Oxidative Dissolution Research Articles

DCB dissolution of iron oxides in aeolian dust deposits controlled by particle size rather than mineral species

Dithionite-citrate-bicarbonate (DCB) treatment is a classical method for removing iron oxides from soil. The DCB-induced dissolution effects on iron oxides are controversial. In this paper, samples from a typical loess-paleosol sequence in the Chinese Loess Plateau (CLP) and from other aeolian dust deposits in southern China were collected, and changes in the grain size composition and magnetic properties of the samples after DCB treatment were analyzed. The results show that the dissolution of iron oxides in loess-paleosol samples from the CLP is highly grain size dependent. In addition to completely dissolving nanometer-sized pedogenic iron oxides (< 0.2 μm), the standard DCB procedure can also dissolve submicron- and micron-sized aeolian iron oxides (0.2–6 μm). For these aeolian iron oxides, the submicron-sized (0.2–1 μm) iron oxides are sufficiently dissolved, and the solubility of the micron-sized (1–6 μm) iron oxides decreases with increasing particle size. The dissolution of > 6 μm aeolian iron oxides is negligible. DCB can neither separate pedogenic iron oxides from aeolian iron oxides nor selectively dissolve magnetite or maghemite. Although the total amount of dissolved iron oxides in the profiles from southern China is higher than that in the LC profile from northern China, the submicron- and micron-sized aeolian iron oxides in the latter are more easily dissolved.

Toward highly robust reversal-tolerant anodes in polymer electrolyte membrane fuel cells

A reversal tolerant anode (RTA) mitigates carbon corrosion under hydrogen starvation by promoting a water oxidation reaction with an oxygen-evolution-reaction catalyst. However, achieving long-lasting and repeatable voltage-reversal tolerance remains a challenge. Herein, we propose highly robust bi-layered RTAs consisting of IrOx and Pt black layers (IrOx//Pt) for use in polymer electrolyte membrane fuel cells. Compared to bi-layered IrOx//Pt/C RTAs, the carbon-free IrOx//Pt RTAs have an exceptionally longer voltage-reversal time and unprecedented level of repeatability. Additionally, placing the IrOx layer on the membrane side of the RTA is more effective in maintaining the water oxidation reaction than placing it on the diffusion layer side. Oxidative dissolution of IrOx in the IrOx//Pt RTAs under repeated voltage reversals emphasizes the importance of lowering the water oxidation potential of RTA. The carbon-free, bi-layered RTA design presented in this work provides a new path for achieving long-lasting and repeatable voltage-reversal tolerance.

Diagenetic dissolution, maghemitization and sulphidization of magnetic minerals in rapidly deposited gas hydrate bearing sediments from the Bay of Bengal

We conducted a comprehensive rock magnetic investigation complemented by a scanning electron microscopy analyses on a 148.8 m sediment core (NGHP-01-20A) from the methane-hydrate bearing site in the Bay of Bengal to systematically evaluate how magnetic minerals selectively respond to a range of diagenetic processes in the sulfidic and methanic sediments. For diagenetic analysis, we defined five distinct sediment magnetic zones (I–V) based on the sediment magnetic signatures. Rock magnetic property is mainly carried by complex magnetic mineral assemblages of detrital (titanomagnetite, silicate hosted magnetic inclusions), altered (titanomaghemite, titanohematite) and fine-grained diagenetic (pyrite) and authigenic (greigite) iron sulfide minerals. Three distinct bands of enhanced magnetic susceptibility in Z-II, Z-III and Z-V mainly comprised of detrital magnetite-rich minerals delivered by the peninsular river systems as a result of higher sedimentation events in the Krishna-Godavari (K-G) basin. Progressive diagenetic dissolution of primary iron oxide and consequent formation of iron sulfide in the uppermost sulfidic zone (Z-I) is clearly mirrored in the magnetic susceptibility (χlf) profile. Presence of moderately altered coarse-grained detrital Fe–Ti particles in the deeper methanic and magnetically enhanced zones (Z-II, Z-III, Z-V) suggest that sediment diagenesis at this site was significantly constrained by the multiple events of rapid sedimentation which might have restricted the complete dissolution of the primary minerals. Decline in magnetic grain size diagnostic proxy (ARM/IRM2.5T) in the uppermost sulfidic zones (Z-I, Z-II) can be attributed to the preferential dissolution of fine-grained magnetite. Further, downcore increases could be linked with the authigenic formation of fine-grained magnetite in methanic zones (Z-III to Z-V). Ferrimagnetic iron sulfide (greigite) indicative (SIRM/χlf) parameter showed sudden rise in Z-II and remain fairly constant throughout, suggesting the presence of authigenic greigite. Scanning electron microscopy in-line with energy dispersive X-ray spectroscopy analyses of magnetic particles from different sediment magnetic zones revealed a range of ferrimagnetic (titanomagnetite, titanomaghemite), antiferromagnetic (titanohematite) iron oxides and iron sulfide (pyrite). Detrital titanomagnetite with angular, irregular, spherical and well-defined octahedral with micron and submicron sized particles mainly derived from Deccan Volcanic Province (DVP) dominates the rock magnetic signal of bulk sediments in the studied core. We noticed several evidence of diagenetic dissolution, sulphidization and maghemitization of magnetic particles in the studied sediment core. Few nanometre-sized detrital magnetic particles occur as inclusions within the silicate minerals and remains protected against the sulfidic dissolution fronts through geologic times. Optical microscopy revealed the dominance of diagenetic pyrite occurring as overgrowth on the ferrimagnetic particles. We demonstrate that the rockmagnetic methods in combination with focussed electron microscope analyses provide valuable insights into the mineralogy, genesis and state of preservation of magnetic particles in sulfidic and methanic environments and thereby enhances the interpretative value of rock magnetic proxies.

Acceleration of corrosion of 304 stainless steel by outward extracellular electron transfer of Pseudomonas aeruginosa biofilm

The influence of outward extracellular electron transfer (EET) of Pseudomonas aeruginosa in accelerating corrosion of 304 stainless steel was investigated. With less NO3− available as electron acceptor, P. aeruginosa biofilm accelerated the pitting corrosion. The ICP-MS and XPS results indicated that P. aeruginosa promoted the bioreductive dissolution of iron oxides in the passive film of stainless steel. Using in situ scanning electrochemical microscopy, we established a relationship between this accelerated deterioration of the passive film and the EET process mediated by the conversion of the redox states of pyocyanin secreted by P. aeruginosa.

New radiolysis-driven matrix dissolution operational model based on stationary UO2 voltametric experiments

In the framework of research on direct deep disposal of spent nuclear fuel, a new α radiolysis-driven matrix dissolution model is proposed. This model is based on an experimental stationary voltametric curve established using a UO2 rotating disk electrode in a neutral pH non-complexing solution under reducing conditions. Kinetic and chemical speciation calculations give access to the equilibrium redox potential of a simulated Callovo-Oxfordian pore water solution containing α-radiolysis products, which is used in the experimentally obtained current-potential relationship to estimate the oxidative dissolution rate. Comparison of model results with literature data show good agreement with previously established α−activity threshold values.

Copper mobilization in the lower continental crust beneath cratonic margins, a Cu isotope perspective

Lower crustal sulfide-bearing cumulates beneath the convergent plate margins represent a major copper reservoir. However, how Cu is mobilized and migrated in the lower crust is still a matter of debate. Here, we analyzed the Cu elemental and isotopic compositions of well-characterized lower crustal xenoliths from the north margin of the North China Craton to decode Cu mobilization in the lower continental crust beneath cratonic margins. The mafic lower crustal rocks have experienced varying degrees of sulfide accumulation, with Cu contents ranging from 15 to 112 ppm. The majority of lower crustal xenoliths have variable and generally low (compared to the Bulk Silicate Earth) δ65Cu (the permil deviation of the 65Cu/63Cu ratio from the NIST 976 standard) values ranging from −3.17‰ to 0.13‰ (n = 24). Many intragranular and interstitial sulfide grains in these lower crustal xenoliths were partially dissolved and oxidized along the mineral fractures and boundaries. Oxidative dissolution of sulfide will preferentially release 65Cu into the liquids, leaving the residual sulfides enriched in the light isotope, implying that oxidized melt-rock interactions could account for the light Cu isotopic compositions of the lower crustal xenoliths. Sulfide accumulation and oxidative dissolution are responsible for the enrichment, mobilization, and transfer of Cu in the lower continental crust beneath cratonic margins.

Drainage chemistry of mine tailings from a carbonatite-hosted Nb-REE deposit, Oka, Québec, Canada

Potential environmental issues associated with the mining of carbonatites are receiving increased attention due to the importance of critical metals for green technologies. This study investigates the chemistry of tailings seepage at the former Saint Lawrence Columbium mine near Oka, Québec, Canada, which produced pyrochlore concentrate and ferroniobium from a carbonatite-hosted Nb-REE deposit. Detailed field sampling and laboratory methods were used to characterize the hydraulic properties of the tailings, their bulk chemistry, mineralogy, pore water and effluent chemistries. The tailings are composed of REE-enriched calcite (64–89 wt %) and fluorapatite (2–22 wt %), as well as biotite (6–17 wt %) and chlorite (0–7 wt %). Minor minerals include ankerite, pyrite, sphalerite, molybdenite, magnetite and unrecovered pyrochlore. Secondary minerals include gypsum, barite, strontianite and rhodochrosite. Geochemical mass balance modeling, constrained by speciation modeling, was used to identify dissolution, precipitation and exchange reactions controlling the chemical evolution of pore water along its flow path through the tailings impoundment. In the unsaturated zone, these reactions include sulfide oxidation and calcite dissolution with acid neutralization. Below the water table, gypsum dissolution is followed by sulfate reduction and FeS precipitation driven by the oxidation of organic carbon in the tailings. Incongruent dissolution of biotite and chlorite releases K, Mg, Fe, Mn, Ba and F and forms kaolinite and Ca-smectite. Cation exchange reactions further remove Ca from solution, increasing concentrations of Na and K. Fluoride concentrations reach 23 mg/L and 8 mg/L in tailings pore water and effluent, respectively. These values exceed Canadian guidelines for the protection of aquatic life. In the mildly alkaline (pH 8.3) pore waters, Mo is highly mobile and reaches an average concentration of 83 μg/L in tailings effluent, which slightly exceeds environmental guidelines. Concentrations (unfiltered) of Zn reach 1702 μg/L in tailings pore water although values in effluent are usually less than 20 μg/L. At the ambient pH, Zn is strongly adsorbed by Fe–Mn oxyhydroxides. Although U forms mobile complexes in tailings pore water, concentrations do not exceed 16 μg/L due to the low solubility of its pyrochlore host. Adsorption and the low solubility of pyrochlore limit concentrations of Nb to less than 49 μg/L. Cerium, from calcite dissolution, is strongly adsorbed although it reaches concentrations (unfiltered) in excess of 1 mg/L and 100 μg/L in pore water and effluent, respectively. Results of this study show that mine tailings from carbonatite deposits are enriched in a wide variety of incompatible elements with multiple mineral hosts of varying solubility. Some of these elements, such as F and Mo, may represent contaminants of concern because of their mobility in alkaline tailings waters.

Efficient separation and purification of indium and gallium in spent Copper indium gallium diselenide (CIGS)

Copper indium gallium diselenide (CIGS), is a promising commercial thin-film solar cell, and its disposal after scrapping and recycling critical metals has attracted tremendous attention since CIGS can be considered an important type of urban mining. The main phase of spent CIGS is selenide, which is a hazardous contaminant that may have a potential impact on the environment and human body. In our previous study, selenium and copper in spent CIGS separated efficiently, while more scarce metals: indium and gallium were obtained in the form of mixed indium gallium oxide (IGO). Therefore, in this study, the separation and purification of indium and gallium was investigated in detail. The solution chemical behavior shows that the dissolution of indium gallium oxide (IGO) in an alkaline environment was significantly different. Selective alkali leaching is feasible to separate indium and gallium effectively. The process realized 97.26% gallium leaching out, while that of indium was 3.37%. Moreover, the mechanism of the leaching process and the removal of copper impurities were explored, with further purification, indium and gallium were obtained in the form of relatively pure indium oxide (96.04%) and gallium oxide (99.83%), respectively. This study will provide guidance for the recycling of critical metals from secondary waste.

Enrichment and speciation of chromium during basalt weathering: Insights from variably weathered profiles in the Leizhou Peninsula, South China

Basalt-derived soils are widespread worldwide. Such soils contain high levels of heavy metals like chromium (Cr), which is a serious environmental concern. However, little is known regarding the enrichment and speciation of Cr during the basalt weathering process. Therefore, two basalt-derived soil profiles (Nitisol and Ferralsol) in the Leizhou Peninsula, south tropical China, were investigated to explore the redistribution and transformation of Cr during basalt weathering. All profiles could be divided into three layers: rocks, saprolites, and soils. The Nitisol and Ferralsol profiles exhibited strong (kaolinization) and extreme (laterization) degrees of weathering, respectively. Results showed that Cr concentrations in the saprolites (234 to 315 mg·kg−1) were higher than those in basalt rocks (139 to 159 mg·kg−1), indicating that Cr was enriched with the continuous loss of Si and other mobile macro-elements. While high levels of Cr were also enriched in the soils (178 to 430 mg·kg−1) accompanied with Fe. However, in the upper soils of the Ferralsol profile, the acidity and organic matter could promote the leaching of Cr. Geochemical fractions and EPMA mapping showed that chromite and olivine were the main Cr-bearing minerals in basalt, but Fe-oxides (e.g., goethite and hematite) contained the highest portion of Cr in weathered saprolites and soils. The availability of Cr in the soil was extremely low due to the high stability of Cr bound to Fe-oxides. However, the decreasing contents of Cr bound to Fe-oxides in the upper soils of the Ferralsol profile indicated that Cr could also be released during Fe leaching. In conclusion, the weathering of basalt can lead to the enrichment of Cr in Fe-(hydro)oxides, which are the main controlling minerals for Cr mobility in basalt-derived soils. Further research is needed to evaluate the effect of Fe-(hydro)oxide formation and dissolution on the release of soil Cr.

High-resolution characteristics and mechanisms of endogenous phosphorus migration and transformation impacted by algal blooms decomposition

Extremely high phosphorus (P) concentrations can be found in eutrophic freshwater sediments during algal blooms (ABs). However, few investigations have revealed the mechanism of labile P production in anoxic sediments following ABs decomposition. This limits our understanding of P cycling and mitigation of ABs in aquatic ecosystems. To identify such a mechanism, we conducted a microcosm experiment to identify how ABs decomposition enhances endogenous P release, using the combined techniques of diffusive gradients in thin films, high-resolution dialysis, and 16S rRNA amplicon sequencing. We show the concentrations of labile iron, manganese, sulfide, and P can be well predicted by quality and quantity of algal biomass. The relative abundance of iron reduction bacteria positively correlated with the decrease of pH induced by ABs decomposition, suggesting that this decomposition facilitates microbial iron and manganese reduction. In addition, the reductive dissolution of iron and manganese oxides leads to the labile P release, resulting in higher concentrations of labile P in those sediments affected by ABs compared with those not affected. The P fluxes in the algae-dominated regions exhibited higher values in the algae group than in the control group, with gains of 14.07–100.04%. Furthermore, endogenous P release is strongly controlled by Mn when the Fe(II):Mn(II) ratio is low (below 0.47), and by both Fe and Mn when the Fe(II):Mn(II) ratio is high (above 0.63). Our results quantify the endogenous P diffusion fluxes across the sediment–water interface can be attributed to ABs decomposition, and are therefore useful for further understanding of P cycling in freshwater.

Photochemical Synthesis of Silver Hydrosol Stabilized by Carbonate Ions and Study of Its Bactericidal Impact on Escherichia coli: Direct and Indirect Effects.

The great attention paid to silver nanoparticles is largely related to their antibacterial and antiviral effects and their possible use as efficient biocidal agents. Silver nanoparticles are being widely introduced into various areas of life, including industry, medicine, and agriculture. This leads to their spreading and entering the environment, which generates the potential risk of toxic effect on humans and other biological organisms. Proposed paper describes the preparation of silver hydrosols containing spherical metal nanoparticles by photochemical reduction of Ag+ ions with oxalate ions. In deaerated solutions, this gives ~10 nm particles, while in aerated solutions, ~20 nm particles with inclusion of the oxide Ag2O are obtained. Nanoparticles inhibit the bacterium Escherichia coli and suppress the cell growth at concentrations of ~1 × 10−6–1 × 10−4 mol L−1. Silver particles cause the loss of pili and deformation and destruction of cell membranes. A mechanism of antibacterial action was proposed, taking into account indirect suppressing action of Ag+ ions released upon the oxidative metal dissolution and direct (contact) action of nanoparticles on bacterial cells, resulting in a change in the shape and destruction of the bacteria.

The influence of redox conditions on aqueous-solid partitioning of arsenic and selenium in a closed coal ash impoundment

A closed coal ash impoundment case study characterized the effects of field redox conditions on arsenic and selenium partitioning through monitoring of porewater and subsurface gas in conjunction with geochemical speciation modeling. When disposed coal ash materials and porewater were recovered for testing, oxidation led to lower arsenic and higher selenium concentrations in leaching test extracts compared to porewater measurements. Multiple lines of evidence suggest multiple mechanisms of arsenic retention are plausible and the concurrent presence of several redox processes and conditions (e.g., methanogenesis, sulfate reduction, and Fe(III)-reduction) controlled by spatial gradients and dis-equilibrium. Geochemical speciation modeling indicated that, under reducing field conditions, selenium was immobilized through the formation of insoluble precipitates Se(0) or FeSe while arsenic partitioning was affected by a progression of reactions including changes in arsenic speciation, reduction in adsorption due to dissolution and recrystallization of hydrous ferric oxides, and precipitation of arsenic sulfide minerals.

Influence of mechanochemical activation on dissolving model corrosion films formed on ion-exchange resins using Trilon B

Inorganic deposits formed during operation and intermediate storage contain radionuclides, whose removal during the chemical decontamination of spent ion-exchange resins used in filters for special water purification at nuclear power plants has proved to be a challenge. In such deposits, radionuclides of the corrosion group (58.60Co, 54Mn, 51Cr) are typically located in the crystal lattice of poorly soluble iron oxides. The present work discusses the possibility of using mechanochemical activation in the decontamination of spent ion-exchange resins polluted with deposits of activated corrosion products from structural materials. Samples of natural and synthesised on the surface of the KU-2-8 cation exchanger in the presence of the 57Co label magnetites were used as model deposits. It was shown that an increase in the duration of mechanochemical activation leads to an increase in the dissolution rate of magnetite in model decontamination solutions based on еthylenediaminetetraacetic acid disodium salt (Trilon B) and nitric acid. It was shown that, when using Trilon B, magnetite dissolves more efficiently, which is explained by the interaction between the oxide surface and organic complexing agents. It can be assumed that solid-phase reactions occur during the mechanochemical activation of magnetite in the presence of dry reagents (Trilon B, oxalic, ascorbic and citric acids). Therefore, a poorly soluble shell formed on the oxide surface hinders the dissolution at a low magnetite/solution ratio. Unlike the reagent-free activation, for magnetite activated in the presence of oxalic acid, an increase in the solution/magnetite ratio promotes the dissolution of iron oxides. Using the example of a model cation exchanger, it was shown that the rate and efficiency of decontamination of spent ion-exchange resins polluted with deposits containing activated corrosion products increase significantly after mechanochemical activation in the presence of oxalic acid.

Combined Effects of Fe(III)-Bearing Nontronite and Organic Ligands on Biogenic U(IV) Oxidation.

Bioreduction of soluble U(VI) to sparingly soluble U(IV) solids was proposed as a remediation method for uranium contamination. Therefore, the stability and longevity of biogenic U(IV) are critical to the success of uranium remediation. However, co-occurrence of clay minerals and organic ligands could potentially reoxidize U(IV) to U(VI). Herein, we report a combined effect of Fe(III)-rich nontronite (NAu-2) and environmentally prevalent organic ligands on reoxidation of biogenic U(IV) at circumneutral pH. After 30 days of incubation, structural Fe(III) in NAu-2 oxidized 45.50% U(IV) with an initial rate of 2.7 × 10-3 mol m-2 d-1. Addition of citrate and ethylenediaminetetraacetic acid (EDTA) greatly promoted the oxidative dissolution of U(IV) by structural Fe(III) in NAu-2, primarily through the formation of aqueous ligand-U(IV) complexes. In contrast, a model siderophore, desferrioxamine B (DFOB), partially inhibited U(IV) oxidation due to the formation of stable DFOB-Fe3+ complexes. The resulting U(VI) species intercalated into an NAu-2 interlayer or adsorbed onto an NAu-2 surface. Our results highlight the importance of organic ligands in oxidative dissolution of U(IV) minerals by Fe(III)-bearing clay minerals and have important implications for the design of nuclear waste storage and remediation strategies, especially in clay- and organic-rich environments.

Selective Scandium (Sc) Extraction from Bauxite Residue (Red Mud) Obtained by Alkali Fusion-Leaching Method.

Bauxite residue, known as “red mud,” is a potential raw material for extracting rare-earth elements (REEs). The main REEs (Sc, Y, La, Ce, Nd, Nb, and Sm) from the raw bauxite are concentrated in RM after the Bayer leaching process. The earlier worldwide studies were focused on the scandium (Sc) extraction from RM by concentrated acids to enhance the extraction degree. This leads to the dissolution of major oxides (Fe2O3 and Al2O3) from RM. This article studies the possibility of selective Sc extraction from alkali fusion red mud (RMF) by diluted nitric acid (HNO3) leaching at pH ≥ 2 to prevent co-dissolution of Fe2O3. RMF samples were analyzed by X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), electron probe microanalysis (EPMA), and inductively coupled plasma mass spectrometry (ICP-MS). It was revealed that Sc concentration in RMF can reach up to 140–150 mg kg−1. Sc extraction was 71.2% at RMF leaching by HNO3 at pH 2 and 80 °C during 90 min. The leaching solution contained 8 mg L−1 Sc and a high amount of other REEs in the presence of relatively low concentrations of impurity elements such as Fe, Al, Ti, Ca, etc. The kinetic analysis of experimental data by the shrinking core model showed that Sc leaching process is limited by the interfacial diffusion and the diffusion through the product layer. The apparent activation energy (Ea) was 19.5 kJ/mol. The linear dependence of Sc extraction on magnesium (Mg) extraction was revealed. According to EPMA of RMF, Sc is associated with iron minerals rather than Mg. This allows us to conclude that Mg acts as a leaching agent for the extraction of Sc presented in the RMF in an ion-exchangeable phase.

Oxidative dissolution of uraninite nanoparticles in the presence of manganite

One of the possible uranium pollution remediation methods is the immobilization of uranium by reduction, transforming from soluble hexavalent uranium to barely soluble uraninite (UO2). However, the uraninite is susceptible to be re-oxidized and releases the uranium into the subsurface environments. Understanding the process of uraninite oxidative dissolution is necessary for evaluating uranium migration behavior and improvements of the uranium remediation strategies. Manganese (hydr)oxides are among the strong inorganic oxidants in natural environments. In this work, we investigated the interaction between manganite, a stable Mn(III) oxyhydroxide, and uraninite nanoparticles in subalkaline solutions under both oxic and anoxic conditions by batch experiments. Under oxic conditions, a small amount of manganite effectively catalyzed the oxidative dissolution of uraninite by oxygen, and the catalysis was suppressed with the increase of the manganite concentration or the decrease of the bicarbonate concentration. Under anoxic conditions, the oxidative dissolution of uraninite happened at a much slower rate with manganite acting as the oxidant. The dissolution process involved two stages of reaction as illustrated by the correlation of uranium concentration and time. Our results suggest under both oxic and anoxic conditions, the oxidative dissolution of uraninite could be strongly affected by the presence of Mn(III) oxyhydroxide minerals.

Providing Atomistic Insights into the Dissolution of Rutile Oxides in Electrocatalytic Water Splitting

Providing Atomistic Insights into the Dissolution of Rutile Oxides in Electrocatalytic Water Splitting

PHYSICAL AND CHEMICAL FOUNDATIONS OF THE EXTRACTION REFINING OF NATURAL URANIUM

The paper presents the results of studies of the physicochemical processes of the extraction and nitric acid purification of uranium salts obtained by the method of precipitation of ammonium uranyl carbonate (AUC) from ore solutions of leaching of uranium and polymetallic ores with their subsequent dissolution in nitric acid. It is shown that the process of extraction on a mixture of tributyl phosphate (TBP) in kerosene makes it possible to obtain high-purity uranium oxide. For the selective extraction of impurities, the process of uranium extraction from the nitric acid medium was carried out with a mixture of TBP and di(2-ethylhexyl) phosphoric acid (DEHPA) in kerosene. The first uranium concentration 40…50 g/L simulated the process of uranium desorption, the second ≤ 100 g/L simulated the process of dissolution of uranium oxide. The study of the uranium extraction made it possible to determine the required number of extraction stages to achieve the minimum uranium content in the raffinate and the maximum extractant capacity, which ensured the specified coefficients of uranium purification from metal impurities (V, Mo, etc.). After extraction, the nitric acid raffinate served as a raw material for the production of a mineral fertilizer – sodium nitrate.

Kinetics and mechanistic details of bulk ZnO dissolution using a thiol-imidazole system.

Oxide dissolution is important for metal extraction from ores and has become an attractive route for the preparation of inks for thin film solution deposition; however, oxide dissolution is often kinetically challenging. While binary “alkahest” systems comprised of thiols and N-donor species, such as amines, are known to dissolve a wide range of oxides, the mechanism of dissolution and identity of the resulting solute(s) remain unstudied. Here, we demonstrate facile dissolution of both bulk synthetic and natural mineral ZnO samples using an “alkahest” that operates via reaction with thiophenol and 1-methylimidazole (MeIm) to give a single, pseudotetrahedral Zn(SPh)2(MeIm)2 molecular solute identified by X-ray crystallography. The kinetics of ZnO dissolution were measured using solution 1H NMR, and the reaction was found to be zero-order in the presence of excess ligands, with more electron withdrawing para-substituted thiophenols resulting in faster dissolution. A negative entropy of activation was measured by Eyring analysis, indicating associative ligand binding in, or prior to, the rate determining step. Combined experimental and computational surface binding studies on ZnO reveal stronger, irreversible thiophenol binding compared to MeIm, leading to a proposed dissolution mechanism initiated by thiol binding to the ZnO surface with the liberation of water, followed by alternating MeIm and thiolate ligand additions, and ultimately cleavage of the ligated zinc complex from the ZnO surface. Design rules garnered from the mechanistic insight provided by this study should inform the dissolution of other bulk oxides into inks for solution processed thin films.

The effect of Fe3+ ions on the electrochemical behaviour of ocean manganese nodule reduction leaching in sulphuric acid solution.

The effect of Fe3+ ions on the ocean manganese nodule reductive leaching in imitated sulphuric acid solutions was investigated. This work is presented in two courses, including the influence of Fe3+ ions on valuable metal extraction and the electrochemical reductive dissolution of manganese nodules. The results show that the beneficial effects of Fe3+ ion can be interpreted based on two aspects: the first is the acceleration caused by the active transformation of Fe3+/Fe2+ pair, and the second is the hydrogen ion buffer action generated by Fe3+ ion hydrolysis on the surface. On one side, Fe3+ ion could lessen the hydrogen consumption happening at the interface layer of the nodule supported by the leaching test and cyclic voltammetry results. On the other side, Fe3+ ions could be converted into Fe2+ ions and then preferentially reduce manganese oxide leading to an acceleration of the charge transfer reaction of the manganese nodule based on cyclic voltammetry, polarization, and impedance analysis results. The reduction leaching of manganese nodules in sulphuric acid solution is mainly controlled by the electrochemical interface reduction corresponding to manganese oxide dissolution, and the active conversion of the Fe3+/Fe2+ couple affects the dissolution of high valence manganese oxide.