Mineralogical Transformations Research Articles

Mackinawite partial oxidation to green rust produces a large, abiotic uranium isotope fractionation

Low-oxygen settings and transition zones between strictly anoxic and oxic conditions may have characterised large expanses of Precambrian continental margins, where oxygen-breathing, complex life emerged and diversified. Accurate reconstructions of oxygen levels in such conditions are therefore required, but current geochemical proxies fail in identifying transitional redox conditions. Uranium isotopes are an emerging palaeoredox proxy, as large isotope fractionations are recorded during the reduction of uranium into anoxic sediments. Their potential application to transitional conditions is, however, unclear, because the redox regulating mineralogy of such environments and the associated isotope fractionations are poorly constrained. Here, we explore the mineralogical transformations occurring during the partial oxidation of mackinawite. We show that green rust, a key mineral of Precambrian oceans, forms as a by-product of mackinawite oxidation, along with uraninite and polysulphide. We also demonstrate that this mechanism records a large abiotic uranium isotope fractionation during its reaction with aqueous iron sulphide.

Mineral-dependent release, migration and enrichment of toxic elements during black shale weathering: An integrated study from profile scale to mineral scale.

Chemical weathering of lithologies with high geochemical backgrounds such as black shale has been proposed to be a critical source for toxic elements in soil and water systems. However, mechanisms controlling the release, migration and enrichment of toxic elements during black shale weathering are poorly understood. This study utilized a suite of micro analytical techniques such as TESCAN integrated mineral analyzer (TIMA), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and electron micro-probe analysis (EMPA) to elucidate the intimate relationship between mineralogical transformations and elemental behaviors from profile scale to mineral scale. Mineralogical and elemental compositions for a black shale weathering profile (and surface strongly weathered materials) suggest a dominant sequence of mineral reactions as oxidation of sulfides, dissolution of carbonates, alteration of aluminosilicates, and transformation of clay minerals. Most of the toxic elements were largely released from the weathering profile and significantly enriched in the strongly weathered materials. Black shale weathering was initiated by oxidation of pyrite, sphalerite and molybdenite, and these chemical reactions dominated the release of toxic elements (e.g., As, Cd, Mo, Mn, Ni and Zn). During oxidation of pyrite, Fe (hydr)oxides pseudomorphically replaced pyrite grains, along with the release of As and Mn and their subsequent retention in Fe (hydr)oxides. Sulfuric acid generated by oxidation of sulfides firstly dissolved surrounding calcite and dolomite to significantly improve the pore-fracture networks in the weathered shale, allowing more water fluxes and transportation of Fe (hydr)oxides and concomitant migration of associated toxic elements. Then, albite and minor orthoclase were altered to illite that was responsible for the secondary enrichment of Tl throughout the weathering profile. In intense weathering stage, Fe/Mn (hydr)oxides were substantially delivered to re-precipitate in fractures and contributed to considerable enrichment of As, Ni, Co, Zn and Cd. Meanwhile, transformation of illite to kaolinite may also influence the enrichment of toxic elements. This work highlights the importance of understanding the control of mineralogical transformation on release, migration and enrichment of toxic elements during black shale weathering, such that this mineral-dependent mechanism can be implemented to risk prediction and assessment of toxic elements in black shale regions.

Plants colonization accelerates galena oxidation, mineralogical transformation, and microbial community reshaping under the soil phytoremediation processes.

The ongoing weathering of metal sulfides has substantially posed threats to the eco-systems. For remediating metal sulfides-contaminated soils, phytostabilization is a promising nature-based technique that immobilizing heavy metals (HMs) that dissolved from metal sulfides in the rhizosphere, preventing their leaching and migrating into soil and groundwater. However, the underlying mechanism regarding the mineral-root interaction involving primary metal sulfides such as galena (PbS) during the remediation processes has yet been well studied. This study aims to investigate the geochemical alterations, mineralogical transformations, and microbial community reshaping of galena-added soils during plants colonization using two representative plants, ryegrass (Lolium perenne L.) and alfalfa (Medicago sativa.). After 11 weeks of plants colonization, the morphology of galena surface was altered, as massive erosion pits (ca. 200 nm) were visualized by SEM (Scanning Electron Microscope). The microspectroscopic analyses indicated that the PbS may have transformed to PbCO3 and PbSO4 during the plants colonization. Additionally, the chemical sequential extraction revealed that the plants colonization could promote the soluble Pb to be associated with carbonates and amorphous Fe/Al (oxyhydr)oxides, thus limiting their bioavailability and mobility. Moreover, the key driving factors of microbial community alteration have shifted from pH and bioavailability Pb to cation exchange capacity (CEC) during the plants colonization process. These findings have uncovered the (bio)geochemical behaviors of PbS in soils during the phytostabilization processes, which may develop an integrated mechanism of mineralogical and geochemical stabilization of HMs for non-pollution outcomes.

Effects of particle sizes and roasting temperature on the Fe-Ni enrichment of limonite ore from the Wolo mine area, Southeast Sulawesi, using corncob char as reductant

Abstract The reduction roasting of a limonite ore sample from the Wolo mine area was investigated using corncob char as a reductant. The objectives of this study were to analyze the effects of particle sizes and roasting temperature on the mineralogical transformation and Fe-Ni enrichment during the roasting process. The limonite ore was prepared into three size fractions of mesh sieves (-100+150, -150+200, and -200 mesh). Limonite ore was roasted with 2g of corn cob char reductant at temperatures ranging between 800 °C and 1100 °C with a 1-hour reduction time. Limonite ore and roasted products were analyzed to determine the mineral and chemical composition using optical microscopy, X-ray diffraction (XRD), and X-ray fluorescence (XRF) methods. Results of the mineralogical analysis indicated that the sample contained chlorite, goethite, lizardite, maghemite, and quartz. Limonite ore is mainly composed of Fe2O3 (53.59%), followed by SiO2 (12.16%), MgO (2.63%), and Ni (1.52%). Results of reduced roasting of limonite ore exhibited that the ore minerals were transformed into spinel, wustite, fayalite, and some tetrataenite (FeNi). The ore with -100+150 mesh particle and heated at 1,000 °C provided the optimum enrichment of 1.74% Ni and 42.87% Fe, respectively.

Influence of calcium carbonate on ferrihydrite bio-transformation and associated arsenic mobilization/redistribution.

The sulfate-reducing bacteria (SRB)-induced ferrihydrite transformation is an important cause for arsenic (As) contamination in the aquifer near mining area. Calcium carbonate (CaCO3) is widespread and has the potential of regulating As fate directly or indirectly. However, the influence of CaCO3 on ferrihydrite transformation and the associated As mobilization/redistribution in SRB-containing environments remains unclear. Therefore, in this research, batch experiments coupled with a series geochemical, spectroscopic, and microscopic technologies were conducted collectively to address the research gap above. The results suggested that under low CaCO3 loading conditions, the reductive transformation of ferrihydrite to Fe-S minerals resulted in a significant release of adsorbed As into the solution and As(V) reduction to more mobile and toxic As(III). Inside the cell of SRB, there existed S and As zone (no Fe), where As(V) might be reduced by S2- without interference of Fe(III). Although the high CaCO3 loadings exerted little effect on Fe(III) reduction, they promoted ferrihydrite transformation into dufrenite and vivianite, which sequestered As effectively via structural incorporation process, retarding As mobilization. Besides, the coprecipitation of As with dufrenite and vivianite enhanced the stability of solid phase As. Overall, the high CaCO3 loadings altered the mineralogical transformation of ferrihydrite and the associated As biogeochemistry significantly in SRB-containing environments. Regulating ferrihydrite transformation and the associated As fate via CaCO3 addition is an effective approach for mitigation of As mobilization in the aquifer near mining area.

Sugarcane bagasse and iron ore tailings thermochemical conversion towards sustainable iron recovery with biogenic carbon and hydrogen production

The recovery of valuable chemical elements from industrial waste is essential for production processes' economic and environmental sustainability. The interaction between the iron ore tailings and sugarcane bagasse, both wastes, has the potential to provide a secondary iron source for future iron and steelmaking processes. This study evaluated the use of volatiles from sugarcane bagasse (SCB) and iron ore tailings (IOT) to the synergistic promotion of carbon deposition, H2 production and conversion of weak magnetic iron oxides in strong magnetic iron phases. The experiments were carried out at 400, 600, 800, and 1000 ºC with different SCB/IOT ratios under an N2 atmosphere. In all tests, SCB and IOT were heated simultaneously in separate beds to prevent direct contact between the materials. The combination of 600 ºC and higher SCB/IOT ratio resulted in a product with 96.7% magnetite, 98% magnetic fraction recovery, and 3.5% deposited carbon. The use of lower SCB/IOT ratio provided an increase in H2 production. Regardless of the mass ratio, heating the IOT and SCB simultaneously up to 1000 ºC led to significant mineralogical transformations, reaching reduced phases such as wüstite, fayalite and metallic iron, which impaired magnetic separation efficiency. The results indicate an alternative for recovering iron from IOT using biomass waste as a renewable reducing agent for the steel industry.

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.

Effect of sulfidogenesis on ferrihydrite geochemistry and associated arsenic fate

The behavior of arsenic (As) in groundwater is closely related to the sulfidation of ferrihydrite. In the ternary ferrihydrite-As-sulfide system, ferrihydrite can either initially adsorb As before sulfide reduction or first encounter sulfide and then interact with the aqueous As, altering As fate. However, their relative contributions to the mineralogical transformation of ferrihydrite and subsequently associated As mobilization/redistribution remain poorly understood. Therefore, batch experiments combined with chemical, microscopic, and spectroscopic analyses were conducted to clarify the geochemistry of ferrihydrite and its influence on As behavior. Results indicated that in the pre-sorption groups, the secondary minerals were predominantly presented in amorphous phase due to the retardative effect of As. At low sulfide concentrations (S/Fe = 0.04), the content of residual ferrihydrite was large, which favored As immobilization. At high sulfide concentrations (S/Fe = 0.8), however, As was initially released into the solution and subsequently re-immobilized by secondary minerals. The adsorption capacity of the secondary minerals for As decreased with the increase in amorphous mackinawite formation. In the pre-sulfidation groups, rapid ferrihydrite reduction promoted the formation of crystalline minerals, significantly reducing their adsorption capacity. At low sulfide concentrations, the released As was partially adsorbed on the surface of crystalline goethite and lepidocrocite. At high sulfide concentrations, magnetite formed and favored As immobilization through its incorporation into magnetite particles. These results provide important insights into the geochemistry of Fe, S, and As in groundwater systems.

Uranium Repartitioning during Microbial Driven Reductive Transformation of U(VI)-Sorbed Schwertmannite and Jarosite.

This study exposes U(VI)-sorbed schwertmannite and jarosite to biotic reductive incubations under field-relevant conditions and examines the changes in aqueous and solid-phase speciation of U, Fe, and S as well as associated microbial communities over 180 days. The chemical, X-ray absorption spectroscopy, X-ray diffraction, and microscopic data demonstrated that the U(VI)-sorbed schwertmannite underwent a rapid reductive dissolution and solid-phase transformation to goethite, during which the surface-sorbed U(VI) was partly reduced and mostly repartitioned to monomeric U(VI)/U(IV) complexes by carboxyl and phosphoryl ligands on biomass or organic substances. Furthermore, the microbial data suggest that these processes were likely driven by the consecutive developments of fermentative and sulfate- and iron- reducing microbial communities. In contrast, the U(VI)-sorbed jarosite only stimulated the growth of some fermentative communities and underwent very limited reductive dissolution and thus, remaining in its initial state with no detectable mineralogical transformation and solid-phase U reduction/repartitioning. Accordingly, these two biotic incubations did not induce increased risk of U reliberation to the aqueous phase. These findings have important implications for understanding the interactions of schwertmannite/jarosite with microbial communities and colinked behavior and fate of U following the establishment of reducing conditions in various acidic and U-rich settings.

Unveiling deep Earth's hidden potential: insights from a new high-pressure phase discovered in a shocked meteorite

In this study, we report the discovery of a novel high-pressure phase within the Suizhou shocked meteorite, shedding light on the extreme conditions encountered during meteorite impacts. Utilizing advanced analytical techniques including electron microprobe and single-crystal X-ray diffraction, we identified a previously unknown crystalline structure formed under high pressures and temperatures. The new mineral, ideally Mg3(Si0.5[]0.5)Si2O8 (the symbol [] stands for structural vacancy), was approved by the International Mineralogical Association (IMA 2024–012) and named ohtaniite in honour of Eiji Ohtani. The phase, a new mineral with the pyroxene chemistry but with wadsleyite structure, was characterized by its distinct crystal lattice and unique physical properties, suggesting a transformation induced by shock compression. This finding expands our understanding of shock-induced mineralogical transformations in extraterrestrial materials and offers insights into the dynamic processes shaping meteorite evolution. Further investigations into these high-pressure phases are crucial for unraveling the geological history of meteorites and their significance in planetary science.

Sustainable valorization of mining waste: Phosphate sludge repurposing for advanced ceramic production

Managing the vast quantities of waste constantly generated by mining activities is one of the major environmental and economic problems facing mankind today. Fluorapatite is separated from the associated gangue minerals by a series of crushing and screening, washing, and flotation processes. These processes produce a significant amount of phosphate sludge, which is stored on the mine site in drift rock and large surface ponds. One possible environmental option is to reuse it as an alternative raw material in ceramics and building materials. Consequently, two phosphate sludges from two different Moroccan towns, Youssoufia and Khouribga, were studied. Due to the complexity of these raw materials resulting from long geological processes, in-depth physical, chemical, mineralogical, and thermal characterization is required. Dry compressed powder pellets were sintered at 900 °C, 1000 °C, and 1100 °C for 2 h. The study focuses on the effect of sintering temperature on mineralogical transformations and ceramic properties such as apparent porosity, water absorption, and mechanical strength. At 1100 °C, a slight increase in density was observed for both phosphate sludges. Water absorption was reduced by 2.51 % in both sludges for pellets sintered at 1100 °C compared to those sintered at 900 °C. Mechanical strength improved significantly, with an increase of about 60 % for samples sintered at 1100 °C, recording 227 N for Youssoufia sludge and 247 N for Khouribga sludge. This work has provided new data on the physical, chemical, mineralogical, and thermal changes in ceramics as the sintering temperature increases. These data will be useful for the manufacture of high-value ceramics.

Exploring the diversity of clays: Impacts of temperature on physicochemical changes, mechanical characteristics, and permeability, and their relevance to membrane applications

This study investigates the characterization of two clays obtained from the Safi and Fez regions, focusing on their analysis for filtration membrane applications. Various analytical techniques were employed, including chemical composition analysis, elemental analysis, mineralogical characterization, carbonate content determination, color assessment, plasticity evaluation, thermal treatment analysis (DTA-TG), mineralogical transformation study, fusion tests, membrane tests, and scanning electron microscopy (SEM).The results reveal significant differences between the two clays regarding their chemical composition. The red clay exhibits a mineralogical composition comprising quartz, calcite, dolomite, hematite, illite, and kaolinite, whereas the gray clay contains quartz, calcite, dolomite, illite, talc, and montmorillonite. Furthermore, upon thermal treatment, both clays exhibit changes in their physical properties.Despite the decrease in porosity and water absorption, as well as the increase in compression strength for both clays, the permeability of the grey clay increases, unlike the red clay, which exhibits a constant permeability beyond 1000°C.These findings highlight the diversity and industrial significance of clays from the Safi and Fez regions for filtration membrane applications. The contrasting properties of red and gray clays provide insights into their potential utilization in different industries. Exploring these clays’ behavior can lead to better filtration membranes and new industrial applications.

Phase transformation of schwertmannite in paddy soil under different water management regimes and its impact on the migration of arsenic in soil

Schwertmannite (Sch) holds a great promise as an iron material for remediating Arsenic (As)-contaminated paddy soils, due to its extremely high immobilization capacities for both arsenate [As(V)] and arsenite [As(III)]. However, there is still limited knowledge on the mineral phase transformation of this metastable iron-oxyhydroxysulfate mineral in paddy soils, particularly under different water management regimes including aerobic, intermittent flooding, and continuous flooding, and how its phase transformation impacts the migration of As in paddy soils. In this study, a membrane coated with schwertmannite was first developed to directly reflect the phase transformation of bulk schwertmannite applied to paddy soils. A soil incubation experiment was then conducted to investigate the mineral phase transformation of schwertmannite in paddy soils under different water management regimes and its impact on the migration of As in paddy soil. Our findings revealed that schwertmannite can persist in the paddy soil for 90 days in the aerobic group, whereas in the continuous flooding and intermittent flooding groups, schwertmannite transformed into goethite, with the degree or rate of mineral phase transformation being 5% Sch >1% Sch > control. These results indicated that water management practices and the amount of schwertmannite applied were the primary factors determining the occurrence and degree of mineral transformation of schwertmannite in paddy soil. Moreover, despite undergoing phase transformation, schwertmannite still significantly reduced the porewater As (As(III) and As(V)), and facilitated the transfer of non-specifically adsorbed As (F1) and specifically adsorbed As (F2) to amorphous iron oxide-bound As (F3), effectively reducing the bioavailability of soil As. These findings contribute to a better understanding of the mineralogical transformation of schwertmannite in paddy soils and the impact of mineral phase transformation on the retention of As in soil, which carry important implications for the application of schwertmannite in remediating As-contaminated paddy soils.

Mineralogical transformations in the Fe-laterite profiles of Saudi Arabia: A study of weathering dynamics and secondary lateritization

Mineralogical transformations in the Fe-laterite profiles of Saudi Arabia: A study of weathering dynamics and secondary lateritization

Metasomatism of the continental crust and its impact on surface uplift: Insights from reactive‐transport modelling

AbstractHigh‐elevation, low‐relief continental plateaus are major topographic features and profoundly influence atmospheric circulation, sediment transport and storage, and biodiversity. Although orogenic surface‐uplift mechanisms for modern continental plateaus near known plate margins like Tibet are well‐characterized, they cannot account for examples in intracontinental settings like the Colorado Plateau. In contrast to canonical plate‐tectonic uplift mechanisms, broad‐scale hydration‐induced metasomatism of the lower crust has been suggested to reduce its density and increase its buoyancy sufficiently to contribute to isostatic uplift. However, the relationships between key petrophysical properties in these environments are not fully quantified, which limits application of this model. Here, we develop a series of petrological models that describe the petrological and topographic effects of fluid–rock interaction in non‐deforming continental crust of varying composition. We apply an open‐system petrological modelling framework that utilizes reactive‐transport calculations to determine the spatial and temporal scales over which mineralogic transformations take place compared with the magnitude of infiltration of aqueous fluids derived from devolatilization of subducting oceanic lithosphere. The buoyancy effect of hydration‐induced de‐densification is most significant for metabasic lower crust, intermediate for metapelitic crust, and minimal for granodioritic crust. We apply these results to a case study of the ~2 km‐high Colorado Plateau and demonstrate that under ideal conditions, hydration of its lower–middle crust by infiltrating aqueous fluids released by the Farallon slab during Cenozoic low‐angle subduction could have uplifted the plateau surface by a maximum of ~1 km over 16 Myr. However, realistically, although hydration likely has a measurable effect on surface tectonics, the uplift of orogenic plateaus is likely dominantly controlled by other factors, such as lithospheric delamination.

Production of lightweight expanded aggregates from smectite clay, palygorskite-rich sediment and phosphate sludge

Abstract Lightweight expanded clay aggregates (LWAs) are porous materials with low density and high strength (EN-13055-1), and they are important in sustainable construction through their lightweight nature and ability to provide thermal or acoustic insulation. The objective of this work was therefore to evaluate the preparation of LWAs using a smectite clay (M1 formulation), whose application in common ceramic production is difficult. An alternative approach was proposed for the valorization of phosphate sludge and a palygorskite-rich sediment by mixing them with expanded clay (M2 formulation) for LWA production. This could result in economically cost-effective products with significant environmental benefits. Pellets were prepared and fired at various temperatures (1100°C, 1125°C and 1150°C), and relevant properties such as bloating index, density, water absorption and compressive strength were determined. Additionally, the microstructure, mineralogical transformations and phase compositions under various sintering temperatures were investigated. Increasing the temperature from 1000°C to 1150°C significantly improved the expansion properties of LWAs, and 1150°C seemed to be the optimal firing temperature at which the best expansion properties were achieved. In addition, the incorporation of the selected waste improved the properties of the final products, leading to lower density, greater strength and greater bloating with the development of the internal pore structure as compared to the LWAs without this addition. Because of their low density (0.6 g cm–3) and sufficient compressive strength (0.86 MPa), the manufactured LWAs can be used in construction (as insulating panels or in lightweight concrete) and in green roofs.

Statistical analysis using the RSM approach of the physical behavior of green polymerized eco-mortar

In order to develop an innovative, environmentally friendly composite materials for the construction industry, this study aims to exploit three types of waste material to manufacture cement mortars for producing lightweight concretes, ecologically friendly paving slabs and pavers. For this purpose, the response surface methodology (RSM) was investigated to predict and optimize the physical properties of mortars made from dune sand (DS) combined with recycled sand (RS), which are abundant in the desert and considered as waste products, reinforced by polymerized polyethylene terephthalate (PET) fibers of two different lengths, 20 mm and 30 mm, respectively. This investigation was carried out to assess the material's capacity in terms of engineering criteria, including air content in the fresh state (Ac), shrinkage (Sh), flexural displacement (Yf), ultrasonic pulse velocity (UPV), and water absorption (WA). Further, the chemical composition and mineralogical transformations at high temperatures of the produced mortar were examined. The ANOVA analysis of variance and a desirability function (DF) test are developed based on the Box-Behnken Design to predict and optimize variables and output responses by maximizing the mechanical properties and minimizing the physical properties. The obtained results reveal a significant improvement in the physical properties of the mortars, 6.25% Sh, 43% Yf, 4.65% UPV, and 6.54% WA, confirming the beneficial effect of fiber-reinforced products compared with those without fibers. The proposed quadratic model proves the validity of the experimental results with a better accuracy of less than 4.5% error. The optimal formulation obtained in this protocol consisted of 50% DS, 50% RS, and 2% PET, with a length of 12.70 mm. This mix yielded 0.799% Ac, −95.28 μm/m Sh, 5.79 mm Yf, 3855.11 m/s UPV, and 11.91% WA, presenting an attractive option for applications in eco-construction sustainability. Therefore, The RSM model correlates well with the experimental data, which has contributed to an improvement in the physical-mechanical features. Consequently, this eco-mortar has several applications in buildings, roads, bridges, for bending elements (beams, slabs) and can also be used for repairing damaged structures.

Long-term stabilization of arsenic-alkali residues via adjusting As redistribution and mineralogical transformation

Increasingly stringent environmental standards pose a huge challenge to the treatment of arsenic alkali residue (AAR). This work proposed an alternative method for stabilizing AAR based on lab and field-scale study. Three methods were discussed by introducing bleach and/or FeCl3 in different dose and order to obtain the optimistic procedure. The redistribution and mineralogical transformation of As in AAR were illustrated based on stoichiometric, XRD, and XPS analyses. The leachate As concentration decreased significantly with high dose of bleach addition (>4%) via supplying sufficient hypochloric acid and labile Ca. The high stability of AAR was obtained through the oxidation of CaHAsIIIO3 and then formation of high alkaline-dependent Ca4(OH)2(AsVO4)2‧4H2O minerals (pH ≥ 12). However, the leachate pH failed to meet the standard for landfill (pH12). In contrast, synchronously introducing low dose of bleach (3 %) and FeCl3 (3 %−5%) could achieve the expected standard of leachate As concentration and pH value. The oxidation efficiency of CaHAsIIIO3 by bleach was facilitated with FeCl3 addition via the accelerated dissolution of CaHAsIIIO3. And then the generation of stable Ca − Fe arsenates (Ca2Fe3(AsVO4)3O2‧3H2O) was promoted via creating an appropriate Ca/Fe/As ratio and pH circumstance (8.23–9.61). Compared with the synchronous treatment, the obvious rebound of leachate As concentrations was observed with sequentially adding bleach and FeCl3. The stability of the formed Ca − AsV minerals with bleach treatment was destroyed by the sequent addition of FeCl3 due to the generated CO2 from CaCO3 dissolution and decreased pH values (10.2–10.9). The redistribution and transformation of As in AAR were remarkably affected by the dose and order of adding remediation agent. The formation of Ca − Fe arsenates with high As capacity and stability was curial for AAR stability via synchronous treatment, which provided an alternative option for AAR stabilization.

A Study on the Long-Term Exposure of a Tailings Dump, a Product of Processing Sn-Fe-Cu Skarn Ores: Mineralogical Transformations and Impact on Natural Water

In the mining industry, one of the principal issues is the management of the waste generated during ore concentration, which represents a potential source of environmental pollution. The most acute issue originates from the mining heritage in the form of dumps formed of mining tailings that were created before the introduction of waste storage standards and may be located in urban areas. This research investigated this problem using the example of the tailings dump “Krasnaya Glinka”, located in a residential area of Pitkäranta (Karelia, Russia) in close proximity to the shoreline of Lake Ladoga. A complex approach, including the investigation of the natural water of the study area and tailings material and an experiment simulating the interaction of this material with atmospheric precipitation, allowed us to obtain the first data on the current status of the tailings dump and its surroundings and to identify environmental pollutants. This research used XRF, XRD, and EPMA analytical methods for assaying the tailings materials obtained from the dump and ion chromatography, potentiometric titration, ICP-MS, and AES for the water samples. The results show the influence of the tailings dump’s materials on the formation of the environmental impact—in the water from the area of the tailings dump, increased concentrations of chalcophilic elements are observed, for example, Zn up to 5028 µg/L. Based on this study of the tailings dump’s materials and the conducted experiment, an attempt is made to connect the chemical compositions shown in the natural water data with the specific mineral phases and processes occurring during supergene transformations in the tailings storage. As a result of the conducted research, it was found that despite more than 100 years of exposure of the tailings materials under natural factors, mostly atmospheric precipitation, equilibrium with the environment has not come. The processes of extracting toxic elements and carcinogenic mineral phases into the environment are continuing. In the process of studying the tailings materials, it was found that they are probably of economic interest as a technogenic source of W and Sn due to the contents of these components exceeding industrially significant values in the exploited fields.

Mineralogical transformation of arsenic at different copper smelting workshops: The impact on arsenic bioaccessibility

Soil arsenic (As) contamination associated with the demolition of smelting plants has received increasing attention. Soil As can source from different industrial processes, and also participate in soil weathering, making its speciation rather complex. This study combined the usage of chemical sequential extraction and advanced spectroscopic techniques, e.g., time of flight secondary ion mass spectrometry (ToF-SIMS), to investigate the mineralogical transformation of soil As at different processing sites from a typical copper smelting plant in China. Results showed that the stability of arsenic species decreased following the processes of storage, smelting, and flue gas treatment. Arsenic in the warehouse area was incorporated into pyrite (FeS2) as well as its secondary minerals such as jarosite (KFe3(SO4)2(OH)6). At the smelting area, a large proportion of As was adsorbed by iron oxides from smelting slags, while some As existed in stable forms like orpiment (As2S3). At the acid-making area, more than half of As was adsorbed on amorphous iron oxides, and some were adsorbed on the flue gas desulfurization gypsum. More importantly, over 86% of the As belonged to non-specifically and specifically adsorbed fractions was found to be bioaccessible, highlighting the gypsum-adsorbed As one of the most hazardous species in smelting plant soils. Our findings indicated the importance of iron oxides in As retention and suggested the potential health risk of gypsum-adsorbed As. Such detailed knowledge of As speciation and bioaccessibility is vital for the management and remediation of As-contaminated soils in smelting plants.