Isomorphous Substitution Research Articles

Compositional heterogeneity of secondary minerals in mine waste rock: Origins and implications for water quality.

Secondary minerals in mine waste materials impose strong controls on water quality by scavenging solutes of concern. This study investigates the mineralogical and compositional characteristics of secondary Fe(oxy)hydroxides and Ca-sulfates, two globally ubiquitous secondary precipitates, in weathered mine waste rock. Bulk analyses show that Si, Ca, Fe, Al, and S-bearing primary phases were the most abundant in the entire samples, but up to a few wt% of secondary Fe(oxy)hydroxides and Ca-sulfates were present as well. In these secondary phases, trace metal impurities like V (37 mg/kg in Ca-sulfates), Cr (23 mg/kg in Fe-oxides and 21 mg/kg in Ca-sulfates), and Cd (up to 15 mg/kg in Fe-oxides and Ca-sulfates) could not be detected by bulk techniques (XRF and XRD), but their deportment to some extent characterized by automated mineralogy, and their spatial distribution assessed at high-resolution through microscale LA-ICP-MS analysis. Element mapping revealed that metal(loid)s were generally enriched at grain rims, reflective of peripheral sequestration through surface adsorption. An exception was V, which was uniformly distributed in the studied secondary Fe-oxides, suggestive of isomorphic substitution during co-precipitation. Factor analysis revealed distinct groups of elements co-associated within each secondary mineral (e.g., divalent transition metal cations versus oxyanionic metalloids), likely caused by similar primary mineral sourcing or a comparable sequestration mechanism. Our results demonstrate the importance of secondary mineral precipitates for scavenging (trace) elements and the insights that can be gained from complementary mineralogical and element analyses for the interpretation of trace element dynamics in waste rock.

Assessment of the durability of hardening products of modified fly ash cement compositions

This work is devoted to the study of the durability of hardening products of modified gold-cement compositions. The influence of sulfate and carbonate additives of various origins on the kinetics of increasing the strength of artificialstone was studied.To reveal the mechanism of the processes of strength synthesis of the developed binder systems, their hydration products and the composition of new formations were studied using X-ray diffraction (XRD), differential thermal analysis(DTA) and electron microscopy.It was established that with simultaneous modification of the plasticized fly ash cement composition with sulfate and carbonate additives, the synthesis of strength is ensured due to the formation of hydration products in the composition atthe early stages of hardening of ettringite and its analogues containing carbonate and ferric components. It has been determined that the presence of hydrosulfoaluminate-type new formations in the hydration products and the presence of active mineral additives in its composition on the one hand, and on the other hand, the contact of cement stonewith the environment can cause the appearance of dangerous compounds (such as thaumasite) in hardening systems, the synthesis of which leads to the emergence of stresses in the structure of the material and its destruction. It has been established that as a result of the processes of isomorphic substitution, compounds of variable composition are formed, similar to solid solutions, due to which the strength of artificial stone is ensured in the later stages of hardening. On the other hand, the released sulfate ions can replace silicon groups in the tobermorite gel and form compounds similar to epistilbite (Ca6(Si(OH)6)3·(SO4)3·24H2O) (d=0.584; 0.399; 0.369; 0.354 nm). The strength indicators of artificial stone basedon modified fly ash cement binder compositions were investigated. It is associated with the directed formation of crystallochemically similar phases that can grow together, and the formation of artificial stone capable of structural and functional adaptation in various operating conditions will likely be due to the formation of solid solutions of hydrosulfoaluminocarbosilicate composition, hydrogarnet phases of the composition 3СаО·Al2O3·1,6SiO2·2,8H2O and modified calcium hydrosilicates of the epistilbite type Ca6(Si(OH)6)3·(SO4)3·24H2O) and scoutite (Са6Si6O18·2H2O·CaCO3). in the composition of new formations.

LA-ICP-MS Trace Element Characteristics and Geological Significance of Stibnite in the Zhaxikang Pb–Zn–Ag–Sb Deposit, Southern Tibet, SW China

Discovered within the North Himalayan Metallogenic Belt (NHMB), the Zhaxikang Pb–Zn–Ag–Sb deposit stands as the sole super-large scale ore deposit in the region. This deposit holds significant quantities of Pb and Zn (2.066 million tons at 6.38% average grade), Ag (2661 tons at an average of 101.64 g/t), and Sb (0.235 million tons at 1.14% average grade), making it one of China’s foremost Sb–polymetallic deposits. Stibnite represents the main carrier of Sb in this deposit and has been of great attention since its initial discovery. However, the trace element composition of stibnite in the Zhaxikang deposit has not yet been determined. This study carried out an analysis of the distribution patterns and substitution processes of trace elements within stibnite gathered from the Zhaxikang deposit, aiming to provide crucial information on ore-forming processes. Utilizing high-precision laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), we discovered that the studied stibnite is notably enriched in arsenic (~100 ppm) and lead (~10 ppm). Furthermore, the notably consistent time-resolved profiles suggest that elements such as Fe, Cu, As, In, Sn, Hg, and Pb predominantly exist as solid solutions within stibnite. Consequently, it is probable that the enrichment of Cu, Pb, and Sn in stibnite is due to isomorphic substitution reactions, including 3Pb2+↔2Sb3+, Cu+ + Pb2+↔Sb3+, and In3+ + Sn3+↔2Sb3+. Apart from that, Mn, Pb, and Hg with the spiky signals indicate their existence within stibnite as micro-inclusions. Overall, we found that the trace element substitutions in stibnite from the Zhaxikang Pb–Zn–Ag–Sb deposit are complicated. Incorporations of trace elements such as Pb, Cu, and In into stibnite are largely influenced by a variety of factors. The simple lattice structure and constant trace elements in studied stibnite indicate a low-temperature hydrothermal system and a relatively stable process for stibnite formation.

The Trace-Element Characteristics of Chrysoberyl: Insights from Compositional and Spectroscopic Analyses

To characterize the trace-element characteristics of chrysoberyl, we studied twenty-six chrysoberyl samples from various localities by using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS), photoluminescence (PL), and ultraviolet–visible–near-infrared (UV–Vis–NIR) spectroscopy. Chemical analysis has confirmed the existence of trace elements, including Fe, Ti, Ga, Sn, B, Cr, and V. The phenomenon of ionic isomorphic substitution frequently occurs at lattice sites within chrysoberyl. Notably, the isomorphic substitution of Al3+ in octahedral sites is significant, with the primary substituting elements being Fe, Ti, Cr, V, Ga, and Sn. The PL spectra of chrysoberyl samples exhibit sharp peaks at 678 and 680 nm, which are attributed to Cr3+, even in samples in which the Cr concentration is below the detection limit of LA-ICP-MS. This demonstrates the high-sensitivity feature of PL spectroscopy. The UV–Vis–NIR spectra of chrysoberyl samples consistently exhibit a band at 440 nm, and strong double narrow bands near 367 nm and 375 nm are observed. These spectral features are associated with Fe3+ chromophores—specifically, Fe3+-Fe3+ pairs or clusters and Fe3+ ions, respectively. By combining LA–ICP–MS analysis and PL mapping on a sample exhibiting color zoning, it has been found that the darker sections contain a higher concentration of Cr compared to the lighter sections, while the concentrations of other elements remain largely consistent. In other words, subtle variations in Cr concentration may be the underlying cause of color zoning in chrysoberyl.

Zheshengite, Pb4ZnZn2(AsO4)2(PO4)2(OH)2: A New Mineral of the Dongchuanite Group and the Influence of As–P Isomorphic Substitution on Unit-Cell Parameters of Dongchuanite Group Minerals

Zheshengite (IMA2022-011), Pb4ZnZn2(AsO4)2(PO4)2(OH)2, is a new mineral from Sanguozhuang Village in the eastern Dongchuan Copper Ore Field, Yunnan Province, China. The new mineral is named after Zhesheng Ma (1937–). Zheshengite occurs as prismatic single crystals with chisel-like terminations on hemimorphite, with crystal sizes ranging from 0.02 to 0.05 mm. It is a brittle mineral with irregular fractures, a Mohs hardness of 2½ to 3, perfect cleavage on {011}, and a calculated density of 6.26 g/cm3. The empirical formula of zheshengite, based on 18 O atoms per formula unit, is (Pb4.12Ca0.01)∑4.13(Zn0.83Cu0.23Fe0.04)∑1.10Zn2.00[(As0.90P0.10)∑1.00O4]2[(P0.94Si0.01)∑0.95O4]2(OH)2. Zheshengite exhibits a triclinic structure (space group P−1, no. 2), with unit-cell parameters: a = 4.7746(4) Å, b = 8.4920 (7) Å, c = 10.4056 (8) Å, α = 97.087 (7)°, β = 101.060 (7)°, γ = 92.996 (7)°, V = 409.66 (6) Å3, and Z = 1. As a member of the dongchuanite group, zheshengite features a dongchuanite-type structure. This study reveals the impact of As–P isomorphic substitution on unit-cell parameters in the dongchuanite group, identifying correlations between As content and changes in parameters a and V, which may serve as diagnostic indicators for dongchuanite group minerals. In addition, the structure studies of zheshengite may have implications for environmental protection.

Variations in chemical compositions of titanite group minerals from ore skarnes in the Ladoga Lake Region (South Karelia, Russia)

Titanite, aluminium- and fluorine-enriched titanite, tin-bearing titanite and malayaite from ore skarns in the Ladoga Lake region were studied. Composition of these minerals from skarns with W-Zn-Pb-Bi (Latvasyrja, Jokiranta) and Sn-Zn-Cu-Fe-In (Pitkäranta Mining District) mineralization, related genetically to S-type and А-type granites, was analyzed. For the first time for ore deposits and occurrences in Karelia, there was detected titanite enriched in aluminum (Al2O3 5—7 wt%) and fluorine (~3 %). Isomorphic substitutions in titanite from skarns with different metallogenic specialization were considered. It is shown that the following isomorphic schemes are realized for studied titanite: (Al, Fe)3+ + F– ↔ Ti4+ + O2–; (Al, Fe)3+ + (OH)– ↔ Ti4+ + O2–, where Al ≥ Fe (skarns with W-Zn-Pb-Bi mineralization); and Sn4+ ↔ Ti4+ (skarns with Sn-Cu-Fe-Zn-In mineralization). The Sn-bearing titanite from Sn-bearing skarns nearly in all cases contains Fe, what it seems due to the high Fe# in rapakivi granites (containing biotite and other mafic minerals with Fe# 0.9) and the associated post-magmatic mineralization (columbite-(Fe), synchysite-(Fe), marmatite). The formation of titanite enriched in aluminum and fluorine was controlled by protolith and fluid compositions rather than temperature and pressure (≤500 ◦C, ≤5 kbar). Crystallization of this titanite in Jokiranta ore occurrences took place during a post-ore-forming process, potentially capable to the remobilization of base-metals ores.

Recent Advances in the Synthesis and Application of TS‐1 Zeolite for Green Catalytic Oxidation

AbstractTS‐1 has a unique structure, and TS‐1/H2O2 oxidation system for composition shows excellent catalytic performance in the oxidation of a variety of organic matter. The response conditions of the reaction system are mild, and the ultimate oxidation product is water. It is a typical “green catalytic” system and has received widespread attention from researchers. Here, the synthesis progress of TS‐1 to improve the accessibility and activity of active sites by doping mesoporous and microporous structures into traditional TS‐1 zeolite in recent five years are reviewed, including hydrothermal synthesis, dry gel conversion synthesis, solvent‐free synthesis, microwave assisted synthesis, and isomorphous substitution. Meanwhile, the application of TS‐1/H2O2 system in oxidative desulfurization, ketone ammonia oxidation, olefin epoxidation, and hydroxylation of aromatic hydrocarbons reactions are summarized and discussed. What's more, the reaction mechanism based on TS‐1/H2O2 system is proposed on regarding the isolated skeleton Ti site in titanium‐silicon zeolite as the active central site. Finally, the challenges and future development prospects of TS‐1 zeolite in synthesis and catalytic applications are predicted.

Aging Process Reduces Arsenic Availability in Precipitates Due to Mineralogical Transformations in Fe and Al (Hydr)oxides

ABSTRACT Crystallinity changes of iron (hydr)oxides can occur due to many factors such as pH alterations, temperature, and aging. These alterations can influence solubility and therefore, the mobilization of potentially toxic elements (PTE) that are associated to iron (Fe) compounds. In this study, precipitates of pure and aluminum (Al) – iron (hydr)oxides with isomorphic substitution that were coprecipitated with arsenic (As) were evaluated regarding As availability and bioaccessibility after 7 years of aging. Both Fe (II) and Fe (III) were used, and both speciation of As were assessed: As (III) and As (V). Chemical composition of these compounds was assessed by using aqua regia and HNO3 digestion. Single chemical extractions with Mehlich-1, CaCl2 (0.01 M), citric acid (2%) and HNO3 0.43 M were performed to evaluate availability and bioaccessibility of As. The leaching behavior of the synthetic compounds was repeated in the aged compounds, compared with the fresh precipitates. Crystallinity of iron (hydr)oxides was tested by dithionite-citrate-bicarbonate and oxalate extractions. The association between As and well crystallized iron oxides is greater when aluminum is in the system, while in the absence of Al, As associated more with oxides of lower crystallinity. Leaching of As was greater in fresh precipitated materials when the primary source was Fe (III), while the aging process did not affect the Fe (II) precipitates. This study reinforces the importance of the long-term evaluation of iron compounds when incorporating trace elements, since the mobilization of them can promote health injuries.

Oxygen Vacancy-Electron Polarons Featured InSnRuO2 Oxides: Orderly and Concerted In-Ov-Ru-O-Sn Substructures for Acidic Water Oxidation.

Polymetallic oxides with extraordinary electrons/geometry structure ensembles, trimmed electron bands, and way-out coordination environments, built by an isomorphic substitution strategy, may create unique contributing to concertedly catalyze water oxidation, which is of great significance for proton exchange membrane water electrolysis (PEMWE). Herein, well-defined rutile InSnRuO2 oxides with density-controllable oxygen vacancy (Ov)-free electron polarons are firstly fabricated by in situ isomorphic substitution, using trivalent In species as Ov generators and the adjacent metal ions as electron donors to form orderly and concerted In-Ov-Ru-O-Sn substructures in the tetravalent oxides. For acidic water oxidation, the obtained InSnRuO2 displays an ultralow overpotential of 183 mV (versus RHE) and a mass activity (MA) of 103.02 A mgRu -1, respectively. For a long-term stability test of PEMWE, it can run at a low and unchangeable cell potential (1.56 V) for 200 h at 50 mA cm-2, far exceeding current IrO2||Pt/C assembly in 0.5 m H2SO4. Accelerated degradation testing results of PEMWE with pure water as the electrolyte show no significant increase in voltage even when the voltage is gradually increased from 1 to 5 A cm-2. The remarkably improved performance is associated with the concerted In-Ov-Ru-O-Sn substructures stabilized by the dense Ov-electron polarons, which synergistically activates band structure of oxygen species and adjacent Ru sites and then boosting the oxygen evolution kinetics. More importantly, the self-trapped Ov-electron polaron induces a decrease in the entropy and enthalpy, and efficiently hinder Ru atoms leaching by increasing the lattice atom diffusion energy barrier, achieves long-term stability of the oxide. This work may open a door to design next-generation Ru-based catalysts with polarons to create orderly and asymmetric substructures as active sites for efficient electrocatalysis in PEMWE application.

Study on the Adsorption Mechanism of Cu2+ by ZnAl-LDH-Containing Exchangeable Interlayer Chloride Ions.

Different Zn/Al ratios of Cl- intercalated ZnAl-layered double hydroxide (ZnAl-LDH) were prepared using the coprecipitation method, and their adsorption performance for Cu2+ in aqueous solution was evaluated. The factors affecting adsorption properties, such as dosage, reaction time, and pH, were determined by adsorption experiments. Then, the adsorption kinetics and isotherm models were fitted to evaluate the adsorption mechanism. The results show that the Zn/Al ratio has a great influence on the adsorption effect, the best adsorption effect is obtained when the Zn/Al ratio is 4:1, and the maximum adsorption capacity of Cu2+ is 213 mg/g. The mechanism study shows that the adsorption of Cu2+ by ZnAl-LDH is mainly an isomorphic substitution. Additionally, during the adsorption of CuSO4, the presence of SO42- undergoes interlayer anion exchange with Cl-, and the process of SO42- entering the interlayer facilitates the isomorphic substitution of Cu2+ and Zn2+. X-ray diffraction (XRD) analysis shows that as the Zn/Al ratio increases, the interlayer spacing of ZnAl-LDH increases, and the crystallinity decreases. The adsorption process conforms to the pseudo-second-order kinetic process and the Langmuir isotherm adsorption model. Therefore, the adsorption type of ZnAl-LDH for Cu2+ is monolayer chemical adsorption. The adsorption thermodynamic results indicate that the adsorption of Cu2+ is a spontaneous endothermic process. The research results revealed the mechanism of ZnAl-LDH adsorbing Cu2+, providing ideas for removing and recovering copper-containing electroplating wastewater.

A Study on Removal of Heavy Metal Ions by MgFe-Layered Double Hydroxides

Heavy metal pollution has posed great threats to the ecological environment, food security and human health. To date, various approaches have been explored, among which mineralization of heavy metals via layered double hydroxides (LDHs) are reported as a promising way to solve the addressed issue. In line with this, the current study attempts to the fabrication of two typical MgFe-LDHs containing different intercalated anions (denoted as MgFe-CO3 and MgFe-NO3) for mineralization of Cd2+. In the experiments, the as-prepared MgFe-NO3 exhibited a high maximum adsorption capacity of 444.44 mg/g, which was 2.82 times higher than that of the contrast sample MgFe-CO3 (157.48 mg/g). Such difference in adsorption capacity can be attributed to the different mineralization mechanism: For MgFe-NO3, the mineralization process was dominated by isomorphous substitution and the CdFe-LDH was the main product, while for MgFe-CO3, the formation of CdCO3 can be observed. This work paves a way in treating Cd2+ by MgFe-NO3 through super-stable mineralization and its further application in the removal of co-existent Cd2+ and AsO43- ions can be expected.

Determination of rare earth elements in synthetic calcium phosphates by high-resolution continuum source electrothermal atomic absorption spectrometry

Ceramic, cement and composite biomaterials have been developed based on hydroxyapatites (HA) and tricalcium phosphates (TCP), which are analogous in phase and chemical composition to the mineral component of bone tissue. The crystal structures of HA and TCP are arranged in isomorphic substitutions. Recently, research has focused on the modification of HA and TCP structures with ions of various metals, including rare earth ions (REEs), with the aim of creating materials with a range of beneficial properties for medical applications. REEs are known to have a number of useful properties, including antibacterial, antitumour, catalytic, magnetic and luminescent properties. The replacement of some of the Ca ions in the structures of HA and TCP with REE ions therefore makes it possible to obtain a material with biocompatibility and biological activity, giving it the required properties depending on the REE used and its concentration. In order to achieve the specified properties, it is necessary to control not only the structure (phase composition, lattice parameters of the powders) and the presence of characteristic functional groups, but also the chemical elemental composition. Modifications of hydroxyapatites and tricalcium phosphates containing from one to several different alloying elements are currently being developed. Various analytical methods are used for this purpose, including X-ray, atomic emission and a number of others. This article is devoted to the study of the analytical capabilities of the method of atomic absorption spectrometry with electrothermal atomization and a continuous spectrum source in relation to the determination of Eu and Yb in hydroxyapatites and tricalcium phosphates. The article considers the optimal conditions and modes of analysis, including temperature-time programs, the use of modifiers, the construction of calibration curves, and other factors that can be adjusted for more precise results. The results demonstrated the possibility of simultaneous determination of both Eu and Yb in the concentration range of 0.09 to 2 wt.%, with a relative standard deviation of less than 6 rel.%.

Rational Design of Isolated Tetrahedrally Coordinated Ti(IV) Sites in Zeolite Frameworks for Methyl Oleate Epoxidation.

The rational design of isolated metals containing zeolites is crucial for the catalytic conversion of biomass-derived compounds. Herein, we explored the insertion behavior of the isomorphic substitution of Ti(IV) in different zeolite frameworks, including ZSM-35 (FER), ZSM-5, and BEA. The different aluminium topological densities of each zeolite framework lead to the creation of different degrees of vacant sites for hosting the tetrahedrally coordinated Ti(IV) active sites. These observations show the precise control of the degree of four-coordinated Ti(IV) sites in a zeolite framework, especially in BEA topology, by tuning the degree of unoccupied sites in the host zeolite structure via dealumination. Interestingly, the more vacancies in the host zeolite structure, the more isolated tetrahedrally coordinated Ti(IV) can be increased, eventually enhancing the catalytic performance in methyl oleate (MO) epoxidation for producing methyl-9,10-epoxystearate (EP). The engineered Ti-β exhibits outstanding performances in bulky MO epoxidation with the amount of produced EP per number of Ti sites up to 17.1±1.8 mol mol-1. This observation discloses an alternative strategy for optimizing catalyst efficiency in the rational design of the Ti-embedding zeolite catalyst, endeavoring to reach highly efficient catalytic performance.

The ore mineralization of the gold-bearing Murunsky node located within the Aldan Shield

Mineralogical and geochemical investigations of the underexplored gold ore deposits within the Murunsky node, specifically the Seredinskoye and Andreevskoye ore fields, were conducted utilizing mineralogical and microprobe analytical techniques. The study identified several minerals, including bismuth minerals such as wittichenite and aikinite; cadmium mineral greenockite; cobalt minerals cobaltite and carrollite; arsenic minerals arsenosulvanite and tennantite; antimony minerals antimonite and tetrahedrite; tellurium minerals hessite and Te-canfieldite; mercury mineral cinnabar; thallium minerals raguinite and copper-rich talcusite; and tin minerals kesterite and jeanbandyite. Additionally, potassium sulfide djerfisherite with an unusual silver admixture was discovered. The findings underscore the remarkable and largely untapped potential of the Murunsky massif, particularly concerning its ore mineralization. A notable characteristic of the identified minerals is their non-stoichiometric composition, which includes the presence of impurities and isomorphic substitution of elements, attributed to the disequilibrium conditions under which they formed. The discoveries of raguinite and jeanbandyite represent the first occurrences of these minerals in Russia.

Enhanced Fenton-like reactions via interface electron reconstruction in low-crystallinity Fe[sbnd]Co bimetallic metal–organic frameworks: Bidirectional control of Fe (III) and Co (II) sites

In this study, the activity and stability of Fenton-like reactions are enhanced by constructing a low-crystallinity FeCo bimetallic metal–organic framework (FeCox-BDC (BDC denotes as terephthalic acid)) through interface electron reconstruction. However, the specific origins and mechanisms of their enhanced activity, particularly in Fenton-like reactions, remains unclear. Systematic analysis revealed that the isomorphic substitution of Co (II) reduces the coordination number and d-electron count at local Fe (III) sites, shifting the d-band centers (−1.59 eV) closer to the Fermi level. Additionally, Co 3d-orbitals can accept electrons, improving the occupation of antibonding orbitals. Notably, Fe (III) and Co (II) sites exhibit a synergistic effect: Fe (III) sites strongly adsorbed the Oα point of the peroxy bond (lOαOβ), while Co (II) sites efficiently activated Oβ. Within 5 min, FeCo1/3-BDC achieved a 98 % reduction in Rhodamine-B (RhB), surpassing Fe-BDC by a factor of 76 and homogeneous Fenton catalytic systems (Co (II)/peroxymonosulfate (PMS) and Fe (III)/Co (II)/PMS). This work provides a profound understanding of interface electron reconstruction, offering valuable insights into guiding Fenton-like mechanisms.

Efficient mineralization of cadmium and arsenic by poorly crystalline CaFe-layered double hydroxide in soil: Performance and mechanism

The co-contamination of arsenic (As) and cadmium (Cd) in the environment is of most concern. In this work, poorly crystalline CaFe-layered double hydroxide (CaFe-LDH) was synthesized with a Ca-to-Fe molar ratio of 4 to ensure effective immobilization of Cd and As in soil. The application of Ca4Fe-LDH in soil remediation demonstrated that the targeted heavy metals gradually mineralized into a relatively stable oxidizable and residual state. At a soil remediation dosage of 1.6%, the availability levels of Cd and As decreased significantly, achieving stabilization efficiencies of 99% and 85.2% respectively. Cd is trapped through isomorphic substitution and dissolution-reprecipitation of calcium (Ca) laminate, resulting in the formation of CdCaFe-LDH mineralization products. As is immobilized through ion exchange with interlayer anions, redox with Fe(III), and Fe-Cd-As complexation. Moreover, the results of the characterization and density functional theoretical (DFT) calculations demonstrate that the CdCaFe-LDH formed by isomeric substitution of Ca for Cd enhanced the adsorption of As on the (110) plane of LDH, indicating that the trap mechanism of Cd and As by Ca4Fe-LDH is synergistically promoted. Overall, the above results prove that mineralization using Ca4Fe-LDH is a promising method to remediate soils combined contaminated by both Cd and As.

The occurrence and enrichment of cobalt in skarn Pb-Zn deposits: A case study of the Niukutou Co-rich deposit, East Kunlun metallogenic belt, western China

The East Kunlun orogenic belt is one of the most important Co-rich polymetallic metallogenic belts in China. Niukutou, a typical Pb-Zn-(Fe) skarn deposit, is situated within the marble formations of the Ordovician-Silurian Qimantagh Group in this belt. Six distinct stages of mineralization have been identified: (1) prograde skarn stage, (2) hydrous mineral-oxide stage, (3) pyrrhotite stage, (4) chalcopyrite stage, (5) sphalerite-galena stage, and (6) carbonate stage. Co enrichment predominantly manifests at chalcopyrite stage, with two distinct Co minerals identified: glaucodot and cobaltite. Co is also present as isomorphous substitution in sulfides (mostly arsenopyrite) and as inclusions in chalcopyrite. Variations in As and S contents in arsenopyrite suggest a steady decrease in ore-forming fluid temperature from the pyrrhotite stage to sphalerite-galena stage. Variations in the Co, Ni, Se, As, Sb, Cu, Sn, Ag, and Zn contents in pyrite indicate fluctuations in temperature, oxygen fugacity, and fluid composition during ore formation. Sulfur isotope compositions (δ34S) through the pyrrhotite stage to the sphalerite-galena stages show a limited range from +3.4 to +7.0 ‰, suggesting a predominantly magmatic source. Whereas, the δ34S of pyrite and marcasite in carbonate stage exhibit significant variations from −22.5 to +22.7 ‰. We propose that this significant variation may be caused by mixing of sulfur from the surrounding rocks and the large fluctuations in oxygen fugacity due to the influx of meteoric water at the carbonate stage. Overall, Co in Pb-Zn skarn system may occur either as independent minerals or as lattice substitution in sulfides such as arsenopyrite. The deposition of Co-bearing minerals is related to decreases in temperature and fO2 during the chalcopyrite stage.

Characterization of Chromium Cations in CrAPO-5 Metal Aluminophosphate

Chromium-substituted aluminophosphate (CrAPO-5) with the AFI crystal structure was prepared for the first time by using microwave conditions at the stage of gel formation and crystallization. This approach allowed the reduction of the time required for the synthesis of CrAPO-5 from 60–70 h to 6 h. CrAPO-5 metal aluminophosphate prepared by microwave-assisted synthesis is studied by UV-visible and IR spectroscopy and X-ray photoelectron spectroscopy. The material is characterized by the presence of Cr3+ and Cr2+ ions in the framework with predominating Cr3+ ions introduced via isomorphous substitution, as well as some minor amounts of extra-framework Cr3+ species, which are present presumably in the state of α-Cr2O3. The latter species can be partially reduced to Cr2+ species in the presence of CO or H2. XPS study of CrAPO-5 revealed the presence of Cr3+ ions in the framework. A TPR experiment showed that the reduction of chromium starts at about 450–500 °C.

Occurrence and enrichment of cobalt and nickel in the Yindongshan ultramafic–mafic intrusion-hosted iron deposit, western Hubei Province, China

The Yindongshan iron deposit in western Hubei Province of China is hosted within Ordovician ultramafic–mafic intrusions. Recent field geological surveys have detected cobalt (Co) and nickel (Ni) enrichment within the Yindongshan clinopyroxenite, suggesting good potential for subeconomic Co-Ni mineralization. This study investigated the occurrence modes and enrichment processes of Co and Ni in the Yindongshan deposit through field geology and in situ analysis of the rock texture, geochronology, and geochemistry of sulfides, Fe-Ti oxides, and silicate minerals. The Yindongshan clinopyroxenites were emplaced at 440.2 ± 7.2 Ma via titanite LA-ICP-MS U-Pb dating, and underwent extensive post-magmatic metamorphism at 401.2 ± 8.6 Ma via apatite U-Pb dating. This metamorphism led to the widespread formation of amphibole via the replacement of clinopyroxene. Subsequently, hydrothermal epidote-albite veins, calcite-pyrite veins, and later actinolite veins developed. Pyrites from both clinopyroxenites and calcite veins show limited δ34S variations from −5.4 ‰ to −1.2 ‰, suggesting a magmatic sulfur source. Late-vein actinolites display geochemical characteristics distinct from those of amphiboles, indicating possible involvement of external fluids. LA–ICP–MS trace element results reveal a general increase in Co and Ni contents from silicate minerals and Fe-Ti oxides to pyrite and from earlier-crystallized coarse-grained clinopyroxenite to later medium- to fine-grained clinopyroxenite. The highest Co and Ni contents observed in pyrite from coarse-grained clinopyroxenite suggest their preferential incorporation into early sulfide minerals and then progressively depleted through magmatic evolution such as fractional crystallization. The positive correlation between Co and Ni with Fe in pyrite, along with the consistent parallel time-resolved LA–ICP–MS depth profiles among different mineral phases, indicates that isomorphic substitution occurred in pyrite. In silicate minerals, the Co and Ni contents increase from pyroxene, amphibole, to actinolite, with almost no Co or Ni present in epidote. The elevated Co and Ni contents in metamorphic amphiboles are attributed to their remobilization from magmatic pyrite to newly formed amphiboles. During the late hydrothermal phase, external fluids might transport additional Co and Ni, contributing to higher concentrations in late actinolite veins. In general, Co and Ni in the Yindongshan iron deposit are primarily hosted in sulfide minerals and can be remobilized during regional metamorphism and metasomatism. Thus, magmatic iron or iron–titanium oxide deposits hosted by mafic–ultramafic intrusions with sulfide mineralization may serve as promising targets for further Co-Ni exploration.

Pb2+ and Cd2+ ion adsorption capability of a novel hydrotalcite-like absorbent FeMnNi-LTH in water

This paper discusses the application of a layered triple hydroxide (FeMnNi-LTH) in removing Pb2+ and Cd2+ ions from aqueous solutions. The material was synthesized via co-precipitation, adhering to a molar ratio of 1:1:2 (Fe:Mn:Ni). It was characterized using FTIR, XRD, SEM and TEM. The results indicate that the synthesized material is classified as a hydrotalcite and exhibits a well-defined layered structure. Batch experiments were conducted to investigate the adsorption of Pb2+ and Cd2+ by FeMnNi-LTH, taking into account various factors such as coexisting ions, pH, temperature, adsorbent dosage, and contact time. The experimental results showed that the adsorption capacity of this material for Pb2+ and Cd2+ was 253.89 mg/g and 56.90 mg/g at 25 °C, respectively. Moreover, it exhibits a consistent high adsorption capacity across a broad pH range (pH 3–5.5). When cations coexist, they compete for adsorption sites in the following order: Zn2+ > Ca2+ > Mg2+ > Cd2+/Pb2+. Based on the calculated thermodynamic parameters, it is inferred that the adsorption process is endothermic and spontaneous. The adsorption mechanism, as analyzed by modeling and characterization, involves isomorphic substitution, surface complexation, precipitation, electrostatic attraction, and physical adsorption. The quantitative analysis of the adsorption mechanism revealed that FeMnNi-LTH primarily adsorbs Pb2+ and Cd2+ via precipitation and surface complexation. It was revealed by comparison with other adsorbents that the synthesized FeMnNi-LTH can be used for remediation of heavy metal pollution in water.