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Brannerite, UTi2O6, is the most common of the refractory uranium minerals and requires leaching under intense conditions to effectively extract the uranium contained within. Brannerite is often found together with apatite in metasomatic uranium deposits. Apatite and other phosphate gangue minerals can inhibit uranium leaching by generating phosphate ions which interfere with the reactions between acidic ferric sulphate and uranium minerals. As part of a detailed fundamental study on the leaching reaction mechanisms for brannerite, tests under a range of selected leach conditions were carried out with the addition of 10 g/L fluorapatite with the goal of identifying conditions where the negative effects of phosphate are reduced. Leaching was carried out for 5 hours with 0.05 mol/L Fe3+ as Fe2(SO4)3 with 0.25–1.00 mol/L H2SO4 and at temperatures between 25 and 96 °C. A single test was performed with 0.05 mol/L Fe3+ as FeCl3 and 1.00 mol/L HCl. In the sulphate system, the effect of phosphate was weakest at the highest acid concentration (1.00 mol/L H2SO4). In the chloride system, phosphate did not suppress uranium extraction, suggesting that HCl leaching could be a viable alternative for the leaching of high-phosphate refractory uranium ores.

The commercialisation of vanadium redox flow batteries for large scale electric energy storage and power grid stabilisation is expected to increase the global demand for vanadium in the coming years. Currently most of the vanadium is used in the production of steel alloys and this amount is expected to remain consistent in the years to come. Much of the new demand is expected to come in the form of electrolytes for the application of vanadium to energy storage in the vanadium redox flow batteries and in the form of ultrapure vanadium salts for use a precursor reagents in the production of cathodes for lithium ion batteries. Unlike other metals such as copper, nickel or zinc, vanadium does not form concentrated deposits. Owing to the similarities between the V3+ and Fe3+ cations, vanadium is often found as a minor component of iron minerals. The vanadium mineral coulsonite, FeV2O4 forms series with chromite, FeCr2O4 and magnetite, Fe3O4. Most of the vanadium is produced from titanomagnetites either directly from titanomagnetite ores/concentrates or indirectly from the slag left from smelting titanomagnetite ores. Titanomagnetite ores are associated with mafic igneous rock and have been found in large quantities in Russia, China, South Africa and other countries. Vanadium can also be produced from vanadiferous sandstone, shale and vanadate deposits, though these are of lesser industrial importance compared to titanomagnetites. Vanadium is usually extracted from ores, concentrates and slags by roasting with sodium carbonate or another sodium salt to convert vanadium into water soluble sodium vanadates. This review summarises the established and proven processes for vanadium production as well as some newer processes which have yet to be commercialised.

In this study, synthetic zirconolite samples with a target composition Ca0.75Ce0.25ZrTi2O7, prepared using two different methods, were used to study the stability of zirconolite for nuclear waste immobilisation. Particular focus was on plutonium, with cerium used as a substitute. The testing of destabilisation was conducted under conditions previously applied to other highly refractory uranium minerals that have been considered for safe storage of nuclear waste, brannerite and betafite. Acid (HCl, H2SO4) leaching for up to 5 h and alkaline (NaHCO₃, Na2CO3) leaching for up to 24 h was done to enable comparison with brannerite leached under the same conditions. Ferric ion was added as an oxidant. Under these conditions, the synthetic zirconolite dissolved much slower than brannerite and betafite. While the most intense conditions were observed previously to result in near complete dissolution of brannerite in under 5 h, zirconolite was not observed to undergo significant attack over this timescale. Fine zirconolite dissolved faster than the coarse material, indicating that dissolution rate is related to surface area. This data and the long term stability of zirconolite indicate that it is a good material for long-term sequestration of radioisotopes. Besides its long term durability in the disposal environment, a wasteform for fissile material immobilisation must demonstrate proliferation resistance such that the fissile elements cannot be retrieved by leaching of the wasteform. This study, in conjunction with the previous studies on brannerite and betafite leaching, strongly indicates that the addition of depleted uranium to the wasteform, to avert long term criticality events, is detrimental to proliferation resistance. Given the demonstrated durability of zirconolite, long term criticality risks in the disposal environment seem a remote possibility, which supports its selection, above brannerite or betafite, as the optimal wasteform for the disposition of nuclear wa

The acidic ferric sulphate system is the industrial standard for the acid leaching of uranium ores. Alternatives such as ferric chloride/hydrochloric acid have been investigated, but never used industrially. Selected ferric sulphate leaching experiments from previous work were repeated in acidic ferric chloride media to evaluate the effectiveness of this alternative system. Leaching experiments were run for 5 h and the effects of acid concentrations between 0.25 and 2.00 mol/L and temperatures between 25 and 96 °C were studied. A single experiment for each system was repeated with the addition of 10 g/L fluorapatite, known to inhibit uranium leaching in ferric sulphate media. Ferric chloride media was less effective than ferric sulphate media for the extraction of uranium from brannerite at same temperature and acidity, except at high (2.00 mol/L) acid concentrations. Acidity had a significantly greater effect on the rate of dissolution in the chloride media. The rate of the dissolution reaction was first order with respect to acid concentration in the chloride system, compared to an order of approximately 0.5 with respect to acid concentration in the ferric sulphate system. This suggests that dissolution in chloride media takes place via a different mechanism in which the acid has a greater role in the leaching reaction. Comparing the results from the chloride and ferric sulphate leaching suggests that the formation of stable uranyl complexes is a key component in the leaching process, as uranyl sulphate complexes are stronger than uranyl chloride complexes. Interestingly, the alternative system was less susceptible to interferences from phosphates, and therefore may be a viable alternative when dealing with high-phosphate refractory uranium ores.

There are several metasomatic uranium deposits in the area around Mount Isa in Queensland, containing a total of 56,400 t of uranium. Many of these ores are refractory in nature, meaning that relatively high leach temperatures (> 75 °C) and reagent dosages (> 50 g/L H2SO4) are needed to effectively extract the uranium from them. Also, these ores are hosted in alkaline rock which means that acid leaching is unlikely to be economical. While refractory uranium ores are not typically leached in alkaline media, previous work has shown that uranium can be extracted from brannerite in alkaline media, albeit slowly. The same leaching conditions previously shown to be effective for the extraction of uranium from brannerite were repeated with a sample of refractory uranium ore from a deposit near Mount Isa in north western Queensland. Mineralogical analysis with a Tescan Integrated Mineralogical Analyser (TIMA) showed that the uranium was present as brannerite (51%) and coffinite (49%). The ore was leached in sodium carbonate media for 24 h. Leach temperatures of 50, 70 and 90 °C, and sparging with oxygen, air and nitrogen were tested. The effect of adding ferricyanide chemical oxidant was also tested. Similar initial uranium extraction rates were observed for the Mount Isa uranium ore compared with Sierra Albarrana brannerite leached under the same conditions in earlier work. The final extractions were lower however, due to the fine-grained nature of the uranium mineralisation in the ore. TIMA analysis on a residue produced under the most intense set of leaching conditions (90 °C, O2 sparged) showed that the extent of coffinite dissolution was greater than that of brannerite dissolution during leaching. Likewise, the TIMA analyses showed that the extent of apparent uranium liberation decreased during leaching, due to poorly liberated particles remaining undissolved. These results indicate that alkaline leaching could be a viable method for the processing of these long overlo

Refractory uranium ores containing uranium as multiple oxides typically require leaching at elevated temperatures (> 75 °C) and acid concentrations (> 50 g/L H2SO4) in order to effectively extract the uranium. Some uranium ores contain large amounts of acid-soluble gangue, such as carbonates or soluble silicates and when the carbonate content exceeds approximately 8%, the acid consumption by gangue may render acid leaching uneconomical. In these situations, leaching in alkaline-carbonate is a potential option. The advantages of this approach include improved selectivity for uranium over other elements, reduced gangue dissolution and the ability to recycle the lixiviant. One disadvantage is slower rates of leaching and hence the need for finer grinding. However, when a uranium ore contains significant amounts of acid-soluble gangue with refractory uranium mineralisation (a double refractory ore), the process options are more limited. Refractory uranium minerals, such as brannerite, are often reported as slow to dissolve in alkaline carbonate media. If a double refractory uranium ore is to be processed effectively, it is necessary to understand the behaviour of minerals like brannerite in the alkaline leaching system. In the present study, a sample of brannerite was leached in a sodium carbonate solution (1 mol/L total carbonate) for 24 h at temperatures from 50 to 90 °C. The effect of potassium ferricyanide (25 mmol/L) added as an oxidant was also examined. All residues were characterised by XRD and SEM-EDX techniques, and both uranium and titanium dissolution rates were monitored. Uranium extraction reached 83% after 24 h of leaching. The leaching rate showed a high dependence on temperature with an activation energy of 45 kJ/mol. The residue was pitted, similar to what has been observed previously after leaching in acidic media. At 80 °C and 90 °C, the titanium re-precipitated within the pits, potentially slowing the dissolution process.

The presence of gangue minerals in the acid leach system affects the extraction of uranium from refractory uranium minerals such as brannerite. The leaching of uranium from brannerite has been studied with and without the addition of fluorapatite and fluorite. It was found that the addition of fluorite significantly increased the rate of uranium dissolution from a brannerite mineral, though it is unclear how large this effect would be when leaching an actual ore. Apatite interfered with brannerite leaching, and phosphate appeared to suppress the dissolution of titanium, forming a titanium oxide coating on the leached brannerite. Based on these results, it appears that reducing the negative effects of phosphate may be achieved by the use of higher acid dosage or may require an alternative chloride leaching system., The presence of gangue minerals in the acid leach system affects the extraction of uranium from refractory uranium minerals such as brannerite. The leaching of uranium from brannerite has been studied with and without the addition of fluorapatite and fluorite. It was found that the addition of fluorite significantly increased the rate of uranium dissolution from a brannerite mineral, though it is unclear how large this effect would be when leaching an actual ore. Apatite interfered with brannerite leaching, and phosphate appeared to suppress the dissolution of titanium, forming a titanium oxide coating on the leached brannerite. Based on these results, it appears that reducing the negative effects of phosphate may be achieved by the use of higher acid dosage or may require an alternative chloride leaching system.

Brannerite, UTi2O6, is one of the most common refractory uranium minerals and it requires aggressive leaching conditions for efficient uranium extraction. It is often associated with apatite and fluorite, which affect the leaching process by formation of iron-phosphate and iron-fluoride complexes, respectively. While the effects of these gangue minerals on uranium leaching processes are well documented, there is little to no information on these effects specific to brannerite containing ores. At the high acid concentrations required for brannerite dissolution (> 25 g/L H2SO4), acid soluble gangue will dissolve faster, posing a bigger problem than under milder conditions. The addition of 10 g/L fluorapatite reduced the extraction of both uranium and titanium from brannerite over the full range of leaching conditions studied (25–96 °C, 25–100 g/L H2SO4, 2.8 g/L Fe3 +). Phosphate caused the formation of secondary titanium oxide on the surface of leached brannerite particles. This was not observed when leaching in the absence of phosphate. The secondary titanium oxide phase was enriched in phosphorus. The negative effects of phosphate on uranium leaching were reduced at higher acid concentrations (> 50 g/L H2SO4) and increased at higher temperatures (96 °C). When leaching high-P refractory uranium ores, higher acid concentrations are needed for effective extraction compared with low-P uranium ores. Elevated temperatures were less effective for increasing uranium extraction, suggesting that the optimum temperature for leaching high-P refractory uranium ores is lower than the optimum temperature for leaching low-P uranium ores. Fluorite (10 g/L) had a positive effect on uranium and titanium extraction. This was attributed to the formation of hydrofluoric acid during the dissolution of fluorite. Brannerite particles were heavily pitted and corroded after leaching in the presence of fluorite, with near complete dissolution occurring in 2–3 h.

Brannerite, UTi2O6, is the most common refractory uranium mineral and is the most important uranium ore mineral after uraninite and coffinite. In order to develop an effective treatment method for the hydrometallurgical extraction of uranium from ores containing brannerite, it is necessary to understand the chemistry of the leaching process. Part 1 of this series described the results of a study of the chemical reaction mechanisms of brannerite under conditions similar to those used industrially. In this paper, the mineralogical data obtained from samples collected during the leaching work is used to derive further insight into the transformations that take place during leaching. Detailed characterisation of the brannerite feed specimen and leach residues was carried out using surface imaging and X-ray diffraction techniques. It was shown that the brannerite specimen is heterogeneous, consisting of at least two phases. The brannerite phase was metamict and showed signs of natural alteration to fine-grained (10-20 nm) crystalline anatase. Comparisons between the feed and residues showed that the X-ray amorphous materials, in particular lead and silicon enriched areas identified near the anatase were most susceptible to leaching while the crystalline material was relatively resistant to leaching. These results demonstrate that the extent of brannerite alteration and its texture are important considerations to the hydrometallurgical behaviour of a particular ore along with the typical concerns such as grade, liberation size and gangue mineralogy.

Brannerite, UTi2O6 is the most important uranium mineral after uraninite, UO2 and coffinite, U(SiO4)1-x(OH)4x. It is also the most common refractory uranium mineral. Ores containing brannerite typically require intense conditions (>50 g/L H2SO4, >75°C) compared to other uranium ores for effective uranium extraction to occur. To develop an effective process for the extraction of uranium from brannerite containing ores and improve the extraction from the ores currently being processed, it is necessary to understand the chemistry of the brannerite leaching process. As this study has shown, brannerite is typically an altered and amorphous mineral, with an extent of alteration depending on the age of the sample and the geological history of the deposit. A sample of brannerite from Cordoba, Spain, was leached over a range of conditions in acidic ferric sulphate media. The sample was filled with cracks and altered zones containing anatase (TiO2). Process parameters studied included temperature (25-96°C), acidity (10-200 g/L H2SO4) and the effect of adding selected gangue minerals (apatite, fluorite and ilmenite). The feed and the leached residues were characterised in detail by XRD and SEM-EDX techniques. The results of this study showed that brannerite dissolution has a stronger dependence on temperature and lesser dependence on free acid concentration. Comparisons between the residues and the feed showed that the altered and amorphous areas of the brannerite sample are more readily leached than crystalline areas. The crystalline areas of the brannerite dissolved congruently, with titanium subsequently precipitating as anatase physically separated from the original brannerite grains.

Brannerite, UTi2O6, is the most important uranium mineral after uraninite and coffinite, and the most common refractory uranium mineral. As the more-leachable ores become exhausted, it is necessary to process complex and refractory ores to meet the growing demand for uranium as an energy source. The present study was carried out to provide information that will enable the development of a more effective processing strategy for the extraction of uranium from ores containing brannerite. A detailed study was carried out to understand the leaching behaviour of brannerite in sulphate media (10–200 g/L H2SO4) under moderate temperature conditions (25–96°C), and in alternative acid and alkaline systems. The feed and the leached residues were characterised by X-ray diffraction and scanning electron microscopy with energy-dispersive spectrometry techniques. The brannerite dissolved up to 95% after 5 h leaching in ferric sulphate media, up to 89% in ferric chloride media under similar conditions, and up to 82% in 24 h in sodium carbonate media. The alkaline leaching was repeated with a high-carbonate brannerite-bearing ore, which showed comparable extractions. Mineralogical characterisation showed that altered and amorphous regions are a regular feature of brannerite, and that pitting is typically observed on the surface of the leached grains. Brannerite was shown to generally dissolve congruently, with altered and amorphous regions in the brannerite grains dissolving faster than the crystalline regions, which implies that the extent of brannerite alteration is a key parameter in the process selection, along with the grade, liberation size and gangue mineralogy.

The uranium titanate mineral brannerite, UTi2O6 is the most common of the uranium minerals which is considered refractory. Ore containing brannerite mineralisation has been mined and processed in several locations around the world. Under typical uranium ore processing conditions, brannerite is often lost to tailings. In order to design an effective process for the leaching of high-brannerite uranium ores, it is first necessary to understand the mechanism of the chemical processes through which brannerite dissolves in the absence of interferences from the host rock. In the present study, a specimen of brannerite obtained as a single crystal was leached in sulphuric acid (10-200 g/L) and ferric sulphate (2.8 g/L Fe3 +) solution at 25-96°C for 5 h. The rate of titanium dissolution was monitored along with uranium. Comparisons between the rates at which these two elements dissolved and the morphological changes that were observed to take place during the dissolution process indicated two different sets of leaching reaction mechanisms. At low temperatures, uranium dissolved at a much higher rate than titanium initially, leaving titanium rich areas on the brannerite particles similar to observations reported in earlier investigations which suggest incongruent dissolution. The calculated activation energies for uranium and titanium dissolution were 36 and 48 kJ/mol respectively. At higher temperatures, uranium and titanium dissolved at similar rates in constant proportions suggesting congruent dissolution. The calculated activation energy for this reaction was 23 kJ/mol. The transition between incongruent and congruent dissolution took place at lower temperatures when the acid concentration was higher. Titanium appeared to undergo hydrolysis after dissolution, forming anatase. This side reaction was most favourable at lower acid concentrations and high temperatures.

As high grade and easily processed uranium ore deposits are exhausted it will become necessary to mine and process lower grade and refractory ore deposits to fuel the world's nuclear reactors and satisfy societal needs for energy. Brannerite is the most abundant of the refractory uranium minerals. It is a uranium titanate with the ideal chemical formula of UTi2O6, though the exact composition varies widely with thorium and light rare earths often replacing uranium. A more general formula for it would be (U, Ca, Y, Ce, La)(Ti, Fe)2O6. Uranium ores containing brannerite mineralisation have been processed in several mines including two active uranium mines in Australia and several uranium-gold mines in the Witwatersrand area of South Africa. Ores in which brannerite is the main uranium mineral have been mined and processed in the Elliot Lake region of Ontario, Canada. Brannerite is present in significant concentrations in many uranium and rare earth element deposits including some of the uranium deposits located near Mount Isa in Queensland, the Crocker Well deposit in South Australia, the Elkon uranium province in Jakutia, eastern Russia, and in some uranium-gold ores from the Witwatersrand area of South Africa. While less reactive than other uranium minerals, brannerite can be leached under relatively practicable conditions. This literature review provides an overview of the mineralogy and leaching behaviour of brannerite reported in studies conducted to date, in order to help understand its dissolution mechanism and establish the required processing strategy.

An overview of the mineralogy of brannerite, UTi2O6 or (U,Ca,Y,Ce,La)(Ti,Fe)2O6 (U:Ti ratio, crystallinity and inclusion of other elements), the general leaching of uranium minerals and the leaching behaviour of brannerite is presented. Reaction mechanisms for brannerite dissolution and the influence of temperature and activation energy on the dissolution reaction are described. High concentrations of free acid are necessary when leaching brannerite ores with, typically, sulphuric acid/ferric sulphate, due to their refractory nature, the acid hindering the formation of an insoluble TiO2 coating on the ore surface. The effects of grinding size and solution redox potential on the leaching of brannerite-containing ores are summarised. Uranium extraction from brannerite increases with increasing concentration of ferric ions, the optimum concentration depending on the temperature and acid concentration, and the influence of various oxidants such as pyrolusite, sodium chlorate and oxygen on the oxidation of Fe2+ to Fe3+ is discussed., An overview of the mineralogy of brannerite, UTi2O6 or (U,Ca,Y,Ce,La)(Ti,Fe)2O6 (U:Ti ratio, crystallinity and inclusion of other elements), the general leaching of uranium minerals and the leaching behaviour of brannerite is presented. Reaction mechanisms for brannerite dissolution and the influence of temperature and activation energy on the dissolution reaction are described. High concentrations of free acid are necessary when leaching brannerite ores with, typically, sulphuric acid/ferric sulphate, due to their refractory nature, the acid hindering the formation of an insoluble TiO2 coating on the ore surface. The effects of grinding size and solution redox potential on the leaching of brannerite-containing ores are summarised. Uranium extraction from brannerite increases with increasing concentration of ferric ions, the optimum concentration depending on the temperature and acid concentration, and the influence of various oxidants such as pyrolusite, sodium chlorate and oxygen on the oxidation of Fe2+ to Fe3+ is discussed.