The need of light weight alloys for future transportation industry puts Sc and Ti under a sudden demand. While these metals can bring unique and desired properties to alloys, lack of reliable sources brought forth a supply problem which can be solved by valorization of the secondary resources. Bauxite residue (red mud), with considerable Ti and Sc content, is a promising resource for secure supply of these metals. Due to drawbacks of the direct leaching route from bauxite residue, such as silica gel formation and low selectivity towards these valuable metals, a novel leaching process based on oxidative leaching conditions, aiming more efficient and selective leaching but also considering environmental aspects via lower acid consumption, was investigated in this study. Combination of hydrogen peroxide (H2O2) and sulfuric acid (H2SO4) was utilized as the leaching solution, where various acid concentrations, solid-to-liquid ratios, leaching temperatures and times were examined in a comparative manner. Leaching with 2.5 M H2O2: 2.5 M H2SO4 mixture at 90 °C for 30 min was observed to be the best leaching conditions with suppressed silica gel formation and the highest reported leaching efficiency with high S/L ratio for Sc and Ti; 68% and 91%; respectively.

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Novel Approach for Enhanced Scandium and Titanium Leaching Efficiency from Bauxite Residue with Suppressed Silica Gel Formation.

Evaluation of red mud as a polymetallic source – A review

The purpose of present work was to provide mineralogical insight into the rare earth element (REE) phases in bauxite residue to improve REE recovering technologies Experimental work was performed by electron probe microanalysis with energy dispersive as well as wavelength dispersive spectroscopy and transmission electron microscopy REEs are found as discrete mineral particles in bauxite residue Their sizes range from <1 μm to about 40 μm In bauxite residue, the most abundant REE bearing phases are light REE (LREE) ferrotitanates that form a solid solution between the phases with major compositions (REE,Ca,Na)(Ti,Fe)O3 and (Ca,Na)(Ti,Fe)O3 These are secondary phases formed during the Bayer process by an in-situ transformation of the precursor bauxite LREE phases Compared to natural systems, the indicated solid solution resembles loparite-perovskite series LREE particles often have a calcium ferrotitanate shell surrounding them that probably hinders their solubility Minor amount of LREE carbonate and phosphate minerals as well as manganese-associated LREE phases are also present in bauxite residue Heavy REEs occur in the same form as in bauxites, namely as yttrium phosphates These results show that the Bayer process has an impact on the initial REE mineralogy contained in bauxite Bauxite residue as well as selected bauxites are potentially good sources of REEs

Rare Earth Element Phases in Bauxite Residue

With the growing awareness to protect the urban environment and the increasing demand for strategic materials, recycling of postconsumer lithium-ion batteries has become imperative. This study aims...

Closed-Loop Recycling of Lithium, Cobalt, Nickel, and Manganese from Waste Lithium-Ion Batteries of Electric Vehicles

Recovery of scandium from Canadian bauxite residue utilizing acid baking followed by water leaching.

Some rare earth elements (REEs) are classified under critical materials, i.e., essential in use and subject to supply risk, due to their increasing demand, monopolistic supply, and environmentally unsustainable and expensive mining practices. To tackle the REE supply challenge, new initiatives have been started focusing on their extraction from alternative secondary resources. This study puts the emphasis on technospheric mining of REEs from bauxite residue (red mud) produced by the aluminum industry. Characterization results showed the bauxite residue sample contains about 0.03 wt% REEs. Systematic leaching experiments showed that concentrated HNO3 is the most effective lixiviant. However, because of the process complexities, H2SO4 was selected as the lixiviant. To further enhance the leaching efficiency, a novel process based on microwave pretreatment was employed. Results indicated that microwave pretreatment creates cracks and pores in the particles, enabling the lixiviant to diffuse further into the particles, bringing more REEs into solution, yielding of 64.2% and 78.7% for Sc and Nd, respectively, which are higher than the maximum obtained when HNO3 was used. This novel process of “H2SO4 leaching-coupled with-microwave pretreatment” proves to be a promising technique that can help realize the technological potential of REE recovery from secondary resources, particularly bauxite residue.

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Technospheric Mining of Rare Earth Elements from Bauxite Residue (Red Mud): Process Optimization, Kinetic Investigation, and Microwave Pretreatment.

Bauxite residue is an environmentally unfriendly byproduct of alumina manufacturing, produced worldwide in large quantities. This material contains 50–100 ppm of scandium, a critical material for the production of stronger, weldable, corrosion resistant, and heat tolerant aluminum products. Aircraft manufacturers are particularly interested in Al–Sc alloys because of its ability to form weldable alloys that could potentially reduce aircraft weight by 15–20%. Because of its abundance and low cost, bauxite residue has the potential to be used as an efficient feedstock for valorization processes to recover its scandium content, while in turn degrading this problematic waste. In this project, we developed an efficient process to recover scandium and rare earth elements from a Canadian bauxite residue with high extraction yields, using industrially scalable and economical techniques. The process employs a modified version of sulfuric acid leaching and subsequent impurity removal by selective precipitation. This article outlines the current progress and design rationale in the development and optimization of this innovative and sustainable recovery process.

Sable Reid

Papers

Technospheric Mining of Rare Earth Elements from Bauxite Residue (Red Mud): Process Optimization, Kinetic Investigation, and Microwave Pretreatment.

Innovative and Sustainable Valorization Process to Recover Scandium and Rare Earth Elements from Canadian Bauxite Residues