Investigating the effect of coarse particle addition on the measured rheological parameters of fine clay slurries

[摘要] ENGLISH ABSTRACT: Due to economic and environmental constraints mining operations are placed underincreasing pressure to effectively manage and operate tailings disposal operations.Restrictions imposed on water usage and tailings operations footprint have led tohigher density and wider particle size distribution slurries conveyed to tailings areas.One means of efficiently disposing the tailings is co-disposal. In this method aconcentrated fine vehicle slurry is used to convey a coarser fraction. This produces ahigher density of tailings, with a number of advantages both upstream and downstreamof the tailings process. Limited research has been conducted on the effect of coarseparticles on the non-Newtonian rheological properties of these slurries. This lack ofinformation complicates the design and reliable operation of these systems.This project aims at gaining a clearer understanding as to the mechanisms involved inthe addition of coarse particles to a fine clay slurry vehicle; and to provide a means ofestimating the measured slurry rheological properties. A number of experiments weredesigned to test the slurry (both Kaolin only, and Kaolin-coarse particle mixtures)rheological properties using a Couette viscometer (for the dynamic flow properties ofyield stress and plastic viscosity) and a vane instrument (for the static yield stressmeasurements).The slurries were prepared in varying Kaolin clay solids concentrations with reverseosmosis water. Glass beads and two types of industrial sand were used as the coarsefractions. All of the coarse particles had a similar size but varied significantly in shape.Slurry pH and temperature readings were monitored throughout the tests.Tests were done initially on clay only slurries. The rheological properties of theseslurries were repeatable, and no noticeable variations of properties with time wereobserved. The yield stress (both static and dynamic) and plastic viscosity data werewell correlated with established relationships.Coarse particles were added to the clay only slurries, and then removed. Theremaining clay only slurry exhibited the same rheological properties as the initial clay only slurry. The presence of coarse particles increased all the measured rheologicalproperties (i.e. dynamic yield stress, Bingham viscosity, and static vane yield stress) ina fashion resembling the effect of adding clay to a clay only slurry. In addition, thechange in measured rheological property by addition of coarse particle wasindependent of the clay fraction in the clay slurry. Furthermore, with both the clay onlyslurries and clay and coarse sand slurries, a constant linear relationship existedbetween the static and dynamic yield stress.Several correlations from the literature were found to provide reasonable prediction ofthe rheological property variations observed. These empirical and semi-empiricalmodels however did little to explain the mechanisms involved in coarse particleaddition. A new correlation has been proposed, Residual Clay Concentration, whichpredicts the change in rheological property based on an additional clay concentration,which in turn is a linear function of the coarse particle concentration. The accuracy ofthis model further strengthens the belief that the coarse particle acts in a similarfashion to a floc.By means of a case study example the importance of selecting an appropriate modelfor design was illustrated. The Residual Clay Concentration method provided the mostconservative results. This combined with its theoretical basis strengthens the modelsrecommendation for use in design.

[发布机构] Stellenbosch University