Manganese Reduction Research Articles

Quantifying zinc and manganese reduction potentials in organic solvents

Quantifying zinc and manganese reduction potentials in organic solvents

Biological two-stage treatment technology for mitigating mining-related heavy metal pollution in Georgian rivers

ObjectivesThe study aimed to investigate heavy metal contamination (copper, arsenic, manganese) in Georgian rivers affected by mining and develop a two-stage water purification technology using Spirulina (Arthrospira platensis) and trehalose lipid (TRL). This technology offers a sustainable and efficient solution to mitigate environmental and health hazards from mining-related pollution, improving river ecosystems and public health.Data DescriptionThis study examines the current state of the Kvirila, Lukhuni, Kazretula, and Mashavera rivers in terms of heavy metal pollution. Data were collected from field application of a two-stage purification process. Initial assessments showed heavy metal concentrations exceeding local regulatory limits (საქართველოს საკანონმდებლო მაცნე. გარემოსდაცვითი ტექნიკური რეგლამენტების დამტკიცების თაობაზე. Environmental Technical Regulations Approval. www.matsne.gov.ge/en/document/view/2196792?publication=0&scroll=0. Accessed 22 Aug 2024.). The purification process involved a 72-h incubation in a primary tank, followed by membrane filtration and the addition of biomass with trehalose lipid (TRL) in a secondary tank. Post-treatment data revealed significant reductions in manganese and copper concentrations, bringing them below permissible thresholds. These data highlight the effectiveness of the two-stage purification technology in removing heavy metal contaminants from water sources impacted by industrial pollution. The findings demonstrate the potential of this technology to improve sustainable water management practices and provide scalable solutions for communities facing similar water quality challenges.

Unusually high oxidation states of manganese in high optical basicity silicate glasses

Unusually high oxidation states of manganese were stabilized within a cesium-barium silicate (CBS) glass system of extremely high optical basicity. The highest basicity was obtained for the metasilicate glass 40Cs2O–10BaO–50SiO2 (mol%) with an optical basicity of Λ = 0.81. The presence of Mn5+ (d2) as well as Mn6+ (d1) is confirmed by UV–Vis, photoluminescence, and Raman spectroscopy. The UV–Vis spectrum is dominated by the Mn3+ (d4) absorption at 526 nm for low-basicity glasses, which is replaced by a peak at 679 nm (Mn5+) and, finally, a band at 603 nm (Mn6+) in the glass with the highest basicity (Λ = 0.81). In this glass, the Mn5+/Mn6+ ratio varies with the melting conditions. Photoluminescence (PL) spectroscopy under 633 nm excitation confirms the presence of Mn5+, showing the narrow, forbidden 1E →3A2 transition located at 1191 nm with vibrational sidebands at 1245 nm and 1290 nm. The measured static fluorescence intensity due to Mn5+ grows exponentially with increasing optical basicity. The near infrared fluorescence decay was bi-exponential, with time constants of 14 and 51 μs. The absence of Mn4+ in CBS glasses was confirmed by PL and electron paramagnetic resonance (EPR) spectroscopy. Despite initial doping as MnO2, metastable Mn4+ disproportionates into lower and higher valent manganese species, followed by reduction or oxidation of manganese to a stable species as ruled by the basicity of the glass and oxygen availability during melting. A structural study of the glasses by Raman spectroscopy revealed a resonance enhancement effect for the symmetric stretching mode of MnO4-tetrahedra at ∼800 cm−1 with overtones observed at higher frequencies.

Recognizing microbial manganese reduction in lacustrine carbonate and its linkage to terrestrial biogeochemical processes

Carbonate authigenesis, the in situ precipitation of carbonate minerals within the sediment porewaters, is a key pathway for carbonate deposition and plays a crucial role in global biogeochemical cycles. Heterotrophic microorganisms are essential in regulating authigenic carbonate formation, primarily through the consumption of organic matter. Although bacterial manganese reduction is known to influence the formation of rhodochrosite and dolomite, its role in limestone deposition is unclear. Here, we present a systematic investigation of mixed calcareous siliciclastic rocks from a Paleogene freshwater lake to identify the formation of authigenic carbonate, decode the role of microbial Mn reduction, and understand the microbial response to ancient lacustrine environmental changes. The positive correlation between carbonate fraction in bulk samples (Carb%) and Mn content in carbonate minerals (Mncarb) suggests that carbonate precipitation is stimulated by Mn2+ enrichment. The dissimilarity between Mncarb and Fecarb, along with the synergic variations of Mncarb and diagenetic indicators, support an authigenic rather than a hydrogenetic origin for the carbonates. Using a one-dimensional diffusion–advection-reaction model, we quantify the impact of Mn reduction on promoting carbonate precipitation. Furthermore, correlations between Pcarb and other values–positive with the chemical index alteration (CIA), negative with Mncarb, and none with TOC–suggest that nitrogen availability, regulated by continental weathering, is likely the primary factor limiting both the primary productivity and the bacterial reduction intensity at the study site. Overall, this study uncovers the role of microbial Mn reduction in stimulating authigenic carbonate precipitation, and reveals the modulation mechanism of Mn-reducing microorganisms in an ancient lake. These findings shed new light on the authigenic limestone formation mechanisms and provide a new perspective on interpreting the authigenic impacts on carbonate chemistry.

Reducing CO[formula omitted] emissions, energy consumption, and decarbonization costs in manganese production by integrating fuel-assisted solid oxide electrolysis cells in two-stage oxide reduction

Manganese is one of the most consumed metals due to its use in iron and steel making, which generates between 7%–9% of all CO2 emissions produced globally per annum. For the first time, this work explores the potential of a novel process concept to reduce CO2 emissions, energy consumption, and decarbonization costs in manganese production, which involves integrating fuel-assisted solid oxide electrolysis cells (FASOECs) in a two-stage scheme for the reduction of raw manganese ores. In this scheme, higher oxides that are present in raw manganese ores (MnO2, Mn2O3, Mn3O4) are pre-reduced using CO, yielding manganese monoxide (MnO) that is further reduced to Mn in a submerged arc furnace (SAF) using coke and electricity. In the proposed FASOEC integration concept, off-gas from the manganese ores after pre-reduction (a mixture of H2, CO, and CO2) is supplied to the FASOECs’ anode as fuel, in order to produce high-purity H2 in the cathode that is directed to the first stage of manganese reduction. H2 has enhanced reaction kinetics for reducing higher manganese oxides in comparison to CO; therefore, integrating FASOECs can improve manganese oxide conversion rates during pre-reduction, resulting in lower consumption rates of coke and energy in the SAF. The off-gas supplied to the FASOECs’ anode also lowers the amount of energy required for H2 production in the cathode (can also generate electricity, simultaneously) and produces anode exhaust gas containing only CO2 and steam. Since steam can be easily condensed from this stream, the integration of FASOECs also enables efficient decarbonization of the manganese production process, thus eliminating the need for a designated CO2 capture system. The techno-economic analysis performed herein demonstrates that directing the full supply of off-gas produced by the SAF to the FASOECs’ anode at 800 °C reduces the overall energy consumption of manganese production by up to 18% in comparison to conventional processes. This results in decarbonization cost reductions by as much as 3%–15% and a corresponding decarbonization price range of $4-32 per ton of manganese product for plant capacities of 50 and 200 kt, respectively.

Migration and transformation mechanisms of iron and manganese during river infiltration affected by the changes in riverbed sediment thickness

Riverbed scouring and siltation, affected by variations in river flow and sediment concentration, can cause changes in the sediment thickness, leading to the complex feedback between riverbed permeability and nutrient–reactive transport processes. Currently, the migration and transformation of iron and manganese under changed riverbed sediment thickness have not been taken into account. Based on indoor one-dimensional soil column simulation experiments, along with in-situ monitoring, Rhizon pore water sampling, and 16 s rRNA high-throughput sequencing technologies, this study revealed the migration and transformation patterns of iron and manganese in the river infiltration zone and their contribution rates under different sediment thickness conditions. The results demonstrated that as the riverbed sediment thickness increased, the river infiltration rate and sediment permeability coefficient demonstrated a significant decrease over time. For instance, a 5 cm sediment thickness can decrease the sediment permeability coefficient by 30 % within 32 d of infiltration, expand the disconnection zone to 25 cm, narrow the oxidation–reduction zone, and cause the iron and manganese reduction zone to evolve from a single peak to a double peak pattern. Additionally, as the sediment thickness increased, the contribution of organic matter bound iron-manganese oxidation and iron-manganese oxide reduction to Mn2+ and Fe2+ concentrations in sediment pore water decreased, while the contribution of adsorption and complexation-precipitation increased. This study holds great significance for ensuring the safety of drinking water supply and promoting the sustainable utilization of groundwater resources.

Geochemistry and microbiology of boreal alluvial soil under salinisation

Soil salinisation in taiga landscapes is in most cases caused by anthropogenic activities. The study was carried out in Perm region (Russia) on the territory of the Verkhnekamskoe Potash Deposit. The inflow of sodium chloride drainage water into ground and surface waters during the production of potash fertilisers contributed to the technogenic salinisation of river valleys in the taiga zone. The purpose of the research was to investigate the microbial composition and chemical properties of alluvial soils in the area affected by NaCl waters in the Lyonva River valley. The chemical properties of soils were determined standard methods such as potentiometric method, titration, and spectrophotometry. The microbial community was determined by 16 s rRNA gene metagenomic analysis. The soil's mineralogical composition was determined using a binocular microscope and diffractometer for XRD. The morphology and microstructure of the samples has been studied using an analytical scanning electron microscope. In Solonchaks, an interdependence of salinity and bacterial species composition was discovered, along with the bacteria's geochemical processes. The topsoil contains a considerable amount of toxic salts, ranging from 5.9 to 17%. The ratio of exchangeable cations in the soil absorption complex changes when exchangeable calcium is replaced by sodium. Salinisation caused the neutralisation of acidic alluvial soils. Bacteria originating from marine and highly mineralised environments predominate in the soil. The soils are dominated by bacteria originating from marine and highly mineralised environments, such as Proteobacteria, Shewanella (75–79%), Thiomicrospira (26%), Desulfuromonas, Marinomonas and Idiomarina (9–10%), Alicyclobacillus (4%). The correlation revealed the connection of some taxa with ions of aqueous extract, as well as with exchangeable sodium, mobile iron and total sulphur. Some bacteria promote azonal geochemical processes within alluvial forest soil, such as the reduction of iron and manganese, the production of sulphides, and the oxidation of sulphur, hydrogen, and iron. Sulphide accumulation resulting in the formation of a hydrotroilite horizon (FeS × nH2O) and iron-bearing formations were found on the soil surface. Studying the properties and degree of soil disturbance makes it possible to identify the contribution of enterprises to environmental pollution, as well as to apply new methods for monitoring, purifying, and storing potassium waste.

Manganese reduction and associated microbial communities in Antarctic surface sediments.

The polar regions are the fastest warming places on earth. Accelerated glacial melting causes increased supply of nutrients such as metal oxides (i.e., iron and manganese oxides) into the surrounding environment, such as the marine sediments of Potter Cove, King George Island/Isla 25 de Mayo (West Antarctic Peninsula). Microbial manganese oxide reduction and the associated microbial communities are poorly understood in Antarctic sediments. Here, we investigated this process by geochemical measurements of in situ sediment pore water and by slurry incubation experiments which were accompanied by 16S rRNA sequencing. Members of the genus Desulfuromusa were the main responder to manganese oxide and acetate amendment in the incubations. Other organisms identified in relation to manganese and/or acetate utilization included Desulfuromonas, Sva1033 (family of Desulfuromonadales) and unclassified Arcobacteraceae. Our data show that distinct members of Desulfuromonadales are most active in organotrophic manganese reduction, thus providing strong evidence of their relevance in manganese reduction in permanently cold Antarctic sediments.

Evaluation of Mesophilic Species Performance in Extraction of Cobalt and Manganese from Hot Filter Cake of Zinc Processing Plant

ABSTRACT Cobalt, recognized as one of the scarcest industrial metals, is typically discarded during the zinc production process in the high-temperature refining section, along with manganese. This waste product is colloquially referred to as ‘hot cake.’ The present study endeavored to segregate cobalt and manganese from the hot cake and transition them into the liquid phase via bioleaching, a method that is both economically and environmentally superior to pyrometallurgical techniques. In the hot cake, cobalt exists as Co (III) and manganese as Mn (IV). Given their oxidized states, both cobalt and manganese are insoluble in acid and necessitate reduction for dissolution. The study employed Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans bacteria to create an environment conducive to the reduction of cobalt and manganese. Under optimal conditions, this biotechnological approach facilitated the recovery of 62.8% of cobalt and 91.6% of manganese. Subsequently, a model was developed to predict the optimal method for processing cobalt from hot cake, based on the recovery rates of cobalt and manganese. This research contributes to the broader goal of resource recovery and waste minimization in the metal industry.

Influence of anti-seasonal inundation on geochemical processes of arsenic speciation in the water-level-fluctuation zone soil of the Three Gorges Reservoir, China

Since the completion of Three Gorges Dam, the water-level-fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) experiences the periodic anti-seasonal inundation. However, knowledge for mechanisms of mobilization and transformation of arsenic (As) in WLFZ soils of the TGR remains scarce. To address this gap, a combination of field observation and simulated flooding experiments attempts to illustrate the As mobilization, the transformation between As(V) and As(III), and the factors driving these processes. The study revealed that anti-seasonal inundation (with a temperature at 13 ℃) mitigated As release from submerged soils. Interestingly, the total As and ratio of As(III) (the more toxic form of As) concentrations in porewater at 13 ℃ was lower, and the prevalence of As(III) occurred later than those at 32 °C (imitate the seasonal inundation condition). The results indicated that the As reduction and the corresponding toxic risks in submerged soils were alleviated under anti-seasonal inundation. The study proposes the reduction of As-bearing manganese (Mn) mineral assemblages and competitive adsorption of dissolved organic carbon (DOC) as primary mechanisms for As mobilization. Furthermore, microorganism-mediated detoxification/reduction processes involving DOC, nitrogen, and Mn (oxyhydr)oxides were identified as central pathways for As(III) enrichment under anti-seasonal inundation. This study enhances understandings of the biogeochemical processes and fate of As in WLFZ soils influenced by artificial regulation of the reservoir.

Produced water treatment by semi-continuous sequential bioreactor and microalgae photobioreactor

Produced water (PW) from oil and gas exploration adversely affects aquatic life and living organisms, necessitating treatment before discharge to meet effluent permissible limits. This study first used activated sludge to pretreat PW in a sequential batch reactor (SBR). The pretreated PW then entered a 13 L photobioreactor (PBR) containing Scenedesmus obliquus microalgae culture. Initially, 10% of the PW mixed with 90% microalgae culture in the PBR. After the exponential growth of the microalgae, an additional 25% of PW was added to the PBR without extra nutrients. This study reported the growth performance of microalgae in the PBR as well as the reduction in effluent’s total organic carbon (TOC), total dissolved solids (TDS), electrical conductivity (EC), and heavy metals content. The results demonstrated removal efficiencies of 64% for TOC, 49.8% for TDS, and 49.1% for EC. The results also showed reductions in barium, iron, and manganese in the effluent by 95, 76, and 52%, respectively.

Effect of hydroxylammonium chloride as a reductant for hydrochloric acid leaching of valuable metals from discarded lithium-ion batteries

The use of hydroxylammonium chloride as a reducing agent is proposed to enhance the acid leaching of cathode material from spent lithium-ion batteries. The current study was conducted using real waste from scooter batteries. The main metals found in this cathode material are Mn (43.6%), Li (4.2%), Ni (8.3%) and Co (2.6%), expressed as % w/w. The effect of the initial concentrations of the extracting agent (HCl) and the reducing agent (NH3OHCl) on the extraction yields of the target metals is investigated. The presence of NH3OHCl in HCl solutions exerts a highly effective influence during the initial 15 min of the leaching process, with a complete solubilization of Mn within that timeframe, in contrast to the 20% achieved in its absence. During that period, over 70% of Li is solubilized, while Ni and Co reach maximum solubilities of 7% and 5%, respectively. Extending the contact time to 24 h between the extracting solution and LIB waste enables nearly complete extraction of Ni and exceeds 60% for Co. An analysis of variance was used to identify significant factors to be included in multivariable regressions to predict extraction yields. These regressions are used to carry out a preliminary economic analysis of the leaching process based on gross profit. The optimum outcome is achieved when the extraction is conducted through two consecutive leaching processes. In the first process, 100% Mn and 75% of Li are recovered, while the second process recovers the remaining Li, 96% of Ni, and 60% of cobalt. Additionally, the stoichiometry of the reduction of manganese(IV) by NH3OHCl is studied through the correlation between the gas volume released during the leaching processes and the Mn solubilization reached. This reduction proceeds through two parallel reactions, resulting in the production of N2O and N2. The first of these reactions predominates, exhibiting an estimated selectivity of 87%.

Enhancing cadmium immobilization by AQDS-mediated dissimilatory reduction under coexisting conditions of iron and manganese oxides

The serious contamination of cadmium (Cd) in sediments has become an urgent environmental problem. Quinones mediated dissimilatory iron and manganese reduction widely occurs in sediments, this process may enhance Cd immobilization by promoting production of secondary minerals. Nevertheless, the enhancing effect of Cd immobilization is still poorly understood. Here, 9,10-anthraquinone-2,6-disulfonic acid (AQDS) was used to facilitate the microbial reduction of iron and manganese oxides by Geobacter metallireducens GS-15, and its effects on Cd species was investigated. Compared to goethite (FeOOH), microorganisms preferentially reduced birnessite (MnO2) due to more dramatic interfacial electron transfer between birnessite and AQDS. AQDS thus significantly enhanced microbial reduction of iron and manganese coexisted minerals as well as Cd2+ immobilization. After 80 days, an impressive 83% of reducible-Cd appeared in the FeOOH–MnO2-AQDS group, demonstrating the most effective Cd immobilization. Furthermore, XANES results suggested that AQDS promoted the increase of vivianite-Cd in secondary minerals in MnO2-AQDS and FeOOH–MnO2-AQDS groups. Based on the structural equation model, HCl-extracted Fe(II) indirectly affected the increase of reducible-Cd mainly through vivianite-Cd. The AQDS enhancement on microbial reduction of iron and manganese oxides promotes the recrystallization of secondary minerals and the immobilization of Cd, offering a promising strategy for the remediation of Cd-contaminated sediments.

Ammonium loss microbiologically mediated by Fe(III) and Mn(IV) reduction along a coastal lagoon system

Anaerobic ammonium oxidation, associated with both iron (Feammox) and manganese (Mnammox) reduction, is a microbial nitrogen (N) removal mechanism recently identified in natural ecosystems. Nevertheless, the spatial distributions of these non-canonical Anammox (NC-Anammox) pathways and their environmental drivers in subtidal coastal sediments are still unknown. Here, we determined the potential NC-Anammox rates and abundance of dissimilatory metal-reducing bacteria (Acidomicrobiaceae A6 and Geobacteraceae) at different horizons (0–20 cm at 5 cm intervals) of subtidal coastal sediments using the 15N isotope-tracing technique and molecular analyses. Sediments were collected across three sectors (inlet, transition, and inner) in a coastal lagoon system (Bahia de San Quintin, Mexico) dominated by seagrass meadows. The positive relationship between 30N2 production rates and dissimilatory Fe and Mn reduction provided evidence for Feammox’s and Mnammox’s co-occurrence. N loss through NC-Anammox was detected in subtidal sediments, with potential rates of 0.07–0.62 μg N g−1 day−1. NC-Anammox process in vegetated sediments tended to be higher than those in adjacent unvegetated ones. NC-Anammox rates showed a subsurface peak (between 5 and 15 cm) in the vegetated sediments but decreased consistently with depth in the adjacent bare bottoms. Thus, the presence/absence of seagrasses and sediment characteristics, particularly the availability of organic carbon and microbiologically reducible Fe(III) and Mn(IV), affected the abundance of dissimilatory metal-reducing bacteria, which mediated NC-Anammox activity and the associated N removal. An annual loss of 32.31 ± 3.57 t N was estimated to be associated with Feammox and Mnammox within the investigated area, accounting for 2.8–4.7% of the gross total import of reactive N from the ocean into the Bahia de San Quintin. Taken as a whole, this study reveals the distribution patterns and controlling factors of the NC-Anammox pathways along a coastal lagoon system. It improves our understanding of the coupling between N and trace metal cycles in coastal environments.

Permanganate (PM) pretreatment improves medium-chain fatty acids production from sewage sludge: The role of PM oxidation and in-situ formed manganese dioxide

Medium-chain fatty acids (MCFAs) production from sewage sludge is mainly restricted by the complex substrate structure, competitive metabolism and low electron transfer rate. This study proposes a novel permanganate (PM)-based strategy to promote sludge degradation and MCFAs production. Results show that PM pretreatment significantly increases MCFAs production, i.e., attaining 12,036 mg COD/L, and decreases the carbon fluxes of electron acceptor (EA)/electron donor (ED) to byproducts. Further analysis reveals that PM oxidation enhances the release and biochemical conversion of organic components via disrupting extracellular polymers (EPS) structure and reducing viable cells ratio, providing directly available EA for chain elongation (CE). The microbial activity positively correlated with MCFAs generation are apparently heightened, while the competitive metabolism of CE (i.e., methanogensis) can be completely inhibited. Accordingly, the functional bacteria related to critical bio-steps and dissimilatory manganese reduction are largely enriched. Further mechanism exploration indicates that the main contributors for sludge solubilization are 1O2 (61.6 %) and reactive manganese species (RMnS), i.e., Mn(V)/Mn(VI) (22.3 %) and Mn(III) (∼16.1 %). As the main reducing product of PM reaction, manganese dioxide (MnO2) can enable the formation of microbial aggregates, and serve as electron shuttles to facilitate the carbon fluxes to MCFAs during CE process. Overall, this strategy can achieve simultaneous hydrogen recovery, weaken competitive metabolisms and provide electron transfer accelerator for CE reactions.

Organic Solvent Contamination in Groundwater Around Natural Gas Plants

Alberta is a province that has vast deposits of natural gas. However, in its natural form it is considered sour in that it has impurities, i.e., it contains hydrogen sulphide (H2S), carbonyl sulfide (COS), carbon dioxide (CO2), mercaptans and organic sulphides. To enable the marketing of the natural gas these impurities must be removed using organic compounds and solvents. As a result of spills, leakage during processes, seepage from unlined storage ponds some of these solvents have contaminated groundwater around natural gas processing facilities. Remediation of the organic solvents is a difficult problem. To achieve an understanding of the processes involved in their degradation, a hydrogeochemical assessment of a site can be done using existing data from the site to track the development of groundwater redox zones across the different hydrostratigraphic units (HSU). This is relevant because the oxidation is hypothesized to have contributed to the biodegradation of the compounds. The objective of this global assessment is to assign a groundwater redox zone for each sample, with special emphasis placed on defining the oxidative groundwater zone (OGZ) due to its relevance to biodegradation. Ideally, the oxic groundwater zone would be defined based on the concentration of molecular oxygen (i.e., dissolved ) in groundwater (McMahon and Chapelle 2008). However, molecular oxygen, normally measured as ‘dissolved oxygen’, was not routinely measured as a field parameter in this study and therefore was unavailable to define the OGZ. The scheme adopted considers the concentrations of terminal electron acceptors (TEA) present in groundwater and measured in commonly measured parameters including oxygen, nitrate, and sulphate and dissolved metals (manganese and iron). These TEA's are consumed under progressively more reducing conditions after oxygen reduction is complete in the order: nitrate reduction, manganese reduction, iron reduction, sulphate reduction, and finally carbonate reduction (one form of methanogenesis). The results show that redox zonation is heterogeneously distributed across the site, both within and between HSUs. Multiple lines of hydrogeochemical evidence support buffered aerobic biodegradation at the site.

Investigating the phytotoxic potential of Carlina acaulis essential oil against the weed Bidens pilosa through a physiological and metabolomic approach

Essential oils (EOs) are widely studied as possible candidates for new eco-friendly herbicides for weed management due to their phytotoxicity. In this study we tested the phytotoxic potential of the EO obtained from the roots of Carlina acaulis L. (Apiaceae) against the weed Bidens pilosa L. This EO, containing 98% of the polyacetylene carlina oxide, showed strong phytotoxic effects on the plant metabolism, such as leaf necrosis, reduction of relative water content and total leaf area, and an increase in the dry weight/fresh weight ratio, suggesting a water status alteration. The EO also damaged the photosynthetic machinery, as evidenced by the significant reduction of the effective quantum yield of photosystem II (ΦII) and the maximum quantum yield of photosystem II (Fv/Fm). In addition, the non-photochemical quenching (ΦNPQ) significantly increased after spraying with C. acaulis EO. Damage to photosystem II was further demonstrated through the reduction of manganese and calcium concentrations, possibly due to an alteration in the correct functionality of the Mn4Ca cluster of the PSII. Metabolomics analysis revealed an accumulation of branched-chain amino acids, such as isoleucine and valine, which is commonly related to osmotic alterations under drought stress situations and a general reduction in sugar content (fructose, glucose, mannose, among others), suggesting reduction of the photosynthetic efficiency too. Overall, these findings suggest C. acaulis EO as a promising natural product with phytotoxic potential against weeds that deserves further investigation.

Changing Sub‐Surface Chemistry Resulting From a 26‐Million‐Year Unconformity: Porewater Chemistry From IODP Site U1553 in the South Pacific

AbstractWhereas changes in pore water chemistry are known to impact carbonate sediment geochemistry, little is known about the impact of long unconformities on carbonate alteration. IODP Site 378‐U1553 on the southern Campbell Plateau, with a 26‐million‐year, erosional unconformity, provides a key location for examining the impact of long‐term unconformities on sub‐surface chemistry and carbonate archives. This study examined 76 interstitial water samples for sulfate sulfur and oxygen isotopes, as well as 28 bulk carbonate samples for carbonate associated sulfate (CAS) sulfur isotopes, to quantify the effects of this unconformity on the sub‐surface redox chemistry of the Site. The current state of the system suggests limited influence of redox processes on the CAS archive. Manganese reduction reaches 30 mbsf, with a decrease in manganese reduction between 20 and 30 mbsf. Below 30 mbsf, the system transitions to iron reduction to a depth of approximately 140 mbsf where sulfate reduction begins. Dissolved sulfate sulfur and oxygen isotope values suggest repeated oxygenation of sulfides. The CAS record from the Site deviates from previously published seawater values. However, the lack of a relationship between the dissolved sulfate and CAS records suggests most of the alteration of the CAS record likely occurred before the unconformity when the carbonate sediments were more reactive. This further supports the CAS record as a relatively robust archive, withstanding most post‐depositional mechanisms of carbonate alteration.

Kinetics and mechanism of manganese reductive leaching from electrolytic manganese anode slag with elemental sulfur in sulfuric acid solution

Recycling EMAS in an eco-friendly manner is crucial to alleviate the demand for manganese resource and reduce environmental pollution. Hydrometallurgical reductive leaching of EMAS with elemental sulfur is proposed, but sulfur is chemically inert. To improve the rate and degree of reductive dissolution of EMAS using elemental sulfur. Reductive leaching kinetics of EMAS by elemental sulfur with the aid of H2SO4 at atmospheric pressure have been conducted. A shrinking core model was used to explain the leaching data obtained, and the apparent activation energy was determined to be 63.8 kJ mol−1, indicating the leaching was controlled by chemical reation. The reaction order with respect to sulfuric acid concentration and mass ratio of sulfur to EMAS were 2.6 and 0.9, respectively. The leaching rate equation was established based on the shrinking core model, and good agreement between experimental data and predicted rate curves was obtained. Mechanism of reductive leaching was reasonably speculated with the assistance of X-ray diffraction and scanning electron microscope, revealing that the manganese reduction and sulfur oxidation progressed step by step, following the order Mn4+→Mn3+→Mn2+ and S0→S1+→S2+→ S4+→S6+. The ring opening reaction of [S8]•+ was identified as the rate-determining step. The results of this research provide a theoretical guidance for improving the speed and degree of manganese reduction leaching.

Effecting pattern study of SO2 on Hg0 removal over α-MnO2 in-situ supported magnetic composite

α-MnO2 was in-situ supported onto silica coated magnetite nanoparticles (MagS-Mn) to study the adsorption and oxidation of Hg0 as well as the effecting patterns of SO2 and O2 on Hg0 removal. MagS-Mn showed Hg0 removal capacity of 1122.6 μg/g at 150 °C with the presence of SO2. Hg0 adsorption and oxidation efficiencies were 2.4% and 90.6%, respectively. Hg0 removal capability deteriorated at elevated temperatures. Surface oxygen and manganese chemistry analysis indicated that SO2 inhibited the Hg0 removal through consumption of adsorbed oxygen and reduction of high valence manganese. This inhibiting effect was observed to be counteracted by O2 at lower temperatures. O2 tended to compete with SO2 for active sites and further create additional adsorbed oxygen sites for Hg0 surface reaction via surface dissociative adsorption rather than replenish the active sites consumed by SO2. The high valence manganese was also preserved by O2 which was essential to Hg0 oxidation. The intervention of O2 in the inhibition of SO2 on Hg0 removal was weakened at temperatures higher than 250 °C. Aa a result, Hg0 tends to be catalytic oxidized in the condition of low reaction temperatures and with the presence of O2 over α-MnO2 oriented composites.