Thesis (PhD (Physics))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Radioactivity is well known and well understood, but its usefulness in industrial
applications to optimise processes or increase economic viability is not yet fully utilised by
many industries. This study focuses on the measurement of natural radioactivity and its
application in heavy mineral separation and vineyard soil classification.
The gamma radiometry set-up consisted of a high purity germanium detector, a Marinelli
beaker as sample container and associated electronics. It was calibrated for laboratorybased
measurements by minimising the background radiation with the use of lead castle
and energy and resolution calibrations. Furthermore, detection parameters were
optimised; these included the counting time, the selection of gamma rays used for analysis
of a sample, the peak area calculation for the detector dead time and the detector
efficiency. Given that the samples had different densities and volumes, the detector
efficiency had to be corrected for volume and density effects. After implementation of the
corrections and optimisations the detection system was tested and found able to
accurately measure radioactivity concentrations. The systematic measurement errors for
238U were 5.1 % in the case of the heavy mineral sands and 34.3 % for the vineyard soils,
4.5 % for the 232Th concentrations and 4.7 % for 40K concentrations. Statistical errors were
kept below 2 %.
The application of radiometry has not been done before at any South African heavy
mineral separation plant. For this reason radiometry is suggested as an easier, faster and
cheaper alternative to X-ray fluorescence (XRF) for effective implementation of grade
control for zircon to improve the cost benefit of the heavy mineral separation process.
Zircon is an example of a heavy mineral that is worldwide in demand with a consumption
of more than a million tonnes per year. It is used in a wide range of industrial applications
and products that include tiles, sanitary ware and plasma displays. South Africa is the
second largest producer of zircon in the world and also has the second largest reserve of
available zircon, making this mineral a viable source of income for several years to come.
Radioactivity, in the form of uranium and thorium, and other impurities such as iron oxide
and titanium oxide are found in the crystal lattice of zircon. For it to be a sellable product,
the sum of the uranium and thorium concentrations must be less than 500 parts per million
for prime or first grade zircon and less than 1000 parts per million for second grade zircon.
At present the concentrations of uranium and thorium in zircon concentrates are measured
on a whole rock basis by XRF during and at the end of the processing cycle before the
final products are ready to be shipped. This is not an ideal situation as the grab samples
are taken periodically and are not necessarily representative of the stream or final
assignment and has resulted in significant losses by the producer. The solution is to
accurately measure the uranium and thorium concentrations fast or immediately,
preferably the measurements must be made online and in real time so that processing
decisions can be implemented quickly to optimise the final product.
Heavy mineral sand samples were obtained from the various separation processes in a
Mineral Separation Plant and their 238U and 232Th concentrations determined. The results
indicated that the samples’ uranium to thorium ratios together with their total
concentrations can be used to differentiate between the samples (i.e. separation
processes). The measurement results were compared with those obtained with XRF. The
correlations with radiometry were excellent for the uranium (r2 = 0.992), thorium (r2 =
0.998) and total concentrations (r2 = 0.998). Radiometric measurements were also
conducted by decreasing the counting time from 3600 s to 1 s to investigate its effect on
the accuracy of the results. Correlations between the different times and 3600 s ranged
from excellent to good. The obtained results are then used to recommend that radiometry
is used in a Mineral Separation Plant to verify that the zircon and zirkwa meet the
specifications, to optimise the entrance feed and the other separation processes and to
monitor the tailings streams. Finally the practical aspects of the implementation of
radiometry are discussed.
As a second application was radiometry applied in an agricultural pilot study to
demonstrate the applicability of radiometry as a possible useful tool in soil classification.
The creation of a vineyard is a long term and expensive investment and its yield and
quality will be influenced by many factors such as the type of soil, viticultural preparations
and climate. Information on the different soil types in a vineyard is therefore indispensable
for the optimisation of land use with respect to vine cultivar, wine quality and production.
Soil samples were obtained from Kanonkop, Simonsig and Spier vineyards and their 238U,
232Th and 40K concentrations determined, assuming that fertilisers would have no effect on
the results. The difference in 40K concentrations were related to the clay fraction of the soil
and demonstrated that the Kanonkop and Simonsig soils are fine-grained and clay-rich
compared to the sandy coarse-grained soils of Spier. The uranium and thorium
concentrations were indicators of whether the mineralogy of the soil is the same as the
underlying bedrock as well as soil maturity. The measurement results were compared with
those obtained with XRF. The correlation with radiometry were poor for the uranium
concentrations (r2 = 0.314), as many of the samples concentrations were below the XRF
detection limit. The correlations were excellent for both thorium (r2 = 0.985) and potassium
(r2 = 0.999). As a positive result from the findings of the study was an in-situ measurement
performed by Newman et al. for the radiometric mapping of a Simonsig vineyard for soil
classification. / AFRIKAANSE OPSOMMING: Radioaktiwiteit is wel bekend en word goed verstaan, tog is die gebruik daarvan in
industriele toepassings om prosesses te optimiseer of winsgrense te verhoog nog nie deur
baie industrië ten volle benut nie. Hierdie studie fokus op die meting van natuurlike
radioaktiwiteit en die toepassing daarvan in swaar mineraal skeiding en wingerd grond
klassifikasie.
Die gamma radiometrie opstelling het bestaan uit ‘n hoë suiwerheid germanium detektor,
'n Marinelli beker as monster houer en verwante elektronika. Dit was gekalibreer vir
laboratorium gebaseerde metings deur die vermindering van die agtergrondstraling met
die gebruik van lood kasteel en energie en resolusie kalibrasies. Verder was deteksie
parameters geoptimaliseer, dit sluit in die teltyd, die keuse van gammastrale wat gebruik
word vir die ontleding van 'n monster, die piek area berekening, die korreksie vir die
detektor se dooie tyd en die detektor doeltreffendheid. Gegee dat die monsters van
mekaar verskil het in terme van dighteid en volume was dit nodig om die detektor
doeltreffendheid te korrigeer vir volume en digtheid effekte. Na die implementering van die
korreksies en optimalisasie was die detektor stelsel getoets en was gevind dat
radioaktiwiteit konsentrasies akkuraat gelewer kan lewer. Die sistematiese meet foute vir
238U was 5.1 % vir die mineraal sand en 34.3 % vir wingerd grond, 4.5 % vir 232Th
konsentrasies en 4.7 % vir 40K konsentrasies. Statistiese foute was onder 2 % gehou.
Die toepassing van radiometrie was nog nie voorheen by enige Suid-Afrikaanse swaar
mineraal skeidings aanleg gedoen nie. Vir die rede is radiometrie voorgestel as ‘n
makliker, vinniger en goedkoper alternatief teenoor XSF vir effektiewe implementering van
graad beheer vir zirkon om die koste voordeel van die swaar mineral skeiding proses te
verbeter. Zirkon is ‘n voorbeeld van ‘n swaar mineraal wat wêreldwyd in aanvraag is met ‘n
verbruik van meer as ‘n miljoen ton per jaar. Dit word in ‘n wye reeks van industriele
toepassings en produkte gebruik onder andere teëls, sanitêre ware en plasma skerms.
Suid Afrika is die tweede grootste vervaardiger van zirkon in die wêreld en het ook die
tweede grootste reserwe van besikbare zirkon. Dit veroorsaak dat die mineraal ‘n
lewensvatbare brom van inkomste is vir nog etlike jare. Radioaktiwiteit, in die vorm van
uraan en thorium, word tesame met ander onsuiwerhede soos ysteroksied en titaanoksied
in zirkon se kristal rooster gevind. Om ‘n verkoopbare produk te wees moet die som van
die uraan en thorium konsentrasies minder wees as 500 dele per miljoen vir prima en
eerste graad zirkon en minder wees as 1000 dele per miljoen vir tweede graadse zirkon.
Huidiglik word die uraan en thorium konsentrasies in die zirkon konsentraat gemeet op ‘n
heel gesteente basis met X-straal fluoroskopie (XSF) gedurende en op die einde van die
prosesering siklus net voor die finale produk reg is om versend te word. Dit is nie die
ideale situasie nie, want die monsters word periodies geneem en is nie noodwendig
verteenwoordigend van die stroom of die finale produk nie en het al tot beduidende
verliese deur die vervaardiger gelei. Die oplossing is om die uraan en thorium
konsentrasies vinnig of onmiddelik te meet, verkieslik moet die metings inlyn en intyds
gedoen word om verwerkings besluite vinnig geimplementeer kan word om die finale
produk te optimaliseer.
Swaar mineraal sand monsters was verkry van die verskeie skeidingsprosesse in ‘n
Mineraal Skeidings Aanleg en hul 238U en 232Th konsentrasies bepaal. Die resultate het
aangetoon dat die monsters se uraan en thorium verhoudings saam met hul totale
konsentrasies gebruik kan word om te onderskei tussen die monsters (oftewel die skeiding
prosesse). Die meting resultate was vergelyk met dié verkry met XSF. Die korrelasies met
radiometrie was uitstekend vir die uraan (r2 = 0.992), thorium (r2 = 0.998) en totale
konsentrasies (r2 = 0.998). Radiometriese metings was ook uigevoer deur die teltyd te
verminder van 3600 s tot 1 s om die uitwerking daarvan op die akkuraatheid van die
resultate te ondersoek. Korrelasies tussen die verskillende tye en 3600 s het gewissel van
uitstekend tot goed. Die bevindinge was dan gebruik om aan te beveel dat radiometrie in a
Mineraal Skeidings Aanleg gebruik kan word om te verifeer dat daar aan die zirkon en
zirkwa spesifikasies voldoen word, om die begin voer en ander skeidings prosesse te
optimaliseer en ook die uitskot strome te monitor. Laastens is die praktiese aspekte van
die implementering van radiometrie bespreek.
Vir die tweede toepassing was radiometrie toepgepas in ‘n loods studie in die landbou om
die toepaslikheid van radiometrie as ‘n moontlike nuttige instrument in grond klassifikasie
te demonstreer. Die skepping van ‘n wingerd is ‘n lang termyn en duur belegging waarvan
die opbrengs en kwaliteit beinvloed sal word deur vele faktore, onder andere die tipe
grond, wynbou voorbereidings en die klimaat. Inligiting oor die verskillende grond tipes in
‘n wingerd is daarom onmisbaar vir die optimalisering van land gebruik in betrekking tot die
wingerdstok kultivar, wyn kwaliteit en produksie. Radiometrie is toegepas om te
demonstreer die toepaslikheid daaran as ‘n moontlike nuttige instrument in grond
klassifikasie.
Grondmonsters was verkry vanaf Kanonkop, Simonsig en Spier wingerde en hul 238U,
232Th en 40K konsentrasies bepaal met die aanname dat kunsmis nie ‘n uitwerking op die
resultate sou hê nie. Die verskil in 40K konsentrasies was verwant aan die kleifraksie van
die grond en het getoon dat die Kanonkop en Simonsig gronde is fyn korrelrig en kleiryk is
in vergelyking met die sanderige growwe korrel grond van Spier. Die uraan en thorium
konsentrasies het gedui op die samestelling van die grond en ook aangedui watter grond
dieselfde is as die onderliggende rots. Die meting resultate was vergelyk met dié verkry
met XSF. Die korrelasie met die radiometrie was sleg vir die uraan konsentrasies (r2 =
0.314) aangesien baie van die monster konsentrasies laer was as die XSF deteksie limiet.
Die korrelasies was uitstekend vir beide thorium (r2 = 0.985) en kalium (r2 = 0.999). As ‘n
positiewe resultaat van die studie se bevindinge was ‘n in-situ meting gedoen deur
Newman et al. om ‘n Simonsig wingerd radiomeries te karteer vir grond klassifasie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6851 |
| Date | 03 1900 |
| Creators | De Villiers, Dawid |
| Contributors | Stander, J. A., Rozendaal, A., University of Stellenbosch. Faculty of Science. Dept. of Physics. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 196 p. : ill. |
| Rights | University of Stellenbosch |
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