Selective Recovery of Rare Earth Elements from a Wide Range of E-Waste and Process Scalability of Membrane Solvent Extraction.

In this study, the scalability of the supported membrane solvent extraction (MSX) process for the recovery of rare earth elements (REEs) from scrap permanent magnets was demonstrated by processing larger quantities of different scrap magnet feedstocks with a membrane area of more than 1 m2. The MSX process was successfully employed to recover high-purity REEs in their oxide form (REOs) from a wide range of end-of-life magnet feedstocks including hard disk drives (HDDs), MRI, cell phone, bonded, swarf, and hybrid car magnets. REEs with the purity of more than 99.5 wt %, recovery of more than 95%, and an extraction rate of as high as 9.3 g/(h m2) were recovered from feed solutions containing REEs of up to 46 000 mg/L. It was found that the extraction rate strongly depends on the initial REE concentration in the feed solution and to some extent on the composition of the scrap magnet source. The results demonstrated that MSX is a scalable and versatile process for the recovery of REEs from a wide range of electronic wastes.

Pore orientation effects on the kinetics of mesostructure loss in surfactant templated titania thin films.

The mesostructure loss kinetics are measured as a function of the orientation of micelles in 2D hexagonal close packed (HCP) columnar mesostructured titania thin films using in situ grazing incidence small angle X-ray scattering (GISAXS). Complementary supporting information is provided by ex situ scanning electron microscopy. Pluronic surfactant P123 acts as the template to synthesize HCP structured titania thin films. When the glass substrates are modified with crosslinked P123, the micelles of the HCP mesophase align orthogonal to the films, whereas a mix of parallel and orthogonal alignment is found on unmodified glass. The rate of mesostructure loss of orthogonally oriented (o-HCP) thin films (∼60 nm thickness) prepared on modified substrate is consistently found to be less by a factor of 2.5 ± 0.35 than that measured for mixed orientation HCP films on unmodified substrates. The activation energy for mesostructure loss is only slightly greater for films on modified glass (155 ± 25 kJ mol(-1)) than on unmodified (128 kJ mol(-1)), which implies that the rate difference stems from a greater activation entropy for mesostructure loss in o-HCP titania films. Nearly perfect orthogonal orientation of micelles on modified surfaces contributes to the lower rate of mesostructure loss by supporting the anisotropic stresses that develop within the films during annealing due to continuous curing, sintering and crystallization into the anatase phase during high temperature calcination (>450 °C). Because the film thickness dictates the propagation of orientation throughout the films and the degree of confinement, thicker (∼250 nm) films cast onto P123-modified substrates have a much lower activation energy for mesostructure loss (89 ± 27 kJ mol(-1)) due to the mix of orientations found in the films. Thus, this kinetic study shows that thin P123-templated o-HCP titania films are not only better able to achieve good orthogonal alignment of the mesophase relative to thicker films or films on unmodified substrates, but that alignment of the mesophase in the films stabilizes the mesophase against thermally-induced mesostructure loss.

Quantum Chemical Simulations of CO2 and N2 Capture in Reline, a Prototypical Deep Eutectic Solvent.

Deep eutectic solvents such as reline are an emerging class of low-cost, environmentally friendly solvents with tunable properties that are potentially applicable for the capture and separation of CO2. Experimental measurements showed that a reline-based membrane contactor can capture and separate CO2 via physisorption through a dissolution process with 96.7% purity from a mixed gas containing CO2 and N2 (50:50% molar ratio). We examine the nature of the interaction of CO2 and N2 with reline employing quantum chemical methods. We focus on explaining the mechanism by which CO2 and N2 bind to reline and the reason for the high selectivity for absorption of CO2 compared to N2. We analyze the dynamics, energetics, and binding motifs for CO2 and N2 in reline employing density functional theory, density functional tight binding, and ab initio molecular dynamics. We also investigate the effect of reline on the vibrational spectra of CO2 and reline. Our simulations indicate that the selective capture of CO2 from the mixture of CO2 and N2 is due to the interplay between attractive electrostatic and charge polarization forces with opposing entropic effects, which shift the energetic balance and make the N2 absorption unfavorable in reline.

Separation of Lithium from Aluminum-Containing Clay Mineral Leachate Solution Using Energy-Efficient Membrane Solvent Extraction.

This study investigated a novel membrane solvent extraction (MSX) process for the recovery and separation of lithium (Li) from clay minerals using a cation exchange organic extractant [di-(2-ethylhexyl)phosphoric acid] (DEHPA). The Li is selectively extracted from clay mineral leachate solution using highly efficient aluminum hydroxide sorbents to form lithium aluminum double hydroxide sulfate (LDH sulfate) as the precipitate. Several delithiation methods have been explored to separate Li from aluminum (Al). LDH sulfate is dissolved in dilute H2SO4 and used as the feed solution, and DEHPA is used to selectively separate Li and Al from the feed solution. The MSX process immobilizes DEHPA in the microporous membrane pores and continuously removes Al from the feed solution to obtain pure Li. The efficiency of DEHPA for the selective separation of Li from Al is determined by measuring its distribution coefficient. This study used the optimum feed solution pH of 3, strip solution concentration of 2 mol/L H2SO4, and an organic phase composition of 30% v/v DEHPA in Isopar-L. The MSX process achieved a Li yield of about 92% and a purity of ⩾ 94%. The results suggest that the innovative MSX technology is a time- and energy-efficient approach for the recovery and separation of high-purity Li for application in Li-ion batteries and other clean energy technologies.

Adsorption and Recovery of Polyphenolic Flavonoids Using TiO2-Functionalized Mesoporous Silica Nanoparticles.

Exploiting specific interactions with titania (TiO2) has been proposed for the separation and recovery of a broad range of biomolecules and natural products, including therapeutic polyphenolic flavonoids which are susceptible to degradation, such as quercetin. Functionalizing mesoporous silica with TiO2 has many potential advantages over bulk and mesoporous TiO2 as an adsorbent for natural products, including robust synthetic approaches leading to high surface area, and stable separation platforms. Here, TiO2-surface-functionalized mesoporous silica nanoparticles (MSNPs) are synthesized and characterized as a function of TiO2 content (up to 636 mg TiO2/g). The adsorption isotherms of two polyphenolic flavonoids, quercetin and rutin, were determined (0.05-10 mg/mL in ethanol), and a 100-fold increase in the adsorption capacity was observed relative to functionalized nonporous particles with similar TiO2 surface coverage. An optimum extent of functionalization (approximately 440 mg TiO2/g particles) is interpreted from characterization techniques including grazing incidence X-ray scattering (GIXS), high-resolution transmission electron microscopy (HRTEM), and nitrogen adsorption, which examined the interplay between the extent of TiO2 functionalization and the accessibility of the porous structures. The recovery of flavonoids is demonstrated using ligand displacement in ethanolic citric acid solution (20% w/v), in which greater than 90% recovery can be achieved in a multistep extraction process. The radical scavenging activity (RSA) of the recovered and particle-bound quercetin as measured by a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay demonstrates greater than 80% retention of antioxidant activity by both particle-bound and recovered quercetin. These mesoporous titanosilicate materials can serve as a synthetic platform to isolate, recover, and potentially deliver degradation-sensitive natural products to biological systems.