An efficient production process that can selectively recover the critical element germanium (Ge) from dilute sources is necessary to address the criticality of Ge. In this study, functionalized polystyrenic beads with catechol (A-Cat), nitro-catechol (A-Cat-N), and pyrogallol (A-Py) were used in a fixed-bed column to recover Ge and the Ge selectivity in the presence of competing ions, the effect of flow rate and inlet concentration, breakthrough modeling, and regeneration and reuse were investigated. Additionally, the synthesized adsorbent A-Cat was compared with commercially available N-methylglucamine resin for recovering Ge from synthetic Zn refinery residues solution. All three adsorbents showed Ge adsorption (>25 mg/g) and good desorption in single-element solution. The adsorbents were selective for Ge(IV) in a multiple-element solution containing 15 elements, and concentrated Ge solution was obtained with A-Cat after elution. The Modified Dose-Response model best explained the breakthrough curve compared to the Thomas and Yoon-Nelson model. Lower flow rates and higher inflow concentration both resulted in higher Thomas adsorption capacity (30 mg/g at 9 bed volumes per hour (BVH) and 62.8 mg/g at 80 mg/L C-o). The adsorbent A-Cat showed great regeneration while retaining >70 % capacity at the end of 5 adsorption-desorption cycles. A-Cat was also selective for Ge in synthetic Zn refinery residue solution containing 10 times Fe and 20 times Cu and Zn. Commercial N-methylglucamine resin showed low selectivity for Ge and reached saturation at very low bed volumes (BV) (<10BV). The current work shows that the A-Cat can be used for industrial applications to recover Ge selectively. A Linear Free Energy Relationship (LFER) was used to estimate log K-ML,K- followed by aqueous complexation modeling. The modeling showed the Ge(IV) selectivity but underestimated the extent of ion complexations, indicating that the apparent stability constants for grafted ligands are higher than solution log K-ML.

A new book explores how more sustainable methods are being applied to the recovery, processing, and purification of rare earths used in everyday technologies.

Platinum group metals (PGM) are a group of elements comprised of platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), osmium (Os), and rhodium (Rh) that are critical for use a wide variety of industries, and their demand will continue to increase with adoption of green energy technologies. This review will describe PGM found in ore and the use of PGM in catalysts, electronics, and fuel cells along with leaching solutions and conditions used for recovery of PGM from both primary and secondary sources. Adsorption has been identified as a promising technology for separating PGM from other base and noble metals from leaching solution due to the physical robustness, high selectivity, and easy tunability of adsorbents. Ligand families, solid supports, capacity, selectivity against base and noble metals, and mechanisms of adsorption found in current literature are described.

The selective separation of palladium (Pd) over platinum (Pt) remains a challenge in metal recycling, because of their similar electronic configuration and chemical properties. This study explored their selective separation using three new adsorbents by grafting sulfur-donor ligands onto cellulose, namely 2-aminothiophenol (Cell-AP), 2-mercaptopyridine (Cell-MP), and 2-mercaptobenzothiazole (Cell-MBT). These adsorbents exhibited excellent adsorption capacity for Pd(II), reaching 163.3 +/- 2.5 mg/g (at pH 1), 92.5 +/- 1.2 mg/g (at pH 1), and 27.5 +/- 0.5 mg/g (at pH 2.5), respectively. Isotherm studies showed that the adsorption process followed Freundlich isotherm, indicating a multilayer adsorption that takes place on a heterogenous surface. Kinetic results fit best with pseudo-second-order and intra-particle diffusion model, suggesting that the rate-limiting process involves chemisorption and intra-particle diffusion. Thermodynamic studies showed that adsorption by Cell-AP and CellMP was a spontaneous exothermic reaction. The materials also showed superior selectivity of Pd(II) over Pt(IV) with a maximum separation factor (SFPd/Pt) of 64.50, which improves over most previous studies. The mechanism of selectivity was further investigated by & Oslash;S, FTIR, SEM and DFT calculations, which showed that PdCl42has smaller size, shorter HOMO-LUMO gap, and lower binding energy to ligands as compared to PtCl62-. This was used to explain the higher affinity for Pd(II) over Pt(IV) of these sulfur-modified adsorbents. This work provides a practical approach for the selective separation of Pd over competing ions that could improve the efficiency for overall metal recovery or recycling processes.

Germanium (Ge) is one of the critical elements that lack an efficient economic recovery process from dilute sources. An improved catechol-based adsorbent, catechol-functionalized chitosan (C-Cat), was synthesized to recover germanium (Ge) from dilute acidic solutions. The adsorbent was also compared with an N-methylglucamine-based commercial adsorbent (Purolite S108) for optimum pH conditions, ion selectivity, adsorption isotherm, adsorption kinetics, and regeneration ability. The newly synthesized C-Cat exhibited higher selectivity against various competing ions than the commercial one (their respective Langmuir capacity was 22.72 and 79.66 mg/g at pH 3) and was more selective for Ge than other adsorbents reported in the literature. Linear free-energy relationships between the distribution coefficients and the metal hydrolysis constants were developed for both C-Cat and S108 at pH 3 and can be used for preliminary prediction of the selectivity of the adsorbents. Adsorptions data followed Langmuir isotherm for both adsorbents, and the kinetics data were well-fitted with pseudo-second-order kinetics. The C-Cat was proven to be completely reusable for multiple cycles after initial re-equilibration.

librium adsorption capacity (q e ) (eq. 1a), maximum adsorption capacity calculated using Langmuir isotherm (q m ) (eq. 1e), % adsorption (eq.1b), solid-liquid distribution (partitioning) coefficient (K d ) (eq. 1c), and selectivity factor (SF) between element A and B (eq. 1d) in case of competitive adsorption or adsorption from a multi-element solution.These parameters are defined as follows:

In the current study, catecholCatechol functionalized chitosanChitosan, C-Cat, was investigated for selective solid-phase extractionSolid-Phase Extraction of germaniumGermanium. GermaniumGermanium is one of the critical elementsCritical element because of its growing demand, supply risk, and inefficient production. The current Ge production processes, such as chlorination-distillation and solvent extractionExtraction, suffer from high energy requirements, high chemical consumptions, impurities co-extractionsExtraction, and waste stream generations. The adsorbent was synthesized via Schiff's base reaction. The adsorbent morphology was different from the chitosanChitosan due to surface modification. C-Cat adsorbed Ge selectively in the presence of competitive ions with Kd values of 10,832.0 mL/g at pH 3 and 7417.6 mL/g at pH 4. The selectivity for Ge was also observed in Ge-spiked coal fly ash leachate. The distribution coefficients were correlated with metalMetal hydrolysis constants, and linear free-energy relationships were developed for C-Cat. These LFERs can be used to predict the selectivity of C-Cat using the metalMetal hydrolysis constants.

Ion-exchange has been extensively explored for the adsorption, separation, and recovery of metal ions. The use of eco-friendly, low-cost, selective, and reusable resins are important for the development of separation technologies for critical elements. Herein, novel chelating adsorbents were synthesized and studied for the selective extraction, separation, and recovery of gallium (Ga) from acidic solutions. Four chelating adsorbents were prepared using 3,4 dihydroxybenzoic acid, and 3,4,5-trihydroxybenzoic acid to functionalize pre-aminated polymeric resins through amide linkage. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis confirmed the functionalization of the resins and revealed that their surface morphology was significantly improved after the chemical modification. Their adsorption performance was investigated, and maximum Ga-adsorption capacity was found at pH 3. Equilibrium Ga-adsorption isotherms were better demonstrated by the Langmuir isotherm model, and adsorption kinetics were better explained by Pseudo-second order model. The proposed new adsorbents were 10-4800 times more selective for Ga than Zn, Al, Cd, Sb, Fe, As and Mn in acidic conditions. Moreover, high Ga selectivity (SelGa/M >1.5) was accomplished in the binary solution of Ga:Zn and Ga:As in 1:10, 1:50 and 1:100 metal ratios, which suggests that adsorbents can separate Ga from Zn and As solution effectively. Desorption preliminary experiments showed > 60% desorption of Ga over 4 adsorption/desorption cycles. The adsorption mechanism was confirmed by XPS and FTIR studies. This study indicates that the synthesized adsorbents could be used for industrial applications, due to their low-cost, abundant raw materials, mature synthetic routes, and lower environmental impact.

The critical element germanium lacks efficient and economical recovery process to recover it from dilute sources such as coal fly ash. In the current study, a novel microwave-based synthesis method was used to functionalize polystyrenic bead with catechol (A-Cat), nitro-catechol (A-Cat-N), and pyrogallol (A-Py). The adsorbents were used to selectively adsorb Ge from dilute acidic solutions and were investigated for pH dependency, adsorption isotherm, adsorption kinetics, Ge selectivity, and regeneration of adsorbent. The functionalization was confirmed with FTIR, and the grafting yields of 50 %, 41.7 %, and 62 % were achieved for catechol, nitro-catechol, and pyrogallol functionalization, respectively. The Ge adsorption followed Langmuir isotherm with Langmuir adsorption capacities of 29.76 mg/g, 39.14 mg/g, and 37.13 mg/g, for A-Cat, A-Cat-N, and A-Py, respectively, at pH 3. The adsorbents were highly selective for Ge against other elements at pH 1-3, showing no adsorption for many competitive ions at pH 1-2. The A-Cat was more selective than A-Cat-N and A-Py. The adsorbents followed pseudo-second-order kinetics. The adsorbents were reusable for multiple cycles; however, A-Cat-N and A-Py lost capacity due to incomplete desorption in the first cycle. The adsorption mechanism was surface complexation of germnaium with catechol ligand resulting in high selectivity. Linear free energy relationship was used to correlate the apparent adsorption equilibrium with metal hydrolysis constants, and these LFERs can be used to predict the relative selectivity of different cations on A-Cat, A-Cat-N, and A-Py.

The selective extraction, separation, and recovery of gallium (Ga), one of the critical elements, is essential due to its role in clean energy technologies and its low reserves. Herein, different catechol derivatives (Pn)-function-alized cellulose substrates were developed using 3,4 dihydroxybenzoic acid (P1), 3,4,5-trihydroxybenzoic acid (P2), and 3,4-dihydroxyhydrocinnamic acid (P3) through esterification reaction and used for selective extraction of gallium from dilute acidic solutions. Adsorption experiments at pH 3 displayed a maximum Ga adsorption capacity of 31.50, 14.22, and 29.50 mg g  1 for P1, P2, and P3, respectively. Langmuir isotherm was illustrated as the best-fitting model to explain the equilibrium adsorption. Kinetic data were best fitted with pseudo-second order and intraparticle diffusion model, indicating that the adsorption process involves chemisorption as well as intraparticle diffusion. The newly synthesized adsorbents P1 and P3 are 10-300 times more selective for Ga than As, Fe, Al, Cd, and Ge from the mixed solution (pH 3.0) of 1:1 metal ratio. Moreover, high selectivity for gallium was achieved from binary solutions of Ga:Zn, Ga:Ge, and Ga:As in 1:10 (SelGa/M > 5), 1:50 (SelGa/M > 2), and 1:100 (SelGa/M > 2) metal ratio, suggesting that the adsorbent can separate Ga (III) from Zn (II), Ge (IV), and As (III) at the optimal conditions. The adsorbents (P1-P3) were characterized with various spectroscopic and microscopic techniques showing that the surface morphology of cellulose was greatly changed after function-alization. The Fourier-transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis demonstrated that the adsorption of Ga onto the developed ad-sorbers was attributed to chelation between hydroxyl groups of catechol and gallium ions. This study shows the synthesis of low-cost, sustainable adsorbents for the selective recovery of gallium in dilute acidic solutions.

Biocides are applied as chemical additives in hydraulic fracturing fluids to control subsurface microbial activity. When biocides are released into the subsurface, their fate is controlled by sorption to solids and heterogeneous electron transfer (redox) reactions at the mineral–fluid interface. The ability to predict whether produced water may contain unreacted biocides, or biocide–mineral transformation products, is relevant for defining optimal produced water treatment and beneficial use approaches. This article reviews major minerals that may impact biocide sorption and reactivity in the Marcellus Shale, with a specific focus on biocide–mineral interactions. The chemical and physical properties of quartz, illite, chlorite, pyrite, calcite and dolomite are presented and their reactions with organic compounds structurally similar to biocides are identified. Oxygen-containing functional groups are common among organic biocides, where the carbonyl (–C=O) substructure is integrated into many biocides. Cationic surfactant biocides are expected to sorb to every mineral. Clays, because of their negative surface charge and comparatively high surface area, make excellent sorbents of positively charged biocides. Sorption to organic matter is expected to be limited due to the very polar groups found in biocides. Pyrite is most likely to cause transformation of biocides due to its ability to reduce halogenated organic compounds and initiate Fenton-like reactions, which generate non-specific hydroxyl radicals that react with biocides. Carbonate minerals may act as potential chemisorption sites for biocides possessing a carbonyl group adjacent to another electronegative group. However, the rapid dissolution of this mineral limits its persistence at the mineral–fluid interface. These potential sorption versus transformation reactions can be applied to predict biocide fate in unconventional oil and gas reservoirs and, where appropriate, other subsurface reservoirs used for energy resource extraction or storage.

Rare earth elements (REE) are a group of valuable metals with growing demand and broad applications. Mineral ores, the traditional sources of REE, require significant capital investment and their refinement has been a source of environmental contamination. Industrial fluids and natural REE-bearing liquids are potential alternative sources for these metals. This work investigated the performance and REE selectivity of polymer resin beads functionalized with N,N-bis(phosponomethyl)glycine (BPG) for extraction of REE from saline solutions in fixed-bed adsorption columns. Competitive batch adsorption experiments were conducted with various metals (Nd, Gd, Ho, Al, Fe, Co, Ni, Ba, Pb, Th, and U) and the BPG-functionalized resins were up to 137 times more selective for REE than aminated resins. In column experiments, the BPG-functionalized resins preferentially adsorbed heavier metals and REE were strongly retained in the functionalized column, taking 270 times longer than the amine column to reach 10% breakthrough and 128 times longer to reach 50% breakthrough. REE bound to the BPG-functionalized resins were recovered with a dilute HNO3 solution, yielding REE concentrations up to 236 times higher than the influent feedstock. This work provides new insight into the operational performance of novel functionalized adsorbents for recovery of REE from saline fluids.

•Efficient and economic production process can mitigate criticality of germanium.•US germanium resources remain unused due to inefficiency in production.•Production processes including leaching, precipitation, and separation are reviewed.•Separation includes precipitation, solvent-extraction, ion-exchange, and adsorption.•Ge chemistry differs from other cations as it remains as neutral species in acidic pH.

Hydraulic fracturing and horizontal drilling in the Marcellus Shale present a novel use of chemical additives at unprecedented volumes. Reuse of produced water has become a popular option in Pennsylvania, complicating our understanding of the fate of chemical additives due to the variability of produced water chemistry. This study investigates the effect of pH, temperature, ionic strength and the presence of pyrite on the kinetics of degradation of dazomet, a commonly-used biocide, under a range of conditions expected during hydraulic fracturing. The results show that the degradation rate of dazomet is highly dependent on many of the variables tested. The hydrolysis is base-catalyzed over the pH range of interest which results in half-lives decreasing from 8.5 h to 3.4 h as the pH is increased from 4.1 to 8.2. Dissolved Fe-II ions catalyze dazomet degradation kinetics with solutions of 0.8 mM Fe-II causing degradation rates to increase by 190% over iron-free water. Increasing temperatures from 34 degrees C to 57 degrees C quadrupled hydrolysis rates (estimated activation energy of 60 kJ/mol). Reaction with oxygen-exposed pyrite surface led to accelerated degradation of dazomet, but unoxidized pyrite had no effect on the degradation rate of dazomet. The key hydrolysis products of dazomet degradation are formaldehyde and methyl isothiocyanate which are shown to be significantly more toxic than the parent compound. The study points to the need to assess the specific environmental conditions and any toxic by-products in conducting risk assessments for geological applications.

Conventional ion exchange resins are widely utilized to remove metals from aqueous solutions, but their limited selectivity precludes dilute ion extraction. This research investigated the adsorption performance of ligand-functionalized resins towards rare earth elements (REE). Functionalized resin particles were synthesized by grafting different ligands (diethylenetriaminepentaacetic dianhydride (DTPADA), phosphonoacetic acid (PAA), or N,N-bis(phosphonomethyl)glycine (BPG)) onto pre-aminated polymeric adsorbents (diameter 0.6 mm). Lanthanide uptake trends were evaluated for the functionalized resins using batch adsorption experiments with a mixture of three REEs (Nd, Gd, and Ho at 0.1-1000 mg/L each). Resin physical-chemical properties were determined by measuring their surface area, ligand concentrations, and acidity constants. The aminated supports contained 4.0 mmol/g primary amines, and ligand densities for the functionalized resins were 0.33 mmol/g (PAA), 0.22 mmol/g (BPG), and 0.42 mmol/g (DTPADA). Kinetic studies revealed that the functionalized resins followed pseudo-second order binding kinetics with rates limited by intraparticle diffusion. Capacity estimates for total REE adsorption based on Langmuir q(max) were 0.12 mg/g (amine; approximate to 0.77 umol/g), 5.0 mg/g (PAA; approximate to 32.16 mol/g), 3.0 mg/g (BPG; approximate to 19.30 mu mol/g), and 2.9 mg/g (DTPADA; approximate to 18.65 mu ol/g). Attaching ligands to the aminated resins greatly improved their REE binding strength and adsorption efficiency. (C) 2019 Elsevier Inc. All rights reserved.

Silica adsorbents were grafted with REE-selective ligands and their lanthanide binding ability was evaluated in the presence of multiple competing ions.