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Title: Tantalum and niobium mineralogy and recovery from kaolinised Cornish granite
Author: Neighbour, Matthew W.
ISNI:       0000 0004 0132 4269
Awarding Body: University of Exeter
Current Institution: University of Exeter
Date of Award: 2010
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The china clay industry in the UK produces vast quantities of benign waste through the production of clay and aggregate products. These wastes contain a wide array of minor quantities of accessory minerals, none of which have been quantitatively studied or properly classified in detail. In view of the potential for recovering rare elements, this project investigates the presence of these accessory minerals with particular focus on the tantalum and niobium ore mineral series, columbite-tantalite. Although these minerals are already known to be present, no research on their distribution within the potential ore body has been undertaken and knowledge of the structure of these and other tantalum minerals present is very limited. The thesis sets out to assess the potential resources available through analysis and interpretation of samples collected from Goonvean Ltd. SW England. Initial samples were taken from five operating pit faces to confirm the presence of tantalum mineralogy across the three areas worked by Goonvean Ltd (Goonvean, Rostowrack and Trelavour Downs's pits) for clay extraction. Detailed information of the elemental and mineralogical differences between these areas was gathered, using a variety of analytical techniques. To determine which single site had the most potential for concentrating tantalum efficiently. Based on element abundance, mineralogical content and characteristics of ore grains to upgrade, (Le. grain size, density and liberation) material from Trelavour Downs pit was selected for investigation. Drill core samples were collected and elemental distribution analysed, including Ta, Nb, Sn, Wand other trace level elements. Using geostatistical techniques the presence of trends or patterns within the area, which can give an insight into the mineralization, was investigated. This information was used to generate an estimate of grade and tonnages available. Although literature reports the presence of tantalum and niobium within the area, only one paper investigates the mineralogy from concentrates, (Scott et al. 1998) which from a small number of grains of columbite-tantalite showed a high variation in chemistry; Manning and Hill (1990) also recorded traces of the niobium and tantalum containing mineral ilmenorutile. In this study, QEMSCAN is applied to measure thousands of grains instead of tens of grains, providing improved detail into the mineralogical variability. The drill core samples were combined into composite samples which respect the geology. This produced eighteen samples which were analysed in full detail utilising mineral processing coupled with analytical techniques. Through this analysis, the tantalum minerals were classified, and other mineral species previously undiscovered in the area were identified. Notably QEMSCAN analyses enabled identification of the minerals present, including the gangue mineralogy and their characteristics. Laboratoryscale tests were conducted to assess the viability and variability of gravity separation for production of a tantalum pre-concentrate as well as monitoring the behaviour of other elements, notably niobium, tin and tungsten. QEMSCAN and XRF analyses of gravity separation products from the composite samples allowed insight into the effect of varying tantalum mineralogy on separation efficiency and a model was devised based on these results to predict the grade and recovery of tantalum for the eighteen composites. Compared to other operations, Tailson's Wodgina mine produces a pre-concentrate grade at 8% Ta20S, Haddington resources Ltd. Produces a pre-concentrate at 7.5% and Noventa's Morrua mine in Mozambique at 10% Ta205 (Serjak, 2004, Antonio, 2008).Tantalum grade after a rougher and cleaner Mozley table circuit was measured at 8.9% Ta20S and the combined tantalum recovery was 66%; this is greater than Tanco's sand recovery circuit at 55% , which has a similar size fraction (200-20 ~m), although their overall recovery reaches 70% (Flemming et aI, 1982) and Haddington's preconcentrate tantalum recovery is 65% (Serjak, 2004). The topaz granite contains variable levels of topaz which is heavy gangue mineral with a density ranging between 3.5-3.6 glcm3 (Barthelmy, 2010). This mineral is dominant in any concentrate produced from heavy liquid and gravity tests. Although its content is significantly reduced through gravity separation on the Mozley table, it remains at high levels and dilutes the concentrates. Niobium and tin were also shown to respond well to gravity separation. However, tungsten responds very poorly due its very fine grain size. It is the opinion of the author that further investigation into the extraction and refinement of these metals may lead to an economic added value product(s) if demand and prices for these metals is favourable. Although concentration by DMS upgraded the grain counts of tantalum mineralogy analysed by QEMSCAN, the grade was still too low to discern the variability of tantalum minerals within a single sample. This resulted in the model incorrectly predicting the Mozley table concentrate grade and recovery. Finally, a relationship between the mineralogy, mineral density and the tantalum and niobium assays of composites is proposed as well as a methodology to predict the mineralogical properties which affect the performance of mineral grains on the Mozley table. An integration of this estimated data is proposed and its uses outlined.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available