Oxyhydroxide Research Articles

Fast degradation of vinyl chloride by green rust and nitrogen-doped graphene

Carbonaceous materials catalyze reductive dechlorination of chlorinated ethylenes (CEs) by iron(II) materials providing a new approach for the remediation of CE polluted groundwater. While most CEs are reduced via β-elimination, vinyl chloride (VC), the most toxic and recalcitrant CE, degrades by hydrogenolysis. The significance of carbon catalysts for reduction of VC is well documented for iron(0) systems, but hardly investigated with iron(II) materials as reductants. In this study, a layered iron(II)‑iron(III) hydroxide sulfate (green rust) was used as reductant for VC, with an N-doped graphene (NG), prepared by co-pyrolysis of graphene and urea, as catalyst. VC (80 μM) was completely reduced to ethylene within 336 h in the presence of 5 g Fe/L GR and 5 g/L NG pyrolyzed at 950 °C, following pseudo-first-order kinetics with a rate constant of 0.017 h−1. Dosing experiments demonstrated that dechlorination of VC takes place on the NG phase. Monitoring of hydrogen formation, cyclic voltammetry, and quenching experiments demonstrated that atomic hydrogen contributes significantly to the dehalogenation reaction, where NG is critical for formation of atomic hydrogen. CE competition experiments demonstrated the presence of specific VC reduction sites with hydrogenolysis being unaffected by concurrent β-elimination reactions. The system exhibited excellent performance in natural groundwaters and in comparison with iron(0) systems. This study demonstrates that GR + NG is a promising system for remediation of VC contaminated groundwater, and the mechanistic part of the study can be used as a reference for subsequent studies.

Self-forming barrier layer for carbon dioxide corrosion protection of mild steel in NaCl solution containing hydroxychavicol isolated from Piper betle L. leaf

Hydroxychavicol compound was isolated from Piper betle L. leaf and identified via preparative high performance liquid chromatography (Prep-HPLC) and nuclear magnetic resonance (NMR) spectroscopy. Hydroxychavicol compound was demonstrated to be a potential inhibitor for mild steel corrosion in carbon dioxide-containing environments due to the formation of a barrier layer on the steel surface. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results indicated that the inclusion of hydroxychavicol in the aggressive environment made steel surfaces more homogeneous and smoother with a rough mean square roughness of 7.78 nm, whereas the steel surface was severely corroded in the blank solution. Moreover, X-ray photoelectron spectroscopy (XPS) results showed an enrichment of hydroxychavicol species combined with iron oxides and hydroxides on the mild steel surface. This can lead to the creation of a protective layer on the mild steel surface, thereby enhancing corrosion protection and localized inhibition. The work suggested a novel approach to isolate corrosion inhibitors from natural products, particularly agricultural by-products for mild steel in carbon dioxide and chloride ion environment with high inhibition performance.

Isolation and Electrochemical Analysis of a Facultative Anaerobic Electrogenic Strain Klebsiella sp. SQ-1.

Electricigens decompose organic matter and convert stored chemical energy into electrical energy through extracellular electron transfer. They are significant biocatalysts for microbial fuel cells with practical applications in green energy generation, effluent treatment, and bioremediation. A facultative anaerobic electrogenic strain SQ-1 is isolated from sludge in a biotechnology factory. The strain SQ-1 is a close relative of Klebsiella variicola. Multilayered biofilms form on the surface of a carbon electrode after the isolated bacteria are inoculated into a microbial fuel cell device. This strain produces high current densities of 625 μA cm-2 by using acetate as the carbon source in a three-electrode configuration. The electricity generation performance is also analyzed in a dual-chamber microbial fuel cell. It reaches a maximum power density of 560 mW m-2 when the corresponding output voltage is 0.59 V. The facultative strain SQ-1 utilizes hydrous ferric oxide as an electron acceptor to perform extracellular electricigenic respiration in anaerobic conditions. Since facultative strains possess better properties than anaerobic strains, Klebsiella sp. SQ-1 may be a promising exoelectrogenic strain for applications in microbial electrochemistry.

Materials analysis in three paintings of Thomas Gainsborough (1727–1788) by portable X-ray fluorescence

Three paintings of Thomas Gainsborough (1727–1788), one of the most influential English portrait painters of the late 18th century, from the collection of the Museu de Arte de São Paulo (MASP) - “Francis Rawdon” (1783–1784), “Portrait of Mrs. John Bolton” (1770), and “Drinkstone Park” (1747) - were investigated using portable X-ray fluorescence (pXRF), employing a W tube anode and an XR-100CR detector. These artworks represent the only paintings by Thomas Gainsborough located in the southern hemisphere. Through an analysis of the behavior of X-ray line net areas for all identified elements in various regions of the oil paintings, it was observed that XRF accurately identified the original materials: Lead White, Calcium Carbonate, Calcium Sulfate, Bone Black, Ivory Black, Yellow Iron Oxide, Prussian Blue, Vermillion, Red Iron Oxide, Umber, and Sienna Earth. Additionally, certain regions exhibited the presence of 19th century pigments: Zinc White, Cobalt Blue, and Chrome Yellow, indicating areas that had undergone restoration. The findings presented in this study align closely with results obtained from other investigations into paintings by Thomas Gainsborough.

Efficacy and mechanism of enhanced Sb(V) removal from textile wastewater using ferric flocs in aerobic biological treatment

Antimony contamination from textile industries has been a global environmental concern and the existing treatment technologies could not reduce Sb(V) to meet the discharge standards. To overcome this shortcoming, ferric flocs were introduced to expedite the biological process for enhanced Sb(V) removal in wastewater treatment plant (WWTP). For this purpose, a series of laboratorial-scale sequential batch reactor activated sludge processes (SBRs) were applied for Sb(V) removal with varied reactor conditions and the transformation of Fe and Sb in SBR system was investigated. Results showed a significant improvement in Sb(V) removal and the 20 mg L−1 d−1 iron ions dosage and iron loss rate was found to be only 15.2%. The influent Sb(V) concentration ranging 153–612 μg L−1 was reduced to below 50 μg L−1, and the maximum Sb(V) removal rate of the enhanced system reached about 94.3%. Furthermore, it exhibited high stability of Sb(V) removal in the face of antimonate load, Fe strike and matrix change of wastewater. Sludge total Sb determination and capacity calculation revealed decreasing in Sb adsorption capacity and desorption without fresh Fe dosage. While sludge morphology analysis demonstrated the aging and crystallization of iron hydroxides. These results verify the distinct effects of fresh iron addition and iron aging on Sb(V) removal. High-throughput gene pyrosequencing results showed that the iron addition changed microbial mechanisms and effect Fe oxidized bacterial quantity, indicating Sb(V) immobilization achieved by microbial synergistic iron oxidation. The present study successfully established a simple and efficient method for Sb(V) removal during biological treatment, and the modification of biological process by iron supplement could provide insights for real textile wastewater treatment.

In-Situ Nanoarchitectonics of Fe/Co LDH over Cobalt-Enriched N-Doped Carbon Cookies as Facile Oxygen Redox Electrocatalysts for High-Rate Rechargeable Zinc-Air Batteries.

The reality of long-term rechargeable and high-performance zinc-air batteries relies majorly on cost-effective and eminent bifunctional electrocatalysts, which can perform both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Herein, we demonstrate a new approach for the synthesis of in-situ-grown layered double hydroxide of iron and cobalt over a cobalt nanoparticle-enriched nitrogen-doped carbon frame (CoL 2:1) by a simple coprecipitation reaction with facile scale-up and explore its electrocatalytic ORR and OER activity for an electrically rechargeable zinc-air battery. Consequently, the developed composite displays excellent ORR and OER activity with an ORR half-wave potential of 0.84 V, a limiting current density of 5.85 mA/cm2, and an OER overpotential of 320 mV with exceptional stability. The outstanding bifunctionality index of the catalyst (ΔE = 0.72 V) inspired us to utilize it as a cathode catalyst in an in-house developed prototype zinc-air battery. The battery could easily supply a specific capacity of 804 mAh/g with a maximum peak power density of 161 mW/cm2. The battery exhibits an attractive charge-discharge profile with a lesser voltage gap of 0.76 V at 10 mA/cm2 with durability for a period of 200 h and a voltage efficiency of 97%, which surpassed the corresponding Pt/C + RuO2-based zinc-air battery. Further, a maximum load of 50 mA/cm2 could easily be sustained during cycling, revealing its outstanding stability. A series-connected two CoL 2:1-based zinc-air batteries effortlessly enlighten a pinwheel fan and LED panel simultaneously, revealing its practicality. The high electrical conductivity and greater specific surface area of Co/N-C and its robust attachment with Fe/Co LDH preserves both active sites, thereby resulting in exceptional performance. Our method is capable of being flexible enough to create various bifunctional Co/N-C-based composite electrodes, opening up a feasible pathway to rechargeable zinc-air batteries with maximum energy density.

Platinum-bearing Fe-Mn oceanic crust on basalts: mineralogy and model of formation

Fe-Mn oceanic crust on basalts of the guyot in the Mid-Pacific Seamount (Pacific Ocean, depth 2486 m, chemical composition (wt %): Mn 24.2, Fe 12.6, Ni 0.59, Co 0.72, Cu 0.13; (ppm) Pt 0.35, Pd 0.0052), was studied using 3D-technology of mineralogical research. In addition to dominaiting vernadite and goethite, the following minerals are identified in the hydroseparation (HS) concentrates of the crust: 1) rock forming and accessory minerals of basalts (clinopyroxene, plagioclase, potassium feldspar, biotite, ilmenite, titanomagnetite, Ti-chrome spinel, zircon, apatite); 2) sulfides that are identical to those from the basalt substrate (pyrite, chalcopyrite, bornite, chalcocite, tennantite, nickel pentlandite Ni4S3, sphalerite, galena, argentite/acantite, molybdenite); 3) native metals (iron, nickel, copper, titanium, tungsten); 4) iron silicides (gupeiite Fe3Si, xifengite Fe5Si3, and hapkeite Fe5Si3); 5) platinum group minerals - unnamed (Cu,Pt)4Si and rustenburgite (Pt,Pd)3(Sn,Sb). The complexes of ore minerals in basalts are identical to those of the Fe-Mn crusts. Basalt accessories are assumed to be primary phases and a source of metals for the formation of native minerals. “Microdroplets” of native iron Fe, (Fe,Ni), nickel Ni, (Ni,Cr), (Ni,Fe) and copper Cu (sizes 20–100 microns, degree of sphericity up to 100%) represent the products of their crystallization from metal melts in basalts, transported by deep fluid into Fe-Mn crusts on these rocks. The zoned microglobules of 20–70 microns sizes with iron or native nickel (core) + successive rims of wüstite-magnetite and Fe-Mn hydroxides were identified. They were apparently formed during the movement of these solid microparticles (from bottom to the top) along intergranular spaces and other permeability channels in basalts under conditions of increasing oxygen fugacity and falling temperature at various levels of deep fluid infiltration. The crystallization of native metals in the Fe-Mn crust that are characterized by low-temperature (10 °C) and oxidizing (fO2 MHG magnetite-hematite-goethite) conditions of mineral formation is impossible. The goethite replacement to different extent of many grains of relict Fe-minerals (sulfides and native metals) that are “foreign” to the Fe-Mn crust have been established. Fe-Mn crusts were formed as a result of the precipitation of colloidal particles Mn2+(Ba2+и Sr2+), to a lesser extent of the iron hydroxide Fe(ОН)3, as well as the concentration and transformation of micrograins of minerals of other metals, extracted by fluid from basaltic substrates. The comparison of the physico-chemical parameters of crystallization of basalts and native metals suggests another source of formation of native minerals in basalts, different from the postmagmatic basaltic fluid, i.e. deep-seated sharply reducing "hot" gas flows associated with superplumes. The mineralogical data determines a volcanogenic-fluid-oceanic model for the formation of Fe-Mn crusts on underwater oceanic elevations.

Application of response surface methodology for optimization of removal sunset yellow from aqueous by Granular Ferric Hydroxide (GFH)

Color is the first pollutant that is detected in wastewater and can be discharged into the wastewater through various industries. Sunset yellow is an azo dye that is used in the food, health and pharmaceutical industries. Due to its low price and good quality, this color is used in industries more than natural colorants. The aim of this study was to investigate the effect of granular ferric hydroxide (GFH) on the removal of sunset yellow color from aqueous solution using the response surface methodology (RSM). In this study, GFH was employed to remove sunset yellow dye from the aqueous solution. Due to saving time, cost and getting to the optimum conditions, the effect of important factors on adsorption was optimized by the RSM. The morphology of the adsorbent was determined by scanning electron microscopy. The results revealed that optimum conditions for sunset yellow removal by GFH with design experiment were dye concentration= 24 mg/L, GFH dose= 2.4 g/L, reaction time= 25 min. In addition, based on the results, the best-fitted model for this study was the quadratic model (R2 =0.966, R2adj=0.79 and R2pred=0.936). According to the obtained results, GFH was successful in sunset yellow removal. Therefore, it is suggested to use this process to remove sunset yellow from aqueous solutions.

Applying biochar coupled with pyrite substrates simultaneously enhanced nutrient and heavy metal removal in constructed wetland: Performance and mechanism

Wastewater polluted by heavy metals with low C/N ratio posed a big challenge to constructed wetlands (CWs) for sustainable advanced wastewater purification. In this study, biochar coupled with pyrite was successfully applied in CWs to simultaneously remove organics, total nitrogen (TN), total phosphorus (TP) and heavy metals, with the highest removal efficiency of 95.78%, 98.78%, 96.22% and 99.91%, respectively. Batch tests proved that the complexation of ferric hydroxide from pyrite oxidation played an important role in TP and heavy metals removal. Meanwhile, fluorescence excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC) further manifested that protein-like substances contributed a lot to heavy metals stabilization. Moreover, the multiplication of Proteobacteria, Chloroflexi at phylum level and Dechloromonas at genus level, which were capable of heterotrophic or autotrophic nitrate reducing process indicated that the denitrification capacity of CWs was significantly enhanced by biochar and pyrite. This study provided a feasible insight into the application of CWs with biochar and pyrite addition to enhance the treatment of low C/N wastewater.

Biochar accelerated Fenton process for roxarsone oxidation, inorganic arsenic adsorption and simultaneous immobilization of arsenic-iron sludge

Complete remediation of organoarsenics from environmental matrix hits the bottleneck, that is, the sluggish efficiency of oxidative degradation towards organoarsenics and unsatisfying immobilization performance towards generated inorganic arsenic. Herein, we establish a biochar accelerated Fenton (BA-Fenton) process to decontaminate water from roxarsone (ROX). In comparison with Fe2+/H2O2 process (10 μΜ/0.2 mM), the incorporation of 0.5 g L-1 biochar promoted ROX degradation from 48.2% to 98.2% and total arsenic elimination from 67.6% to 97.3%, respectively. In BA-Fenton process, •OH as the dominant reactive oxygen species (ROS), exhibited a cumulative concentration of 0.42 mM, three times higher than that in classical Fenton process. Crucially, the presence of biochar in Fenton process significantly enhanced the stability of arsenic-iron sludge, whereas the secondary leaching of total arsenic decreased from 433.8 μg-As L-1 to 13.9 μg-As L-1, meeting the prescribed environmental quality standards for surface water in China (50 μg-As L-1, GB 3838-2002). Mechanistic studies unveiled ROX remediation mechanism by BA-Fenton process, highlighting the dual functionality of biochar. On one hand, biochar efficiently reduced Fe3+ to Fe2+ with a rate constant of 0.225 min-1, overcoming the rate-determining step of classical Fenton process for •OH production, consequently promoting the transformation of ROX to As(V). On the other hand, molecular spectroscopy analysis elucidated that in-situ formed As(V) was adsorbed by ferric hydroxides with the formation of arsenic-iron sludge. Subsequently, biochar immobilized arsenic-iron sludge through hydrogen bonds, electrostatic attraction and surface complexation. Furthermore, real water studies demonstrated the effective remediation of organoarsenics by BA-Fenton process in tap water, lake water and chicken manure leachate. This “Two Birds with One Stone” strategy with low-cost, environmental-friendly and sustainable biochar holds great promise for the ultimate disposal of industrial wastewater containing organoarsenics.

A Fenton-based approach at neutral and un-conditioned pH for recalcitrant COD removal in tannery wastewater: Experimental test and sludge characterization

The combination of raw animal skin manufacturing processes involves the use of large amounts of chemicals, resulting in the generation of complex and highly polluted tannery wastewater. In this context, the high concentration of chloride in tannery wastewater represents a crucial bottleneck. Indeed, sodium chloride, commonly used in tannery industry to prevent skin rot, increases the concentration of chlorides up to 50 %. At the same time, most of the advanced oxidation processes usually employed in tannery wastewater treatment to remove recalcitrant COD involve the use of conditioning agents, thus increasing the overall concentration of chlorides in the treated effluent. The aim of this study was to evaluate the electrochemical peroxidation process (ECP) efficiency in the treatment of tannery wastewater without changing pH, to improve Fenton technology by avoiding the use of chemicals. The influence of different electric currents on COD and color removal was investigated. The characterization of the produced sludge was conducted through FTIR, SEM and XRD analysis, exploring the morphology and composition of precipitate, depending on the applied current. Although an electrical current of 750 mA yields the highest COD and color removal efficiency (69.7 % and 97.8 %, respectively), 500 mA can be considered the best compromise because of energy consumptions. Iron oxides and hydroxides were generated during the ECP process, playing the role of coagulants through the absorption of organic and inorganic contaminants. The consumption of energy increased as a function of time and applied current; however, cost analysis showed that the electrodes contributed the most to the total cost of the process. In authors' knowledge, the application of ECP process as a tertiary treatment for the removal of recalcitrant COD in tannery wastewater represents a novelty in the literature and the results obtained can be considered as the basis for scaling up the process in future research.

Preparation of highly adsorptive biochar by sequential iron impregnation under refluxing and pyrolysis at low temperature for removal of tetracycline

Iron-doping modification is a prevailing approach for improving adsorption capability of biochar with environmental friendliness, but usually requires high temperature and suffers from iron aggregation. Herein, a highly adsorptive biochar was manufactured via sequential disperse impregnation of iron by refluxing and pyrolysis at low temperature for eliminating tetracycline (TC) from aqueous solution. Iron oxides and hydroxides were impregnated and stably dispersed on the carbon matrix as pyrolyzed at 200 °C, meanwhile abundant oxygen and nitrogen functional groups were generated on surface. The iron-doped biochar exhibited up to 891.37 mg/g adsorption capacity at pH 5, and could be recycled with high adsorption capability. The adsorption of TC should be mostly contributed to the hydrogen bonding of N/O functional groups and the hydrogen bonding/coordination of iron oxides/hydroxides. This would provide a valuable guide for dispersedly doping iron and conserving functional groups on biochar, and a super iron-doped biochar was prepared with superior recyclability.

SYNTHESIS OF ALUMINA FROM KAOLIN FOUND IN AJEBO, OGUN STATE, NIGERIA

This study proposes the utilization of kaolin as an alternate resource for alumina production due to the decreasing availability of bauxite ores in Nigeria. This project covers the procedures and operations required to produce a high surface area γ-alumina using kaolin, a refractory material. The kaolin used in this study was sourced from Ajebo in Ogun State, Nigeria. The mineral processing of kaolin was the initial step involving removing inherent impurities from the clay. Subsequently, calcination was performed to eliminate crystallised water and impurities and activate the kaolin's limited alumina content. This activation process facilitated the subsequent acid-leaching reactions. At 90oC, 5M HCl acid was used to leach meta-kaolin, which was then filtered. The filtrate was mixed with 5M NaOH at 900oC and was transformed into sodium aluminate. This reaction also facilitated the removal of magnesium and iron hydroxides. Subsequently, HCl was introduced to adjust the pH of the solution. The resulting aluminium hydroxide was then calcinated at temperatures of 700oC and 900oC for 2 hours each to produce γ-alumina. Ultimately, the calcined material was cooled to ambient temperature inside the furnace. The produced γ-alumina was further characterised using X-ray Fluorescence (XRF), Fourier Transform Infrared spectrometer (FTIR), and Scanning Electron Microscopy (SEM).

Zero-valent iron in phosphate removal: Unraveling the role of particle size and dissolved oxygen

The effect of particle size and dissolved oxygen (DO) on zero-valent iron (ZVI) oxidation needs further study to propose strategies for improving phosphate (P) removal performance. In this study, batch and column experiments were conducted to investigate P removal by ZVI with five different particle sizes under aerobic and anaerobic conditions. The oxidation status of ZVI before and after the reaction was characterized. Under aerobic conditions, as ZVI size increased, the P removal rate initially increased and then decreased, while the difference in P removal was not obvious under anaerobic conditions. Furthermore, the P removal rate exhibited a significant positive correlation with the degree of ZVI oxidation (R2 = 0.877, p = 0.008), highlighting its pivotal role in P removal. The ZVI size and DO on ZVI oxidation primarily affect the types and quantities of iron corrosion products (FeCPs). Under aerobic conditions, the ZVI with small particle sizes (ZVIsps) (50 nm, 500 nm, and 5 μm) tended to form passivation layers composed of amorphous iron oxide (ap-FexOy) and FePO4, limiting ZVI oxidation and resulting in lower P removal rates (17.6%). Conversely, in situations with less passivation, amorphous iron hydroxides (ap-FexOHy) play a dominant role in the P removal process. The 50 μm ZVI eventually generated lepidocrocite (γ-FeOOH) under aerobic conditions, this sufficient oxidation was also the reason for its high P removal rate. Therefore, future research and applications of ZVI materials in P removal should concentrate on enhancing ZVI corrosion and regulating the formation of suitable FeCPs.

Recovery of sulfuric acid and iron from titanium dioxide waste acid by membrane electrolysis combined with selective electrodialysis

The waste acid generated during the production of titanium dioxide contained a high proportion of ferrous ions. Comprehensive utilization of these waste acid involves the recovery of sulfuric acid and iron. However, traditional methods faced difficulty in attaining the desired outcome. Therefore, this study proposed a treatment process primarily based on membrane electrolysis. Initially, selective electrodialysis was employed to recover sulfuric acid from the waste acid. The effects of initial acid concentration, potential, and operating time on the performance of selective electrodialysis were investigated. Subsequently, a three-chamber membrane electrolysis method was utilized to oxidize Fe2+ to Fe3+ in the anode chamber and generate OH– in the cathode chamber. Both compounds were directed to the precipitation chamber through ion exchange membranes, resulting in the formation of iron hydroxide and the successful recovery of iron. The findings revealed that when the waste acid had a high initial concentration, it was recommended to operate at a higher potential. When treating 18 % of the waste acid, 77.5 % of the sulfuric acid can be recovered while 78 % of the ferrous ions were retained. As the acidity decreased, the potential could be reduced, resulting in a higher recovery rate of sulfuric acid and retention rate of Fe2+. By using a current of 150 mA during membrane electrolysis and maintaining a pH of 2.4 in the precipitation chamber, a purity of 94 % iron hydroxide was achieved. The ion flux of the anion exchange membrane decreased by 19 % after 8 h of electrolysis. This reduction could be mitigated by cleaning the membrane with titanium dioxide waste acid with a pH of 0.4 for 30 min. This study is expected to introduce innovative ideas and methods for the efficient and high-purity recovery of resources from titanium dioxide waste acid.

Loess doll from Pleistocene loess-like sediments in the Vishera diamond-bearing area (Perm region)

The purpose of the study is to investigate the cranes from loess-like deposits as indicator formations for the glacial epochs of the late Pleistocene – Holocene using current lithology methods. The motivating reason for the study was that loess-like deposits directly “seal” the industrial placer of the Silurian diamond-bearing reservoir in the Vishera diamondiferous region.Loess doll (loess pupae, dutiki) are concretions weakly cemented by iron hydroxides, consisting of quartz grains with an admixture of fine-silty feldspars. In terms of granulometry and mineral composition, the cranes correspond to the loess-like deposits that host them and are the frame of the root system of tundra-type grass vegetation. In the center of the concretion, in place of the disappeared grass root, a hollow tubule is preserved, sometimes filled with silty sand from the surrounding rocks.The granulometric composition of loess-like deposits was studied using an Analysette 22 MicroTec plus laser diffraction analyzer. Mineral composition of the heavy fraction of loess-like and underlying sediments – using quantitative mineralogical analysis. Quantitative gross mineral composition and the ratio of clay minerals in the pelitic fraction – using a D2 Phaser X-ray powder diffractometer (Bruker, Germany).The data obtained can be used for geological surveying and exploration of diamond-bearing placers in the Urals and in regions with a similar geological structure. It must be borne in mind that in the study area the described loess-like deposits do not have a direct connection with industrial placer diamond content.

Features of the Tanalyk gold placer and its primary sources (the Baymak ore-placer cluster, Southern Urals)

The article presents the results of a study of the Tanalyk placer, which is part of the Baymak ore-placer cluster. It is shown that gold is predominantly bright yellow in color and has lump-shaped, wedge-shaped, plate-shaped and wire-rod-shaped forms. In terms of granulometric composition, it belongs to the large and medium class and is characterized mainly by medium roundness. The uniformity of morphological varieties of gold in different lithological and stratigraphic horizons indicates the inheritance of gold from ancient deposits to young ones.
 Placer gold is of high quality and has a fairly consistent composition; the main impurity here is silver, the content of which varies from 0.2 to 9%. The average fineness of gold in the placer in the following areas: Baymak pond – 938, Shurinsky log – 935, Aktash log – 943, Tanalyk (lines 1502-1559) – 917. Hypergene new formations on the surfaces of gold grains are represented by high-fineness rims. A common feature for gold of all size classes is the presence in the depressions and on their surface of films of iron and manganese hydroxides, crusts of fine-grained quartz, chlorite, and less commonly biotite, in which a large number of microparticles of very high-fine gold measuring 0.1–0.5 μm were found.
 The typomorphism of schlich gold, its composition and features of the internal structure indicate that the main source of gold was gold-quartz mineralization in the zones of wall-metasomatites of the Kul-Yurt-Tau gold-pyrite deposit, gold-polymetallic and gold-barite deposits Grafskoye, Troitsk and Novo-Troitsk. The junction points of diagonal neotectonically active lineaments with meridional magma- and ore-supplying faults form polychronic and polygenic through ore-concentrating structures. Dispersed gold occurrences in these structures are placer-forming and serve as the main source of the formation of large placers.

Ultrasonic-enhanced selective arsenic removal and sulfide conversion from iron slag

There are numerous valuable metals and the hazardous element arsenic in the iron slag produced in the zinc hydrometallurgy. The arsenic must be removed for comprehensive recovery of valuable elements. Generally, the alkaline arsenic removal produces large amounts of iron hydroxide colloids and iron slag agglomeration. Here, ultrasonic enhancement of NaOH–Na2S system is proposed to selectively remove arsenic from iron slag. Ultrasound destroys the agglomeration and encapsulation of zinc-containing iron slag and promotes the liquid-solid interfacial reaction. The arsenic removal percentage is 92.24% under ultrasonic power of 400 W, which is 12.14% higher than the conventional alkaline arsenic removal. The apparent activation energy of ultrasonic-enhanced alkali leaching for arsenic removal is calculated to be only 8.84 kJ/mol by kinetic experiments. Diffusion is proved to be the limiting link in the ultrasonic-enhanced leaching process for arsenic removal. This study proves that ultrasonic-enhanced Na2S–NaOH system has a good prospect for selective removal of arsenic from iron slag.

Research on lignin-modified flexible polyurethane foam and its application in sound absorption

Lignin is a sustainable biomass resource with abundant hydroxyl groups that holds great promise for use as a feedstock for polyurethane foam production. Therefore, the flexible polyurethane foams (FPUFs) were prepared using the oxidized alkali lignin (OAL) as the matrix to enhance its compatibility. The OAL was obtained under the following conditions of 60 °C, 80 min treatment, a ratio of hydrogen peroxide to lignin of 1.2:1, and a ratio of iron hydroxide to lignin of 0.01. It was demonstrated that incorporating OAL enhanced the density, compressive strength, sound-absorbing performance and degradability of foam composites. The compressive strength was also improved by more than five times than that of blank foam under the optimal conditions, reaching 0.11 MPa. The thermogravimetric analysis (TGA) revealed that the foam composite containing 30 % modified lignin content exhibited the highest thermal stability. The results of solvent resistance testing demonstrated the durability of the foam composites in both water and solvents. Lignin-modified polyurethane foam exhibited an acoustic absorption coefficient above 0.2 across a wide frequency range, with the highest value reaching 0.84, meeting the conventional requirements for sound absorption materials (α > 0.2). The results suggested that this environmentally friendly preparation method was feasible for producing high-performance polyurethane foams, which was appropriate for the production of sound absorption boards for industry, transportation by train and automobile.

Influence of Al/Fe ratio on the hydration of brownmillerite in the presence of calcium sulfate

The brownmillerite, as an indispensable mineral phase in Portland cement, is actually a series of solid solution of Ca2(AlyFe(2–y))O5 (0 ≥ y ≤ 1.33). The varying values of y would significantly influence the hydration characteristic of brownmillerite. The hydration performance of brownmillerite where y = 0.9, 1.1 and 1.3 in Ca2(AlyFe(2–y))O5 in the presence of calcium sulfate, is deeply researched in this work. The brownmillerite Ca2(Al1.1Fe0.9)O5 and Ca2(Al1.3Fe0.7)O5 show a doublet of heat flow curve corresponding to formation of different amounts of ettringite while a single exothermic peak appears in Ca2(Al0.9Fe1.1)O5 due to generation of a layer of gel-like phases. Combining with density functional theory (DFT) calculations, it is concluded that the hydration reactivity of brownmillerite increases with reducing Al/Fe ratio. Fe is inclined to occupy octahedral sites as augment of Fe content in brownmillerite. Due to highly hydraulic activity of these sites, the lowest Al/Fe ratio of brownmillerite corresponds to highest hydration rate in first few hours. However, more iron hydroxide radicals aggregate in the surface of unhydrated brownmillerite and form a layer of iron-rich hydration products which would dramatically slow down the following hydration progress. In addition, this postponement to hydration will gradually recede with reduction of Fe content in brownmillerite. This finding provides a novel perspective on the understanding of Al/Fe ratio to the hydration performance of brownmillerite.