Comprehensive Study on the Mechanism of Sulfating Roasting of Zinc Plant Residue with Iron Sulfates

Zinc plant residue (ZPR) is a secondary material generated during hydrometallurgical zinc production that contains considerable contents of valuable elements such as Zn, Cu, Fe, Pb, Cd, Ag, In, Ga, Tl. Zinc, copper and accompanying elements in ZPR are in different minerals, mainly in the ferrites. A promising approach for recycling ZPR is the sulfating roasting using iron sulfates followed by water leaching. In this study, the composition of ZPR and the obtained products were thoroughly investigated by various methods including X-ray diffraction analysis (XRD), chemical phase analysis and Mössbauer spectroscopy. The effect of temperature, amount of iron sulfates and roasting time on the conversion of valuable metals into a water-soluble form was thermodynamically and experimentally studied both using pure ferrites and ZPR. Based on the results of time-resolved XRD analysis and synchronous thermal analysis (STA), a mechanism of the sulfation roasting was elucidated. The rate-controlling step of zinc and copper sulfation process during the ZPR roasting was estimated. The sulfating roasting at 600 °C during 180 min with the optimal Fe₂(SO₄)₃∙9H₂O addition followed by water leaching enables to recover 99% Zn and 80.3% Cu, while Fe, Pb, Ag, In, Ga retained almost fully in the residue.     

Recovery of Tantalum and Manganese from Epoxy-Coated Solid Electrolyte Tantalum Capacitors through Selective Leaching and Chlorination Processes

Electronic products are ever growing in popularity, and tantalum capacitors are heavily used in small electronic products. Spent epoxy-coated solid electrolyte tantalum capacitors, containing about 22 wt.% of tantalum and 8 wt.% of manganese, were treated with selective leaching by hydrochloric acid and chlorination after removing the epoxy resin, and the products converted, respectively, to Mn(OH)₂ and TaCl₅. The effects of acid type, acid concentration, liquid–solid ratio, and reaction time were investigated to dissolve the manganese. The optimal selective leaching conditions were determined as 3 mol/L of HCl, 40 mL/g at 25 °C for 32 min. Next, residues of selective leaching after washing and drying were heated with ferrous chloride to convert to pure TaCl₅. Mixing 48 wt.% of chloride and 52 wt.% of residues for a total of 5 g was conducted to complete the chlorination process in the tube furnace at 450 °C for 3 h. A total of 2.35 g of Ta was collected and the recovery of Ta achieved 94%. Finally, Mn(OH)₂ and TaCl₅ were separated and purified as the products.     

A Study on the Mechanism and Kinetics of Ultrasound-Enhanced Sulfuric Acid Leaching for Zinc Extraction from Zinc Oxide Dust

As an important secondary zinc resource, large-scale reserves of zinc oxide dust (ZOD) from a wide range of sources is of high comprehensive recycling value. Therefore, an experimental study on ultrasound-enhanced sulfuric acid leaching for zinc extraction from zinc oxide dust was carried out to investigate the effects of various factors such as ultrasonic power, reaction time, sulfuric acid concentration, and liquid–solid ratio on zinc leaching rate. The results show that the zinc leaching rate under ultrasound reached 91.16% at a temperature of 25 °C, ultrasonic power 500 W, sulfuric acid concentration 140 g/L, liquid–solid ratio 5:1, rotating speed 100 r/min, and leaching time 30 min. Compared with the conventional leaching method (leaching rate: 85.36%), the method under ultrasound increased the zinc leaching rate by 5.8%. In a kinetic analysis of the ultrasound-enhanced sulfuric acid leaching of zinc oxide dust, the initial apparent activation energy of the reaction was 6.90 kJ/mol, indicating that the ultrasound-enhanced leaching process was controlled by the mixed solid product layers. Furthermore, the leached residue was characterized by XRD and SEM-EDS, and the results show that, with ultrasonic waves, the encapsulated mineral particles were dissociated, and the dissolution of ZnO was enhanced. Mostly, the zinc in leached residue existed in the forms of ZnFe₂O₄, Zn₂SiO₄, and ZnS.     

A New Hydrometallurgical Process for Metal Extraction from Electric Arc Furnace Dust Using Ionic Liquids

This research proposes a new hydrometallurgical method for Zn, In, and Ga extraction, along with Fe as a common impurity, from electric arc furnace dust (EAFD), using ionic liquids. EAFD is a metal-containing waste fraction generated in significant amounts during the process of steelmaking from scrap material in an electric arc furnace. With valuable metal recovery as the main goal, two ionic liquids, [Bmim⁺HSO₄⁻] and [Bmim⁺Cl⁻], were studied in conjunction with three oxidants: Fe₂(SO₄)₃, KMnO₄, and H₂O₂. The results indicated that the best combination was [Bmim⁺HSO₄⁻] with [Fe₂(SO₄)₃]. An experimental series subsequently demonstrated that the combination of 30% v/v [Bmim⁺HSO₄⁻], 1 g of [Fe₂(SO₄)₃], S/L ratio = 1/20, a 240 min leaching time, and a temperature of 85 °C was optimal, resulting in maximum extractions of 92.7% Zn, 97.4% In, and 17.03% Ga. In addition, 80.2% of the impurity metal Fe was dissolved. The dissolution kinetics of these four elements over a temperature range of 55–85 °C was found to be diffusion controlled. The remaining phases present in the leached residue were low amounts of ZnO, Fe₃O₄, ZnFe₂O₄, and traces of Ca(OH)₂ and MnO₂, and additional sharp peaks indicative of PbSO₄ and CaSO₄ appeared within the XRD pattern. The intensity of the peaks related to ZnO and Fe₃O₄ were observed to have decreased considerably during leaching, whereas some of the refractory ZnFe₂O₄ phase remained. SEM-EDS analysis revealed that the initial EAFD morphology was composed of spherical-shaped fine-grained particle agglomerates, whereas the leached residue was dominated by calcium sulphate (Ca(SO₄))-rich needle-shaped crystals. The results clearly demonstrate that [Bmim⁺HSO₄⁻] is able to extract the target metals due to its acidic properties.     

Physico-Chemical Modifications Affecting the Activity and Stability of Cu-Based Hybrid Catalysts during the Direct Hydrogenation of Carbon Dioxide into Dimethyl-Ether

The direct hydrogenation of CO₂ into dimethyl-ether (DME) has been studied in the presence of ferrierite-based CuZnZr hybrid catalysts. The samples were synthetized with three different techniques and two oxides/zeolite mass ratios. All the samples (calcined and spent) were properly characterized with different physico-chemical techniques for determining the textural and morphological nature of the catalytic surface. The experimental campaign was carried out in a fixed bed reactor at 2.5 MPa and stoichiometric H₂/CO₂ molar ratio, by varying both the reaction temperature (200–300 °C) and the spatial velocity (6.7–20.0 NL∙g_cat⁻¹∙h⁻¹). Activity tests evidenced a superior activity of catalysts at a higher oxides/zeolite weight ratio, with a maximum DME yield as high as 4.5% (58.9 mg_DME∙g_cat⁻¹∙h⁻¹) exhibited by the sample prepared by gel-oxalate coprecipitation. At lower oxide/zeolite mass ratios, the catalysts prepared by impregnation and coprecipitation exhibited comparable DME productivity, whereas the physically mixed sample showed a high activity in CO₂ hydrogenation but a low selectivity toward methanol and DME, ascribed to a minor synergy between the metal-oxide sites and the acid sites of the zeolite. Durability tests highlighted a progressive loss in activity with time on stream, mainly associated to the detrimental modifications under the adopted experimental conditions.     

Solidification/Stabilization of Arsenic-Containing Tailings by Steel Slag-Based Binders with High Efficiency and Low Carbon Footprint

The disposal of nonferrous metal tailings poses a global economic and environmental problem. After employing a clinker-free steel slag-based binder (SSB) for the solidification/stabilization (S/S) of arsenic-containing tailings (AT), the effectiveness, leaching risk, and leaching mechanism of the SSB S/S treated AT (SST) were investigated via the Chinese leaching tests HJ/T299-2007 and HJ557-2010 and the leaching tests series of the multi-process Leaching Environmental Assessment Framework (LEAF). The test results were compared with those of ordinary Portland cement S/S treated AT (PST) and showed that the arsenic (As) curing rates for SST and PST samples were in the range of 96.80–98.89% and 99.52–99.2%, respectively, whereby the leached-As concentration was strongly dependent on the pH of the leachate. The LEAF test results showed that the liquid–solid partitioning limit of As leaching from AT, SST, and PST was controlled by solubility, and the highest concentrations of leached As were 7.56, 0.34, and 0.33 mg/L, respectively. The As leaching mechanism of monolithic SST was controlled by diffusion, and the mean observed diffusion coefficient of 9.35 × 10⁻¹⁵ cm²/s was higher than that of PST (1.55 × 10⁻¹⁶ cm²/s). The findings of this study could facilitate the utilization of SSB in S/S processes, replacing cement to reduce CO₂ emissions.     

Effect of Ga on the Oxide Film Structure and Oxidation Resistance of Sn–Bi–Zn Alloys as Heat Transfer Fluids

The effect of gallium on the oxide film structure and overall oxidation resistance of low melting point Sn–Bi–Zn alloys was investigated under air atmosphere using thermogravimetric analyses. The liquid alloys studied had a Ga content of 1–7 wt.%. The results showed that the growth rates of the surface scale formed on the Sn–Bi–Zn–Ga alloys conformed to the parabolic law. The oxidation resistance of Sn–Bi–Zn alloys was improved by Ga addition and the activation energies increased from 12.05 kJ∙mol⁻¹ to 22.20 kJ∙mol⁻¹. The structure and elemental distribution of the oxide film surface and cross-section were found to become more complicated and denser with Ga addition. Further, the results of X-ray photoelectron spectroscopy and X-ray diffraction show that Ga elements accumulate on the surface of the liquid metal to form oxides, which significantly slowed the oxidation of the surface of the liquid alloy.     

Analysis of Hydrometallurgical Methods for Obtaining Vanadium Concentrates from the Waste by Chemical Production of Vanadium Pentoxide

The paper describes hydrometallurgical methods to recycle wastes of vanadium pentoxide chemical fabrication. Sludges containing a significant amount of V₂O₅ can be considered as an additional source of raw materials for vanadium production. We studied the one-stage leaching method using various iron-based reductants for converting V⁵⁺ to V⁴⁺ in a solution allowing to precipitate V when its concentration in the solution is low. As a result of the reduction leaching with further precipitation, we obtained concentrates with V₂O₅ content of 22–26% and a high amount of harmful impurities. Multistage counterflow leaching can be used to fabricate solutions with vanadium pentoxide concentration suitable for vanadium precipitation by hydrolysis and adding ammonium salts. The solutions with V₂O₅ content of ≈15 g/L can be obtained from the initial sludge by three-stage counterflow vanadium leaching. A concentrate with a content of 78 wt% V₂O₅ can be precipitated from these solutions at pH = 2.4 by adding ammonium chloride. Additionally, concentrate with V₂O₅ content of ≈94 wt% was precipitated from the solution with a concentration of >20 g/L V₂O₅ obtained from the roasted sludge. The concentrates were purified for increasing the vanadium content to 5–7%. The consumption and technological parameters of the considered processes are presented in the paper.     

Adsorptive-Oxidative Removal of Sulfides from Water by MnO2-Loaded Carboxylic Cation Exchangers

Hybrid ion exchangers (HIX) containing manganese(IV) oxide (MnO₂) based on macroporous and gel-type carboxylic cation exchangers as supporting materials were obtained. The hybrid materials were characterized using scanning electron microscopy with energy dispersive spectrometry (SEM/EDS), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and nitrogen adsorption isotherms at 77 K and mercury porosimetry. HIX with introduced MnO₂ (20.0–32.8 wt% Mn) were tested for removal of dissolved sulfides from anoxic aqueous solutions with 100–500 mg S²⁻/dm³ concentrations. The process proceeded effortlessly at pH 10–13 despite unfavorable electrostatic interactions of the reactants. The highest exhibited sorption capacity was 144.3 ± 7.1 mg S²⁻/g. Approximately 65% of dissolved sulfides were oxidized to S₂O₃²⁻ ions and repelled from HIX structure. On average, 13% of sulfide removal products were adsorbed by the MnO₂ surface. The impact of MnO₂ load and the ionic form of HIX functional groups on removal of sulfides and resulting products was examined. The mechanism of the process is suggested.     

Performance Evaluation of Cementless Composites with Alkali-Sulfate Activator for Field Application

This study analyzed the performance evaluation of alkali-activated composites (AAC) with an alkali-sulfate activator and determined the expected effects of applying AACs to actual sites. Results revealed that when the binder weight was increased by 100 kg/m³ at 7 days of age, the homogel strength of ordinary Portland cement (OPC) and AAC increased by 0.9 and 5.0 MPa, respectively. According to the analysis of the matrix microstructures at 7 days of age, calcium silicate hydrates (C–S–H, Ca_1.5SiO_3.5·H₂O) and ettringite (Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O) were formed in AAC, which are similar hydration products as found in OPC. Furthermore, the acid resistance analysis showed that the mass change of AAC in HCl and H₂SO₄ solutions ranged from 36.1% to 88.0%, lower than that of OPC, indicating AAC’s superior acid resistance. Moreover, the OPC and AAC binder weight ranges satisfying the target geltime (20–50 s) were estimated as 180.1–471.1 kg/m³ and 261.2–469.9 kg/m³, respectively, and the global warming potential (GWP) according to binder weight range was 102.3–257.3 kg CO₂ eq/m³ and 72.9–126.0 kg CO₂ eq/m³. Therefore, by applying AAC to actual sites, GWP is expected to be 29.5 (28.8%)–131.3 (51.0%) kg CO₂ eq/m³ less than that of OPC.     

Rare-Earth Elements Extraction from Low-Alkali Desilicated Coal Fly Ash by (NH4)2SO4 + H2SO4

Coal fly ash (CFA) obtained from pulverized coal furnaces is a highly refractory waste that can be used for alumina and rare-earth elements (REEs) extraction. The REEs in this type of CFA are associated with a mullite and amorphous glassy mass that forms a core-shell structure. In this research, it was shown that complete dissolution of amorphous aluminosilicates from the mullite surface with the formation of the low-alkali mullite concentrate prior to sulfuric acid leaching with the addition of (NH₄)₂SO₄ helps to accelerate the extraction of REEs. The extraction degree of Sc and other REEs reaches 70–80% after 5 h of leaching at 110 °C and acid concentration of 5 M versus less than 20% for the raw CFA at the same conditions. To study the leaching kinetics of the process, the effects of temperature (90–110 °C), liquid-to-solid ratio (5–10), and leaching time (15–120 min) on the degrees of Al and rare-earth elements (REEs) extraction were evaluated. After 120 min of leaching at 110 °C and L/S ratio = 10, the extraction of Al was found to be lower than 30%. At the same time, total REEs (TREE) and Fe extraction were greater than 60%, which indicates that a part of the TREE was transferred into the acid soluble phase. After leaching, the residues were studied by laser diffraction (LD), X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM-EDS) to evaluate the leaching mechanism and the solubility of Al- and Fe-containing minerals, such as mullite, hematite, and amorphous aluminosilicate.     

Novel H-Bonded Synthons in Copper Supramolecular Frameworks with Aminoethylpiperazine-Based Ligands. Synthesis,Structure and Catalytic Activity

New Schiff base complexes [Cu₂(HL¹)(L¹)(N₃)₃]∙2H₂O (1) and [Cu₂L²(N₃)₂]∙H₂O (2) were synthesized. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction analysis. The HL¹ ligand results from the condensation of salicylaldehyde and 1-(2-aminoethyl)piperazine, while a new organic ligand, H₂L², was formed by the dimerization of HL¹ via a coupling of two piperazine rings of HL¹ on a carbon atom coming from DMF solvent. The dinuclear building units in 1 and 2 are linked into complex supramolecular networks through hydrogen and coordination bondings, resulting in 2D and 1D architectures, respectively. Single-point and broken-symmetry DFT calculations disclosed negligible singlet–triplet splittings within the dinuclear copper fragments in 1 and 2. Catalytic studies showed a remarkable activity of 1 and 2 towards cyclohexane oxidation with H₂O₂ in the presence of nitric acid and pyridine as promoters and under mild conditions (yield of products up to 21%). Coordination compound 1 also acts as an active catalyst in the intermolecular coupling of cyclohexane with benzamide using di-tert-butyl peroxide (^tBuOO^tBu) as a terminal oxidant. Conversion of benzamide at 55% was observed after 24 h reaction time. By-product patterns and plausible reaction mechanisms are discussed.     

Sulfur radical formation from the tropospheric irradiation of aqueous sulfate aerosols

The sulfate anion radical (SO₄^•–) is known to be formed in the autoxidation chain of sulfur dioxide and from minor reactions when sulfate or bisulfate ions are activated by OH radicals, NO₃ radicals, or iron. Here, we report a source of SO₄^•–, from the irradiation of the liquid water of sulfate-containing organic aerosol particles under natural sunlight and laboratory UV radiation. Irradiation of aqueous sulfate mixed with a variety of atmospherically relevant organic compounds degrades the organics well within the typical lifetime of aerosols in the atmosphere. Products of the SO₄^•– + organic reaction include surface-active organosulfates and small organic acids, alongside other products. Scavenging and deoxygenated experiments indicate that SO₄^•– radicals, instead of OH, drive the reaction. Ion substitution experiments confirm that sulfate ions are necessary for organic reactivity, while the cation identity is of low importance. The reaction proceeds at pH 1–6, implicating both bisulfate and sulfate in the formation of photoinduced SO₄^•–. Certain aromatic species may further accelerate the reaction through synergy. This reaction may impact our understanding of atmospheric sulfur reactions, aerosol properties, and organic aerosol lifetimes when inserted into aqueous chemistry model mechanisms.

Atmospheric aerosol particles, which are mixtures of organics, inorganics, water, and other components suspended in air (1), are critical drivers of air pollution and short-term forcers of climate impacts (2). Sulfate anions (SO₄^2–, HSO₄⁻) are ubiquitous in aerosols. With mass fractions of >40% in several areas, sulfate is the largest anthropogenic contributor to fine-mode aerosols (1). Under typical atmospheric conditions, ionic strengths of sulfate in aerosol water are high [e.g., >4 M predicted at less than 80% relative humidity (RH) (3)]. We found that these high aqueous sulfate activities can induce considerable chemistry through the formation of sulfate anion radicals (SO₄^•–), and potentially other sulfur oxy radicals, under solar light available in the troposphere in a chemical reaction that has yet to be accounted for in atmospheric model mechanisms.Much of the discussion of SO₄^•– formation in atmospheric clouds, fogs, and aerosol water is centered on the autoxidation chain of sulfur dioxide (SO₂) that is emitted from fossil fuel combustion (4). SO₄^•– is formed when S(IV) species are oxidized, e.g., by the hydroxyl (OH) radical. There are also small sources of SO₄^•– radicals from the reactions of bisulfate (HSO₄⁻) with OH, or HSO₄⁻/SO₄^2– with NO₃ (5). Once formed, SO₄^•– may react with organics through electron transfer, addition to double bonds, and H-abstraction (6). The ability for SO₄^•– to form covalent C-O-S bonds through addition (7) strongly contribute to organosulfate formation in the atmosphere (8). While SO₄^•– reactions with organics are included in computational models of atmospheric aerosol chemistry, their importance has been considered limited due to the minor SO₄^•– source strength of known reactions and the notion that other highly reactive radicals (OH, NO₃) are needed to initiate SO₄^•– chemistry (4, 9).Yet, prior studies provide evidence of unexplained sulfur chemistry that did not result from OH or NO₃ radicals when sufficient ionic strength of sulfate ions is used. Nozière and coworkers (10) observed the formation of organosulfate compounds when high-ionic-strength solutions of ammonium sulfate (AS) were irradiated with UV B (UVB) radiation in the presence of alkenes and in absence of radical sources. However, without a clear mechanism of formation, they attributed the phenomenon to the HSO₄⁻ + OH reaction. It is not clear if the pH of the solutions under study would allow a sufficient population of HSO₄⁻ to exist, nor from where the OH radicals originate. The authors speculate that the organics in the solution produce OH radicals via unknown pathways. At approximately the same time, Galloway and coworkers (11) showed that glyoxal uptake onto wet AS particles produce organosulfates, but only when the particles were irradiated with UVA light, not in the dark. While glyoxal is known to react with sulfate anions in the dark, it is not clear why light was needed to produce organosulfates. We now understand these prior observations in the context of new data: SO₄^•– radicals are produced when AS solutions and AS particle water are irradiated together with organics using light available in the solar spectrum. However, these reactions cannot be attributed to any known formation pathways of SO₄^•–. Rather a new reaction needs to be invoked; the exact mechanism at this point remains elusive.     

Zeolite NaP1 Functionalization for the Sorption of Metal Complexes with Biodegradable N-(1,2-dicarboxyethyl)-D,L-aspartic Acid

The possibility of application of chitosan-modified zeolite as sorbent for Cu(II), Zn(II), Mn(II), and Fe(III) ions and their mixtures in the presence of N-(1,2-dicarboxyethyl)-D,L-aspartic acid, IDHA) under different experimental conditions were investigated. Chitosan-modified zeolite belongs to the group of biodegradable complexing agents used in fertilizer production. NaP1CS as a carrier forms a barrier to the spontaneous release of the fertilizer into soil. The obtained materials were characterized by Fourier transform infrared spectroscopy (FTIR); surface area determination (ASAP); scanning electron microscopy (SEM-EDS); X-ray fluorescence (XRF); X-ray diffraction (XRD); and carbon, hydrogen, and nitrogen (CHN), as well as thermogravimetric (TGA) methods. The concentrations of Cu(II), Zn(II), Mn(II), and Fe(III) complexes with IDHA varied from 5–20 mg/dm³ for Cu(II), 10–40 mg/dm³ for Fe(III), 20–80 mg/dm³ for Mn(II), and 10–40 mg/dm³ for Zn(II), respectively; pH value (3–6), time (1–120 min), and temperature (293–333 K) on the sorption efficiency were tested. The Langmuir, Freundlich, Dubinin–Radushkevich, and Temkin adsorption models were applied to describe experimental data. The pH 5 proved to be appropriate for adsorption. The pseudo-second order and Langmuir models were consistent with the experimental data. The thermodynamic parameters indicate that adsorption is spontaneous and endothermic. The highest desorption percentage was achieved using the HCl solution, therefore, proving that method can be used to design slow-release fertilizers.     

Study of Forms of Compounds of Vanadium and Other Elements in Samples of Pyrometallurgical Enrichment of Ash from Burning Oil Combustion at Thermal Power Plants

The results of the processing of ash from the combustion of fuel oil after roasting with the addition of Na₂CO₃ followed by aluminothermic melting are presented. As a result, metallic nickel and vanadium slag were obtained. Studies of slag, metal, and deposits on the electrode were carried out. The resulting metal contains about 90 wt% Ni. The main phases of scurf on the electrode are a solid solution based on periclase (Mg_{1–x–y–z}Ni_xFe_yV_zO), sodium-magnesium vanadate (NaMg₄(VO₄)₃), and substituted forsterite (Mg_2–x–yFe_xNi_ySiO₄). The processing of ash made it possible to significantly increase the concentration of vanadium and convert it into more soluble compounds. Vanadium amount increased from 16.2 in ash to 41.4–48.1 V₂O₅ wt% in slag. The solubility of vanadium was studied during aqueous leaching and in solutions of H₂SO₄ and Na₂CO₃. The highest solubility of vanadium was seen in H₂SO₄ solutions. The degree of extraction of vanadium into the solution during sulfuric acid leaching of ash was 18.9%. In slag, this figure increased to 72.3–96.2%. In the ash sample, vanadium was found in the form of V⁵⁺, V⁴⁺ compounds, vanadium oxides VO₂ (V⁴⁺), V₂O₅ (V⁵⁺), and V₆O₁₃, and nickel orthovanadate Ni₃(VO₄)₂ (V⁵⁺) was found in it. In the slag sample, vanadium was in the form of compounds V⁵⁺, V⁴⁺, V³⁺, and V^(0÷3)+; V⁵⁺ was presented in the form of compounds vanadate NaMg₄(VO₄)₃, NaVO₃, and Ca_xMg_yNa_z(VO₄)₆; V³⁺ was present in spinel (FeV₂O₄) and substituted karelianite (V_{2–x–y–z}Fe_xAl_yCr_zO₃). In the obtained slag samples, soluble forms of vanadium are due to the presence of sodium metavanadate (NaVO₃), a phase with the structure of granate Ca_xMg_yNa_z(VO₄)₆ and (possibly) substituted karelianite (V_{2–x–y–z}Fe_xAl_yCr_zO₃). In addition, spinel phases of the MgAl₂O₄ type beta-alumina (NaAl₁₁O₁₇), nepheline (Na_4–xK_xAl₄Si₄O₁₆), and lepidocrocite (FeOOH) were found in the slag samples.     

Research on Three-Dimensional Porous Composite Nano-Assembled α-MnO2/Reduced Graphene Oxides and Their Super-Capacitive Performance

A series of three-dimensional porous composite α-MnO₂/reduced graphene oxides (α-MnO₂/RGO) were prepared by nano-assembly in a hydrothermal environment at pH 9.0–13.0 using graphene oxide as the precursor, KMnO₄ and MnCl₂ as the manganese sources and F⁻ as the control agent of the α-MnO₂ crystal form. The α-MnO₂/RGO composites prepared at different hydrothermal pH levels presented porous network structures but there were significant differences in these structures. The special pore structure promoted the migration of ions in the electrolyte in the electrode material, and the larger specific surface area promoted the contact between the electrode material and the electrolyte ions. The introduction of graphene solved the problem of poor conductivity of MnO₂, facilitated the rapid transfer of electrons, and significantly improved the electrochemical performance of materials. When the pH was 12.0, the specific surface area of the 3D porous composite material αMGs-12.0 was 264 m²·g⁻¹, and it displayed the best super-capacitive performance; in Na₂SO₄ solution with 1.0 mol·L⁻¹ electrolyte, the specific capacitance was 504 F·g⁻¹ when the current density was 0.5 A·g⁻¹ and the specific capacitance retention rate after 5000 cycles was 88.27%, showing that the composite had excellent electrochemical performance.     

Preparation and Properties of Electrodeposited Ni-B-Graphene Oxide Composite Coatings

With the rapid development of modern industries, the surface quality and performance of metals need to be improved. Composite electrodeposition (co-deposition) has evolved as an important technique for improving the surface performance of metal materials. Herein, a new type of graphene oxide (GO)-reinforced nickel–boron (Ni-B) composite coating was successfully prepared on a 7075 aluminum (Al) alloy by co-deposition. Characterization revealed a significant improvement in the mechanical and anti-corrosion properties of the composite with the incorporation of GOs. The composite showed a rougher, compact, cauliflower-like morphology with finer grains, a higher hardness (1532 HV), a lower rate of wear (5.20 × 10⁻⁵ mm³∙N⁻¹∙m⁻¹), and a lower corrosion rate (33.66 × 10⁻³ mm∙y⁻¹) compared with the Ni-B alloy deposit (878 HV, 9.64 × 10⁻⁵ mm³∙N⁻¹∙m⁻¹, and 116.64 × 10⁻³ mm∙y⁻¹, respectively). The mechanism by which GOs strengthen the Ni-B matrix is discussed.     

Resistance of Soda Residue–Fly Ash Based Geopolymer Mortar to Acid and Sulfate Environments

The early mechanical performances of low-calcium fly ash (FFA)-based geopolymer (FFA–GEO) mortar can be enhanced by soda residue (SR). However, the resistance of SR–FFA–GEO mortar to acid or sulfate environments is unclear, owing to the various inorganic calcium salts in SR. The aim of this study was to investigate the long-term mechanical strengths of up to 360 d and evaluate the resistance of SR–FFA–GEO mortar to 5% HCl and 5% Na₂SO₄ environments through the losses in compressive strength and mass. Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS) and Fourier Transform Infrared Spectrometer (FTIR) experiments were conducted for the SR–FFA–GEO mortars, both before and after chemical attack, to clarify the attack mechanism. The results show that the resistances of the SR–FFA–GEO mortar with 20% SR (namely M10) to 5% HCl and 5% Na₂SO₄ environments are superior to those of cement mortar. The environmental HCl reacts with the calcites in SR to produce CaCl₂, CO₂ and H₂O to form more pores under HCl attack, and the environmental Na⁺ cations from Na₂SO₄ go into Si-O-Al network structure, to further enhance the strength of mortar under Na₂SO₄ attack. These results provide the experimental basis for the durability optimization of SR–FFA–GEO mortars.     

Adducts of the Zinc Salt of Dinitramic Acid

Herein, we describe the synthesis of coordination compounds starting from carbohydrazide ((H₂NHN)₂C=O (CHZ)) and the Zn²⁺ salt of dinitramic acid (HDN), which are high-nitrogen substances that exhibit properties similar to those of a burning-rate inhibitor of pyrotechnic compositions. This study demonstrates that these compounds react with glyoxal to furnish adducts of metal–organic macrocyclic cages bearing the elements of carbohydrazide, complexing metals and the HDN anion, depending on the ratio of the starting reactants. The assembled macrocyclic cage has “host–guest” properties and is a safe container for the storage of HDN salts. X-ray crystallographic analysis of the resultant coordination compound, [Zn(chz)₃(N(NO₂)₂)₂]), indicated that the metal–ligand association occurs via the N and O atoms of carbohydrazide. The zinc salt of dinitramic acid, which is enclosed into adducts with a macrocycle, is thermally stable and insensitive to mechanical impacts. The complex zinc salt of dinitramide was shown herein to exhibit inhibitory activity towards the burning rate of pyrotechnic compositions.     

Eluviation and Leaching of Elements from Broken Fly-Ash-Based Porous Geopolymer

The fly ash from powerplants used for coal mine end backfilling can effectively reduce the impact of ground fly ash accumulation on the environment. However, due to the long-term action of the overlying strata and groundwater, when the backfilling body is broken, heavy metals will also be leached, thus having an impact on the groundwater. Therefore, in this paper, the eluviation and leaching of elements from a broken fly-ash-based porous geopolymer is studied. The fly-ash-based geopolymer material was prepared to perform a dynamic eluviation and static leaching test, and it was found that the amount of Cu and Zn in the leachate was less abundant, whereas Pb was more abundant, but far less than the limit of the Class III groundwater quality standard. An acidic environment and a smaller solid–liquid ratio can promote the leaching of Cu and Zn, while the leaching of Pb is basically unaffected by the pH value. Moreover, the amount of Cu, Zn, and Pb in the lixivium increased with the increase in leaching time, and the amount of Cu and Zn in the lixivium was still low after 150 h of leaching, whereas the amount of Pb was high, approaching the limit value of the Class III groundwater quality standard, showing a tendency to increase after 100 h of leaching. A leaching orthogonal experiment was designed, and the results showed that the main order of each factor affecting the leaching of heavy metals from the fly-ash-based geopolymer was grain size > pH > solid–liquid ratio; thus, the leaching of heavy metals from fly-ash-based geopolymer can be controlled, which is significant with respect to the extensive use of fly-ash materials underground.