Mineral processing involves the transportation and processing of large quantities of materials.

Mineral processing involves the transportation and processing of large quantities of materials. Combining solid materials with a carrier fluid (usually water) to create a slurry has long been popular in the industry, principally due to the increased efficiency and alacrity of mineral processing steps through use of a slurry, since the finely ground particles afford greater surface area exposure to the extracting medium. Also, the ease with which the particulate matter can be processed in this form is important for unit processes including grinding, classification, separation processes (settling, thickening, screening, filtration) and transport processes like pump/gravity flow through pipes and launders, mixing, etc.

Slurry characteristics pose many engineering challenges. These characteristics include particle settling, pH, bulk/carrier fluid viscosity, particulate flocculation or dispersion, attrition, pipe/fitting/impeller wear, degradation of flocculated or friable solids and the pumpability of the slurry. The effects of these challenges can be further altered by process or environmental variables such as temperature or solids loading. Wet communition and classification can be effected by viscosity, particle size distribution, fines concentration etc. For example, hydrocyclone classification is effected by the presence of a yield stress (the minimum force required for a slurry to flow). Often, cut point increases and efficiency decreases with increasing yield stress. Separation processes are influenced by inter-particle attraction and viscosity (how easily the fluid flows once it is in motion). These variables may be manipulated through the addition of modifying agents to the slurry. The key effects of these additions should be monitored through changes in the rheological parameters of the slurry, which are directly related to process performance. In-transit particle settling causes uneven and excessive wear or complete blockage in the transport system. Particle attrition may be a QC matter both for disposal and in-process and, changes in particle size distribution may affect the ability of the particles to remain suspended. Problems with the pumpability of slurries include the high cost of initiating and continuing pumping of fluids with high yield stresses or viscosities.

Rheological techniques can help assess process design and manipulation processes. A range of instruments is available to measure the rheological effects, through knowledge of the characteristic flow properties of the slurry. These rheometers allow the engineer to directly measure and assess the causes and effects listed above. Physical quantities such as yield stress, plastic viscosity and hysteresis (the changes in plastic viscosity and/or yield stress which are due, usually, to particle attrition or settling) can be quantified and predicted with the appropriate equipment.

Sensitive, precise equipment is available for repeatable and reliable measurement of flow properties in the laboratory, and durable, robust units for in-the-field use are also available. These units are of value for both QC and product development.

A full copy of the application note is available on request by quoting Rheo-014