Phd DBOF Scholarschips
- A monthly allowance for a 4 year period (a preceeding predoctoral year may be included depending on the prior qualifications)
- Social security and insurances
Applications are invited from enthusiastic graduates in any relevant science and engineering area with an excellent study track record.
We offer a challenging research environment and an intense experience leading to a PhD degree.
Recovery of rare earths from bauxite residue (red mud) |
Promoter: Koen Binnemans details
Description: Bauxite, the most important aluminium ore, contains only between 30–50% alumina, Al2O3, the rest being silica, various iron oxides, and titanium dioxide. The alumina must be purified before it can be refined to aluminium metal. This is done using the Bayer process, where bauxite is digested in a hot sodium hydroxide solution. This converts the alumina to aluminium hydroxide, which dissolves in the hydroxide liquor. The other components of bauxite do not dissolve. The solution is clarified by filtering off the solid impurities. This bauxite residue is a mixture of solid impurities and is called red mud. With a worldwide annual production of 120 millions of tonnes and a total inventory of 2.7 billion of tonnes, stored in huge holding ponds, red mud poses a significant and hazardous problem. The latter was revealed recently by the dam failure of the Ajka refinery in Hungary and the resulting loss of human lives and environmental catastrophe. In Europe, besides Hungary, refineries exist in Bosnia Herzegovina, France, Germany, Greece, Ireland, Italy, Romania, Slovakia and Spain. Unlike other high volume wastes (fly ash, metallurgical slags), red mud finds no industrial application besides minor use in cement and ceramic production. Many researchers have already looked at the valorisation of red mud, besides its use in the construction industry. Red mud has a high metal content and extraction of metals from red mud can be economically feasible. Iron is the major constituent of red mud, followed by alumina, silica, sodium oxide and titania. Red mud contains many scarce elements (e.g. gallium and rare-earth elements) in significant concentrations. Of the rare-earth elements (REE), the concentration of scandium is particularly high. Scandium is used in high-strength aluminium alloys for the production of oil drill pipes. This project will focus on the recovery of REE from red mud. Red mud samples from different locations will be analysed for their REE content. A first stage in the processing of red mud will be the removal of iron by smelting. Red mud will be treated in a blast furnace in the presence of a reducing agent where the iron oxides are reduced, generating pig iron and a titanium-rich oxide slag (also containing the REE). In a second stage, the REE will be leached from the oxide slag. The efficiency of different leaching methods for the recovery of REE will be compared. Leaching will be done by: (1) aqueous solutions of inorganic acids such as sulphuric acid, nitric acid or hydrochloric acid; (2) inorganic acids in non-aqueous solvents; (3) chelating agents such as EDTA; (4) ionic liquids. The REE will be recovered from the leachates by solvent extraction or selective precipitation. In a final stage, the separation of scandium from the other REE will be investigated. The student will use different analytical techniques to monitor the REE concentrations at different stages of the process: ICP-MS, ICP-OES, UV-VIS absorption spectroscopy and total-reflection X-ray fluorescence (TXRF) spectroscopy. Key words: rare earths; rare-earth elements; lanthanides; bauxite; red mud; critical raw materials; scandium; recycling Start date: 2012-10-01 Application date: 2012-05-31 Publication date: 2012-03-24 Financing: dbof-scholarship Type of Position: scholarship Duration of the Project : 3 years Research group: Remarks: Prof. Tom Van Gerven (Chemical Engineering Department) is copromoter of this project, and the pyrometallurgical part of the process (iron smelting) will be done in close collaboration with Prof. Bart Blanpain (Metallurgy and Materials Engineering Department, MTM). This project is part of the diversified approach targeted by the so-called Sustainable Inorganic Materials Management Research Consortium (SIM²@KULeuven), under the umbrella of the KU Leuven Materials Research Centre. KU Leuven research groups have been investigating the recovery and recycling of inorganic materials, more specifically metals and minerals, for some time now. Recently, there have been several successful developments that have increased the focus on inorganic resource recovery and recycling. Apply to Click here to apply to this project |
Electrolytic recovery of iron from bauxite residue (red mud) |
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Promoter: Jan Fransaerdetails
Description: Bauxite, the most important aluminium ore, contains only between 30–50% alumina, Al2O3, the rest being silica, various iron oxides, and titanium dioxide. The alumina must be purified before it can be refined to aluminium metal. This is done using the Bayer process, where bauxite is digested in a hot sodium hydroxide solution. This converts the alumina to aluminium hydroxide, which dissolves in the hydroxide liquor. The other components of bauxite do not dissolve. The solution is clarified by filtering off the solid impurities. This bauxite residue is a mixture of solid impurities and is called red mud. With a worldwide annual production of 120 millions of tonnes and a total inventory of 2.7 billion of tonnes, stored in huge holding ponds, red mud poses a significant and hazardous problem. The latter was revealed recently by the dam failure of the Ajka refinery in Hungary and the resulting loss of human lives and environmental catastrophe. In Europe, besides Hungary, refineries exist in Bosnia Herzegovina, France, Germany, Greece, Ireland, Italy, Romania, Slovakia and Spain. Unlike other high volume wastes (fly ash, metallurgical slags), red mud finds no industrial application besides minor use in cement and ceramic production. Many researchers have already looked at the valorisation of red mud, besides its use in the construction industry. Red mud has a high metal content and extraction of metals from red mud can be economically feasible. Iron is the major constituent of red mud, followed by alumina, silica, sodium oxide and titania. For complete recycling of red mud, efforts have been attempted to recover major metallic constituents (such as Fe, Al and Ti), and extract rare and rare-earth metals (e.g. Sc, Ga, In). The red colour of red mud is caused by the oxidized iron (mostly hematite or Fe2O3), which can make up to 60% of the mass of the red mud. In view of the rather large content of iron oxide, attempts have been made in the past to use red mud as a source of iron in blast furnaces in the production of pig iron. However, the large sodium content of red mud prohibits the use of it in blast furnaces where the high temperatures lead to the evaporation of sodium oxide in the lower (hotter) regions of the blast furnace and its redeposition in the colder regions, where it attacks the ceramic brick of the blast furnace and also leads to the formation of so-called sodium nests, which are hard outgrowths that obstruct the free flow of the charge inside the furnace. Moreover, red mud contains a lot of water, which would have to be removed first, which would represent a high cost if fossil fuels are used for drying. However, the very high pH of the red mud and its semi-liquid state can be turned to an advantage. Recently, the direct oxidation of metal oxides (known as the FFC or Cambridge process) has been proposed where a metal oxide, e.g. TiO2 is reduced at higher temperatures (> 800 °C) in the solid state using electrons as the reducing agent. For TiO2 this reduction is carried out in molten calcium chloride. These conditions are needed as titanium oxide is thermodynamically very stable and its reduction potential lies far below the electrochemical window of most solvents. However, hematite is much nobler than titanium oxide and it has recently been found that it is possible to perform direct reduction of iron oxide at 100 °C from strongly alkaline solutions. Prerequisite is that the hematite particles are small as the electric conductivity of hematite is low and would otherwise impede the electron transfer. Serendipitously, most of the hematite particles in red mud are smaller than 20 micron, which is ideal for the direct reduction of solid hematite. We propose to investigate the direct reduction of hematite from red mud. However, the direct reduction of iron oxide is still ill-understood and it is not clear how the reduction of the solid iron oxide happens and what the contribution is of dissolved versus insoluble iron species, neither is it clear how the presence of the other insoluble compounds like silica and alumina will influence the reduction process. These solids are not supposed to codeposit with the iron, so compact iron deposits need to be made otherwise particles will get occluded in the growing deposit during electroreduction. The direct reduction of iron oxide has a lot in common with codeposition, i.e. the deposition of solid particles intentionally added to electroplating baths to form composite coatings. This process has been thoroughly studied at MTM which is recognized as a leader in this research area. As MTM has a rather comprehensive know-how on the mechanism that results in the incorporation of particles, we can also use this information to prohibit the incorporation of particles. The very high pH of red mud has a second advantage. Certain elements that are present in bauxite, become soluble at high pH and are hence concentrated in red mud. This is the case for gallium and indium which are both present in red mud and are soluble when the pH is above 10 for gallium and above 11 for indium. Moreover, both metals are relatively rare and no suitable minerals exist for either metal in significant deposits. Hence they are currently produced as by-products of the zinc production. As a result of all this, there is a shortage of both metals which are used in thin-film solar cells and flat screen TV. Both metals however are relatively noble and can easily be electrochemically reduced from aqueous solutions. Hence, it is possible to not only recover Fe from red mud, but at the same time also recover In and Ga. However, as a typical concentration of Ga in red mud is about 500 ppm the mass transfer in the liquor during the electrodeposition will have to be studied and optimized in order to recover the maximum amount of In and Ga. Micromixing can be induced for example with the aid of ultrasound. During the electrolytic reduction of hematite from red mud, the anodic reaction is the oxidation of water according to the electrochemical equation: 4 OH- -> 2 H2O + O2 + 4e-, which will lead to a decrease in the pH of the red mud. Hence, after the electrolytic removal of most of the iron oxide, In, and Ga, red mud will consist mostly of silica, sodium silicate, residual alumina and titanium oxide, with a pH that is much less aggressive and which could perhaps more easily be used as building material. The main emphasis of the experimental work will be on different electrochemical methods, such as cyclic voltammetry, coulometry and electrodeposition experiments. The deposits will be characterized by scanning electron microscopy (SEM) and by energy-dispersive X-ray spectroscopy (EDX). The particle distribution of the hematite particles in solution can be measured by light scattering experiments. The amount of iron, gallium and indium in the solutions will be measured by total-reflection X-ray analysis (TXRF), ICP-OES or AAS. For the speciation of the iron oxides, Raman spectroscopy will be used. Key words: electrochemistry; electrodeposition; iron; red mud; bauxite Start date: 2012-10-01 Application date: 2012-05-31 Publication date: 2012-03-24 Financing: dbof-scholarship Type of Position: scholarship Duration of the Project : 3 years Research group: Remarks: Prof. Bart Blanpain is copromoter of this project. This project is part of the diversified approach targeted by the so-called Sustainable Inorganic Materials Management Research Consortium (SIM²@K.U.Leuven), under the umbrella of the K.U.Leuven Materials Research Centre. K.U.Leuven research groups have been investigating the recovery and recycling of inorganic materials, more specifically metals and minerals, for some time now. Recently, there have been several successful developments that have increased the focus on inorganic resource recovery and recycling. Apply to Click here to apply to this project |
