The leachability of a ternary CaO-Al2O3-SiO2 slag produced from smelting-reduction of low-grade bauxite for alumina recovery

Azof, Fabian Imanasa; Vafeias, Michail; Panias, Dimitrios; Safarian, Jafar

doi:10.1016/j.hydromet.2019.105184

Cited by 24 publications

(24 citation statements)

References 14 publications

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“…The first important observation from the laboratory scale experiments was the low extraction rates for aluminum. Though the known effect of coating of the slag particles by CaCO 3 is one of the reasons that further extraction is hindered [29], a closer examination to the XRD graphs of the residues elucidated that it was also the crystallographic composition of the slag that played a significant role. The slag used in the laboratory scale experiments was produced with an excess of CaO in order to dilute its SiO 2 content and avoid the formation of C 2 AS.…”

Section: Correlation Between Slag Composition and Aluminium Extraction Ratesmentioning

confidence: 99%

“…As stated earlier, the leaching of slags consisting of calcium aluminates with molar ratios of CaO/Al 2 O 3 ≥ 1, has been described as a process that has two major outcomes, the production of CaCO 3 and the dissolution of Al, according to the generic chemical Equation (1). Moreover, C 3 AH 6 is regularly reported as a by-product and is considered a measure of Al losses, along with any unleached calcium aluminate phases [24,29]. This view of the process is rather simplistic as it considers that the only possible reactions during leaching are between (a) CaO and the CO 3 2− ions, for the production of CaCO 3 , (b) between the calcium aluminates and water, for the production of C 3 AH 6 and (c) between Na+ and Al(OH) 4 − ions, leading to the dissolution of the latter.…”

Section: Effect Of the Hydraulic Character Of Calcium Aluminatesmentioning

confidence: 99%

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Leaching of Ca-Rich Slags Produced from Reductive Smelting of Bauxite Residue with Na2CO3 Solutions for Alumina Extraction: Lab and Pilot Scale Experiments

et al. 2021

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Sustainable utilization of Bauxite Residue (BR) is currently one of the greatest challenges being tackled by the alumina industry, due to its high production rates and limited reuse options. The present work is concerned with the use of BR as a candidate metallurgical raw material for iron (Fe) production and aluminum (Al) extraction. In more detail, at first, BR undergoes reductive smelting to extract its Fe content and produce a slag of mainly calcium aluminate composition. In a second step, Al contained in the calcium aluminate phases is extracted hydrometallurgically by leaching with a Na2CO3 aqueous solution. The focus of the current study is the optimization of this leaching process, and it was performed in two stages. The first was a laboratory scale investigation on the main parameters affecting the extraction rate of Al. The second stage was performed in pilot scale and incorporated observations and suggestions based on the laboratory scale investigation. Laboratory work showed that more than 50% of aluminum could be easily extracted in less than 1 h, in 5% S/L, at 70 °C and with an 20% excess of Na2CO3. Pilot scale work, by successfully applying the suggestions derived from laboratory scale work, achieved an average Al extraction of 68% from a 10% S/L pulp, with a slag of optimized composition in relation to the one used in the laboratory scale.

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Section: Correlation Between Slag Composition and Aluminium Extraction Ratesmentioning

confidence: 99%

Section: Effect Of the Hydraulic Character Of Calcium Aluminatesmentioning

confidence: 99%

Leaching of Ca-Rich Slags Produced from Reductive Smelting of Bauxite Residue with Na2CO3 Solutions for Alumina Extraction: Lab and Pilot Scale Experiments

et al. 2021

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“…Marked particles are quantified in more detailed in Table 7 leaching (Fig. 8a), which is known to limit the reaction between particles and the leaching solution [16]. This suggests that the recovery is sensitive to the physical properties of the particles, such as particle size and the presence of cracks.…”

Section: Slag Characteristics and Leachingmentioning

confidence: 99%

“…On the other hand, monocalcium dialuminate (CA2; CaAl 4 O 4(s) ) appear to be insoluble in a Na 2 CO 3 solution. It was argued that the leaching is surface driven, and the reduced leachability was related to the buildup of an insoluble layer of calcite on the calcium aluminates that effectively inhibits the dissolution of Al 2 O 3 [16]. Moreover, a less leachable calcium aluminate phase may also affect the leachability of others.…”

Section: Introductionmentioning

confidence: 99%

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

Ekstroem

Bugten

Eijk

et al. 2021

J. Sustain. Metall.

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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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“…Much of the work done in Ensureal is not published yet, but a sort of impression of the ongoings is shown in the published papers [34][35][36][40][41][42][43][44][45] included here.…”

Section: The Pedersen Process -Ensurealmentioning

confidence: 99%

The beginning and the end of the aluminium value chain

Kolbeinsen¹

2020

Matériaux & Techniques

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Metallic aluminium does not naturally occur in nature, and it was largely unknown, virtually a mystery, until 200 years ago. The modern aluminium production using a hydrometallurgical refining process for making alumina followed by electrolysis of this mineral was first developed in 1886 and, in principle, the same technology is still used to this day. About 90% of alumina refineries in the world use the Bayer process for refining Bauxite ore. It is very efficient, but it can only be used on high quality bauxite with low content of admixtures, especially silicon. The Bayer process also generates a Bauxite Residue (BR), maybe better known as Red Mud (RM) which is a thick red-brown, high-basicity paste consisting of silicon, iron, aluminium, titanium and others. The International Institute of Aluminium estimates that since 1886 almost a billion tonnes of aluminium were produced around the world with three fourths of this amount still being in use today, of which about 35% is located in buildings and structures, 30% in electric cables and equipment and 30% in transport. Aluminium scrap is collected all over the world. In the home, it mostly consists of aluminium beverage cans. It is claimed that 1 ton of recycled empty beverage cans save 8 tons of bauxite, 4 kg of various fluorides and 14 kWh of electricity. Additionally, recycling aluminium significantly reduces the negative environmental impact of ever-expanding RM landfills. As the idea of environmental responsibility is gaining more and more traction, separate household scrap recycling is becoming more and more popular around the world. How challenges related to such activity can be met will be the main topic of this paper alongside discussing new developments for alumina production without RM generation.

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The leachability of a ternary CaO-Al2O3-SiO2 slag produced from smelting-reduction of low-grade bauxite for alumina recovery

Cited by 24 publications

References 14 publications

Leaching of Ca-Rich Slags Produced from Reductive Smelting of Bauxite Residue with Na2CO3 Solutions for Alumina Extraction: Lab and Pilot Scale Experiments

Leaching of Ca-Rich Slags Produced from Reductive Smelting of Bauxite Residue with Na2CO3 Solutions for Alumina Extraction: Lab and Pilot Scale Experiments

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

The beginning and the end of the aluminium value chain

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