Thesis (MScIng)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Due to economic and environmental constraints mining operations are placed under
increasing pressure to effectively manage and operate tailings disposal operations.
Restrictions imposed on water usage and tailings operations footprint have led to
higher density and wider particle size distribution slurries conveyed to tailings areas.
One means of efficiently disposing the tailings is co-disposal. In this method a
concentrated fine vehicle slurry is used to convey a coarser fraction. This produces a
higher density of tailings, with a number of advantages both upstream and downstream
of the tailings process. Limited research has been conducted on the effect of coarse
particles on the non-Newtonian rheological properties of these slurries. This lack of
information complicates the design and reliable operation of these systems.
This project aims at gaining a clearer understanding as to the mechanisms involved in
the addition of coarse particles to a fine clay slurry vehicle; and to provide a means of
estimating the measured slurry rheological properties. A number of experiments were
designed to test the slurry (both Kaolin only, and Kaolin-coarse particle mixtures)
rheological properties using a Couette viscometer (for the dynamic flow properties of
yield stress and plastic viscosity) and a vane instrument (for the static yield stress
measurements).
The slurries were prepared in varying Kaolin clay solids concentrations with reverse
osmosis water. Glass beads and two types of industrial sand were used as the coarse
fractions. 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 these
slurries were repeatable, and no noticeable variations of properties with time were
observed. The yield stress (both static and dynamic) and plastic viscosity data were
well correlated with established relationships.
Coarse particles were added to the clay only slurries, and then removed. The
remaining clay only slurry exhibited the same rheological properties as the initial clay only slurry. The presence of coarse particles increased all the measured rheological
properties (i.e. dynamic yield stress, Bingham viscosity, and static vane yield stress) in
a fashion resembling the effect of adding clay to a clay only slurry. In addition, the
change in measured rheological property by addition of coarse particle was
independent of the clay fraction in the clay slurry. Furthermore, with both the clay only
slurries and clay and coarse sand slurries, a constant linear relationship existed
between the static and dynamic yield stress.
Several correlations from the literature were found to provide reasonable prediction of
the rheological property variations observed. These empirical and semi-empirical
models however did little to explain the mechanisms involved in coarse particle
addition. A new correlation has been proposed, Residual Clay Concentration, which
predicts 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 of
this model further strengthens the belief that the coarse particle acts in a similar
fashion to a floc.
By means of a case study example the importance of selecting an appropriate model
for design was illustrated. The Residual Clay Concentration method provided the most
conservative results. This combined with its theoretical basis strengthens the models
recommendation for use in design. / AFRIKAANSE OPSOMMING: As gevolg van ekonomiese en omgewings beperkinge word mynwese nywerhede
onder toenemende druk geplaas om doeltreffende afvalstroom bestuur en operasie toe
te pas. Beperkinge geplaas op water gebruik en afvalstroom area-groote ly tot hoër
digthede en wyer partikel-grooteverspreidings van flodders vervoer na afval areas.
Een manier om van die afval doeltreffend ontslae te raak en te berg is deur medeberging.
In die metode word ‘n gekonsentreerde fyn flodder gebruik as draer van ‘n
growwer partikel-fraksie. Dit ly tot ‘n hoër digtheid flodder, met verskeie voordele in
beide die op – en afstroom prosesse. Beperkte navorsing is gedoen op die effek van
growwe partikels op die nie-Newoniese rheolgiese eienskappe van hierdie flodders.
Hierdie tekort aan informasie maak die effektiewe, betroubare bedryf en operasie van
die sisteme meer ingewikkeld.
Hierdie projek is daarheen gemik om ‘n beter begrip te ontwikkel met betrekking tot
die meganismes betrokke in die byvoeging van growwe partikels aan ‘n fyn klei-agtige
flodder draer; en om ‘n manier te voorsien wat die rheologiese eienskappe kan beraam.
Verskeie eksperimente was ontwerp om die flodders (beide slegs Kaolien, en Kaoliengrowwe
partikel mengsels) se rheologiese eienskappe te toets deur die gebruik van ‘n
Couette-viskometer. Die Couette viskometer was gebruik om die dinamiese
eienskappe (van grens-spanning, en plastiese viskositet) te meet. ‘n Vaan apparaat is
gebruik om die eienskap van statiese grens-spanning te meet.
Die flodders was voorberei in verskeie Kaolien konsentrasies met tru-osmosis water.
Glas krale en twee tipes industriële sand is gebruik as die growwe fraksies. Al die
growwe partikels het soortgelyke groottes gehad, maar het grootliks verskil in vorm.
Die flodder pH en temperatuur lesings is deurentyd nagegaan.
Toetse was aanvanklik gedoen op die klei-alleenlike flodders. Die gemete reologiese
eienskappe van die flodders was herhaalbaar, en geen opmerkbare veranderinge van
die eienskappe met betrekking tot tyd is gemeet nie. Die grens-spanning (beide statiese
en dinamiese) en plastiese viskositeit is goed gekorrelleer met gevestigde verhoudinge. Growwe partikels is aan die klei-alleenlike flodders bygevoeg, en daarnae verwyder.
Die oorblywende klei-alleenlike flodder het dieselfde gemete rheologiese eienskappe
getoon as die oorspronklike klei-allenlike flodder. Die teenwoordigheid van growwe
partikels het na ‘n toename van al die gamete rheologiese eienskappe gelei wat fisies
baie soortgelyk is aan die byvoeging van klei tot ‘n klei-alleenlike flodder. Verder, met
beide die klei-alleenlike en klei-growwe partikel flodders het ‘n konstante liniëre
funksie tussen die statiese en dinamiese grens-spannings bestaan.
Verskeie verhoudings uit die literatuur het goeie korrelasie bewerkstellig met die
waargenome rheologie veranderinge. Hierdie empiriese en semi-empiriese modelle
doen egter min om die megansimes betrokke in die toevoeging van growwe partikels
te verduidelik. ‘n Nuwe korrelasie is voorgestel, naamlik die Residu Klei Konsentrasie.
Hierdie model voorspel die verandering in reologiese eienskappe gebaseer op ‘n
addisionele klei konsentrasie, wat ‘n liniëre funkise is van die growwe partikel
konsentrasie. Die goeie korrelasie gesien met die model versterk die idée dat die
growwe partikel in ‘n soortgelyke manier as ‘n flok gedra in die teenwoordigheid van
ander flokke.
Deur middel van ‘n tipiese industriële voorbeeld is die belangrikheid in die keuse van
die regte korrelasie geillustreer. Die Residu Klei Konsentrasie metode het die mees
konservatiewe resultate gelewer. Hierdie feit gekombineerd met die model se soliede
teoreitiese beginsels versterk dit as voorgestelde korrelasie vir ontwerp.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/18629 |
| Date | 12 1900 |
| Creators | Paulsen, Eric |
| Contributors | Aldrich, C., Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xix, 231 p. : ill. |
| Rights | Stellenbosch University |
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