wear in the transport system, and in extreme cases, pipeline blockage due to solids build-up around fittings or inclined sections. Particle attrition has several drawbacks. Firstly, the product before the pump and pipe is not identical to that afterwards if the particles are friable, this may be a QC matter both for disposal and in-process. Secondly, changes in particle size distribution may affect the ability of the particles to remain suspended in the carrier fluid. Problems with the pumpability of slurries potentially include the fact that they often behave as a solid, e.g. when at rest, making it expensive to initiate pumping. Many fluids, including slurries have flow properties which depend on the ‘rate of deformation’ (analogous to their flow-rate).
Rheological techniques can help the engineer or technician to design for and manipulate processes. A range of instruments is available which measure the effects of solids loading, carrier fluid, particle size distribution and viscosity or pH modifiers on the propensity of particulate matter to flocculate, be suspended, settle etc. through a knowledge of the characteristic flow properties of the slurry. These rheometers and viscometers allow the engineer to directly measure and assess the causes and effects listed above. Physical quantities such as yield stress (the minimum force required for a slurry to flow), plastic viscosity (how ‘runny’ a slurry will be at a given laminar flow-rate), hysteresis (the changes in plastic viscosity and/or yield stress which are due, usually, to particle attrition or settling) can be better predicted with the appropriate equipment.
Sensitive, high precision versatile equipment is available for repeatable and reliable measurement of all flow properties in the laboratory, and durable, precise, robust units for in the field use are also commercially available. These units have been shown to be of value for both QC and product development.
A full copy of the application note is available on request by quoting Rheo-013