Multi-decadal geochemical evolution of drainage from underground coal mines in the Appalachian basin, USA.

Coal mine drainage (CMD) in Appalachia is a widespread source of dissolved metals, SO4, and acidity that can degrade aquatic habitats and water supplies for decades following mine closure and flooding. In the bituminous coalfield of Pennsylvania, the Irwin Coal Basin (ICB) contains a series of partly to completely flooded, abandoned underground mines separated by leaky barriers within the Pittsburgh coal seam. CMD originated throughout the basin from minepool aquifers that formed after mine closures dating from 1910 to 1957. Historical and recent water quality data for eight CMD sites across the ICB, plus mineralogy and cation-exchange capacity of overburden lithologies, were analyzed to quantify important reactants and evaluate spatial and temporal water-quality trends. As overburden thickness and residence time increase along a ~ 50-km flowpath northeast to southwest in the basin, CMD becomes more alkaline, and Na concentrations increase. Since the 1970s, all eight ICB discharges have become less acidic, with exponential decreases in acidity, SO4, and Fe concentrations; only two CMD remain net-acidic (acidic pH at equilibrium). Exponential decay models that include a steady-state asymptote consistent with background groundwater chemistry and siderite equilibrium describe the early-stage, rapid contaminant concentration decay immediately after the "first flush" (initial flooding) and the progressive evolution toward late-stage background conditions. A geochemical evolution PHREEQC model indicates that spatial and temporal trends in pH, net-acidity, SO4, Fe, and major cations could be explained by the continuous dilution of first flush water by ambient groundwater combined with sustained water-mineral reactions involving pyrite and carbonates (calcite, dolomite, siderite) plus cation-exchange by clays (illite, chlorite, mixed-layer illite/smectite). These data and model results indicate that 1) cation-exchange reactions enhance calcite dissolution and alkalinity production, resulting in the evolution of CMD to Na-SO4-HCO3 type waters, and 2) siderite equilibrium could maintain dissolved Fe >16 mg/L over the next 40 years.

Siderite and vivianite as energy sources for the extreme acidophilic bacterium Acidithiobacillus ferrooxidans in the context of mars habitability.

Past and present habitability of Mars have been intensely studied in the context of the search for signals of life. Despite the harsh conditions observed today on the planet, some ancient Mars environments could have harbored specific characteristics able to mitigate several challenges for the development of microbial life. In such environments, Fe2+ minerals like siderite (already identified on Mars), and vivianite (proposed, but not confirmed) could sustain a chemolithoautotrophic community. In this study, we investigate the ability of the acidophilic iron-oxidizing chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans to use these minerals as its sole energy source. A. ferrooxidans was grown in media containing siderite or vivianite under different conditions and compared to abiotic controls. Our experiments demonstrated that this microorganism was able to grow, obtaining its energy from the oxidation of Fe2+ that came from the solubilization of these minerals under low pH. Additionally, in sealed flasks without CO2, A. ferrooxidans was able to fix carbon directly from the carbonate ion released from siderite for biomass production, indicating that it could be able to colonize subsurface environments with little or no contact with an atmosphere. These previously unexplored abilities broaden our knowledge on the variety of minerals able to sustain life. In the context of astrobiology, this expands the list of geomicrobiological processes that should be taken into account when considering the habitability of environments beyond Earth, and opens for investigation the possible biological traces left on these substrates as biosignatures.

Optimization of "sulfur-iron-nitrogen" cycle in constructed wetlands by adjusting siderite/sulfur (Fe/S) ratio.

Sulfur-siderite autotrophic denitrification (SSAD) has been proved to solve the key problem of low nitrogen removal efficiency caused by the shortage of carbon source in constructed wetlands (CWs). In this study, five vertical flow constructed wetlands (VFCWs) were constructed with different Fe/S ratios (0/0, 0/1, 1/1, 2/1 and 1/2) to optimizing SSAD process, labeled S.0, S.1, S.2, S.3 and S.4. The results showed that the best NO3--N and TN removal rates were achieved with a Fe/S ratio of 2:1 (S.3), which were 96.26 ± 1.40% and 93.63 ± 3.12%, respectively. The abundance of denitrification genes (nirS, nirK and nosZ) in S.3 was significantly increased. Illumina high-throughput sequencing analysis indicated that the abundance and diversity of microorganisms involved in the "Sulfur-Iron-Nitrogen" cycle were enriched in S.3. The current study provided that the "Sulfur-Iron-Nitrogen" cycle in CWs was optimized by adjusting Fe/S ratio, and more types of denitrifying bacteria could be enriched, thereby enhancing nitrogen removal.

Grinding siderite with ferric sulfate to generate an active ferrous source for Cr(VI) reduction.

Activated siderite, endowed with excellent properties, was simply prepared by co-grinding with Fe sulfate to enhance its high reducing ability for Cr(VI). Batch experiments were conducted to investigate the main affecting parameters, such as material ratio, pH, temperature, etc. The removal of Cr(VI) by activated siderite was completed within 4 h of the reaction. The activated siderite maintained a high removal effect of Cr(VI) within a wide pH range (3-9). Various analytical methods, including XRD, SEM/EDS, XPS, etc., were employed to characterize the samples and discover variations before and after the reaction. The Fe (Ⅱ) in activated siderite becomes highly active, and it can even be released from the solid phase in the mildly acidic liquid phase to efficiently reduce Cr(VI) and mitigate its toxicity. These findings introduce an innovative approach for activating various minerals widely distributed in nature to promote the recovery of the ecological system.

Morphological, Microstructural, and In Situ Chemical Characteristics of Siderite Produced by Iron-Reducing Bacteria.

Dissimilatory iron-reducing bacteria (DIRB) oxidize organic matter or hydrogen and reduce ferric iron to form Fe(II)-bearing minerals, such as magnetite and siderite. However, compared with magnetite, which was extensively studied, the mineralization process and mechanisms of siderite remain unclear. Here, with the combination of advanced electron microscopy and synchrotron-based scanning transmission X-ray microscopy (STXM) approaches, we studied in detail the morphological, structural, and chemical features of biogenic siderite via a growth experiment with Shewanella oneidensis MR-4. Results showed that along with the growth of cells, Fe(II) ions were increasingly released into solution and reacted with CO32- to form micrometer-sized siderite minerals with spindle, rod, peanut, dumbbell, and sphere shapes. They are composed of many single-crystal siderite plates that are fanned out from the center of the particles. Additionally, STXM revealed Fh and organic molecules inside siderite. This suggests that the siderite crystals might assemble around a Fh-organic molecule core and then continue to grow radially. This study illustrates the biomineralization and assembly of siderite by a successive multistep growth process induced by DIRB, also provides evidences that the distinctive shapes and the presence of organic molecules inside might be morphological and chemical features for biogenic siderite.

Enhanced dewaterability and triclosan removal of waste activated sludge with iron-rich mineral-activated peroxymonosulfate.

High water and pharmaceutical and care products (PPCPs) bounded in sludge flocs limit its utilization and disposal. The advanced oxidation process of perxymonosulfate (PMS) catalyzed by iron salts has been widely used in sludge conditioning. In this study, two iron-rich minerals pyrite and siderite were proposed to enhance sludge dewatering performance and remove the target contaminant of triclosan (TCS). The permanent release of Fe2+ in the activation of PMS made siderite more effective in enhancing sludge dewater with capillary suction time (CST) diminishing by 60.5 %, specific resistance to filtration (SRF) decreasing by 79.2 %, and bound water content (BWC) dropping from 37.1 % to 2.6 % at siderite/PMS dosages of 0.36/0.20 mmol/g-TSS after 20 min of pretreatment. Pyrite/PMS performed slightly inferior under the same conditions and the corresponding CST and SRF decreased by 51.5 % and 71.8 % while the BWC only declined to 17.8 %. Rheological characterization was employed to elucidate the changes in sludge dewatering performance, with siderite/PMS treated sludge showing a 48.3 % reduction in thixotropy, higher than 28.4 % of pyrite/PMS. Oscillation and creep tests further demonstrated the significantly weakened viscoelastic behavior of the sludge by siderite/PMS pretreatment. For TCS mineralization removal, siderite/PMS achieved a high removal efficiency of 43.9 %, in comparison with 39.9 % for pyrite/PMS. The reduction in the sludge solids phase contributed the most to the TCS removal. Free radical quenching assays and EPR spectroscopy showed that both siderite/PMS and pyrite/PMS produced SO4-·  and ·OH, with the latter acting as the major radicals. Besides, the dosage of free radicals generated from siderite/PMS exhibited a lower time-dependence, which also allowed it to outperform in destroying EPS matrix, neutralizing the negative Zeta potential of sludge flocs, and mineralizing macromolecular organic matter.

3D Quantification of Pore Networks and Anthropogenic Carbon Mineralization in Stacked Basalt Reservoirs.

Basalt formations are promising candidates for the geologic storage of anthropogenic CO2 due to their storage capacity, porosity, permeability, and reactive geochemical trapping ability. The Wallula Basalt Carbon Storage Pilot Project demonstrated that supercritical CO2 injected into >800 m deep Columbia River Basalt Group stacked reservoir flow tops mineralizes to ankerite-siderite-aragonite on month-year time scales, with 60% of the 977 metric tons of CO2 converted within 2 years. The potential impacts of mineral precipitation and consequent changes in the rock porosity, pore structure, pore size, and pore size distributions have likely been underestimated hitherto. Herein, we address these knowledge gaps using X-ray microcomputed tomography (XMT) to evaluate the pore network architecture of sidewall cores recovered 2 years after CO2 injection. In this study, we performed a detailed quantitative analysis of the CO2-reacted basalt cores by XMT imaging. Reconstructed 3D images were analyzed to determine the distribution and volumetric details of porosity and anthropogenic carbonate nodules in the cores. Additional mineralogic quantification provided insight into the overall paragenesis and carbonate growth mechanisms, including mineralogic/chemical zonation. These findings are being used to parametrize multiphase reactive transport models to predict the fate and transport of subsurface CO2, enabling scale-up to commercial-scale geologic carbon storage in basalts and other reactive mafic-ultramafic formations.

Thermodynamic Inhibition of Microbial Sulfur Disproportionation in a Multisubunit Designed Sulfur-Siderite Packed Bioreactor.

Sulfur disproportionation (S0DP) poses a challenge to the robust application of sulfur autotrophic denitrification due to unpredictable sulfide production, which risks the safety of downstream ecosystems. This study explored the S0DP occurrence boundaries with nitrate loading and temperature effects. The boundary values increased with the increase in temperature, exhibiting below 0.15 and 0.53 kg-N/m3/d of nitrate loading at 20 and 30 °C, respectively. A pilot-scale sulfur-siderite packed bioreactor (150 m3/d treatment capacity) was optimally designed with multiple subunits to dynamically distribute the loading of sulfur-heterologous electron acceptors. Operating two active and one standby subunit achieved an effective denitrification rate of 0.31 kg-N/m3/d at 20 °C. For the standby subunit, involving oxygen by aeration effectively transformed the facultative S0DP functional community from S0DP metabolism to aerobic respiration, but with enormous sulfur consumption resulting in ongoing sulfate production of over 3000 mg/L. Meanwhile, acidification by the sulfur oxidation process could reduce the pH to as low as 2.5, which evaluated the Gibbs free energy (ΔG) of the S0DP reaction to +2.56 kJ, thermodynamically suppressing the S0DP occurrence. Therefore, a multisubunit design along with S0DP inhibition strategies of short-term aeration and long-term acidification is suggested for managing S0DP in various practical sulfur-packed bioreactors.

Siderite's green revolution: From tailings to an eco-friendly material for the green economy.

Siderite, extensively mined as a natural iron mineral, is often discarded as tailings due to the low grade of the ore and due to the high cost of current sorting technologies. Yet, this mineral has demonstrated significant potential in several pivotal areas of the environmental remediation. Siderite not only possesses exceptional adsorption, catalytic, and microbial carrier capabilities but also offers an eco-friendly and cost-effective solution for the environmental pollution management. This article consolidates research advancements and achievements over the past few decades concerning siderite's role in pollution control, delving deeply into its various remediation pathways. Initially, the paper contrasts the performance differences between natural and synthetic siderite, followed by a comprehensive overview of siderite's adsorption mechanisms for various inorganic pollutants. Furthermore, this paper analyzes the unique physicochemical attributes of siderite as both, a reductant and the catalyst, with a special emphasis on its use in the preparation of SCR catalysts and in the catalytic advanced oxidation processes for organic pollutants' degradation. This paper also enumerates and discusses the myriad advantages of siderite as a microbial carrier, thereby enhancing our understanding of biogeochemical cycles and pollutant transformations. In essence, this review systematically elucidates the mechanisms and intrinsic physicochemical properties of siderite in pollution control, paving the way for novel strategies to augment siderite's environmental remediation performance.

New insights into inhibition of high Fe(III) content on anaerobic digestion of waste-activated sludge.

The impacts of the increased iron in the waste-activated sludge (WAS) on its anaerobic digestion were investigated. It was found that low Fe(III) content (< 750 mg/L) promoted WAS anaerobic digestion, while the continual increase of Fe(III) inhibited CH4 production and total chemical oxygen demand (TCOD) removal. As the Fe(III) content increased to 1470 mg/L, methane production has been slightly inhibited about 5 % compared with the group containing 35 mg/L Fe(III). Particularly, as Fe(III) concentration was up to 2900 mg/L, CH4 production, and TCOD removal decreased by 43.6 % and 37.5 %, respectively, compared with the group with 35 mg/L Fe(III). Furthermore, the percentage of CO2 of the group with 2900 mg/L Fe(III) decreased by 52.8 % compared with the group containing 35 mg/L Fe(III). It indicated that Fe(II) generated by the dissimilatory iron reduction might cause CO2 consumption, which was confirmed by X-ray diffraction that siderite (FeCO3) was generated in the group with 2900 mg/L Fe(III). Further study revealed that Fe(III) promoted the WAS solubilization and hydrolysis, but inhibited acidification and methane production. The methanogenesis test with H2/CO2 as a substrate showed that CO2 consumption weakened hydrogenotrophic methanogenesis and then increased H2 partial pressure, further causing VFA accumulation. Microbial community analysis indicated that the abundance of hydrogen-utilizing methanogens decreased with the high Fe(III) content. Our study suggested that the increase of Fe(III) in sludge might inhibit methanogenesis by consuming or precipitating CO2. To achieve maximum bioenergy conversion, the iron content should be controlled to lower than 750 mg/L. The study may provide new insights into the mechanistic understanding of the inhibition of high Fe(III) content on the anaerobic digestion of WAS.

Highly Efficient Coremoval of Nitrate and Phosphate Driven by a Sulfur-Siderite Composite Reactive Filler toward Secondary Effluent Polishing.

Reactive fillers consisting of reduced sulfur and iron species (SFe-ReFs) have received increasing attention in tertiary wastewater treatment for nitrate and phosphate coremoval. However, the existing SFe-ReFs suffer from either low performance (e.g., pyrrhotite and pyrite) or unsatisfactory use in terms of combustible risk and residual nonreactive impurities (e.g., sulfur mixing with natural iron ores). Here, we developed a new type of sulfur-siderite composite ReF (SSCReF) with a structure of natural siderite powders eventually embedded into sulfur. SSCReFs exhibited many excellent properties, including higher mechanical strengths and hardness and especially much poorer ignitability compared to pure sulfur. By using SSCReF to construct packed-bed reactors, the highest denitrification and dephosphorization rates reached 829.70 gN/m3/d (25 wt % siderite) and 36.70 gP/m3/d (75 wt % siderite), respectively. Dephosphorization was demonstrated to be dependent on sulfur-driven denitrification, in which the acid produced from the later process promoted Fe(II) dissolution, which then directly combined with phosphate to form vivianite or further converted into phosphate adsorbents (ferrihydrite, a green rust-like compound). Water flush was an effective way to finally wash out these surface deposited Fe-P compounds, as well as those nonreactive impurities (Si and Al-bearing compounds) detached from SSCReF. Such a highly efficient and safe SSCReF holds considerable application potential in secondary effluent polishing.

Facile Metal Release from Pore-Lining Phases Enables Unique Carbonate Zonation in a Basalt Carbon Mineralization Demonstration.

Carbon-negative strategies such as geologic carbon sequestration in continental flood basalts offers a promising route to the removal of greenhouse gases, such as CO2, via safe and permanent storage as stable carbonates. This potential has been successfully demonstrated at a field scale at the Wallula Basalt Carbon Storage Pilot Project where supercritical CO2 was injected into the Columbia River Basalt Group (CRBG). Here, we analyze recovered post-injection sidewall core cross-sections containing carbonate nodules using µ-XRF chemical mapping techniques that revealed compositional zonation within the nodules. The unique nature of the subsurface anthropogenic carbonates is highlighted by the near absence of Mg in an ankerite-like composition. Furthermore, a comparison between pre- and post-injection sidewall cores along with an in-depth chemical mapping of basalt pore lining cements provides a better understanding into the source and fate of critical cationic species involved in the precipitation of carbon mineralization products. Collectively, these results provide crucial insights into carbonate growth mechanisms under a time-dependent pore fluid composition. As such, these findings will enable parameterization of predictive models for future CO2 sequestration efforts in reactive reservoirs around the world.

New insights into arsenate removal during siderite oxidation by dissolved oxygen.

Nowadays, arsenic (As) pollution in aquatic environments severely threatens the health of human beings. Although it has been known that siderite is capable of As adsorption and dissolved oxygen (DO) enhances the adsorption, effects of DO concentrations on As(V) adsorption onto siderite remain elusive. In this study, As(V) removal was investigated by synthesized siderite from aqueous solutions with different DO concentrations. Arsenic(V) adsorption kinetics were conformed to the pseudo-second-order model. As(V) adsorption onto siderite was enhanced in the presence of dissolved oxygen, but the excess DO concentration did not increase As(V) adsorption since Fe(III) oxides were coated onto the pristine siderite surface, preventing the mineral from further oxidation. With the increase in DO concentration, the rate of Fe(II) oxidation decreased, which was the kinetic-limited step during As(V) removal by siderite with the presence of DO. The theoretically generated Fe(III) was stoichiometrically proportional to the consumed oxygen. Microscopic characteristics by means of XRD, SEM, TEM, FTIR and XPS indicated that the adsorption was dominated by the chemical process via the As(V) complexation with siderite and co-precipitation with produced Fe(III) oxides. This study reveals the mechanisms of As(V) adsorption during siderite oxidation under different DO concentrations and emphasizes the importance of siderite oxidation in As(V) fate in aqueous systems.

New insights into the degradation and detoxification of methylene blue using heterogeneous-Fenton catalyzed by sustainable siderite.

The huge application of synthetic dyes caused a severe impact in the environment. In the present study, a physico-chemical strategy of heterogeneous-Fenton catalyzed by the natural ferrous ore has been established for toxic chemical degradation, of which the complex and high-expense repetitive pH adjustment procedures were escaping. And this natural heterogeneous catalyst also could be recycled and sustainable for toxic substances treatment involved in synergetic adsorption and oxidation. The siderite, served as an adsorbent and catalyst for the degradation of methylene blue (MB). Siderite exhibited a better adsorption capacity with a saturated adsorption capacity of ∼11.08 mg/g. Batch adsorption experiments have verified that adsorption rate and adsorption equilibrium followed pseudo-second-order rate model and Langmuir isotherm equation, respectively. The combination with H2O2, showed significant enhancement of MB degradation without any pH adjustment. The effect of siderite dosage, H2O2 dosage, MB concentration, initial pH, and reaction temperature on MB degradation was investigated, which also has indicated the excellent catalytic performance of siderite. About 99.71% of MB was degraded in 480 min with initial pH of 7.0, reaction temperature of 25 °C, siderite, and H2O2 dosage of 2.5 g/L and 122.38 mM, respectively. It was found that siderite could be reused and remained high degradation efficiency on MB after 5 times reutilization, which also could demonstrate the sustainable and effective process to degrade organic pollution. The generation of reactive species including ·OH and O2·- have been confirmed based on scavenger test and electron spin resonance (ESR) analysis, which was dominated by heterogeneous reaction. The possible degradation mechanisms of MB have been predicted based on spectrum scanning and GC-MS analysis. Moreover, acute toxicity assessment with marine photobacterium Vibrio fisheri was conducted to investigate the toxicity change in the adsorption/oxidation coupled process. This sustainable heterogeneous-Fenton technology has been verified as a promising and applicable process for toxic organic chemicals removal due to effective mineralization and detoxification assisted with the natural ore mineral through the simple operation and mild condtions.

In-situ production of iron flocculation and reactive oxygen species by electrochemically decomposing siderite: An innovative Fe-EC route to remove trivalent arsenic.

The removal of trivalent arsenic (As (III)) from water has received extensive attention from researchers. Iron electrocoagulation (Fe-EC) is an efficient technology for arsenic removal. However, electrode passivation hinders the development and application of Fe-EC. In this work, an innovative Fe-EC route was developed to remove As (III) through an electrochemical-siderite packed column (ESC). Ferrous ions were produced from siderite near the anode, and hydroxide was generated near the cathode during the electrochemical decomposition of siderite. As a result, an effect of Fe-EC-like was obtained. The results showed that an excellent removal performance of As (III) (>99%) was obtained by adjusting the parameters (As (III) concentration at 10 mg/L, pH at 7, Na2SO4 at 10 mM and the hydraulic retention time at 30 min) and the oxidation rate of As (III) reached 84.12%. The mechanism analysis indicated that As (III) was oxidized to As (Ⅴ) by the produced active oxide species and electrode, and then was removed by capturing on the iron oxide precipitates. As (III) was likely to be oxidized in two ways, one by the reactive oxygen species (possibly •OH, Fe(IV) and •O2- species), and another directly by the anode. The long-term effectiveness of arsenic removal demonstrated that ESC process based on the electrochemical-siderite packed column was an appropriate candidate for treating As (III) pollution.

Natural siderite derivatives activated peroxydisulfate toward oxidation of organic contaminant: A green soil remediation strategy.

Natural siderite (FeCO3), simulated synthetic siderite and nZVI/FeCO3 composite were used as green and easily available iron-based catalysts in peroxydisulfate activation for remediating 2-chlorophenol as the target contaminant and this technique can effectively degrade organic pollutants in the soil. The key reaction parameters such as catalysts dosage, oxidant concentration and pH, were investigated to evaluate the catalytic performance of different materials in catalytic systems. The buffering property of natural soil conduced satisfactory degradation performance in a wide pH range (3-10). Both the main non-radical of 1O2 and free radicals of SO4·- and OH· were evidenced by quenching experiment and electron paramagnetic resonance. The reduction of nZVI on FFC surface not only has the advantage for electronic transfer to promote the circulation of Fe(III) to Fe(II), but also can directly dechlorinate. Furthermore, the intermediates were comprehensively analyzed by GC-MS and a potential removal mechanism of three oxidant system for 2-CP soil degradation was obtained. Briefly, this research provides a new perspective for organic contaminate soil treatment using natural siderite or simulated synthetic siderite as efficient and environmental catalytic material.

Estrogen toxicity reduction of industrial biochemical tailwater by electrolysis biofilters with ceramsite­sulfur-siderite fillers.

Biochemical tailwater of the industrial park wastewater treatment plant is facing the growing demand of advanced treatment and toxicity reduction. However, existing information on toxicity reduction of real industrial biochemical tailwater is still limited so far. Herein, the water quality of biochemical tailwater from an integrated industrial park in Taihu Lake Basin, China, was systematically investigated, and typical endocrine disrupting chemicals (EDCs) and estrogen toxicity were detected. Estrogen toxicity reduction by previously proposed electrolysis biofilters with ceramsite­sulfur-siderite fillers was further verified. Results showed that total nitrogen (TN) and estrogen toxicity removal increased by 41.0 % and 30.3 % respectively under the optimal voltage of 4 V and electric loading of 24 h/d, and significantly positive correlation between estrogen toxicity reduction and TN removal (p < 0.05) was observed. The lowest effluent estrogen toxicity was 0.79-0.95 ngE2/L (in estradiol equivalent concentration) by the biofilter with ceramsite­sulfur-siderite fillers, which was lower than the estrogen disruption effects mass concentration threshold of 1 ng/L. Electrical stimulation promoted the increase of the abundance of denitrifying bacteria Thauera and electroactive bacteria Hydrogenophaga, thus enhancing the removal of TN, furthermore, the abundance of Thiobacillus and Sulfuritalea were significantly correlated with the reduction of estrogen toxicity. The study highlights the potential of electrolysis biofilter in realizing the synergy of estrogen toxicity reduction and autotrophic denitrification of industrial biochemical tailwater, and paves the way for the application of electrolysis biofilter in the advanced purification of industrial biochemical tailwater.

Hydrothermal Synthesis of Siderite and Application as Catalyst in the Electro-Fenton Oxidation of p-Benzoquinone.

A weak aspect of the electro-Fenton (EF) oxidation of contaminants is the dependence of the Fenton reaction on acidic pH values. Therefore, the rationale of this work was to develop a novel catalyst capable of promoting the EF oxidation process at near-neutral and basic pH values. In this framework, rhombohedral FeCO3 was synthesized hydrothermally and used as a catalyst in the EF oxidation of p-benzoquinone (BQ). The catalyst was characterized using various surface and spectroscopic methods. Moreover, the effects of applied current (100-500 mA), time (1-9 h), catalyst dosage (0.25-1.00 g L-1), and initial concentration of BQ (0.50-1.00 mM) on the total organic carbon removal efficiency were determined. The results indicated that a 400 mA current was sufficient for a 95% total organic carbon removal and that the increase in catalyst dosage had a positive effect on the mineralization of BQ. It was determined that at pH 3, FeCO3 behaved like a homogeneous catalyst by releasing Fe3+ ions; whereas, at the pH range of 5-7, it shifted to a homogeneous/heterogeneous catalyst. At pH 9, it worked solely as a heterogeneous catalyst due to the decrease of Fe ions passing into the solution. Finally, the spent catalyst did not undergo structural deformations after the EF treatment at higher pH values and could be regenerated and used several times.

High-Efficiency Iron Extraction from Low-Grade Siderite via a Conveyor Bed Magnetization Roasting-Magnetic Separation Process: Kinetics Research and Applications.

Upgrading and utilizing low-grade iron ore is of great practical importance to improve the strategic security of the iron ore resource supply. In this study, a thermal analysis-infrared (IR) analysis-in-situ IR method was used to investigate the reaction mechanism and kinetics of Daxigou siderite. Experiments were conducted using a conveyor bed magnetization roasting process (CBMRP) to investigate the magnetization of siderite. Multi-stage magnetic separation processes were adopted to extract magnetite. The results show that simultaneously the iron carbonate in siderite decomposes, and magnetite is formed between 364 °C and 590 °C under both inert and reducing atmospheres. The activation energy of the magnetization roasting reaction is 106.1 kJ/mol, consistent with a random nucleation and growth reaction mechanism. Magnetization roasting at 750-780 °C for approximately 3.5 s in the CBMRP results in a magnetic conversion rate of >0.99 of the iron minerals in the siderite. A beneficiation process of one roughing, one sweeping, and three cleaning processes was adopted. A dissociation particle size of -400 mesh accounting for 94.78%, a concentrate iron grade of 62.8 wt.%, and a recovery of 68.83% can be obtained. Overall, a theoretical and experimental basis is presented for the comprehensive utilization of low-grade siderite.

Exotic Carbonate Mineralization Recovered from a Deep Basalt Carbon Storage Demonstration.

Mitigating climate change requires transformational advances for carbon dioxide removal, including geologic carbon sequestration in reactive subsurface environments. The Wallula Basalt Carbon Storage Pilot Project demonstrated that CO2 injected into >800 m deep Columbia River Basalt Group flow top reservoirs mineralizes on month-year timescales. Herein, we present new optical petrography, micro-computed X-ray tomography, and electron microscopy results obtained from sidewall cores collected two years after CO2 injection. As no other anthropogenic carbonates from geologic carbon storage field studies have been recovered, this world-unique sample suite provides unparalleled insight for subsurface carbon mineralization products and paragenesis. Chemically zoned nodules with Ca/Mn-rich cores and Fe-dominant outer rims are prominent examples of the neoformed carbonate assemblages with ankerite-siderite compositions and exotic divalent cation correlations. Paragenetic insights for the timing of aragonite, silica, and fibrous zeolites are clarified based on mineral texture and spatial relationships, along with time-resolved downhole fluid sampling. Collectively, these results clarify the mineralogy, chemistry, and paragenesis of carbon mineralization, providing insight into the ultimate fate and transport of CO2 in reactive mafic-ultramafic reservoirs.