Leaching characteristics and mechanism of the synthetic calcium-aluminate slags for alumina recovery

Azof, Fabian Imanasa; Yang, Yongxiang; Panias, Dimitrios; Kolbeinsen, Leiv; Safarian, Jafar

doi:10.1016/j.hydromet.2019.03.006

Cited by 31 publications

(24 citation statements)

References 43 publications

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“…The slag numbers here are based on the labeled slags in our previously published work and are kept in this research to be more convenient for the readers. [24] The slags were made from different raw material purity and atmospheric conditions. The compositions of the CaO and Al 2 O 3 powders used for the pure mixture are 99.9 wt pct CaO and 99.95 wt pct Al 2 O 3 , whereas the less pure mixtures were made from 96 wt pct CaO and the same 99.95 wt pct Al 2 O 3 .…”

Section: A Slagmakingmentioning

confidence: 99%

“…[3] calcium-aluminate slags that can be further leached in the Na 2 CO 3 solution for alumina recovery. [24][25][26][27][28][29][30][31][32] One of the known leachable and favorable phases in the slags is the C 12 A 7 phase, which has been reported in several studies. [24,[33][34][35] However, the formation of the C 12 A 7 phase in slags produced from the smelting reduction of bauxite, and its behavior under different conditions is still unclear.…”

Section: Introductionmentioning

confidence: 99%

“…[24][25][26][27][28][29][30][31][32] One of the known leachable and favorable phases in the slags is the C 12 A 7 phase, which has been reported in several studies. [24,[33][34][35] However, the formation of the C 12 A 7 phase in slags produced from the smelting reduction of bauxite, and its behavior under different conditions is still unclear. [27] Therefore, it is necessary to study the stability of C 12 A 7 as well as other known metastable phase, C 5 A 3 , that are produced from calcium-aluminate melts at different conditions.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis and Characterization of 12CaO·7Al2O3 Slags: The Effects of Impurities and Atmospheres on the Phase Relations

Azof

Tang

You

et al. 2020

Metall Mater Trans B

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Synthesis of crystalline slags of 12CaO·7Al2O3 phase from the corresponding melt compositions in different atmospheric conditions and different purities is investigated. Observations using a thermogravimetry coupled with differential thermal analysis showed that the dehydration of a zeolitic 12CaO·7Al2O3 phase occur at 770 °C to 1390 °C before it congruently melts at 1450 °C. The X-ray diffraction pattern of the slag showed that a single 12CaO·7Al2O3 phase is produced from a mixture, which has small SiO2 impurity with a 49:51 mass ratio of CaO to Al2O3. A scanning electron microscope and electron probe micro-analyzer showed that a minor Ca-Al-Si-O-containing phase is in equilibrium with a grain-less 12CaO·7Al2O3 phase. Moreover, 12CaO·7Al2O3 is unstable at room temperature when the high-purity molten slag is solidified under oxidizing conditions contained in an alumina crucible. On the other hand, a high-temperature in-situ Raman spectroscopy of a slag that was made of a higher purity CaO-Al2O3 mixture showed that 5CaO·3Al2O3 phase is an unstable/intermediate phase in the the CaO-Al2O3 system, which is decomposed to 12CaO·7Al2O3 above 1100 °C upon heating in oxidizing conditions. It was found that 5CaO·3Al2O3 is present at room temperature when the 12CaO·7Al2O3 dissociates to a mixture of 5CaO·3Al2O3, 3CaO·Al2O3, and CaO·Al2O3 phases during the cooling of the slag at 1180 °C ± 20 °C in reducing atmosphere. It is proposed that low concentrations of Si stabilize 12CaO·7Al2O3 (mayenite), in which Si is a solid solution in its lattice, which is named Si-mayenite. Regarding the calculated CaO-Al2O3-SiO2 diagram in this study, this phase may contain a maximum of 4.7 wt pct SiO2, which depends on the total SiO2 in the system and the Ca/Al ratio.

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Section: A Slagmakingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Synthesis and Characterization of 12CaO·7Al2O3 Slags: The Effects of Impurities and Atmospheres on the Phase Relations

Azof

Tang

You

et al. 2020

Metall Mater Trans B

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“…Hence, the process can be integrated into Al production plant to recycle metallic components of a dross into the process for the alloy production. The produced slag byproduct is consumable and can be used in other industries such as steelmaking, the cement industry, and even the alumina industry as a feedstock for metallurgical alumina production [50,51]. The proposed process here has several advantages as compared with the existing treatment process for the AWD.…”

Section: Process Evaluationmentioning

confidence: 99%

Valorization of Aluminum Dross with Copper via High Temperature Melting to Produce Al-Cu Alloys

et al. 2021

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The valorization of aluminum dross for Al recovery was performed via its mixing with metallic copper to produce Al-Cu alloys. This approach was with the intention of establishing a new smelting process to treat the dross with Cu scrap use. To evaluate the high temperature interaction of the materials, the wettability of a Cu-containing aluminum alloy with the non-metallic components of the dross was studied by the sessile drop method. It was found that the wetting was weak via temperature changes at 973–1373 K, and consequently no proper metal separation occurred. To better separate the metallic and non-metallic phases with larger density differences, a higher Cu portion was considered to obtain a significantly denser metallic phase, and it was found that partial separation of the Al in an Al-Cu alloy is possible. The complete separation of the metallic components of the dross was, however, experienced by the dross and copper melting with the addition of pre-melted calcium aluminate slags at elevated temperatures. It was found that Al-Cu alloys were produced and separated from the adjacent slags, and the aluminum oxide of the dross ended up in the slag phase. Moreover, the characteristics of the produced slags depend on the process charge.

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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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Leaching characteristics and mechanism of the synthetic calcium-aluminate slags for alumina recovery

Cited by 31 publications

References 43 publications

Synthesis and Characterization of 12CaO·7Al2O3 Slags: The Effects of Impurities and Atmospheres on the Phase Relations

Synthesis and Characterization of 12CaO·7Al2O3 Slags: The Effects of Impurities and Atmospheres on the Phase Relations

Valorization of Aluminum Dross with Copper via High Temperature Melting to Produce Al-Cu Alloys

The beginning and the end of the aluminium value chain

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