Crystallization of nickel sulfate and its purification process: towards efficient production of nickel-rich cathode materials for lithium-ion batteries.

NiSO4·6H2O is an important salt for the battery-making industry. The extraction of nickel sulfate relies on the hydrometallurgical processing of nickel ores as well as the recycling of nickel-containing products. The last step in hydrometallurgical processing is the crystallization of nickel sulfate. Because of the similar ionic radius and ionic charge between nickel and magnesium ions, magnesium undergoes isomorphous substitution and replaces nickel ions in the crystal lattice structure of NiSO4·6H2O. This poses a challenge as achieving the desired metal salt purity is difficult, resulting in an inferior cathode material for nickel-containing batteries. In this work, the removal of magnesium during the purification process of NiSO4·6H2O crystals via a repulping process was thoroughly investigated. Moreover, the impurity uptake mechanisms of magnesium into NiSO4·6H2O crystals were investigated. The results indicated that repulping NiSO4·6H2O crystals with a saturated NiSO4 solution results in 77% removal of magnesium. Using a second-stage repulping process is less effective with only 26% magnesium removal. The purification efficiency of the two repulping stages was quantified by the equilibrium distribution coefficient, which corroborates the trend of decreased removal of magnesium in the second stage of repulping compared with the first stage. The primary impurity uptake mechanisms of magnesium into NiSO4·6H2O crystals were identified to be surface adsorption and lattice substitution (isomorphous substitution).

Investigating Metal-Tributyl Phosphate Complexes during Supercritical Fluid Extraction of the NdFeB Magnet Using Density Functional Theory and X-ray Absorption Spectroscopy.

Supercritical fluid extraction (SCFE) is gaining significant interest as a green technology for the recycling of end-of-life waste electrical and electronic equipment (WEEE). Neodymium iron boron (NdFeB) magnets, which contain large quantities of critical rare-earth elements such as neodymium, praseodymium, and dysprosium, are widely used in wind turbines and electric/hybrid vehicles. Hence, they are considered a promising secondary resource for these elements when they reach their end-of-life. Previously, the SCFE process was developed for recycling WEEE, including NdFeB; however, the process mechanism remains unexplored. Here, density functional theory, followed by extended X-ray absorption fine structure and X-ray absorption near-edge structure analyses, are utilized to determine the structural coordination and interatomic interactions of complexes formed during the SCFE of the NdFeB magnet. The results indicate that Fe(II), Fe(III), and Nd(III) form Fe(NO3)2(TBP)2, Fe(NO3)3(TBP)2, and Nd(NO3)3(TBP)3 complexes, respectively. This theory-guided investigation elucidates the complexation chemistry and mechanism during the SCFE process by rigorously determining the structural models.

A rechargeable Mg|O2 battery.

Rechargeable Mg|O2 batteries (RMOBs) offer several advantages over alkali metal-based battery systems owing to Mg's ease of transport/storage in ambient environment, low cost originating from its high abundance, as well as the high theoretical specific energy of RMOBs. However, research on RMOBs has been stagnant for the past decade, largely owing to unacceptably poor electrochemical performance. Here, we present a RMOB that employs Mg anode, Mg((CF3SO2)2N)2-MgCl2 in diglyme (G2) electrolyte, and commercial Pt/C on carbon fiber paper (Pt/C@CFP) oxygen cathode. This battery demonstrates unparalleled improvement over existing RMOBs by rendering a discharge capacity over 1.6 mAh cm-2, achieving cycle lives up to 35 cycles with a cumulative energy density of ∼3.2 mWh cm-2 at room temperature. This RMOB system seeks to reignite the pursuit of novel electrochemical systems based on Mg-O2 chemistries.

Urban mining of terbium, europium, and yttrium from real fluorescent lamp waste using supercritical fluid extraction: Process development and mechanistic investigation.

There is a significant global push towards recycling of waste electrical and electronic equipment (WEEE) to enable the circular economy. In this study an environmentally sustainable process using supercritical carbon dioxide as the solvent, along with a small volume of tributyl-phosphate-nitric acid (TBP-HNO3) adduct as the chelating agent, is developed to extract rare earth elements (REEs) from fluorescent lamp waste. It is found that mechanical activation using oscillation milling improves extraction efficiency. To elucidate the process mechanism, an in-depth characterization of solids before and after the process using transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy (XPS)is performed. Furthermore, UV visible spectroscopy is performed to determine the coordination chemistry of the rare earths of interest, i.e., yttrium, europium, and terbium during the complexation with TBP-HNO3 adduct. It is found that Al3+ and Ca2+ cations from the aluminium oxide (Al2O3) and hydroxyapatite (Ca5(PO4)3OH) present in the fluorescent lamp waste compete with REEs in reacting with TBP-HNO3 adduct; hence, REE extractions from real fluorescent lamp waste is less than previously reported extractions from synthetic feeds. Not only can management of fluorescent lamp waste help conserve natural resources and protect ecosystems, but it can also facilitate efficient utilization of materials and promote the circular economy.

Electrorefining for direct decarburization of molten iron.

Recycling iron and steel is critical for environmental sustainability and essential to close material loops in circular economics. A major challenge is to produce high-value products and to control impurities like carbon in the face of stringent consumer requirements and volatile markets. Here, we develop an electrorefining process that directly decarburizes molten iron by imposing an electromotive force between it and a slag electrolyte. Upon anodic polarization, oxide anions from the slag discharge directly on carbon dissolved in molten iron, evolving gaseous carbon monoxide. In a striking departure from conventional practice that highly relies on reaction with solubilized oxygen, here electrorefining achieves decarburization by direct interfacial reaction. We demonstrate that this technique produces ultra-low-carbon steels and recovers silicon as a by-product at the cathode, requiring a low energy input and no reagents. We expect this process to be scalable and integrable with secondary steel mills.

Quantification of nickel, cobalt, and manganese concentration using ultraviolet-visible spectroscopy.

Ultraviolet-visible spectroscopy is one of the most effective, inexpensive, flexible, and simplest analytical techniques to measure species concentration in the liquid phase. It has a wide range of applications such as wastewater treatment, dye degradation, colloidal nanoparticle characterization. It is used in almost every spectroscopy laboratory for routine analysis or research. In the present study, a feasibility study was carried out to find the application of UV-Vis spectroscopy for onsite measurement of nickel, cobalt, manganese, and lithium as a replacement for the conventional method to measure the concentrations of these elements in battery and other applicable industries. Samples with different concentrations of individual elements and composites were prepared and analyzed using an ultraviolet-visible spectrometer. Based on the obtained results, mathematical relationships between concentration and absorbance were defined. The calculated concentration of different elements using the developed relationships was compared with the measured concentration using ICP-OES to find any deviation between the two. The effect of various parameters such as concentration, path length, number of elements in the solution, density, and pH was analyzed to verify the feasibility. The obtained results show that this technique can be effectively used to measure the concentration of nickel and cobalt with high accuracy.

Scale-Phobic Surfaces Made of Rare Earth Oxide Ceramics.

Scaling or precipitation fouling involves crystallization of hard and chalky solid salts from a solution. Scaling results in significant production and energy losses and is a major concern in many industries. Here we investigate the scale-phobicity of rare earth oxide (REO) ceramics (particularly CeO2, Gd2O3, and Er2O3) in comparison with glass and stain-less steel. We quantify the surface energy and its polar and apolar components for these materials using the Van Oss-Chaudhury-Good approach and show a direct correlation between surface energy and scale deposition. We also show that the polar component of surface energy is the main contributor to scale deposition; hence, REOs with minimal polar component represent high barrier to scale deposition. Moreover, we study the weight gain due to calcium sulfate dihydrate (gypsum) scale accumulation on these materials and show 55% and 77% reduction on REOs in comparison with bare glass and stainless-steel, respectively. We also evaluate the adhesion forces between salt and test materials using atomic force microscopy with a gypsum microparticle adhered onto a tipless cantilever. We show adhesion force between salt particles and REO surfaces is about half that of bare glass and stainless-steel because of the lower surface energy and polar component. We expect REO ceramics would find widespread applicability as robust scale-phobic surfaces in various industries.

Recovery and separation of phosphorus as dicalcium phosphate dihydrate for fertilizer and livestock feed additive production from a low-grade phosphate ore.

With the rapid increase in the world population, the global demand for food production has been increasing steeply. This increase has resulted in an increased demand for phosphorus crop fertilizers and livestock feed additives. Considering recent predictions that the global reserves of high-grade phosphorus resources would deplete within 15 years, new initiatives have begun to utilize low-grade resources to ensure sustainable supply of this essential nutrient. The main challenge with the use of low-grade resources is the difficulty with the efficient and economical separation of phosphorus from the other constituent elements, such as iron, aluminum, and magnesium. Most previous studies on the adoption of low-grade phosphate ores have focussed on ore beneficiation processes which are expensive, complex, and in some cases inefficient. In this study, we develop an integrated process for the direct recovery and separation of dicalcium phosphate dihydrate for fertilizer and livestock feed additive production from a low-grade (2.0 wt% P) iron-rich (19.7 wt% Fe) phosphate ore. The process combines leaching using dilute sulfuric acid (0.29 M) and selective precipitation using calcium oxide. During selective precipitation, ethylenediaminetetraacetic acid (EDTA) is used as a stabilizing agent to prevent iron and phosphorus co-precipitation. This process can be operated as a closed loop, allowing the recovery and recycling of both water and EDTA, while eliminating the production of liquid waste. The developed process achieves around 70% phosphorus recovery as an industrial-grade (19 wt% P) dicalcium phosphate dihydrate product with minimal iron, magnesium, and aluminum contamination, while also producing value-added calcium sulfate dihydrate (gypsum) and iron/magnesium byproducts. This process enables economical and sustainable recovery of phosphorus from low-grade ores, which can address the rising global demand for food production.

Recovery of scandium and neodymium from blast furnace slag using acid baking-water leaching.

The current study puts the emphasis on developing a pyro-hydrometallurgical process, called acid baking-water leaching, to recover scandium and neodymium from blast furnace slag produced by the ironmaking industry. In this process, the feed is mixed with concentrated sulfuric acid, digested at 200-400 °C, and leached in water at ambient conditions. This process offers several advantages including less acidic waste generation and rapid kinetics. With fundamental investigations into the digestion mechanism, acid to slag mass ratio and baking temperature are determined to have the most significant positive and negative impacts, respectively. At low acid to slag ratio, the silicate bearing phases in the feed do not digest, resulting in low extraction. At 200 °C baking temperature, a hydrated aluminum sulfate ((Al(H2O)6)2(SO4)3(H2O)4.4) phase with weak hydrogen bonds is formed that leaches in water rapidly (<10 min); while at 400 °C, Al2(SO4)3 with strong ionic bonds is formed that leaches at slower kinetics (>4 h). Fundamental investigations into the water leaching process indicate that the diffusion of water through the firm solid product (ash layer) is the rate determining step. We expect the results of this study would help enable valorization of industrial byproducts, in particular ironmaking slag.

ZSM-5 decrystallization and dealumination in hot liquid water.

Zeolites have recently attracted attention for upgrading renewable resources in the presence of liquid water phases; however, the stability of zeolites in the presence of liquid-phase water is not completely understood. Accordingly, the stability of the ZSM-5 framework and its acid sites was studied in the presence of water at temperatures ranging from 250 to 450 °C and at pressures sufficient to maintain a liquid or liquid-like state (25 MPa). Treated samples were analyzed for framework degradation and Al content and coordination using a variety of complementary techniques, including X-ray diffraction, electron microscopy, N2 sorption, 27Al and 29Si NMR spectroscopy, and several different types of infrared spectroscopy. These analyses indicate that the ZSM-5 framework retains >80% crystallinity at all conditions, and that 300-400 °C are the most aggressive. Decrystallization appears to initiate primarily at crystal surfaces and share many characteristics in common with alkali promoted desilication. Liquid water treatment promotes ZSM-5 dealumination, following a mechanism analogous to that observed under steaming conditions: initiation by Al-O hydrolysis, Al migration to the surface, and finally deposition as extra framework Al or possibly complete dissolution under some conditions. As with the framework, dealumination is most aggressive at 300-400 °C. Several models were evaluated to capture the non-Arrhenius effect of temperature on decrystallization and dealumination, the most successful of which included temperature dependent values of the water auto-ionization constant. These results can help interpretation of previous studies on ZSM-5 catalysis in hot liquid water and suggest future approaches to extend catalyst lifetime.

Supercritical fluid extraction for purification of waxes derived from polyethylene and polypropylene plastics.

Polyethylene (PE) and polypropylene (PP) feedstock contain various additives, such as fillers and colorants, which either degrade or carry through the depolymerization process; thereby causing intense dark colors and a pungent petroleum odor. The combination of color and odor imposes several challenges, limiting the potential markets of the wax products. This study put emphasis on the development of an innovative and environmentally sustainable process based on supercritical fluid extraction (SCFE) to remove organic and inorganic contaminants that cause color and odor in waxes derived from recycled polymers. In terms of organic impurity removal, for PE 81% and for PP 97% removal efficiency was achieved. The color of PE and PP in terms of lightness under CIELAB (lightness, green-red, blue-yellow) color space was improved by 13 and 40 units, respectively. The purified waxes could be utilized in a variety of market segments, including color masterbatch, roofing shingles, rubber, and coatings. Compared with traditional purification technologies based on solvent extraction and absorbent filters, SCFE process offers exceptional advantages, including fast reaction rates, little liquid waste, ease of separation of solutes, and fewer separation stages. This novel process enables producing high-value water white waxes from reclaimed polymeric feedstock with a focus on clean technologies and enhanced resource efficiency.

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

The current study put the emphasis on developing a novel and environmentally friendly waste valorization process, called "acid-baking water-leaching", to recover scandium from bauxite residue produced by the aluminum industry. In this process, bauxite residue is mixed with concentrated sulfuric acid, baked in a furnace at 200-400 °C, and leached in water at ambient conditions. Compared with direct acid leaching processes, the developed process offers the advantages of less acid consumption, less wastewater generation, and fast kinetics. With fundamental investigation into the reaction mechanism, acid baking temperature was shown to be the controlling factor that dictates the final phases of the process. Baking at 200 °C results in the formation of (H3O)Fe(SO4)2 that leaches in water rapidly (<5 min), but extraction efficiency is low (58% scandium). In contrast, baking at 400 °C results in the formation of Fe2(SO4)3 that leaches at slower kinetics (>45 min), but results in higher extraction efficiency (80% scandium). The acid baking water leaching process proves to be a promising technique as the first step of a potential near-zero-waste integrated process for the sustainable valorization of bauxite residue to help build the circular economy.

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.

Superhydrophobic Ceramic Coatings by Solution Precursor Plasma Spray.

This work presents a novel coating technique to manufacture ceramic superhydrophobic coatings rapidly and economically. A rare earth oxide (REO) was selected as the coating material due to its hydrophobic nature, chemical inertness, high temperature stability, and good mechanical properties, and deposited on stainless steel substrates by solution precursor plasma spray (SPPS). The effects of various spraying conditions including standoff distance, torch power, number of torch passes, types of solvent and plasma velocity were investigated. The as-sprayed coating demonstrated a hierarchically structured surface topography, which closely resembles superhydrophobic surfaces found in nature. The water contact angle on the SPPS superhydrophobic coating was up to 65% higher than on smooth REO surfaces.

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.