IRON REMOVAL FROM BAUXITE ORES Good morning, it is a great pleasure for me to be here, and presenting this work on conference dedicaded to the ReD MuD problematic. As you can see fro the title this work it not focus on BR, it is more about prevention of generation of BR. Sum up of the project. Michal KSIAZEK, E. RINGDALEN, P.H. HØGAAS, C. van der EIJK SINTEF Industry, Process Metallurgy and Raw Materials

1) Introduction 2) Experimental 3) Results 4) Conclusion Outline 1) Introduction 2) Experimental 3) Results 4) Conclusion

Main conclusions Reduction by CO and H2 at temperatures ranging from 350 °C to 800 °C made the bauxite rendered magnetically susceptible. Extent of iron removal is more affected by conditions used during the magnetic separation than the conditions used during the reduction process. Pre-treatment of bauxite with hydrogen made the bauxite leached residue magnetic.

The main objective of the project was to investigate whether it is possible to extract iron from bauxite before the Bayer process, to reduce BR production. Motivation Waste hierarchy, Most common practice is disposal, which creates some ecological issues, We will herar about recycling etc. Since 60% RED Mud Is iron oxides colegues One colluge cam up with ide a to remove iron , lets reduce do magnetite and remove by some ore dressing method.

4-7 tons 1-2 tons The proposed process has a considerable potential for increased value creation by reducing or removing the cost for chemicals for leaching and by reducing the cost for waste disposal. Additionally separated iron bearing materials can be sold as a valuable product instead of disposing it as part of red mud. Bayerprosessen er en metallurgisk proesess hvor aluminiumoksid utvinnes av bauksitt. Bauksitt vaskes i natriumhydroksid ved 175°C, aluminiumoksiden løses da opp i den flytende natriumhydroksiden og blir til aluminiumhydroksid, mens resten av bauksitten danner slagg. Al2O3 + 2 OH- + 3 H2O → 2 [Al(OH)4]- Når blandingen nedkjøles vil aluminiumhydroksiden bli liggende som fast stoff og kan hentes ut. Aluminiumhydroksiden varmes så ppp til 1050°C, vannet i aluminiumhydroksiden fordamper da og vi sitter igjen med ren aluminiumoksid. 2 Al(OH)3 → Al2O3 + 3 H2O The red colour arises from iron oxides, which comprise up to 60% of the mass of the red mud. The mud is highly basic with a pH ranging from 10 to 13.[2][3][4] In addition to iron, the other dominant components include silica, unleached residual alumina, and titanium oxide.[1] 2 tons

Previous work Sadler et al. (1991) reported that calcination of refractory-grade bauxite with reducing gas converts present iron to magnetite or elemental iron. Removal of organic carbon from bauxite by hydrogen pretreatment was examined by MacDonald et al (1991). (partially magnetic after the calcination between 240-400°C in hydrogen atmosphere). Carbothermal upgrading of the Ghana Awaso bauxite showed that it is possible to remove over 90% of the iron oxide content from the bauxite as magnetic fraction. Dankwah et al. (2015) They observed that bauxite and its leached residue become partially magnetic after the calcination between 240-400°C in hydrogen atmosphere. 90-450 µm

Experimental Characterization of bauxite (XRD, EPMA, TOC) Determining distribution of iron in the bauxite, whether it occurs as separate grains or incorporated in the lattice of the aluminium hydroxides. Selective reduction (ENTECH 1800, DISvaDRI ) Type of gas used for the direct reduction process. (H2/CO/Natural) Operating temperature (350-800 °C) Particle size of bauxite (1-3mm, 3-6mm). Characterization of treated bauxite and separation of iron phase Investigation on how the iron phases can be liberated from the alumina containing species in the bauxite ore (wet low intensity magnetic separator, wet/dry high intensity magnetic separator with permanent magnets). X-ray diffraction, u

Selective reduction (DISvaDRI, ENTECH 1800) Characterisation of bauxite (XRD, EPMA, TOC) Determining distribution of iron in the bauxite, whether it occurs as separate grains or incorporated in the lattice of the aluminium hydroxides. Selective reduction (ENTECH 1800, DISvaDRI ) Thermodynamic calculation Type of gas used for the direct reduction process. (H2/CO/Natural) Operating temperature (350-800 °C) Particle size of bauxite (1-3mm, 3-6mm). Characterization of treated bauxite and separation of iron phase Investigation on how the iron produced can be liberated from the alumina containing species in the bauxite ore. charge. The crucible is hooked up beneath a balance thus the measurement of the mass loss during experiment was possible.

Experimental Characterization of bauxite (XRD, EPMA, TOC) Determining distribution of iron in the bauxite, whether it occurs as separate grains or incorporated in the lattice of the aluminium hydroxides. Selective reduction (ENTECH 1800, DISvaDRI ) Type of gas used for the direct reduction process. (H2/CO/Natural) Operating temperature (350-800 °C) Particle size of bauxite (1-3mm, 3-6mm). Characterization of treated bauxite and separation of iron phase Investigation on how the iron phases can be liberated from the alumina containing species in the bauxite ore (wet low intensity magnetic separator, wet/dry high intensity magnetic separator with permanent magnets).

Wet high intensity magnetic field separation

Results Characterization of bauxite Wt.% Gibbsite 54.7 Kaolinite 26.5 Brazilian bauxite X-ray diffraction phase identification of the raw ore showed gibbsite (Al2O3·3H2O) as the major phase, presents with kaolinite (Al2O3·2SiO2·2H2O) and hematite (Fe2O3). Electron Probe Microanalysis (EPMA) images presented on the Figure 1 and Figure 2 show overview of minerals distribution inside the ore. Wt.% can be divided in to groups: relatively coarse fraction between 50-5µm and those, which are finely, disperse in the ore, where particles are smaller than 1µm Total Organic Carbon (TOC) analyse of tested material is presented in Table 2. Bauxite contains low amount of organic carbon around 0.1 wt.%, which is still low in comparison to Australian or Jamaican ores where TOC differ between 0.15-0.3 wt.%. Wt.% Gibbsite 54.7 Kaolinite 26.5 Hematite 19.9 Sample 1 2 3 TOC [wt.%] 0.111 0.11 0.115

Selective reduction (DISvaDRI) No. Gas Particle size Target temp. Holding time Weight I1 CO 1l/min 1-3mm 800°C no 100g I2 H2 1l/min I3 Ar 1l/min T1 3-6mm 600°C 1h 150g T2 400°C 3h T3 T4 350°C T5 T6 charge. The crucible is hooked up beneath a balance thus the measurement of the mass loss during experiment was possible.

Calcination of bauxite in argon atmosphere resulted in highest weight loss, where in this case no reduction reaction should occur. Observed weight loss during the heating was mostly due to the liberation of both unbound and chemically bound moisture from the ore samples, for example Gibbsite dehydrates at 357°C.3

Characterization of treated bauxite and separation of iron phases Phases containing iron are very inhomogeneous and appear in different arrangements. Figure 6 shows occurrence of phase containing iron in two different manner. Figure 6a shows most likely ilmenite (white spots) as separate grains spread in Al rich matrix. Figure 6b shows opposite situation where matrix is most likely magnetite (bright phase) with dark Al-oxide matrix. : EPMA picture showing occurrence of iron rich phase in two particles from the same batch. (sample reduced in H2 at 600°C) Test number Gas atmosphere Temperature [°C] TOC [%] I1 CO 800 0.67 I2 H2 <0.1 I3 500

Separation of iron phases Iron content was reduced by 43%, while 75% of the feed was recovered as non magnetic fraction. Wet high intensity magnetic field separator. 37µm . During the last stage, pulsation was used. For initial test, 20 gram of sample was used as a feed. After the separation test, 15.09g was collected as non-magnetic and 3.49g occur as magnetic fraction. 1.44g of sample were lost during the separation or draying process. In other words about 75% of the feed material was recovered as non-magnetic product while 17,5% was recovered as magnetic fraction.   Non-magnetic Magnetic Raw sample stage 1, 1000 A 2, 400 A 3, 100 A 5, 50 A Fe2O3 (%) 11,17 11,71 12,23 12,75 33,02 20,60 Al2O3 (%) 53,62 53,65 52,89 53,59 37,14 42,40 Wet high intensity magnetic field separation

Since the non-magnetic fraction should be used as feed for Bayer process, combination of the minimum iron content with high recovery as non-magnetic fraction should be the ultimate target. Figure 9 presents bauxite recovery as a non-magnetic fraction and iron removal level for test performed in Slon separator. The highest values gives the initial experiment where bauxite reduced at 800°C in CO atmosphere was separated through 5 stages cycle. Impact of multiple-pass magnetic separation seems to have significant influence for both iron removal and bauxite recovery, which also can be seen in case of sample T3b1. The influence of reduction conditions parameters on iron removal or bauxite recovery as non-magnetic product is not evident. It is worth to remember at all reduced samples became very magnetic. Longer holding time in case of bauxite reduced at 350°C do not change any of the values. However, in samples heated at 400°C, longer holding time increases the amount of generated non-magnetic fraction. Reduction at high temperature also does not indicate better separation output. Material reduced in CO at 800°C gave the highest separation results, while material reduced in H2 at 800°C did not follow this trend. Of course, the influence of reduction gas can play here an important role, however the use of CO gas for reduction of bauxite ore is not practicable due to increase of carbon content. Bauxite reduced at 600°C at H2 gave high iron removal level, but quite small fraction was separated as non-magnetic material.

EPMA mapping image of magnetic fraction after the initial Slon test Digestion time was 70 minutes. The leaching test was performed by Hydro Alumina Quality Support laboratory. As it was examined by hand-held low intensity magnet the residue was still strongly magnetic. Magnetic fraction from sample T2 was leached at 143°C with 189ml of 2.5M NaOH. Digestion time was 70 minutes.

Conclusions Reduction of bauxite with reducing gas, both CO and H2 at temperatures ranging from 350 °C to 800 °C was investigated. Iron impurities in bauxite were rendered magnetically susceptible for all temperatures when reduction gas was applied, presumably by forming magnetite. Reduction in H2 gave decrease total organic carbon. Wet high intensity magnetic field separation showed to be suitable method for removal of iron phase from bauxite ore. Extent of iron removal is more affected by conditions used during the magnetic separation than the conditions used during the reduction process. Pre-treatment of bauxite with hydrogen made the bauxite leached residue magnetic.

Wet high intensity magnetic field separation showed to be suitable method for removal of iron phase from bauxite ore. Extent of iron removal is more affected by conditions used during the magnetic separation than the conditions used during the reduction process. Iron content was reduced by 43% in comparison to untreated bauxite ore with 75% bauxite recovery as non-magnetic fraction.

Pre-treatment of bauxite with hydrogen made the bauxite leached residue magnetic.

Thank you for your attention!