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The beneficiation of ferruginous rare earth bearing ores derived from lateritic deposits by conventional mineral dressing processes is usually difficult due to characteristics of these ores such as fine grain size, complex texture and similar physical characteristics between rare earth minerals and iron oxide gangue. The removal of iron oxides would offer significant advantages with respect to downstream rare earth mineral processing. The purpose of this study was to demonstrate at bench scale the feasibility of magnetically separating iron oxides from a ferruginous lateritic rare earth ore after the ore had been subjected to reduction roasting to convert feebly magnetic iron (III) oxides to magnetite. The effects of magnetic field strength and feed top size on the efficiency of low intensity magnetic separation (LIMS) was explored through rougher magnetic separation tests using a Davis tube tester and chemical and mineralogical analysis of the rougher magnetic concentrates and tails was performed. Magnetic separation was successful in removing iron (as magnetite) to the concentrate at a minimum field strength of 0.2 T; this was however non-selective, with significant amounts of rare earths reporting to the magnetic fraction. The rare earth enriched tails showed decreased grade and recovery and this was due to a number of factors including insufficient liberation, presence of iron oxide coatings on mineral surfaces and heteroflocculation. The findings of this study provided insight towards the potential optimisation and viability of the proposed process of magnetising roasting and low intensity magnetic separation as a means to beneficiate ferruginous lateritic rare earth ores.

Compared with processing high-TiO2 concentrates such as ilmenite ores, processing an anatase ore to achieve impurity levels acceptable for pigment production is more difficult because of the extensive number of accessory minerals present, the significant intergrowths between minerals and the fact that impurity elements may be distributed in several different minerals. In this paper, conditions applicable to processing anatase ores are reviewed with an aim of identifying conditions that may produce a suitable feedstock for processing to titania pigment by either the sulphate or chloride routes. Anatase ores containing 25–35 wt% TiO2 currently are processed using mineral dressing techniques of crushing and grinding, classification, magnetic separation and flotation to produce a concentrate with around 65 wt% TiO2. This concentrate is then typically upgraded to over 90 wt% TiO2 using combinations of heating and leaching treatments, often with the addition of a fluxing reagent to assist in impurity removal. The suitability of these products as a feedstock for the sulphate and chloride routes to pigment is discussed.

Detailed characterisation of a lateritic rare earth ore formed from the weathering of a primary carbonatite was carried out to determine the mode of occurrence and distribution of rare earths and gangue species in the ore. The ore was characterised by a number of techniques including chemical analysis, quantitative X-ray diffraction, screen analysis, QEMSCAN and SEM/EDX. The primary rare earth bearing mineral identified was monazite in its various forms; florencite the other rare earth mineral identified is of secondary importance. The main gangue species was goethite with lesser amounts of dolomite and apatite. As a result of the weathering process, the ore was enriched in rare earth oxides with the head grade being 7.65 wt%. Screen analysis of the crushed ore shows that it consists predominantly of fine and ultra-fine particles below 38 μm with the rare earths and iron distributing in the finer size fractions. Microstructural characterisation of the rare earth minerals in crushed ore showed that the rare earth minerals were of very fine grain size and occurred as polycrystalline aggregates and fine disseminations in gangue. Compositionally, monazite was cerium dominant and contained calcium and strontium as impurities whilst florencite was either cerium or lanthanum dominant and was enriched in strontium. The rare earth content in monazite was much higher relative to florencite, making it an important source of rare earths in the ore. Concentrate grades are likely to be impacted by the presence of structural impurities (Ca, Sr, Al) associated with monazite and florencite. In light of these findings, potential processing options such as magnetic separation and froth flotation for recovering rare earths from this ore are discussed which are also potentially applicable to the beneficiation of other ferruginous rare earth bearing ores of similar mineralogy.

A synthetic coffinite was hydrothermally prepared and characterized before conducting a series of acid sulfate leach tests under conditions of relevance to uranium extraction. The results were then compared with similar studies on synthetic versions of the related U4+ minerals uraninite (UO2) and brannerite (UTi2O6) to identify and differentiate the rate and U extraction among these important uranium minerals. Tests examining the influence of residence time on uranium dissolution from synthetic coffinite, uraninite and brannerite showed that under similar experimental conditions, complete dissolution of uranium from coffinite was obtained between 36 and 48 h. The activation energy for this reaction was calculated to be 38.4 kJ/mol. This represented a significantly slower rate of dissolution than that indicated for uraninite which dissolved in 3 h (Ea=15.2 kJ/mol). The synthetic brannerite was leached at a much slower rate than the coffinite and reached a maximum dissolution of ∼18% U in 144 h (Ea=42–84 kJ/mol). The clear differentiation in rates and U extraction among the three minerals is consistent with previous literatures which suggest that in terms of leachability, uraninite>coffinite>brannerite. It is expected that the presence of impurities in natural coffinites would further inhibit leachability.

A novel approach for the removal of chrome-bearing spinel impurities (chromite) from weathered ilmenite concentrates has been proposed. This involves a two-stage process where in Stage 1 the spinel impurities are subjected to selective surface sulphidation followed by physicochemical separation in Stage 2. In this Part 1 paper, the applicability of the selective sulphidation of spinel impurities at 1100 °C was investigated for different ilmenite concentrates sourced from the Murray Basin region in south-eastern Australia and from Bangka Island Indonesia. The results demonstrated that the selective sulphidation of the impurities can be applied to the Murray Basin ilmenites. This was indicated by the formation of sulphide-rich rims on the spinel impurities. The chrome spinels from the Indonesian ilmenite, however, were not sulphidised. This was most likely due to the refractory nature of the spinels as they contain higher concentrations of Mg and Al. The current study also simulated an industrial Becher kiln process in a laboratory roller-bed-furnace. The results show that the selective sulphidation conditions can be achieved using char and sulphur sources. It was also observed from these experiments that Mn impurities are also sulphidised. The current study also identified and presented the range of high temperature and gaseous conditions (pO2 and pS2) that promote the selective sulphidation of Mg, Mn, Sn and Y impurities.

The factors influencing goethite to magnetite conversion during magnetizing roasting of an iron-rich rare earth ore using coal as the reductant were explored in the present paper. The effect of temperature, time and reductant addition on magnetite conversion; and the optimal conditions which resulted in complete conversion of goethite to magnetite were determined through the use of satmagan and quantitative X-ray diffraction. For this particular ore, optimal roasting conditions were determined to be a roasting temperature of 600–650 °C with the addition of 10–20 wt% coal in the mixture and a roasting time of 90 min. The mineralogical changes occurring during magnetizing roasting were also investigated using X-ray diffraction. Magnetite formation was found to proceed by the reduction of hematite formed from the dehydroxylation of goethite. X-ray diffraction showed that further reaction of magnetite to form wustite and fayalite had taken place under highly reducing conditions and temperatures exceeding 650 °C. The primary rare earth mineral in this ore, monazite was stable at all roasting conditions whilst florencite underwent thermal decomposition resulting in an increase in the monazite content of the roasted ore.

The uranium ore mineral coffinite (USiO 4 ·nH 2 O) has previously been characterized using infrared spectral techniques however the spectral behavior of coffinite in relation to concentration and commo2nly associated mineral assemblages is poorly understood. This study addresses some uncertainties by quantifying the coffinite content in a series of 18 artificial mineral mixtures using near infrared (NIR). In the process, a limit of detection for coffinite was determined to be ~ 0.15 wt% (~ 0.1% U 3 O 8 ), with limits of quantification restricted by mixture composition and instrument capability. Methods defined in this study were applied to a metasomatic albitite uranium ore deposit where the presence of coffinite detected via NIR was validated by scanning electron microscopy (SEM) techniques.

This study presents a theoretical pathway to the production of sodium and potassium metal from lunar regolith at ambient lunar conditions via the selective thermal decomposition of oxides in the regolith using concentrated solar energy. The proposed process for the recovery of the products is systematically evaluated via thermodynamic modelling based on Gibbs energy minimalization using the FactSage software package. Initial modelling predicts that at ambient lunar pressures (10−15 ​atm), and assuming equilibrium conditions, a thermal decomposition process run at 800 ​°C, followed by a fractional deposition sequence with stage temperatures of 550 ​°C and −50 ​°C can result in the concentration of FeO in the first deposition and Na and K metal in the second deposition. These results support the feasibility of a thermal decomposition process for the beneficiation and reduction of mineral resources on the lunar surface.

The oxidation behaviour of rare earth permanent magnets contributes significantly to the understanding and efficiency of their high temperature recycling processes. The current paper evaluated the high temperature oxidation kinetics of end-of-life Ni/Cu/Ni coated NdFeB rare earth permanent magnets at 973−1473 K under ambient air conditions. The general microstructure observations and kinetics measurements showed that the oxidation was controlled by a diffusion mechanism that followed the Ginstling–Brounshtein model. The overall activation energy was calculated to be 168 kJ/mol. Results suggest that the presence of a Ni/Cu/Ni coating has a negative effect, reducing the overall kinetic rates by ten times.

Microwave-assisted reduction roasting of a goethite-rich, reject iron ore waste stream (−2 mm) was used to produce a high-grade concentrate. Reduction roast experiments were conducted at 370 °C, 450 °C, 600 °C and 1000 °C under gas atmospheres of 30:70 and 40:60 CO/CO2, with a soak time of 20 min. Goethite was converted to hematite above 370 °C under both gas mixtures while at the higher roasting temperatures, increasing amounts of magnetite formed. Roasting conditions for the best conversion of goethite to synthetic magnetite were 600 °C in a gas atmosphere of 40:60 CO/CO2, with a soak time of 20 min. Laboratory-based magnetic separations in a Davis tube indicated that a blast furnace grade (+62 wt% Fe) pellet concentrate could be produced with an acceptable iron recovery of > 88 wt%. Under both gas atmospheres, a higher reduction temperature of 1000 °C achieved a greater conversion of goethite to magnetite but resulted in over-reduction and the generation of wustite, fayalite and Fe-rich spinel phases with different magnetic susceptibilities that are expected to make subsequent beneficiation difficult. Further processing to optimize the microwave-assisted magnetizing roast and the magnetic separation conditions can be expected to maximize the efficiency of upgrading the iron content in low grade goethite-rich iron ores.

We explore the role of various solution environments – chloride brines, acid mine drainage (sulfate) and groundwater (carbonate), as well as pore pressure in producing secular disequilibrium among the various radionuclides (RN) in the U-decay series upon leaching of uraninite – the most abundant U-ore and a widespread accessory mineral in U-rich rocks. We observed that the end products of the U-decay chain, 206Pb and 207Pb, exist primarily at the surface/edges of grains or within large pores in the uraninite. In contrast, the intermediate daughters 226Ra, 210Pb, 210Po, and 234/230Th, exist primarily within the bulk of uraninite, requiring breakdown by leaching for subsequent mobility to occur. Overall, pore pressure had little effect on RN mobility, with solution environment being the primary factor in creating significant mobility and disequilibrium among the RN, as it drives the initial breakdown of uraninite and influences the subsequent differential solubility of individual RNs. This was particularly the case for carbonate-bearing fluids, leading to significant fractionation of the various daughter RN arising from variable complexation and sorption phenomena. Understanding the geochemical behaviour of the RN in the U-decay series is important for predicting and managing the risks associated with RN in both environmental (acid-mine drainage) and engineered (metallurgical extraction) processes. Effective modelling of long-term RN behaviour should incorporate this strong relative fractionation caused by contrasting geochemical behaviour of individual RN during and after their release into the water from uraninite and subsequent interaction with the surrounding aquifer host rocks.

Anthropogenic activities can redistribute the constituents of naturally occurring radioactive materials (NORM), posing potential hazards to populations and ecosystems. In the present study, the co-sorption of several RN from the U decay chain- 238U, 230Th, 226Ra, 210Pb and 210Po, onto common minerals associated with mining activities (chalcopyrite, bornite, pyrite and barite) was investigated, in order to identify the various factors that control long-term NORM mobility and retentivity in environmental acid-mine drainage systems and hydrometallurgical processing. The results show selective RN co-sorption to the various natural minerals, suggesting that mineral-specific mechanisms govern the variability in NORM mobility and retentivity. Both 226Ra and 210Po underwent significant sorption onto the natural minerals investigated in this study. The order of co-sorption in sulfate media for chalcopyrite and bornite was 210Po>226Ra>206Pb>210Pb>238U/230Th. Conversely, both pyrite and barite showed increased affinity for 226Ra; the order of co-sorption in sulfate media was 226Ra>210Po>206Pb/210Pb>238U/230Th for pyrite and 226Ra>206Pb/210Pb>230Th/238U/210Po for barite. Similar orders of co-sorption were observed in the nitrate media: for chalcopyrite and bornite the order was 210Po>226Ra/206Pb/210Pb/238U/230Th compared to 226Ra>210Po/206Pb/210Pb/238U/230Th for pyrite and barite. The behavior of 210Po was found to the anomalous: in both sulfate and nitrate solutions, 210Po had little affinity for barite compared to the sulfides. Thermodynamic modeling indicated the formation of a reduced PoS(s) phase at the surface of sulfide minerals, leading to the suggestion that 210Po likely undergoes reductive precipitation on the surface of sulfide minerals. The high sorption of both 206Pb and 210Pb observed in the sulfate systems were likely as a result of co-precipitation as insoluble anglesite compared to nitrate where they mainly remained in solution. Overall, barite showed the highest affinity for 226Ra, given its propensity to sorb 226Ra (similar ionic size). Both 238U and 230Th were highly mobile in acidic sulfate and nitrate solutions. The results highlighted here identify the various constraints on the natural variability and fractionation of NORM in the environment, as well as the mineral-specific mechanisms that control co-sorption of RN. This information provides a framework for predicting RN transport within soils and ground waters with variable geochemical conditions and in metallurgical extraction processes, in order to develop effective strategies towards NORM mitigation.

This review is concerned with the application of ferrous pyrometallurgy to the beneficiation and comprehensive utilization of rare earth ores enriched in iron and other valuable metals such as niobium of which a large number of such deposits exist and are located in Australia, Brazil, China, Russia and USA. Due to the complex mineralogical and textural characteristics and very fine grain size of the minerals, these ores are refractory to conventional mineral beneficiation processes. Pyrometallurgical processes typically used in the beneficiation of fine grained iron ores may solve these problems. The largest deposit of this kind and the supplier to over 90% of the world’s rare earths is the Bayan Obo Fe-REE-Nb deposit of Inner Mongolia, China. This deposit has had the most research conducted regarding pyrometallurgical processing as a means to beneficiate the contained iron and rare earth metal values. A detailed case study is presented of the research carried out to date on the application ferrous pyrometallurgy for the comprehensive utilization of Bayan Obo ore and the applicability of these processes to the beneficiation of similar ore deposits outside of China is considered.

Chalcopyrite ore was roasted at 200, 550 and 800 °C in reducing (5%H2/95%Ar) and inert (N2) atmospheres to examine the effects of the thermal pre-treatment on the phase mineralogy and on subsequent copper extraction using sulfuric acid media. No mineralogical changes occurred in the pre-leached samples heated to 200 °C under both inert and reducing conditions while at 550 °C partial decomposition of chalcopyrite resulted forming bornite and metal-rich derivatives talnakhite and mooihoekite. Further heating to 800 °C saw differences in chalcopyrite decomposition according to the atmosphere. In the inert atmosphere chalcopyrite decomposed to the metal-rich derivatives and minor bornite and geerite while in the reduced atmosphere copper metal, bornite, troilite, cubanite and chalcocite formed. Leaching at 50 °C of the chalcopyrite pre-treated in an inert atmosphere saw a slight increase in %Cu extraction with increasing temperature of treatment. A maximum copper extraction of 16%Cu was measured in the sample treated at 800 °C. Leaching of the chalcopyrite pre-treated in a reduced atmosphere led to modest increases in copper extraction between the 200 °C and 550 °C samples with 21%Cu and 24%Cu leached. Treatment at 800 °C resulted in a significant increase reaching 78%Cu extraction.

The leaching of uranium from of a synthetic form of the naturally occurring pyrochlore group mineral betafite, was investigated in acid sulfate media. Uranium leaching curves obtained over a range of time, temperature, [H2SO4], [FeTOT] and redox potential conditions were similar with each having three discrete segments representing significantly different rates of uranium leaching. The first segment occurred in the initial min and involved extremely rapid leaching. This segment made up for the majority of the overall uranium leaching obtained over the test period (~ 2.10% U). The high rate of leaching in this segment was demonstrated to be attributed to liberation of surface oxidized uranium from the betafite structure. The second segment between 1 and 120 min was characterised by slow uranium leach rates which could be partially influenced by altering the experimental conditions. Uranium leaching within this period was most likely due to oxidation of uranium by ferric iron which was progressively slowed by the competing diffusion reaction. The uranium leach rate in the third segment was negligible. This negligible leach rate was demonstrated to occur when approximately 2.10% U had leached from the sample and was shown to be due to passivation of the sample surface. Investigations into leaching betafite using various iron salts showed the uranium leaching more than doubling when iron fluoride was substituted for iron sulfate. The additional solubility was attributed to leaching of Nb, Ti, and Ta due to the in-situ formation of HF, where the HF either slowed the formation of a passivating layer or the HF was able to slowly dissolve the passivating layer.

The behaviour of rare earth permanent magnets during oxidation profoundly determines the high temperature recycling processes. This current study analysed the microstructure evolution of end-of-life, coated NdFeB rare earth permanent magnets after oxidization at 973−1473 K under ambient air conditions. Four distinct categories of microstructure evolution were observed at the temperatures of 973 K, 1073 K, 1173−1273 K, and 1373−1473 K. The presence of a Ni/Cu/Ni coating was found to significantly affect the oxidation mechanism. The distinct oxide morphologies developed at these temperatures have different implications for designing strategies for the recycling process.

In this study, the effects of bio-oxidative leaching on several synthetic uranium minerals - Uraninite [UO2], Pitchblende [U3O8], Coffinite [USiO4], Brannerite [UTi2O6] and Betafite [(U,Ca)2(Ti,Nb,Ta)2O7]) compared to chemical leaching in the presence of pyrite was investigated. In all cases, bio-oxidative leaching was faster and increased overall %U extraction compared to chemical leaching. The results indicated that the bio-oxidative leachability of the uranium minerals was in the order: pitchblende≈ uraninite > coffinite>> brannerite > betafite. The leaching of pitchblende and uraninite was fast and complete; U extraction from coffinite was slower over 28 days' during the bioleaching. The use of thermophiles doubled the recovery of U from refractory brannerite. The results highlight the significant capability of bio-leaching in the recovery of U from brannerite; both mesophilic and thermophilic bacteria was found to enhance U recovery likely through enhanced breakdown of the titanate structure. Brannerite is often found in significant quantities within ore tailings due to its refractory nature, which can lead to subsequent release of U into the environment. Conversely, betafite is highly stable in the presence of mesophile and moderate thermophiles, which suggested that betafite materials can be a viable future host for long term storage for spent nuclear fuels.

With high-grade ilmenite (FeTiO 3 ) ores becoming scarce, there is a need to process lower-grade and more weathered ilmenite ores. These alternative sources provide complexities in terms of physical characteristics, mineral compositions, and impurity levels, all of which can significantly affect the subsequent processing route. In the production of high purity white pigment from ilmenite, chromia (Cr 2 O 3 )-containing impurities such as chrome-rich spinels need to be removed from the ilmenite concentrates down to commercially accepted levels. Existing magnetising roast processes currently used in the industry do not allow a clean separation of the chrome-rich spinels from the ilmenite due to overlapping physical properties. It has been suggested that selective sulfidation of chrome-rich spinels could be a potential route for chromia separation from ilmenite. However, the detailed conditions under which the selective sulfidation can occur are not well known. This work focuses on a systematic study of selective sulfidation of chromite FeCr 2 O 4 (one end member of the spinel series) for the purpose of chromia impurity removal from a weathered ilmenite concentrate. Detailed thermodynamic assessment and experimental studies have been carried out to determine the conditions at which selective chrome spinel sulfidation occurs. The results suggest that there are two regimes (Area-1 and Area-2) where selective chrome spinel sulfidation is possible. Area-1 is in the range of pO 2 ≈ 2.37 × 10 − 09 atm to 5.01 × 10 − 15 atm, while Area-2 is at lower pO 2 (≤ 6.92 × 10 − 19 atm) and pS 2 (≤ 1 × 10 − 06 atm) region relative to Area-1. Targeted experimental analyses of the two regimes revealed that selective sulfidation of chrome spinel occur only under the reaction conditions at Area-2. It is suggested that the lack of selective chrome spinel sulfidation under Area-1 conditions is the change in activity of iron ( a Fe ) due to weathering action on chrome spinel grain.

A long-term leach investigation was undertaken on particles of a sulfide ore to determine the nature of solution transport into large particles and to identify the primary roles concentrations of acid and oxidant on controlling solution transport. Bulk leaching results showed that in the case of Fe leaching, both [Fe3+] and [H2SO4] promoted the extent of Fe extraction whereas the extent of Zn and Pb extraction was dependent only on [H2SO4]. Based on the bulk extraction of Al and Mg, it appears that [H2SO4] drives the expansion of inner particle pores by promoting the dissolution of gangue minerals. The findings indicated that the generation of cracks and/or pores to enhance solution contact with the value minerals remains the critical factor in improving value metal recovery from this type of material during heap leaching. Comparative laboratory and synchrotron X-CT studies were also undertaken on single ore particles using a novel in–situ leach cup technique. Similar to the solution results, the acid concentration was shown to be critical in creating effective porosity and pore networks through the centre of the particles for the transport of solution to value minerals and subsequent leaching and transport to the bulk solution. This occurred primarily through the dissolution of auxiliary aluminosilicate gangue minerals, which in turn created networks of porosity for effective bulk solution transport into large particles during heap leaching. This, in turn, enables local solution micro-environments where leaching occurs at the solid-liquid interface. Following the accessibility of bulk solution into the particle, the reaction is then governed by surface-mineral reactions between the sulfidic minerals.

Bangladesh has known concentrations of heavy mineral (HM) sand resources in shoreline placer deposits along the southern and eastern coastlines and also within river sand bar placer deposits associated with the extensive river systems throughout the country. The high-grade Cox’s Bazar beach placer deposits are in populated and environmentally sensitive areas making the future of mineral sands exploitation uncertain. In comparison, the Brahmaputra fluvial deposits are less rich in total HMs but constitute a potential major resource. The recovery of Ti-rich ilmenite from beach placer deposits is widespread but rare from fluvial deposits however many river systems in Bangladesh are annually dredged to maintain open waterways offering a new source of heavy minerals. Exploitation will depend on the quality of the ilmenite compared to existing commercially traded material. In this study, ilmenite concentrates derived from fluvial deposits (Brahmaputra River) and beach placer deposits (Cox’s Bazar) were compared using XRF, XRD and EPMA techniques. The level of impurities associated with the Brahmaputra River ilmenite was higher than in the equivalent Cox’s Bazar fractions suggesting possible issues with liberation or the properties of the associated gangue minerals reacted differently to the separation conditions, or both. Ilmenite from both regions exhibited texturally alike grain types and chemically similar compositions with detrital ilmenite from Cox’s Bazar characterised by TiO2 contents ranging from 49–53 wt-% (average 51 wt-%) while the range for the Brahmaputra River was 44–53 wt-% (average 49 wt-%). The slightly higher and much narrower range in TiO2 for the Cox’s Bazar material was consistent with this material having been subject to more chemical weathering resulting from a longer transit time and reworking through wave action. Based on the major and minor element compositions of ilmenites from both sources, the most likely route for processing the ilmenite-rich component would be via the sulphate route to pigment.

A mineralogical and chemical investigation of surface and subsurface samples from the upper, middle and lower parts of the Jamuna River was carried out with a view to assessing the distribution and recovery potential of the heavy minerals ilmenite and garnet. The HM component in the Jamuna sands is ~10% consisting predominantly of amphibole, epidote and garnet with significant amounts of opaque minerals (ilmenite, magnetite, titanomagnetite, etc). A greater abundance of garnet was present in the fine to medium sized fractions (125–250 µm) and lower garnet concentrations were observed in the very fine sized fraction ( The ilmenite grains are characterised by TiO2 content between 34.2 and 52.8 wt-% with low levels of impurities. The garnet geochemistry is more variable but dominated overall by almandine-rich compositions. The characteristic heavy mineral suite of garnet, epidote, amphibole, kyanite, and staurolite, as well as the garnet and ilmenite chemistry reveals the sediments are derived from mixed source areas of varying metamorphic grade (low to high) facies and igneous rocks. Based on these results, the Jamuna River sands have good potential for recovery and exploitation of both garnet and ilmenite.

The adsorptive capability of rice-husk for the sorption of thorium ions from aqueous solutions in batch mode was studied. The key process variables (initial metal ion concentration, initial solution pH and S/L (solid-to-liquid ratio) were optimized for achieving maximum bioremoval efficiency (B%) by employing the Box-Behnken design (33) in response surface methodology (RSM). A quadratic model developed by fitting the experimental data predicted 93% of the responses and estimated the local maximum of B% as >99% for an initial ThIV concentration of 150 g/L, S/L ratio of 5, and an initial pH of 4, and the reported biosorption capacity (qe) is 15.95 mg/g for the same conditions. Freundlich isotherm (R2 = 0.9841) and pseudo-first-order (R2 = 0.9416) kinetic models had the best concurrence with the experimental data in the thorium concentration range used implying the sorption mechanism involves surface biosorption and intraparticle diffusion.

Phosphorus is one of the most deleterious elements in iron ore as it follows iron during downstream reduction processes, forming iron phosphides that make steel brittle. Excess phosphorus increases the cost of steelmaking and the steel industry has placed an upper limit of 0.07–0.08 wt-% P on the iron ore feed. Goethite grains containing high levels of phosphorus are abundant in many iron ores and can be difficult to remove without also discarding valuable iron-containing units. The goethite forms during supergene metasomatic enrichment of BIF-derived ores and the phosphorus is typically associated in goethite with other impurity elements such as Si and Al. The current study focusses on determining the distribution and association of phosphorus within goethite present in a high-P Brockman type iron ore from the Pilbara region of Western Australia. Detailed characterisation of the chemistry and mineralogy of the goethite-rich ore was conducted using XRF, optical microscopy and EPMA to determine the distribution of phosphorus and other impurity elements. Using this knowledge, we speculate on the possible P substitution mechanisms in goethite. The latter has important implications in designing strategies for beneficiating high-P goethitic iron ores.

Samples of natural betafite from Ambatofotsy Madagascar, Miarinarivo Madagascar and Silver Crater Mine, Canada were characterised using a range of techniques before being leached to extract uranium. The three samples were also heat treated to 1200 °C to investigate the effect of recrystallization on uranium extraction. X-ray diffraction analysis showed that anatase was the only crystalline compound present in each of the unheated samples. After being heated to 1200 °C all samples exhibited diffraction lines characteristic of betafite and rutile, indicating that the betafite present in the preheated samples was amorphous (metamict). Electron probe microanalysis of the samples showed a high degree of compositional heterogeneity throughout each sample, most likely caused by aqueous fluid interactions forming secondary alteration products. The Ambatofotsy sample was the most altered while the Silver Crater sample was the least altered. All unheated samples were subject to a sulfuric acid leach over 6 h with the extent of uranium dissolution correlated with the degree of alteration. The most highly altered sample had 42% dissolution while the least-altered exhibited only 7%. Dissolution experiments over the temperature range 35–95 °C with lower activation energies recorded for the highly-altered samples compared to the less-altered samples. Moreover, increased leaching with increasing metamictisation was observed in studies using variable sulfuric acid concentrations. The compositional and microstructural results presented herein indicates that characterisation prior to leaching is beneficial in determining the feasibility and viability of processing betafite as a potential uranium resource.

Uraninite is mined/processed more than any other uranium mineral for the production of uranium based compounds that are subsequently used to produce nuclear fuel. This review article provides a concise account of the available literature on one of the major processes involved in processing uraninite bearing ores, acid leaching. Improvements in the processes used to leach uraninite are required in order to ensure efficiency in the processing of lower grade uraninite bearing ores with minimal environmental impacts. This in turn requires improvements in our understanding of uraninite leaching. The main topics covered in this review include: uraninite structure, composition and low temperature geochemistry; the chemistry of uraninite leaching; key factors that influence uraninite leaching; and leach process technologies. The research that has been reviewed clearly establishes the influence of parameters such as temperature, acid concentration and particle size. The influence of other parameters however, such as solution Fe3 + to Fe2 + ratio (solution Eh), total Fe concentration, foreign ions present in the leach slurry and uraninite composition is yet to be established. Based on the literature available on the aforementioned factors the chemistry/processes involved in uraninite leaching are quite complex and require significant further studies. From the literature reviewed it is clear that variations in mineral chemistry in individual ore types across multiple deposits also make it essential that before any extraction process is considered, detailed ore characterisation studies of pre- and post-leach residues are of vital importance in order to fully understand the interrelationship between chemistry, mineralogy (ore and gangue), mineral liberation and potential leaching behaviour of uranium.

Ilmenite concentrates from the Murray Basin region of southeastern Australia are contaminated with chromium impurities that must be removed for the ilmenite to become a satisfactory feedstock for the sulphate route to titania pigment production. The chromia is present primarily as discrete, compositionally variable, chrome-rich spinel grains with a smaller amount as intra-grain chromia distributed as coatings in fractures and pores of weathered ilmenite grains. Characterisation of chromia deportment through a simulated acid sulphate digestion process showed a small but non-negligible solubility of the spinels. Most spinels were resistant to dissolution with the exception of those containing high Fe(Al,Cr)2O4 and magnetite (Fe3O4) components. Intra grain chromia was highly soluble. Processing to achieve low bulk chromia using a magnetising roast procedure must ensure that well crystallised rutile is not produced because of its insolubility in the sulphate process. It is also important that the roast conditions do not substantially increase the magnetite content of the spinels making them more susceptible to dissolution. This work highlights the importance of characterising all spinel composition types within ilmenite concentrates in addition to the level of intra-grain chromia associated with the ilmenite when considering the suitability of Murray Basin primary ilmenites as a feedstock to sulphate route titania pigment plants.

Betafite of composition [(Ca,U) 2 (Ti,Nb,Ta) 2 O 7 ] was prepared via a solid state synthesis route. The synthesis was shown to be sensitive to initial reactant ratios, the atmosphere used (oxidising, neutral, reducing) and time. The optimum conditions for the synthesis of betafite were found to be heating the reactants required at 1150 °C for 48 h under an inert gas atmosphere. XRD characterisation revealed that the synthesised betafite contained minor impurities. EPMA analysis of a sectioned surface showed very small regions of Ca-free betafite on grain boundaries as well as minor rutile impurities. Some heterogeneity between the Nb:Ta ratio was observed by quantitative EPMA but was generally within the nomenclature requirements stated for betafite. SEM analysis revealed the synthesised betafite was comprised mostly of hexaoctohedral crystals of ∼3 μm in diameter. XPS analysis of the sample showed that the uranium in the synthesised betafite was predominately present in the U 5+ oxidation state. A minor amount of U 6+ was also detected which was possibly due to surface oxidation.

The dissolution of synthetic Pb-doped UO2 and Th-doped UO2 was systematically studied to determine the influence of leach parameters [Fe]TOT and ORP under standard leach conditions of: T = 50 °C, [H2SO4] = 15 g/L (0.15 M), and UO2 = 100 mg/L. Results demonstrated reduced uranium dissolution in both systems compared to pure UO2. This effect was greatest for Th-doped UO2. The decrease in uranium dissolution between the doped systems and pure UO2 was attributed to the formation of precipitate layers at the surface of the solid, slowing down or blocking uranium release. In the case of Pb-doped UO2, the formation of a Pb sulphate phase was directly detected but in the case of Th-doped UO2, no layer was found. For the latter system it was postulated that passivation of the Th-doped UO2 surface occurs due to the formation of oxidised Th-rich phases Th(OH)4, ThO2 and ThO2·nH2O at the surface of grains preventing uranium release. In tests varying the ORP, there was an approximately linear dependence of the dissolution rate on [Fe]TOT for both systems however the rate orders indicated a step change between an ORP of 420 and 460 mV. The specific influence of FeII showed that both Pb–UO2 and Th–UO2 exhibited two distinct regions of dissolution rate dependency similar to that previously noted for pure UO2.

Uranium leaching tests were conducted on two naturally occurring, highly metamict brannerite ores from the Crockers Well and Roxby Downs deposits, South Australia. The ores were leached over a range of temperatures and Fe (III) and H 2 SO 4 concentrations. As well, samples of the ores were calcined at 1200 °C in air to investigate the effect of thermally induced recrystallisation on uranium dissolution. For the unheated samples, a maximum of ∼80% U dissolution was obtained using an Fe (III) concentration of 12 g/L, an acid concentration of 150 g/L H 2 SO 4 and a temperature of 95 °C. The heat treated samples performed poorly under identical conditions, with maximum uranium dissolution of

Australian uranium ores are often composed of complex mineral assemblages. Differences in ore compositions and textures are seen between deposits as well as within a single deposit, which can host a range of ore types. Such a wide variety of uranium ores make it impossible for a single extraction or treatment process to be developed that will accommodate all of the ores. From a mineralogical perspective, key issues confronting the Australian uranium mining industry include: the prevalence of low grade ores; a lack of detailed chemical and mineralogical information (uranium speciation, texture, grainsize) for the various ore deposit types; and the presence of refractory uranium-bearing minerals and highly acid-consuming gangue minerals. This paper reviews some of the main controls on uranium geometallurgy by linking concepts relating to ore genesis and the resulting ore mineralogy, with the processing behaviour of specific Australian uranium ore types. Emphasis is placed on the value of detailed ore mineralogical analysis and the insight this provides into the factors of importance when considering uranium extraction.

The effect of varying standard leach parameters (particle size, total iron content, acid addition, oxidation–reduction potential and temperature) on the dissolution of uranium from natural uraninite was studied. Tests were conducted using two uraninite ores from Australia and results contrasted with equivalent studies conducted on a synthetic UO2 sample. Mineralogical studies, including EPMA analysis of selected leach residues, were also carried out. Results indicated that under standard leach conditions (0.15 M H2SO4, 50 °C, ORP 460 mV, 6.7E10−3 M FeTOT), both natural samples exhibited lower uranium extraction rates when compared to synthetic UO2. Decreasing particle size, increasing temperature and increasing FeTOT all resulted in an increase in the rate of uranium dissolution whereas changing acid concentration and changing the ORP had a negligible effect on dissolution. Minor differences were observed when comparing results between the two natural samples however in all cases the synthetic UO2 proved easier to extract uranium. The changes in dissolution rates between the natural ores and the synthetic uraninite was attributed to lead impurities within the natural uraninites being preferentially leached and then re-precipitated as a sulphate. The precipitated Pb sulphate was observed coating individual uraninite particles and filling pores and fractures, thus preventing further ingress of the leach solution. This study emphasises the uncertainties in extrapolating experimental results obtained using synthetic systems to studies involving real ores.

Composition, structure, texture and gangue minerals associated with three naturally occurring uraninite samples (USG – Saxony, Germany; UPA – Palette mine, Australia and; UEA – El Sharana mine Australia) were investigated. The UEA sample contained uraninite associated with uranyl oxide species, Pb-rich uranylphosphate and Pb/Al phosphate phase with trace levels of galena and sulphides. The UPA sample contained uraninite associated with meta-autunite, Pb/Al phosphate phase and other minor phases including carbonates, quartz, fluorapatite, gold and various Zn/Fe/Cu sulphides. The USG mineralogy was dominated by the sulphides sphalerite and galena with uraninite only a minor component along with unidentified Fe/Mg-rich aluminosilicate, muscovite, coffinite and other sulphides. All samples exhibited complex textural and chemical modifications compared to stoichiometric UO 2 . The uraninites were substituted mainly by Ca and radiogenic Pb and were highly altered. Alteration was associated with significant variations in chemistry with unaltered uraninite in samples UPA and UEA typically being richer in U, Ca and Pb compared to altered regions. The altered uraninite also was more hydrated. Altered uraninite in sample USG had higher Fe, Pb, S and As compared to less altered uraninite and was significantly depleted in U and Ca. The high Pb in the uraninite was opposite to that observed in the UEA and UPA samples but may be related to the high abundance of galena in the sample. The compositional, textural and microstructural aspects of uraninite are likely to play an important role in any process to extract uranium from uraninite-containing ores.

Two naturally occurring brannerite samples from the Crockers Well and Roxby Downs deposits in South Australia were characterised to assess their compositional, mineralogical, and textural properties. Characterisation was undertaken using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman Spectroscopy and an Electron Probe Micro-analysis (EPMA). The samples were also heat treated to examine the effect of temperature on recrystallisation, mineral stability and deportment of impurities. In each sample, the brannerite was found to be thorium-rich (∼8–10 wt.% Th) indicating partial solid solution between brannerite and thorutite (ThTi2O6). Other minerals identified in the samples were thorutite (ThTi2O6), uranothorite ([Th, U]SiO4), a thorianite–uraninite solid solution ([Th, U]O2) and gangue minerals including rutile, quartz, aluminosilicates, zircon, titanite, apatite and unidentified REE-containing phosphates. The brannerite in both samples was amorphous having undergone radiation-induced metamictisation. Crystallinity of the brannerite was restored upon heating of the samples to 1200 °C for 24 h in air. For the Crockers Well sample, radiation damage annealing/recrystallisation began at temperatures as low as 800 °C while the Roxby Downs sample did not begin to show evidence for recrystallisation until 900 °C. The main mineralogical changes after heating and recrystallisation involved a decrease in the amount of thorianite-uraninite phase due to decomposition into ThO2 and UO2 as well as the formation of Pb-rich glass films at grain boundaries. Compositional, textural and microstructural aspects of brannerite are likely to play an important role in any process to extract uranium from brannerite-containing ores.

We used µ-XANES spectroscopy to measure the oxidation state of europium in-situ at near-µm resolution in hydrothermal scheelite from the giant Archean gold deposits of Kalgoorlie, Western Australia. By combining these measurements with µ-XRF imaging, it is possible to distinguish inhomogeneities in Eu2+/Eu3+ ratios that developed during mineral precipitation from the effects of subsequent hydrothermal alteration and weathering. Thermodynamic analysis reveals that under the conditions typical of the formation of many Au deposits, the Eu2+/Eu3+ ratio in the hydrothermal fluid is highly sensitive to pH. The range in pH calculated from the Eu2+/Eu3+ ratios in the analyzed scheelite corresponds to a maximum in Au solubility under the ore-forming conditions, and suggests buffering of pH by the CO2(aq)-rich fluid. The primary heterogeneity of the Karlgoorlie scheelite most likely results from pH oscillating between fluid- and rock-buffered conditions, and reflects the dynamics of the hydrothermal system.

Recent discoveries of extensive mineral sand deposits in the eastern part of the Eucla Basin, South Australia, have generated much interest in their potential as a new world-class resource for heavy minerals. A detailed mineral characterisation study of a range of ilmenite concentrates from the Eucla Basin was undertaken using automated electron microprobe-based mineral mapping and quantitative analysis methods. Results showed that the ilmenite concentrates have a high bulk TiO2 content (>60 wt.%) consistent with a mineral assemblage dominated by the hydrated, Ti-rich alteration phase pseudorutile (Fe3+2−xTi3O9−3x(OH)3x). Minor accessory phases (

The demand for accurate composition and phase distribution analyses in complex ore assemblages is increasing rapidly as mineral processing studies become more sophisticated. In response to this need, an EPMA-based microanalysis procedure for characterising minerals was developed. The method uses an electron microprobe to collect combined X-ray, backscattered electron and cathodoluminescence (CL) maps. By scanning over a specified target area, CL wavelength and X-ray element distribution maps of grains are acquired in parallel enabling direct comparison between elemental concentrations and textural features. Composition data can be displayed on element scatter diagrams enabling clusters, each representing individual mineral phases, to be readily identified. For systems characterised by highly complex mineral phase assemblages, an automated cluster recognition technique has been developed. The mapping technique has proved beneficial in a range of mineral characterisation studies where traditional SEM-based analysis methods were not applicable.

Phase relations and the stability of crystallographic shear (CS) structure compounds (Cr,Fe)2Tin−2O2n−1 in the system Fe2O3–Cr2O3–TiO2 were investigated between 1000 and 1300°C. The ternary comprises five major solid solution series. These are as follows: an M2O3 series; an M3O5 series made up of two separate solid solution series—the first an orthorhombic pseudobrookite M3O5 solid solution and the second a monoclinic M3O5 series based on the V3O5 structure type; an M4O7 series; and an M5O9 series. These latter three series represent lower homologues (n=3, 4, and 5) of the (Cr,Fe)2Tin−2O2n−1CS compound series. Between adjacent M3O5 and M4O7 and M4O7 and M5O9 solid solutions, ordered intergrowths may occur. The stability and compositional limits of the solid solution series and intergrowth phases are dependent upon the temperature and Fe:Cr ratio. At high-TiO2 contents, assemblages may contain either members of the Andersson phase series Cr2Tin−2O2n−1, a continuous CS structure series extending into the ternary, or a rutile-based solid solution. A comparison of results from this study with previously published phase relations has led to a revised version of the Fe2O3–Cr2O3–TiO2 phase diagram.

The ilmenite-rutile-ironequilibriaand ulvospinel-ilmenite-iron equilibria have been studied in the temperature range 990–1320 and 1050–1355 K, respectively, using an electrochemical technique. Effects on experimental results from deviations from the ideal stoichiometries FeTiO 3 , TiO 2 and Fe 2 TiO 4 have been modelled from available data in the literature. For ilmenite-rutile-iron (IRI), μO 2 ( ± 140) = −570745 + 97.278 T + 50278 T In T (800 T T (1042 T T (1184 T μO 2 ( ± 100) = −505563 + 4.990 T + 13.315 T In T (900 T T (1042 T T - 54.3800 T In T (1184 T μO 2 = joules per mole ; T = Kelvins ; reference pressure = 10 5 Pa (1 bar); quoted uncertainties are one standard deviation). Results from the IRI equilibrium are in good agreement with most of the previous phase equilibrium studies. In detail, however, there is evidence of possible error in the calorimetric data for TiO 2 or FeTiO 3 , or both. For the UII equilibrium, results indicate Fe 2 TiO 4 probably has the theoretically ideal zero point entropy of 2 R In 2, caused by mixing of Fe 2+ and Ti on the octahedral site of this inverse spinel.