Removal Of Mn Research Articles

Selective Leaching of Lithium and Beyond: Sustainable Eggshell-Mediated Recovery from Spent Li-Ion Batteries

This study introduces an innovative strategy for the selective leaching of lithium from spent Li-ion batteries. Based on thermodynamic assessments and exploiting waste eggshells as a source of calcium carbonate, an impressive 38% of lithium was dissolved selectively through mechanical milling and water leaching, outperforming conventional thermochemical methods. Afterwards, a hydrogen peroxide-assisted sulfuric acid leaching was also implemented to solubilize targeted elements (Mn, Co, Ni, and Li), with an exceptional 99% efficiency in Mn removal from the leachate using potassium permanganate and a pH range of 1.5 to 3.5. Selective separations of Co and Ni were then facilitated utilizing CYANEX 272 and n-heptane. This comprehensive study presents a promising and sustainable avenue for the effective recovery of Li and associated co-elements from spent lithium batteries.

Predicting removal of arsenic from groundwater by iron based filters using deep neural network models

Arsenic (As) contamination in drinking water has been highlighted for its environmental significance and potential health implications. Iron-based filters are cost-effective and sustainable solutions for As removal from contaminated water. Applying Machine Learning (ML) models to investigate and optimize As removal using iron-based filters is limited. The present study developed Deep Learning Neural Network (DLNN) models for predicting the removal of As and other contaminants by iron-based filters from groundwater. A small Original Dataset (ODS) consisting of 20 data points and 13 groundwater parameters was obtained from the field performances of 20 individual iron-amended ceramic filters. Cubic-spline interpolation (CSI) expanded the ODS, generating 1600 interpolated data points (IDPs) without duplication. The Bayesian optimization algorithm tuned the model hyper-parameters and IDPs in a Stratified fivefold Cross-Validation (CV) setup trained all the models. The models demonstrated reliable performances with the coefficient of determination (R2) 0.990–0.999 for As, 0.774–0.976 for Iron (Fe), 0.934–0.954 for Phosphorus (P), and 0.878–0.998 for predicting manganese (Mn) in the effluent. Sobol sensitivity analysis revealed that As (total order index (ST) = 0.563), P (ST = 0.441), Eh (ST = 0.712), and Temp (ST = 0.371) are the most sensitive parameters for the removal of As, Fe, P, and Mn. The comprehensive approach, from data expansion through DLNN model development, provides a valuable tool for estimating optimal As removal conditions from groundwater.

Evaluating manganese removal in groundwater using pilot scale biofilters: The role of filter media characteristics during start-up

This study investigated the influence of filter media characteristics on manganese (Mn) removal in groundwater biofilters during the start-up phase. Six pilot scale biofilters containing three different granular activated carbons (GAC), two anthracite, and one sand media were run for 133 days to examine their Mn removal performance at a drinking water utility, while also monitoring ATP and bacterial growth as indicators of biological activity. Key findings demonstrate the critical role of media characteristics, especially for GAC media. Initial Mn adsorption on GAC, with its higher surface area, higher macropore volume, and surface charge, promoted physicochemical and biological oxidation, thus contributing to the early onset of Mn removal during the start-up of the GAC biofilters. In contrast, biological processes dominated Mn removal on anthracite and sand biofilters during start-up. As expected, the presence of Mn-oxidizing bacteria was detected in biofilters, and ATP levels were correlated to Mn removal until the biofilters were acclimated, showing the potential of ATP as an acclimation monitoring metric. Once acclimated, all biofilters consistently reduced Mn levels from 60.9 ± 4.5 µg/L to below 5 µg/L (>90 % removal), while concurrently removing iron, thereby highlighting the biofilter's effectiveness at low water temperatures (<15 °C). This study demonstrates the advantage of GAC media for Mn removal in biofilters during start-up in regions with lower water temperatures.

Structure–reactivity relationships in the removal efficiency of catechol and hydroquinone by structurally diverse Mn-oxides

Catechol and hydroquinone are widely present hydroxybenzene isomers in the natural environment that induce environmental toxicities. These hydroxybenzene compounds can be effectively removed by manganese (Mn)-oxides via sorption and oxidative degradation processes. In the present study, we investigated the structure–reactivity relationships in the sorption and oxidation of catechol and hydroquinone on Mn-oxide surfaces. Two widely present Mn-oxides, including hydrous Mn oxide (HMO) and cryptomelane, comprised of layer and tunnel structures, respectively, are specifically studied. Effects of Mn-oxide structures and environmental pH conditions on the removal efficiency of these hydroxybenzene compounds, via sorption and oxidative degradation, are investigated. Cryptomelane, which has a higher specific surface area than HMO, possesses a higher sorption and oxidation capacity. The complexation mechanisms of catechol and hydroquinone vary due to their structure-induced difference in reactivity. Catechol reduced and dissolved more Mn from Mn-oxides than hydroquinone, accompanied by a higher C loss of catechol-C, suggesting a higher reactivity of catechol. Structural changes occurred in the Mn-oxides resulting from reaction with catechol and hydroquinone: reduction of Mn(IV), corresponding formation of Mn(III) and Mn(II) in the mineral, and free Mn2+ ions released into the suspension. These insights could help us better understand and predict the fate of hydroxybenzene compounds in Mn-oxide-rich soils and wastewater treatment systems that generate Mn-oxides via Mn removal and the associated environmental toxicity.

Removal of Impurities from Nickel and Cobalt in Mixed Hydroxide Precipitate with Solvent Extraction Using Di(2-Ethylhexyl) Phosphoric Acid

ABSTRACT This study investigates the removal of major impurities, namely Fe, Al, Zn, and Mn, in a solution produced by sulfuric acid leaching of mixed hydroxide precipitate from the Ni and Co via solvent extraction using di(2-ethylhexyl) phosphoric acid (D2EHPA). The results of extraction experiments showed that the extracted Ni, Co, Fe, Al, Zn, Mn, and Mg increased as the equilibrium pH, D2EHPA concentration, and O/A ratio increased. The optimum extraction condition was achieved at a pH of 3.5, a 20% (v/v) D2EHPA concentration, and an O/A ratio of 1, with a complete (>99.9%) extraction of Al, Fe, Zn, and 97.33% Mn with co-extracted Ni and Co of 22.32% and 29.13%, respectively, in a single extraction stage. Complete Mn removal can be achieved in two extraction stages. Co-extracted Ni and Co can be scrubbed out using a mild sulfuric acid solution at a pH of 1.2 with only less than 2% of the Al, Fe, Zn, and Mn co-scrubbed. McCabe-Thiele diagrams of the scrubbing processes were constructed, and the results showed that Ni and Co can be scrubbed out using a mild acidic solution at a pH of 1.2, O/A ratio of 1, and temperature of 40°C for 10 min of mixing. Zn and Mn can be stripped completely using 0.5 M sulfuric acid solution at an O/A of 1 and temperature of 40°C for 10 min of mixing, while Fe and Al remained unstripped. Fe and Al can subsequently be stripped via reductive stripping.

Fe and Mn Removal from Acid Mine Drainage by Utilizing Chlorella sorokiniana and Monoraphidium neglectum as Biosorbent

The mining industry generates acid mine drainage (AMD) characterized with a low pH value and high dissolved metal concentration that leads to the negative impacts on the environment and human health. The objectives of this research were to investigate the growth response of mixed culture of microalgae Chlorella sorokiniana and Monoraphidium neglectum in a liquid media contaminated with AMD; generate the optimum environmental conditions (pH value and contact time) to determine the efficiency biosorption of iron and manganese contained in the solution of AMD into the consortium of microalgae; and quantify the maximum removal amount of iron and manganese contained in the solution of AMD by utilizing microalgae consortium of Chlorella sorokiniana and Monoraphidium neglectum as biosorbent. AMD used in this research was characterized with a pH value of 1.65 with iron and manganese concentrations of 8.28 mg/L and 4.57 mg/L. The research of biosorption was conducted in 150 rpm with pH level variations of 4, 5, and 6, and contact time variations of 60, 120, and 180 min. The maximum value of iron and manganese removals occurred when pH level reached 5 at 180 min of contact time with removal efficiency of 89.73% for iron and 94.53% for manganese. The results proved that the mixed culture of microalgae namely Chlorella sorokiniana and Monoraphidium neglectum can be utilized to remove iron and manganese contained in acid mine drainage.

Development and validation of a 1D gas–liquid model for dissolved Mn(II) removal by oxidation process in a square bubble column

Modeling multiphase reactors requires an in-depth multidisciplinary analysis of various phenomena including the chemical kinetics, oxygen mass transfer, as well as the simulation of flows within these contactors. In this study, a 1D model of two-phase flow for Mn(II) removal from drinking water by aeration process is developed and validated. This model is based on the Eulerian description of two-phase gas–liquid flow with the comparison between a one-medium bubble size and a two-bubble class description to represent the bubble population in the heterogeneous flow regime. All the relevant chemical species are simulated by coupling hydrodynamics, gas–liquid mass transfer, and reaction kinetic. A pseudo-first-order model accounting for homogeneous and heterogeneous kinetics is considered for Mn(II) oxidation. The performance of the developed 1D model is compared and validated with experimental data. The 1D model was able to predict quantitatively Mn oxidation as a function of pH, initial Mn(II) and initial Mn(IV) concentrations.

Coupled effects of iron (hydr)oxides and clay minerals on the heterogeneous oxidation of aqueous Mn(II) and crystallization of manganese (hydr)oxides

The formation of nanominerals and mineral nanoparticles (NMMNs) has drawn broad attention due to their high reactivity and omnipresence in the environment. While the heterogeneous formation of NMMNs on surfaces of various minerals has been extensively studied, little is known about how mineral heteroaggregates influence this process. Herein, we investigated how heteroaggregates of iron (hydr)oxides and clay minerals affect the heterogeneous oxidation of Mn(II) and crystallization of manganese (hydr)oxides (MnOx). Our results revealed that iron (hydr)oxides (ferrihydrite) and clay minerals (kaolinite or montmorillonite) in heteroaggregates can exert coupled effects on these processes, dictating the distribution of Mn and the morphology of MnOx. Specifically, ferrihydrite catalyzed gradual oxidative removal of Mn(II) and triggered MnOx nucleation; in contrast, kaolinite/montmorillonite rapidly adsorbed Mn(II) but hardly catalyzed its oxidation. These reactions collectively caused fast adsorption and gradual oxidation of Mn(II) on the heteroaggregates. Further, MnOx nanoparticles formed on ferrihydrite surfaces migrated to kaolinite/montmorillonite surfaces, which resulted in MnOx interacting with various component minerals of the heteroaggregates. This strongly altered the further growth pathways and the eventual morphology of MnOx. Consequently, while MnOx nanoparticles in the ferrihydrite-only system aggregated freely and formed well-extended nanowires, most of those in the ferrihydrite-kaolinite system became short nanorods due to the immobilization by kaolinite surfaces; in the ferrihydrite-montmorillonite system, considerable MnOx nanoparticles attached to montmorillonite surfaces due to strong electrostatic attraction, and further grew into blocky particles via particle attachment. These results illustrate that surface reactivities of heteroaggregated ferrihydrite and kaolinite/montmorillonite are coupled when they interact with Mn(II) or MnOx. Our work, for the first time, exemplify the cooperation between surfaces of various minerals during the heterogeneous formation of NMMNs. Findings from this study also help advance our understanding of MnOx formation on surfaces with diverse atomic structures, and also Mn cycling in the environment.

Sr, Mn, and Zn extraction and separation from zinc electrolyte crystallization sediment with Ca and Sr sulfate cocrystallization structure: Reduction roasting reconstruction mechanism

Zinc electrolyte crystallization sediment (ZECS) generated in the zinc hydrometallugy industry contains valuable metals of strontium (Sr), manganese (Mn), and zinc (Zn), which has economical value but poses potential detrimental to the environment. However, the extraction and recovery of Sr is extremely difficult due to the thermodynamically stable Ca and Sr sulfate cocrystallization structure in ZECS. The destruction of refractory sulfate cocrystallization structure is a prerequisite for Sr extraction, and the carbothermal reduction roasting method is demonstrated to be efficient for the phase reconstruction. In this study, a stepwise Sr, Mn, and Zn recovery process from ZECS via carbothermal reduction roasting-acid leaching-selective precipitation-multistage extraction was proposed. In the reduction roasting procedure, all the sulfates including CaSO4, SrSO4, and Ca0.7Sr0.3SO4 are reduced to soluble sulfides. Meanwhile, most MnO2 is converted to a low-valence Mn product (MnO) that is soluble in acid, and the reduced Zn(g) is volatilized which can be collected from the flue dust. In the acid leaching procedure, the leaching efficiencies of Sr, Ca, and Mn are as high as 97.34 %, 97.44 %, and 95.49 % respectively, while 99.50 % Si in the form of silica is enriched in the leaching residue. After that, high-purity Sr solution was obtained after selective precipitation for Mn removal and D2EHPA multistage extraction for Ca removal. 97.41 % Mn in the leaching solution is precipitated by adjusting the pH value to 9.5 with NaOH solution. After four-stage extraction, 79.60 % Sr and only 0.35 % Ca are retained in the aqueous phase. The purified solution contains 2.88 g/L Sr, 0.052 g/L Ca, and 0.014 g/L Mn, which can be used to prepare industrial SrCO3 product via the carbonation operation. Thermodynamic behavior and reduction roasting reconstruction mechanism of Ca and Sr sulfate cocrystallization structure in ZECS were discussed in this work. The distributions of main metal elements (Sr, Ca, Mn, and Zn) in ZECS during the carbothermal reduction roasting-acid leaching-selective precipitation-multistage extraction process were also systematically studied.

Zeolite functionalized with macroalgae as novel material for Fe and Mn removal from real acid mine drainage

The treatment of heavy metals such as Fe and manganese Mn remains a critical global issue, necessitating solutions that are not only effective and efficient but also cost- effective and easy to implement. Adsorption has been identified as one of the most efficient techniques for removing heavy metals. This study investigates adsorption method applied to real AMD, characterized by high levels of heavy metal contamination and low pH. Key parameters analyzed include adsorption performance, isotherm and kinetic models, thermodynamic properties, and adsorption characteristics. The adsorbent used was zeolite functionalized with carboxyl, hydroxyl, and sulfate groups derived from macroalgae. Material characterization was conducted using SEM, XRD, and FTIR. The results indicate that zeolite functionalized with carboxyl, hydroxyl, and sulfate groups from macroalgae effectively reduced Fe and Mn concentrations by up to 99 % within just five minutes. Furthermore, the adsorption process followed a pseudo-second-order kinetic model and conformed to the Langmuir isotherm model.

Ca2+-controlled Mn(II) removal process in Aurantimonas sp. HBX-1: Microbially-induced carbonate precipitation (MICP) versus Mn(II) oxidation

The application of manganese-oxidizing bacteria (MnOB) to produce manganese oxides (MnOx) has been widely studied, but often overlooking the concurrent formation of MnCO3. In this study, we found Ca2+ plays a crucial role in controlling Mn(II) removal in the bacterium Aurantimonas sp. HBX-1. Under conditions with 6.8 mM Ca2+ and without adding Ca2+, 100 μM Mn(II) was removed by 96.96 % and 38.28 % within 8 days, respectively. X-ray photoelectron spectroscopy (XPS) showed that adding Ca2+ increased the average oxidation state (AOS) of the solid products from 2.05 to 2.37. X-ray absorption fine structure (XAFS) analysis revealed the product proportions as follows: under Ca2+-supplemented condition, the ratio of MnOx (1 < x ≤ 2) to MnCO₃ was 52 % to 28.1 %, while under Ca2+-free condition, the ratio shifted to 4.6 % for MnOx (1 < x ≤ 2) and 55.2 % for MnCO₃. Urease activity assay and proteomic analysis confirmed the expression of urease and carbonic anhydrase, leading to the formation of MnCO3. Additionally, animal heme peroxidase (AHP) in strain HBX-1 was found to be responsible for Mn(II) oxidation through superoxide production, with Ca2+ addition promoting its expression level. Given the widespread presence of Ca2+ in wastewater, its potential impact on the biogeochemical Mn(II) cycle driven by bacteria should be reconsidered.

Homogeneous versus heterogeneous Mn(II) oxidation in peroxymonosulfate assisting chlorination: Synergistic role for enhanced Mn(II) oxidation in water treatment

Removal of Mn(II) is an essential step for addressing water discoloration in water treatment utilities worldwide. However, conventional chlorination suffers from poor oxidation of Mn(II) due to its low homogeneous oxidation kinetics. This study explored the oxidation capability of a new chemical dosing strategy employing peroxymonosulfate (PMS) to assist the chlorination process (PMS@Cl2) for effective Mn(II) oxidation. The study comprehensively explored both oxidation kinetics and underlying mechanisms associated with homogeneous and heterogeneous oxidation within the PMS@Cl2 system. At an [Mn(II)]0 of 1 mg/L, chlorination demonstrated inability in oxidizing Mn(II), with <10 % oxidation even at an elevated [Cl2] of 150 μM (∼10 mg/L). By contrast, PMS completely oxidized 100 % Mn(II) within a 30-minute reaction at a much lower [PMS] of 60 μM (kobs = 0.07 min−1 and t1/2 = 9 min), demonstrating its superior Mn(II) oxidation kinetics (over one order of magnitude faster than conventional chlorine). PMS@Cl2 exhibited an interesting synergistic benefit when combining a lower dose PMS with a higher routine dose Cl2 (loPMS@hiCl2), e.g. [PMS]:[Cl2] at 15:30 or 30:30 μM. Both conditions achieved 100 % Mn(II) oxidation, with even better values of kobs and t1/2 (0.16–0.17 min−1 and ∼4 min) relative to PMS alone at 60 µM. The synergic benefit of PMS@Cl2 was attributed to distinct functions played by PMS and Cl2 in both homogeneous and heterogeneous oxidation processes. Reactive species identification excluded the possible involvement of SO4•−, OH•, or chlorine radicals in the homogeneous oxidation of the PMS@Cl2 system. Instead, the dominant species was O2•− radical generated during the reaction of Mn(II) and PMS. Furthermore, the heterogeneous oxidation emphasized the important role of combining Cl2 dosing, which demonstrated an increased reactivity and electron transfer with the Mn−O−Mn complex, surpassing PMS. Overall, heterogeneous oxidation accelerated the oxidation kinetics of the PMS@Cl2 system by 1.1–2 orders of magnitude relative to the homogeneous oxidation of Cl2 alone. We here demonstrated that PMS@Cl2 could offer a more efficient mean of soluble Mn(II) mitigation, achieved with a relatively low routine dose of oxidant in a short reaction period. The outcomes of this study would address the existing limitations of traditional chlorine oxidation, minimizing the trade-offs associated with high residual chlorine levels after treatments for soluble manganese-containing water.

Advances in Research on Bacterial Oxidation of Mn(II): A Visualized Bibliometric Analysis Based on CiteSpace.

Manganese (Mn) pollution poses a serious threat to the health of animals, plants, and humans. The microbial-mediated Mn(II) removal method has received widespread attention because of its rapid growth, high efficiency, and economy. Mn(II)-oxidizing bacteria can oxidize toxic soluble Mn(II) into non-toxic Mn(III/IV) oxides, which can further participate in the transformation of other heavy metals and organic pollutants, playing a crucial role in environmental remediation. This study aims to conduct a bibliometric analysis of research papers on bacterial Mn(II) oxidation using CiteSpace, and to explore the research hotspots and developmental trends within this field between 2008 and 2023. A series of visualized knowledge map analyses were conducted with 469 screened SCI research papers regarding annual publication quantity, author groups and their countries and regions, journal categories, publishing institutions, and keywords. China, the USA, and Japan published the most significant number of research papers on the research of bacterial Mn(II) oxidation. Research hotspots of bacterial Mn(II) oxidation mainly focused on the species and distributions of Mn(II)-oxidizing bacteria, the influencing factors of Mn(II) oxidation, the mechanisms of Mn(II) oxidation, and their applications in environment. This bibliometric analysis provides a comprehensive visualized knowledge map to quickly understand the current advancements, research hotspots, and academic frontiers in bacterial Mn(II) oxidation.

Geochemical drivers of manganese removal in drinking water reservoirs under hypolimnetic oxygenation

Manganese (Mn) is a naturally occurring contaminant commonly found in drinking water supplies. In lakes and reservoirs, water authorities increasingly use in situ treatment by hypolimnetic oxygenation (HOx) systems to remove metals such as Mn from the water column. HOx systems introduce dissolved oxygen (DO) to the bottom waters (hypolimnion) to promote oxidation and subsequent removal of metals from the water column. Previous laboratory studies have shown the importance of individual geochemical drivers (pH, alkalinity, mineral surfaces) on Mn oxidation, but few studies have examined the influence of these drivers of Mn removal in concert. In this study, we conducted field monitoring and laboratory experiments to examine how pH, alkalinity and the presence of mineral particles influence Mn removal at two drinking water reservoirs in southwest Virginia, both with HOx systems: Falling Creek Reservoir (FCR) and Carvins Cove Reservoir (CCR). Both reservoirs have had historical issues with elevated (>0.05 mg/L) Mn concentrations during seasonal stratification (May–October). Watershed geology contributes to differences in pH and alkalinity between the reservoirs, with FCR having lower historical medians of hypolimnetic pH and alkalinity (6.6 and 18 mg/L CaCO3, respectively) than CCR (7.2 and 62 mg/L CaCO3, respectively).Results of laboratory experiments examining the influence of pH on Mn removal showed substantial Mn loss within 14 days only under high pH (10) conditions. Mn removal did not occur at pH 6 or 8 over the same 14-day period. In experiments with pH 10 and alkalinity >70 mg/L CaCO3, near-total Mn removal occurred within 2 h. Mn removal occurred concurrently with precipitation of microscopic (<5 μm) particles, followed by formation of macroscopic (>100 μm) particles. Particles of both size classes were identified as Mn oxides (MnOx). These observations suggest that increasing pH and alkalinity promotes Mn oxidation and subsequent removal from solution. Results of experiments with pH 10 and alkalinity >70 mg/L CaCO3 suggest that heterogeneous oxidation by MnOx partially drives rapid Mn removal. Thus, initial formation of MnOx creates a positive feedback loop that can enhance additional Mn loss. In experiments using water collected from FCR and CCR, we observed rapid Mn removal in unfiltered water (0.002–0.05 d−1) but no significant removal of Mn in filtered water. These results, in combination with results of analysis of particles collected from reservoir water, suggest that minerals present in the water column likely catalyze MnOx formation. Together, our experimental results suggest that heterogenous oxidation is an important process of Mn removal, while pH and alkalinity variations of the range expected in natural freshwaters contribute less to differential Mn removal. The formation of MnOx particles during in situ oxygenation, as well as the presence of suspended minerals that occur naturally in water columns, play an important role in promoting Mn oxidation and should be accounted for in Mn removal treatment strategies.

Removal of Fe and Mn from Co leach solutions by adsorption on activated carbon based on post-consumer polyethylene terephthalate (PET) - Mechanism insights through linear and nonlinear isotherm and kinetic models

ABSTRACT The removal of Fe2+ and Mn2+ from cobalt sulfate-saturated solutions is frequently problematic for Cu-Co hydrometallurgical process performance. Among the applied and developed methods for the removal of these metals, adsorption has drawn less attention. This study investigates on the removal of Fe2+ and Mn2+ in industrial cobalt solutions known as raffinates by adsorption on activated carbon prepared from post-consumer polyethylene terephthalate (PET). The adsorption operating conditions were studied in synthetic solutions and industrial solutions. The Langmuir, Freundlich, and Temkin isotherms were then used to fit the adsorption data, while the pseudo-first-order (PFO), pseudo-second-order (PSO), and Elovich models were used to describe the kinetics. Linear and nonlinear kinetic and isotherm models were studied and compared. Furthermore, intraparticle diffusion (IPD) models were used to study the transfer mass mechanism. The results show that Fe2+ and Mn2+ are removed from Co solutions with the efficiencies of 62.14 and 68.43, respectively. The Langmuir model fits the Fe2+ and Mn2+ adsorption data better, indicating that chemisorption is preferred over physisorption, whereas the Freundlich model fits the Co2+ adsorption data better, indicating that physisorption is preferred over chemisorption. The PFO model describes well the kinetic behavior of Fe2+ and Mn2+, whereas the Elovich model describes better the kinetic behavior of Co2+. According to the IPD model, the step that limits the adsorption of Fe2+, Mn2+, and Co2+ is essentially diffusion through the activated carbon pores. The reported experimental results will highlight the use of activated carbon in the removal of Fe2+ and Mn2+ in Cu and Co hydrometallurgy.

Anaerobic manganese oxidation coupled to denitrification by novel autotrophic microbial consortium

Human activities have more than doubled the pre-industrial supply of reactive nitrogen to the biosphere, while manganese is the fifth most abundant metal in the crust of Earth with main redox states of Mn(II) and Mn(IV), which could provide electrons for denitrification driving nitrogen cycling. Although few microorganisms performing nitrate-dependent anaerobic manganese oxidation (NDMO) were identified, their active metabolic pathways have not been confirmed. Here, a microbial consortium was enriched from the mixture of freshwater sediment and activated sludge with nitrate and dissolved divalent manganese. After 528 days of enrichment, the nitrate and Mn(II) removal rate was stable at 7.54 mg N L−1 d−1 and 19.60 mg Mn L−1 d−1, respectively. The mass balance showed that nitrate was reduced into N2, and Mn(II) was converted into manganese oxides. Three novel bacteria were uniquely identified in this microbial consortium: Candidatus Nitratireduceret manganoxidans (17 %) and Candidatus Nitratoreduceret manganoxydans (3.27 %) within the order of Anaerolineales, Candidatus Nitrooxidireductor manganoxidant (6.33 %) affiliated to the order of Phycisphaerales. Ca. N. manganoxidans and Ca. N. manganoxydans encode cotA and moxA for Mn(II) oxidation and denitrification gene for NO3- reduction to N2O, while genes in Ca. N. manganoxidant, moxA, and nosZ only encoded manganese oxidase and nitrous-oxide reductase, which convert N2O further to N2. The two orders of bacteria cooperated in completing a NDMO process, which could be a profound link between nitrogen and manganese cycling in environments that should be investigated in future research. SynopsisThree novel bacteria cooperate to perform autotrophic denitrification coupled with manganese oxidation, and metagenomic analysis revealed their metabolic pathway.

Hydroxyl-aluminum pillared bentonite enhanced Mn(II) removal by chlorine oxidation

Al-PILC was used to catalyze the chlorine oxidation of Mn(II) in aqueous solution. The effects of various catalysts, catalyst dosage, chlorine dosage, pH value, temperature and organic content on the oxidation process were investigated. Results show that 1.5 mg/L chlorine can quickly oxidize Mn(II) from 0.5 mg/L to less than 0.04 mg/L with 10 mg/L Al-PILC. Using catalysts with higher porosity and higher SA, increase in chlorine concentration, increase in catalyst dosage, higher pH, and higher temperature can significantly enhance the rate of Mn(II) catalytic oxidation. The Mn(II) oxidation process includes the homogeneous oxidation, catalytic oxidation on the surface of the catalysts and self-catalytic oxidation produced by the newly produced MnOx. Al-PILC surface provides active sites for chlorine oxidation Mn(II) in the water, and also provides binding sites for the newly produced MnOx, which has higher catalytic activity and thus has an self-catalytic oxidation effect. The higher the porosity and SA of Al-PILC, the more catalytic oxidation active sites and loading sites, and the better the catalytic oxidation effect. The study promotes the understanding of chlorine catalyzed oxidation Mn(II) in aqueous solution, but also provide important guide to study newly efficient catalysts to oxidize Mn(II) with chlorine in aqueous solution.

Optimisation of Aspergilus flavus-Mediated Biosorption Process for Removal of Cr (VI) and Mn (II) Ions by Response Surface Methodology Approach

Optimisation of Aspergilus flavus-Mediated Biosorption Process for Removal of Cr (VI) and Mn (II) Ions by Response Surface Methodology Approach

Closed-loop resynthesis of LiNiCoAlO2 cathode active materials from the industrial leachate of spent li-ion batteries

The burgeoning electric vehicle market is significantly leading to a substantial increase in spent lithium-ion batteries (LIBs), emphasizing the need for efficient recycling to address raw material supply challenges. The resynthesis of cathode active materials, one of emerging efficient LIB recycling methods, refers to the synthesis of precursors from the leachate of spent LIBs without the separation of each element. While the resynthesis of LiNixCoyMnzO2 (NCM) from the Mn-rich industrial leachate of spent LIBs becomes popular nowadays, there is no practical approach for the resynthesis of LiNixCoyAlzO2 (NCA) from the industrial leachate. For the resynthesis of NCA, an additional purification step of solvent extraction with di(2-ethylhexyl) phosphoric acid for Mn removal is necessary. NCA is resynthesized from the Mn-removed leachate, after adjusting the Ni:Co ratio of precursors and sintering with Li and Al sources. While the initial discharge capacity of resynthesized NCA is slightly reduced to the electrochemically inactive impurities of Mg and Mn, its rate capability and cyclability are improved compared to pristine NCA from virgin materials. The effects of major impurities of Mg and Mn on the crystal structure and electrochemical properties of resynthesized NCA are further elucidated. Whereas the controlled Mg/Mn doping positively impacts both rate capability and cyclability, excessive Mn leads to degraded cyclability. Overall, our study expands the scope of resynthesis process of cathode active materials from spent LIBs, highlighting the intricate role of impurities and their impact on LIB performance.

Accelerated manganese(II) removal by in situ mine drainage treatment system without organic substrate amendment: Metagenomic insights into chemolithoautotrophic manganese oxidation via extracellular electron transfer

Mine drainage waters often contain elevated concentrations of toxic metals and can be a source of environmental pollution. Manganese (Mn)-oxidizing bacteria (MnOB), which can oxidize soluble Mn(II) to insoluble Mn(III, IV) under neutral pH conditions, are expected to be a promising biological agent in passive mine drainage remediation. However, the diversity, functionality and applicability of MnOB for mine drainage treatment remain mostly unknown. Given that many mine environments are poor in organic substances, it is necessary to elucidate the functions of MnOB communities that contribute to metal removal without supplementation with extra organic matter. Here, we constructed in situ continuous-flow bioreactors for treating mine drainage containing approximately 20 mg L−1 Mn(II) and 6 mg L−1 zinc (Zn) (II) and operated these bioreactors without amended organic matter. The removal of Mn(II) and Zn(II) ions reached more than 98 % at a hydraulic retention time of 0.5 days. The X-ray diffraction pattern of Mn oxides deposited on the surface of limestone carriers indicated woodruffite-like mineral accumulation in the reactors. Several heterotrophic MnOB were isolated from the bioreactor, and metagenomic analysis revealed a predominance of diverse lineages of heterotrophs, including Elusimicrobiota, which harbored MoxA-like multicopper oxidase genes. Furthermore, the metagenomic analysis also suggested the involvement of gammaproteobacterial species that possessed putative genes for extracellular electron uptake and CO2 fixation. Our findings offer the first insights into the potential for chemolithoautotrophic Mn(II) oxidation processes via electron transfer from Mn(II/III) and application of chemolithoautotrophic and heterotrophic MnOB in mine drainage remediation without supplying organic materials.