The Utilization of Bauxite Residue with a Calcite-Rich Bauxite Ore in the Pedersen Process for Iron and Alumina Extraction

AbstractMetallurgical grade alumina is produced worldwide through the well-known Bayer process, which unavoidably generates bauxite residue (BR, also known as red mud) in almost equal amounts to alumina. This study aims the valorization of BR through a smelting-reduction process to obtain calcium aluminate slags that can be a proper feed for alumina recovery via the Pedersen process. It investigates the thermodynamics and characteristics of the slags and pig iron produced from mixtures of BR, a bauxite beneficiation byproduct, and lime. In this context, the evolution of the different phases in the slags is studied with advanced analytical techniques and thermodynamic calculations. According to the results, a CaO/Al2O3 mass ratio within 1.3 to 1.4 in the slags can yield more Al2O3-containing leachable phases, such as CaO·Al2O3 and 12CaO·7Al2O3. The cooling dictates the amount and the characteristics of these phases, and the slower cooling rate yields improved slag characteristics. The distribution of the elements between the slag and metal phases shows that iron is separated, and the majority of the P, Cr, Ni, and V are distributed in the produced pig iron, while S, Ti, and Si are mostly concentrated in the slags.

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Evaluation of Calcium Aluminate Slags and Pig Irons Produced from the Smelting-Reduction of Diasporic Bauxite

Materials ◽

10.3390/ma14247740 ◽

2021 ◽

Vol 14 (24) ◽

pp. 7740

Author(s):

Adamantia Lazou ◽

Leiv Kolbeinsen ◽

Jafar Safarian

Keyword(s):

Calcium Aluminate ◽

Analytical Techniques ◽

Graphite Crucible ◽

Low Grade ◽

Atmospheric Conditions ◽

Smelting Reduction ◽

Alumina Crucible ◽

Process Framework ◽

Bauxite Ore ◽

Lime Addition

This work evaluates the characteristics of calcium aluminate slag and pig iron samples obtained from the smelting of calcined and reduced diasporic bauxite ore. The study is conducted in the Pedersen process framework, which is a method to produce alumina from low-grade resources. Parameters such as the effect of crucible type, lime addition, and atmospheric conditions are studied considering the characteristics of the product pig irons and calcium aluminate slags for further uses. The behavior of the bauxite and distribution of the species between slag and metal was assessed based on the applied analytical techniques and thermodynamic calculations. Iron was reduced and separated from the slags in the presence of carbon (graphite crucible) for both the reduced and calcined bauxite. Si and Ti were mainly concentrated in the slags. Iron was separated from the slag in the absence of carbon (alumina crucible) for the H2-reduced bauxite. The results show that slags with increased lime additions are composed mainly of 5CaO.Al2O3 and CaO.Al2O3, that are considered highly leachable compounds. An optimum CaO/Al2O3 mass ratio of 1.12 was suggested. The presence of O2 and/or OH- in the furnace atmosphere will result in the formation of 12CaO.7Al2O3.

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Recovery of Iron and Aluminum from Bauxite Residue by Carbothermic Reduction and Slag Leaching

Journal of Sustainable Metallurgy ◽

10.1007/s40831-021-00422-7 ◽

2021 ◽

Author(s):

K. E. Ekstroem ◽

A. Voll Bugten ◽

C. van der Eijk ◽

A. Lazou ◽

E. Balomenos ◽

...

Keyword(s):

Large Volume ◽

Calcium Aluminate ◽

Volume Expansion ◽

Carbothermic Reduction ◽

Bauxite Residue ◽

Pig Iron ◽

Post Processing ◽

Reaction Surface

Abstract The recovery of major components of bauxite residue by carbothermic reduction at 1550–1750 °C and subsequent slag leaching in a Na3CO3(aq) solution is studied. Iron recovers primarily to pig-iron and lime is added to tune the calcium aluminate slags towards the highly leachable mayenite phase. The concentration of aluminum in the leachate correlates well with the occurrence of mayenite and aluminum recoveries up to 50–60% are observed. However, slags with low CaO additions are vulnerable to gehlenite formation and display reduced leachabilities. Formation of an inhibiting layer of CaCO3(s) on the reaction surface of calcium-aluminate particles during leaching and immobilization of aluminum in CaTiO3(s) are also suggested to play important roles in limiting the aluminum leachability. Costs related to post-processing may be reduced by achieving disintegrating slags, a behavior which is observed for slags holding high γ- to β-Ca2SiO4 ratios. The disintegration is caused by the large volume expansion associated with the β-to-γ transformation and as such, various factors that are known to stabilize the β-polymorph are discussed. Graphical Abstract

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Characteristics of Calcium-Aluminate Slags and Pig Iron Produced from Smelting-Reduction of Low-Grade Bauxites

Metallurgical and Materials Transactions B ◽

10.1007/s11663-018-1353-1 ◽

2018 ◽

Vol 49 (5) ◽

pp. 2400-2420 ◽

Cited By ~ 7

Author(s):

Fabian Imanasa Azof ◽

Leiv Kolbeinsen ◽

Jafar Safarian

Keyword(s):

Calcium Aluminate ◽

Low Grade ◽

Pig Iron ◽

Smelting Reduction

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High Temperature Treatment of Selected Iron Rich Bauxite Ores to Produce Calcium Aluminate Slags

Materials Proceedings ◽

10.3390/materproc2021005036 ◽

2021 ◽

Vol 5 (1) ◽

pp. 36

Author(s):

Adamantia Lazou ◽

Casper van der Eijk ◽

Michail Vafeias ◽

Amalia Bempelou ◽

Efthymios Balomenos ◽

...

Keyword(s):

Calcium Aluminate ◽

Bauxite Residue ◽

Temperature Treatment ◽

High Temperature Treatment ◽

Chemical Compositions ◽

Smelting Reduction ◽

Slag Chemistry ◽

Reduction Of Iron ◽

And Control ◽

Feedstock Material

The Pedersen process is a method to produce alumina from Al-containing sources, and it is a more material-efficient method than the current commercial Bayer process, since the formation of bauxite residue (red mud) is avoided, and the bauxite can be holistically consumed. The smelting reduction (SR) part of the Pedersen process yields pig iron and a calcium aluminate slag, and the latter is a feedstock material for alumina extraction via alkaline leaching. In the present study, three different bauxite ores (Greek, Turkish and Jamaican) were smelted with lime to ease the process and control the slag chemistry and coke for the carbothermic reduction of iron oxides. The slags produced were analyzed with XRD, XRF, and EPMA to identify the phases and chemical compositions. According to the results, the slags composed of Al-containing leachable phases. Moreover, it is shown that the amount and distribution of both the leachable and non-leachable phases in the slags depend on the ore chemical composition. The results are discussed regarding the characteristics and potential leachability of the slags. Standard leaching tests were performed to examine the actual leachability.

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Development of a Smelting Reduction Process for Low-Grade Ferruginous Manganese Ores to Produce Valuable Synthetic Manganese Ore and Pig Iron

Mining Metallurgy & Exploration ◽

10.1007/s42461-020-00271-0 ◽

2020 ◽

Vol 37 (5) ◽

pp. 1681-1692

Author(s):

Veerendra Singh ◽

Arijit Biswas ◽

Nilamadhaba Sahu

Keyword(s):

Reduction Process ◽

Low Grade ◽

Manganese Ore ◽

Pig Iron ◽

Smelting Reduction ◽

Manganese Ores

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Material Ratio Optimization of Low Mass Ratio of Alumina to Silica of Calcium Aluminate Slag Based on Thermodynamic Calculation Method

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.402.288 ◽

2011 ◽

Vol 402 ◽

pp. 288-292

Author(s):

Zhi Fang Tong ◽

Sen Lin Xie ◽

Li Heng Zhang ◽

Tao Chen ◽

Wei Liu ◽

...

Keyword(s):

Phase Composition ◽

Calcium Aluminate ◽

Red Mud ◽

Thermodynamic Calculation ◽

Particle Size Analysis ◽

Molar Ratio ◽

Size Analysis ◽

Mass Ratio ◽

Smelting Reduction ◽

The Impact

For the low m(Al2O3)/m(SiO2) (mass ratio, for short A/S) calcium aluminate slag obtained from smelting reduction Pingguo red mud, the impact of different n(CaO)/n(Al2O3))(molar ratio, for short C/A) and A/S on the separateing out phase of slag in cooling and solidification process was studied by FactSage thermodynamic calculation software, and the material ratio of the slag was optimized. The physical-chemical properties of slag prepared in the experiment were analyzed by means of XRD, EMS, EDS, Particle size analysis and Chemical analysis. The thermodynamic calculation results indicate that the effect of C/A on the phase composition of the slag is great, but the influnce of A/S from 0.5 to 1.0 is small, the material ratio optimized is C/S=2, A/S=0.5～1.0, C/A=1.61～1.81, under the conditions, the phase composition is mainly Ca2SiO4, Ca12Al14O33and even a small amount of less than 5% of CaAl2O4or Ca3Al2O6. The phase composition of experimental slag is consistant with that of thermodynamic calculation. In the material proportion optimized scope, the calcium aluminate slag has better the self-disintegrating and the alumina leaching performance, and satisfies completely the technological requirements of extracting alumina. The results provide the scientific basis for using the low A/S calcium aluminate slag obtained from smelting reduction Pingguo red mud producting alumina.

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