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[Display omitted] • Synthesis of Mg-Al-CO 3 LDH. • Effective and environmental desilication method. • Not Cr(VI)-containing compounds formation. • Synergistic effect between ion exchange of Si(IV) and zeolite formation. The Mg-Al-CO 3 LDH was synthesized as a desilication agent to effectively and environmentally remove Si(IV) from Na 2 CrO 4 -NaAlO 2 -NaVO 3 -Na 2 SiO 3 -H 2 O solutions. It was observed that the changes of reaction parameters including temperature, NaOH concentration, time, the dosage of Mg-Al-CO 3 LDH and NaAlO 2 concentration significantly affected the desilication efficiency, while the effect of Cr(Ⅵ) and V(Ⅴ) concentration on the desilication was negligible. The results showed that 91.5% Si(IV) could be removed after desilication at 90 °C for 6 h with the additive of 4 g/L Mg-Al-CO 3 LDH, without the formation of hazardous Cr(VI)-containing compounds. It could be concluded that the desilication mechanism was dominated by the synergistic effect between the ion exchange of Si(IV) and the formation of zeolite compounds. The method proposed in this study provides a new insight for Si(IV) removal from the highly concentrated Cr(VI) solutions in the chromate clean production. [ABSTRACT FROM AUTHOR]

The leach liquor of sodium-roasted vanadium slag in vanadium industry is an alkaline solution containing vanadium, sodium, chromium, and other impurities, and preparing high-purity vanadyl sulfate electrolyte (used in vanadium redox flow battery) directly from this solution is challenging but cost-effective. A novel process consisting of selective reduction–precipitation of chromium and solvent extraction of vanadium was proposed and optimized in this study. Approximately 90% of Cr(V I) in the solution was reduced to Cr(III) and precipitated after adding sodium sulfite at a pH of 5.77 and 25 °C, while V(V) remained in this process and needed a further reduction to V(IV) prior to extraction. More than 99.9% of V(IV) remained in the solution was extracted by two-stage extraction using the "P507 + TBP + kerosene" extractant system at a pH of 2.00 and an organic-to-aqueous phase ratio of 1.5:1. Sodium entrained in the organic phase was washed off through three-stage scrubbing. A high-purity vanadyl sulfate solution of 2.1 mol L−1 was prepared by two-stage stripping using 5.5 mol L−1 sulfuric acid. According to the slope analysis and infrared spectra, the extraction of V(IV) by P507 follow the cation exchange mechanism. This study provides a feasible way to remove chromium and recover vanadium in the form of vanadyl sulfate from the industrial leach liquor of sodium-roasted vanadium slag. • VOSO 4 solution was produced from leaching solution of sodium-roasted vanadium slag. • Chromium(VI) was removed by selective reduction–precipitation. • Vanadium was extracted by the "P507 + TBP + kerosene" extractant system. • Parameters of precipitation, extraction, scrubbing, and stripping were optimized. • Cation exchange mechanism was involved in the extraction of vanadium. [ABSTRACT FROM AUTHOR]

The mesoporous tobermorite with high removal efficiency of Pb2+ was hydrothermally synthesized from fly ash (FA). The physicochemical characteristics of the synthesized tobermorite were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller specific surface area analyzer, and Fourier transform infrared spectroscopy (FTIR). It was found that the specific surface area and pore volume of the mesoporous tobermorite were 29.98 m2/g and 0.1325 cm3/g, respectively, which were much higher than those of FA. The tobermorite showed high removal efficiency for Pb2+ of 99.93%, and the adsorption kinetic data for Pb2+ adsorption on tobermorite were better fitted with the pseudo-second-order model. Besides, the Langmuir isotherm model provided better description of the Pb2+ adsorption isotherm, and the maximum adsorption capacity for Pb2+ adsorption on tobermorite was 266.67 mg/g, which was much higher than that on FA (86.13 mg/g). What's more, the adsorption mechanisms of the tobermorite towards Pb2+ were analyzed by XRD, SEM-energy dispersive spectroscopy, and FTIR. It was found that the high adsorption capacity of the tobermorite towards Pb2+ was ascribed to its mesoporous structure, a mass of –OH, the ion-exchange of Ca2+ with Pb2+, and the precipitation of 2PbCO 3 ·Pb(OH) 2. This work presents the tobermorite synthesized from FA as an effective and low-cost adsorbent towards Pb2+, and provides a potential application method of FA in treatment of industrial wastewater containing Pb2+. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The kinetics of the forward extraction of TaF7 2− by MIBK from stock was investigated using a Lewis cell. Different parameters such as the tantalum concentration, fluoride ion concentration, hydrogen ion concentration, and MIBK concentration, as well as extracting temperature were studied separately to examine their effect on the extraction rate of TaF7 2−, and a rate equation was deduced based on the analysis. The experimental results demonstrate that the rate of TaF7 2− extraction is controlled by a chemical reaction at the interface rather than in the bulk phase. Further analysis suggests that the TaF7 2− extraction rate is first order with respect to MIBK concentration, hydrogen ion concentration, and tantalum concentration, and zero order with respect to fluoride ion concentration, respectively. The mechanism of TaF7 2− extraction is controlled by the slow distribution of the H·MIBK+ at the interface to form HTaF7·MIBK− (i) between the pulp phase and the interface. [Copyright &y& Elsevier]

Abstract: The decomposition of NaCaHSiO4 is an important step in the hydro-chemical process to recover sodium when treating red mud. In this study, the phase transformation during the NaCaHSiO4 decomposition and the key influential factors, including sodium concentration, reaction temperature, CaO addition and particle size were investigated. In addition, the sodium content in the residue, where NaCaHSiO4 had completely exhausted, was also studied. Finally, the kinetic data were fitted by the Avrami–Erofeev equation and the activation energy of the reaction was calculated. [Copyright &y& Elsevier]

Niobium consumption has burgeoned owing to the increasing application of niobium in critical industries, including the aerospace and oil and gas industries. Conventional metallurgical technologies and separation methods for niobium extraction use highly concentrated HF, which is hazardous to both humans and the environment. A solvent extraction system comprising trioctyl tertiary amine (N235) and 4-methyl-2-pentanone (MIBK) that can extract and separate niobium from an oxalate-containing H 2 SO 4 solution is proposed in this paper. Niobium solutions tend to contain titanium and iron impurities; therefore, the effects of various conditions on the separation of the three elements were investigated. The extraction mechanism and thermodynamics of the process were also examined. Over 82% niobium was extracted at an organic-to-aqueous phase ratio of 1:1 and the H+ concentration of 8.29 mol/L using an organic phase with 50 vol% N235 and 50 vol% MIBK as the extractants at 20 °C. Only 18.4% titanium and 3.35% iron were co-extracted. Two stripping processes, both of which further separated niobium and titanium, are also proposed herein. The possible composition of the niobium-containing extraction complex was [(R 3 NH)·NbO(C 2 O 4) 2 (H 2 O) 2 ], as supported by a Fourier transform infrared spectroscopy (FT-IR) analysis and ultraviolet–visible (UV–vis) spectrophotometry. The extraction mechanism was inferred to be the association of R 3 NH+ in N235 with the [NbO(C 2 O 4) 2 (H 2 O) 2 ]− from the acidic niobium-containing solution, and the stripping mechanism was concluded to be anion exchange. The enthalpy change (∆Ho) of the extraction system was −11.0 kJ/mol at 288.15–313.15 K, which indicated that niobium extraction from the H 2 SO 4 solution with oxalate using N235 and MIBK was an irreversible exothermic process. • The N235 and MIBK system enables niobium extraction in H 2 SO 4 liquor system containing oxalate. • The extraction system avoids the use of dangerous HF. • The method demonstrates excellent niobium extraction efficiency and selectivity. • The stripped organic phase is reusable and easily regenerated. [ABSTRACT FROM AUTHOR]

Titanium is a highly valued metal for its outstanding properties. Its production is costly due to its strong reactivity with oxygen, thus there are strong demands to reduce oxygen content in Ti scraps, turnings, chips, chunks, and powders for the purpose of recycling, reuse and high-quality powder production. This article reviews the current methods for reducing oxygen content (i.e. methods of deoxygenation) in Ti and its alloys, particularly metal in powder form, including Ca metal-based methods, Mg metal-based methods, electrochemical methods, and others based on remelting. Even though the details of the operations of each process vary, they share some of the same theoretical basis of relative chemical stabilities. Here we outline and evaluate these methods in terms of the fundamental principles, processing techniques, results and the pros and cons of each method. • The methods for reducing oxygen content in Ti and alloys is reviewed in this paper. • The establishment of various methods are all based on the relative thermodynamic stabilities. • The main approaches for deoxygenation include Ca metal-based, Mg metal-based, electrochemical and remelting-based methods. [ABSTRACT FROM AUTHOR]

An efficient method for recovering and separating Ce3+ and La3+ rare earth elements from spent fluid catalytic cracking (FCC) catalyst is described. Initially, the spent FCC catalyst was leached with 2 M HNO 3 at 80 °C then removal of iron from the leach solution was carried out by solvent extraction with 25% (v/v) diisooctyl phosphinic acid (DiOAP) in n -octane. Extraction of the above rare earths was then undertaken from the nitric acid leach solution using an organic phase consisting of 25% (v/v) di(2-ethylhexyl) phosphoric acid (D2EHPA) and 25% (v/v) tri- n -butyl phosphate (TBP) in n -octane. Both rare earths were stripped form the organic phase using H 2 SO 4. Separation of the Ce3+ from La3+ was then achieved by means of an in situ electrochemical oxidation coupled with a simultaneous solvent extraction process. In this, the Ce3+ was electrochemically oxidized to Ce4+ and removed from the aqueous phase by solvent extraction employing 100 mM D2EHPA in n -octane. This led to efficient separation of the above rare earths, giving rise to La3+ in high purity of up to 99.5% and Ce4+ up to 100%. The separation occurs via a single extraction step without the need for pH adjustment or for the use of additional reagents. Unlabelled Image • Development of an in situ electrolysis/extraction process for La/Ce separation. • Optimized separation of rare earths in a single extraction step. • Application of a process for rare earth recovery from spent FCC catalyst. • Recovery of La and Ce in very high purity (> 99.5%). [ABSTRACT FROM AUTHOR]

• A MoS 2 /rGO heterojunction is introduced to a graphite felt electrode. • The electrode utilizes both dissolved O 2 and gaseous O 2 in 2e− ORR. • The MoS 2 /rGO heterojunction is a nanoscale p-n junction. • Gaseous O 2 adsorbing onto sulfur vacancies is reduced by electrons from rGO. • OH generated by autocatalysis of HAFA promotes As(III) and Cr(III)oxidization. Accumulation of high-arsenic fly ash (HAFA) poses a serious environmental threat due to the toxicity of As and release of other heavy metals especially Cr. In this work, a novel graphite felt (GF) cathode modified with the nanoscale MoS 2 /reduced graphene oxide (rGO) heterojunction is prepared by blending with PTFE emulsion for efficient synergistic oxidative dissolution of As(III) and Cr(III) in HAFA. By taking advantage of the p-n junction characteristics of the heterojunction and appropriate hydrophobicity of the PTFE coating, the modified GF efficiently utilizes both dissolved O 2 and gaseous O 2 in the 2e− oxygen reduction reaction (ORR). Our theoretical assessment indicates that gaseous O 2 adsorbs stably on sulfur vacancies and is reduced by electrons transmitted from rGO. Experimentally, the modified GF shows superior ORR catalytic activity as exemplified by a high peak current density of 8.41 mA cm−2 and onset potential of 0.53 V vs. RHE. OH generated by the Cr and Fe-triggered autocatalysis mechanism promotes oxidization of As(III) and Cr(III) in detoxification of HAFA resulting in 96.1% As removal as well as 70.74% Cr removal in 135 min. The modified GF with excellent stability and durability has immense industrial prospect in detoxification of HAFA and treatment of other types of As-containing hazardous wastes. [ABSTRACT FROM AUTHOR]

Lithium supply risk is increasing and driving rapid progress in lithium recovery schemes from spent lithium-ion batteries (LIBs). In this study, a facile recycling process consisting mainly of reduction roasting and NaHCO 3 leaching was adopted to improve lithium recovery. The Li of spent LiNi x Co y Mn 1- x - y O 2 powder were converted to Li 2 CO 3 and LiAlO 2 with the reduction effect of C and residual Al in the roasting process. NaHCO 3 leaching was utilized to selectively dissolve lithium from Li 2 CO 3 and water-insoluble LiAlO 2 . The activation energy of NaHCO 3 leaching was 9.31 kJ∙mol -1 and the leaching of lithium was a diffusion control reaction. More than 95.19 % lithium was leached and recovered as a Li 2 CO 3 product with a purity of 99.80 %. Thus, this approach provides a green path to selective recovery of lithium with good economics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Gibbsite, bayerite, and boehmite are important aluminum (oxy)hydroxide minerals in nature and have been widely deployed in various industrial applications. They are also major components in caustic nuclear wastes stored at various U.S. locations. Knowledge of their crystallization and phase transformation processes contributes to understanding their occurrence and could help optimize waste treatment processes. While it has been reported that partial conversion of bayerite and gibbsite to boehmite occurs in basic solutions at elevated temperatures, systematic studies of factors affecting the phase transformation as well as the underlying reaction mechanisms are nonexistent, particularly in highly alkaline solutions. We explored the effects of sodium hydroxide concentrations (0.1-3 M), reaction temperatures (60-100 °C), and aluminum concentrations (0.1-1 M) on the crystallization and transformation of these aluminum (oxy)hydroxides. Detailed structural and morphological characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) spectrometry revealed that these processes depend largely on the reaction temperature and the Al/OH - ratio. When 1 ≤ Al/OH - ≤ 2.5, the reactions favor formation of high-crystallinity precipitates, whereas at an Al/OH - ratio of ≥2.5 precipitation ceases unless the Al concentration is higher than 1 M. We identified pseudoboehmite, bayerite, and gibbsite as intermediate phases to bayerite, gibbsite and boehmite, respectively, all of which transform via dissolution-reprecipitation. Gibbsite transforms to boehmite in both acidic and weak caustic environments at temperatures above 80 °C. However, a "bar-shaped" gibbsite morphology dominates in highly caustic environments (3 M NaOH). The findings enable a robust basis for the selection of various solid phases by tuning the reaction conditions.

The rapid economic development in China places a large demand for energy, and as a result, thermal power plants in China are producing an enormous amount of coal fly ash (CFA) which causes severe environmental pollution. This paper briefly describes the current production and utilization status of CFA in China and identifies the challenges confronting sustainable CFA utilization as the Chinese economy is being transformed. These issues include a regional imbalance in supply and demand, reducing demand in the real estate industry as well as stricter laws for environmental protection. Viable directions for future CFA utilization are proposed, for example, production of CFA-based ceramic tiles, recovery of elemental resources, agricultural melioration, treatment of wastewater and flue gas, and production of high-volume CFA concretes. This paper has some guiding significance for sustainable and cleaner utilization of CFA in China and even worldwide. Graphical abstract.

The development of earth-abundant transition-metal-based electrocatalysts with bifunctional properties (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) is crucial to commercial hydrogen production. In this work, layered double hydroxide (LDH)-zinc oxide (ZnO) heterostructures and oxygen vacancies are constructed synchronously by plasma magnetron sputtering of NiFe-LDH. Using the optimal conditions, ZnO nanoparticles are uniformly distributed on the NiFe-LDH nanoflowers, which are prepared uniformly on the three-dimensional porous Ni foam. In the LDH-ZnO heterostructures and oxygen vacancies, electrons are depleted at the Ni cations on the NiFe-LDH surface and the active sites change from Fe cations to Ni cations during OER. Our theoretical assessment confirms the change of active sites after the deposition of ZnO and reveals the charge-transfer mechanism. Owing to the significant improvement in the OER dynamics, overall water splitting can be achieved at only 1.603 V in 1 M KOH when the Ni/LDH-ZnO and Ni/LDH are used as the anode and cathode, respectively. The work reveals a novel design of self-supported catalytic electrodes for efficient water splitting and also provides insights into the surface modification of catalytic materials.

The incorporation of relatively minor impurity metals onto metal (oxy)hydroxides can strongly impact solubility. In complex highly alkaline multicomponent radioactive tank wastes such as those at the Hanford Nuclear Reservation, tests indicate that the surface area-normalized dissolution rate of boehmite (γ-AlOOH) nanomaterials is at least an order of magnitude lower than that predicted for the pure phase. Here, we examine the dissolution kinetics of boehmite coated by adsorbed Cr(III), which adheres at saturation coverages as sparse chemisorbed monolayer clusters. Using 40 nm boehmite nanoplates as a model system, temperature-dependent dissolution rates of pure versus Cr(III)-adsorbed boehmite showed that the initial rate for the latter is consistently several times lower, with an apparent activation energy 16 kJ·mol -1 higher. Although the surface coverage is only around 50%, solution analysis coupled to multimethod solids characterization reveal a phyicochemical armoring effect by adsorbed Cr(III) that substantially reduces the number of dissolution-active sites on particle surfaces. Such findings could help improve kinetics models of boehmite and/or metal ion adsorbed boehmite nanomaterials, ultimately providing a stronger foundation for the development of more robust complex radioactive liquid waste processing strategies.

The development of advanced functional nanomaterials for selective adsorption in complex chemical environments requires partner studies of binding mechanisms. Motivated by observations of selective Cr(III) adsorption on boehmite nanoplates (γ-AlOOH) in highly caustic multicomponent solutions of nuclear tank waste, here we unravel the adsorption mechanism in molecular detail. We examined Cr(III) adsorption to synthetic boehmite nanoplates in sodium hydroxide solutions up to 3 M, using a combination of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), scanning/transmission electron microscopy (S/TEM), electron energy loss spectroscopy (EELS), high-resolution atomic force microscopy (HR-AFM), time-of-fight secondary ion mass spectrometry (ToF-SIMS), Cr K-edge X-ray absorption near edge structure (XANES)/extended X-ray absorption fine structure (EXAFS), and electron paramagnetic resonance (EPR). Adsorption isotherms and kinetics were successfully fit to Langmuir and pseudo-second-order kinetic models, respectively, consistent with monotonic uptake of Cr(OH) 4 - monomers until saturation coverage of approximately half the aluminum surface site density. High resolution AFM revealed monolayer cluster self-assembly on the (010) basal surfaces with increasing Cr(III) loading, possessing a structural motif similar to guyanaite (β-CrOOH), stabilized by corner-sharing Cr-O-Cr bonds and attached to the surface with edge-sharing Cr-O-Al bonds. The selective uptake appears related to short-range surface templating effects, with bridging metal connections likely enabled by hydroxyl anion ligand exchange reactions at the surface. Such a cluster formation mechanism, which stops short of more laterally extensive heteroepitaxy, could be a metal uptake discrimination mechanism more prevalent than currently recognized.

Neural impairments accompanying chronic obstructive pulmonary disease (COPD) have received growing research attention. Previous neuroimaging studies exclusively used volumetric methods to measure cortical volume as a whole rather than focusing on anatomical and neuropathological distinct indices. Here we decomposed the cortical architecture into cortical thickness (CTh), surface area (SA), and gyrification, for the first time, to provide a more integrative profile of brain damage in COPD. Clinical T1-weighted MRI scans were acquired in 25 stable COPD patients (mean age 69) and 25 age-matched controls. Images were processed using surface-based morphometry to obtain cortical parameters enabling more accurate measurement in deep sulci and localized regional mapping. Demographic, physiological, and cognitive assessments were made and correlated with cortical indices. Compared to controls, COPD patients showed significantly reduced CTh broadly distributed in motor, parietal, and prefrontal cortices, together with more circumscribed SA reduction in dorsomedial prefrontal cortex and Broca's area (cluster-level P < 0.05 corrected). No abnormal gyrification was detected. Decreased CTh in parietofrontal networks strongly correlated with visuospatial construction impairment in COPD patients. Furthermore, thinner dorsolateral prefrontal cortex (DLPFC) best predicted poorer performance (r (2)  = 0.315, P = 0.004), and was associated with lower arterial oxygen saturation. These data indicate that cortical thinning is a key morphologic feature associated with COPD that could be partly attributed to oxygen desaturation and contributes to COPD visual memory and drawing deficits. Surface-based morphometry provides valuable information concerning COPD, and could ultimately help us to characterize the neurodegenerative pattern and to clarify neurologic mechanisms underlying cognitive dysfunction in COPD patients.

Bayer red mud (RM) is an alumina refinery waste product rich in aluminum oxides and alkalis which are present primarily in the form of sodium hydro-aluminosilicate desilication product (DSP). A hydrothermal process was employed to recover alumina and alkali from "Fe-rich" and "Fe-lean" RM, the two representative species of RM produced in China. The hydrothermal process objective phase is andradite-grossular hydrogarnet characterized by the isomorphic substitution of Al and Fe. Batch experiments were used to evaluate the main factors influencing the recovery process, namely reaction temperature, caustic ratio (molar ratio of Na(2)O to Al(2)O(3) in sodium solution), sodium concentration and residence time. The results revealed that the Na(2)O content of 0.5 wt% and A/S of 0.3 (mass ratio of Al(2)O(3) to SiO(2)) in leached residue could be achieved with Fe-rich RM under optimal conditions. However, the hydrothermal treatment of Fe-lean RM proved less successful unless the reaction system was enriched with iron. Subsequent experiments examined the effects of the ferric compound's content and type on the substitution ratio., (Copyright © 2011 Elsevier B.V. All rights reserved.)