Gisele Azimi

Hydrophobicity of rare-earth oxide ceramics

Hydrophobic materials that are robust to harsh environments are needed in a broad range of applications. Although durable materials such as metals and ceramics, which are generally hydrophilic, can be rendered hydrophobic by polymeric modifiers, these deteriorate in harsh environments. Here we show that a class of ceramics comprising the entire lanthanide oxide series, ranging from ceria to lutecia, is intrinsically hydrophobic. We attribute their hydrophobicity to their unique electronic structure, which inhibits hydrogen bonding with interfacial water molecules. We also show with surface-energy measurements that polar interactions are minimized at these surfaces and with Fourier transform infrared/grazing-angle attenuated total reflection that interfacial water molecules are oriented in the hydrophobic hydration structure. Moreover, we demonstrate that these ceramic materials promote dropwise condensation, repel impinging water droplets, and sustain hydrophobicity even after exposure to harsh environments. Rare-earth oxide ceramics should find widespread applicability as robust hydrophobic surfaces.

Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides

Hydrophobic surfaces that are robust can have widespread applications in drop-wise condensation, anti-corrosion, and anti-icing. Recently, it was shown that the class of ceramics comprising the lanthanide series rare-earth oxides (REOs) is intrinsically hydrophobic. The unique electronic structure of the rare-earth metal atom inhibits hydrogen bonding with interfacial water molecules resulting in a hydrophobic hydration structure where the surface oxygen atoms are the only hydrogen bonding sites. Hence, the presence of excess surface oxygen can lead to increased hydrogen bonding and thereby reduce hydrophobicity of REOs. Herein, we demonstrate how surface stoichiometry and surface relaxations can impact wetting properties of REOs. Using X-ray Photoelectron Spectroscopy and wetting measurements, we show that freshly sputtered ceria is hydrophilic due to excess surface oxygen (shown to have an O/Ce ratio of ∼3 and a water contact angle of ∼15°), which when relaxed in a clean, ultra-high vacuum environment i...

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

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.

Supercritical Fluid Extraction of Rare Earth Elements from NiMH Battery

Today’s world relies upon advanced green technologies that are made of critical elements with unique properties. Examples include rare earth elements (REEs) that are critical in the manufacturing of wind turbines and electric/hybrid vehicle batteries, key components of a greener future that face supply uncertainty and near zero recycling. To tackle their supply challenges, activities have begun for urban mining from waste electrical and electronic equipment (WEEE) that contain considerable amount of REEs, but their current level of recycling is less than 1%. Current recycling practices use either pyrometallurgy, which is energy intensive, or hydrometallurgy that utilizes large volumes of acids and solvents and generates large volumes of hazardous waste. In this study, we developed a novel and sustainable process to recycle REEs from WEEE, NiMH batteries in particular. The developed process relies on supercritical fluid extraction (SCFE) utilizing CO2 as the solvent, which is abundant, safe, cost effective, and inert. The effect of seven operating parameters, namely temperature, pressure, residence time, sample to chelating agent ratio, agitation rate, complex formulation, and methanol addition on REE extraction efficiency was investigated, and optimum operating conditions were determined. This work is the first to utilize a very efficient and safe process that runs at low temperature to extract metals from postconsumer products with minimum hazardous waste generation, while offering about 90% leaching efficiency for REEs. We expect our process to find widespread applicability in urban mining of REEs using green chemistry.

Efficient Recovery of Neodymium from Neodymium–Iron–Boron Magnet

Many postconsumer electrical and electronic equipment wastes contain a considerable amount of rare earth elements (REEs); however, the current level of REE recycling from them is limited (<1%). Neodymium–iron–boron (NdFeB) magnets, used at both small- and large-scale, from computer hard disk drives and small tools to wind turbines and cars, are a good example of such waste materials that contain high content of neodymium (Nd) and dysprosium (Dy). These elements are considered critical metals because they are the main building block of emerging green technologies that will allow for GHG emission reductions. Because demand for these green products is increasing around the world, the demand for REEs is increasing quickly, putting their supply at risk in the near future. Thus, it is critical to develop efficient, robust, and cost-effective processes to recycle these elements from this class of electronic waste materials. Here, we performed a thorough characterization of a N52–NdFeB magnet to identify its composition, crystal structure, and morphology. Furthermore, we developed an efficient hydrometallurgical process to extract Nd and Dy with high efficiency (more than 95%).

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

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.

Matrix Complexity Effect on Platinum Group Metals Analysis using Inductively Coupled Plasma Optical Emission Spectrometry

Recent global actions to mitigate climate change have sparked the development of critical green technologies that rely on strategic materials with unique properties. Examples include Platinum Group Metals (PGMs) that are in increasingly high demand in the manufacturing of green catalysts, but facing supply uncertainty. For tackling the sustainability challenges associated with PGMs supply, activities have been initiated to mine these elements from low-grade ores and postconsumer automotive catalytic converters. However, such sources are highly concentrated with other elements, such as iron, aluminum, and silicon, causing analytical interferences during PGM quantitative analyses, making the measurements unreliable. Here, we performed a systematic investigation to determine the effect of matrix complexity in terms of analyte concentration, number of interferents, concentration of interferents, and identity of interferents on the measurement performance of nine emission lines of PGMs, when inductively coupled plasma optical emission spectrometry (ICP-OES) is utilized. Results indicate that depending on the combination of parameters, the concentration of all PGMs, except for osmium, is underestimated when the matrix contains Fe, Ca, Mn, Cr, Mg, Al, Si, Pb, and Cu. This observation is attributed to spectral interferences and inter-element effects, caused by ionization and chemical interferences. The distinctive behavior of osmium is attributed to the memory effect because of its high volatility and stickiness in the nitrate media. Statistical analyses were utilized to evaluate the coefficient of determination, error distribution, and precision of the instrument to establish a set of guidelines for selecting PGMs emission lines, depending on the matrix complexity. To highlight the practical implication of this study, NIST 2557 auto-catalyst standard was analyzed as a reference material, indicating the applicability of the developed guidelines. We expect our findings will help address some critical aspects of selecting suitable emission lines during PGMs quantifications in complex matrices, such as ores and automotive catalytic converters.

Microwave Treatment for Extraction of Rare Earth Elements from Phosphogypsum

Many advanced technologies in modern society require the use of rare earth elements (REEs). Since these technologies are dominating the world, the demand for REEs is increasing fast. Therefore, finding new sources for them is highly of interest. One of the secondary sources for REEs is phosphogypsum (PG) that is a by-product generated by phosphoric acid production. This research builds upon our previous studies investigating the hydrometallurgical recovery of REEs from PG. Here, we investigate the effect of microwaving the PG sample before leaching in acid. Microwave radiation results in the dielectric heating of water molecules in the PG crystals and vaporization, causing the formation of breaks and pores in these particles as the vapor escapes. The lixivant would then be able to penetrate and diffuse further into the PG particles, bringing more REEs into solution. Our results show that REEs leaching efficiency increases when microwave treatment is used.

Sustainable Processing of Phosphogypsum Waste Stream for the Recovery of Valuable Rare Earth Elements

Rare earth elements (REEs) are among the strategic materials that have revolutionized modern industry. These materials have unique properties, so they are essential to the production of many technologically advanced products that are dominating the world; thus the REEs demand is continuously rising. To address this challenge, finding new sources for them is highly of interest. Here, we identified a waste stream from phosphoric acid production plants, called phosphogypsum, which contains some amounts of REEs. We developed a novel hydrometallurgical process to recover REEs from phosphogypsum. We investigated several leaching agents at various conditions and identified the optimum leaching parameters. Not only can the developed process decrease the size and associated environmental risks with the existing phosphogypsum stacks, but also can slow down the need for additional stacks. In addition to waste valorization, this novel process provides a new source for REEs production, addressing the sustainability challenges associated with them.