Removal Of Mn Research Articles

Efficient chemical and microbial removal of iron and manganese in a rapid sand filter and impact of regular backwash

Aeration followed by rapid sand filtration is a common method in drinking water treatment to remove iron (Fe) and manganese (Mn) from anoxic groundwater. To ensure the successful removal of Fe and Mn within a single filter, several factors such as raw water characteristics, backwash procedures and chemical and microbial interactions with the filter medium need to be considered. Here, we assess the characteristics of a single medium rapid sand filter with highly efficient removal of Fe and Mn. Using synchrotron X-ray spectroscopy, we show that formation of ferrihydrite-type Fe oxides in the top of the filter (0–50 cm) accounts for >95 % of the removal of dissolved Fe2+ in the filter. Birnessite-type Mn- oxides, which are thought to be biogenic, form over a wider depth interval (0–110 cm). Results of 16S rRNA gene amplicon sequencing indicate a corresponding distinct vertical stratification of the microbial community, with potential iron-oxidizing Gallionella, Leptothrix and Sideroxydans dominating in the upper part of the filter, and nitrifiers being more prevalent deeper in the filter. Besides Fe and Mn-oxide, Fe-flocs and bacteriological hollow sheets form in the upper part of the filter. Both the Fe-flocs, hollow Fe-sheets and part of the Fe and Mn coatings are removed through backwashing, thereby reducing the pressure difference measured over the filter medium linked to clogging of pores (from 14 kPa to 1.5 kPa) and ensuring continued water flow. Backwashing removes part of the Gallionella, but this does not negatively impact the filter performance. Strikingly, SEM imaging with EDS mapping revealed alternating layers of Fe and Mn-oxides on the coated grains throughout the filter. This indicates slow mixing of the filter medium between the upper 30 cm and the rest of the filter during backwashing. Slow mixing likely contributes to continued success of the filter by ensuring homogeneous filter bed growth, while still allowing for stratification of the microbial community.

Mass scale production and purification of graphite oxide from Sri Lankan vein graphite and spectroscopic characterization

Discovery of graphene has enhanced attention on industrial scale production of graphene using natural graphite which involves oxidation followed by reduction processes. Aiming for the first time, mass scale production of graphite oxide from Sri Lankan vein graphite of natural purity 99.5% carbon, following an improved Hummer’s method was experimented at optimized conditions minimizing chemical, energy and time wastage. The present study further aimed at determination of pH and manganese ions on successive purification processes of graphite oxide. The X-ray diffraction spectroscopy (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) characterizations were followed for verification of products. The wastewater produced from graphite oxide preparation process was systematically tested for Mn2+ ion using Atomic Absorption Spectroscopy (AAS). XRD peaks verified the formation of graphite oxide successfully through a complete oxidation of graphite. FTIR spectrum exhibited characteristic peaks related to typical graphite oxide while SEM shows the typical morphological features. XPS analysis verified complete removal of Mn from graphite oxide after purification. AAS analysis reveals entire removal of Mn after several washing cycles using only water. The investigation concludes that even mass scale production of quality graphite oxide is possible from Sri Lankan pure vein graphite which can subsequently be used to produce precious graphene and derivatives for various high-end applications.

Efficiency of electrocoagulation for simultaneous treatment of As and Mn in neutral mine water

Despite the efficiency and ease of implementation of electrocoagulation (ECG), its industrial application for the treatment of contaminated mine water is limited due to high energy and electrode consumption. The main objective of the present study was to identify the most performant ECG conditions using Fe–electrodes for the simultaneous removal of As(III) and Mn(II) from synthetic and surrogate neutral mine water, while limiting energy and electrode consumption. Treatability tests were performed on i) single synthetic effluents containing only 3.5mg/L As (SAs) or 4.5mg/L Mn (SMn), ii)binary synthetic effluents containing both As and Mn (SAs+Mn), and iii) surrogate mine water (Elow and Ehigh). The effect of current density (CD), ionic strength, and retention time were first evaluated for the treatment of SAs, SMn, and SAs+Mn. Then, the most performant conditions were used to treat Elow and Ehigh. The toxicity to Daphnia magna of Elow and Ehigh was evaluated before and after ECG treatment. The results showed that the increase of CD from 0.25 to 10 mA/cm2 greatly improved the removal of Mn and to a lesser extent of As, as well as energy and electrode consumption. Despite a negligible effect on the removal efficiency of As and Mn, the ionic strength (from 0.25 to 2.5mS/cm) and inter-electrode distance (from 10 to 50 mm) strongly affected the energy consumption. Results showed that ECG efficiently removed As (>97 %) from SAs at low CD (0.5 mA/cm2), while Mn required a 3.3-fold higher CD to achieve satisfactory removal (>60 %) from SMn. For the treatment of SAs+Mn, As removal was more efficient and faster than Mn removal (99 vs. 60 % and 20 vs. 60 min, respectively) at a CD of 2.0 mA/cm2. Moreover, the simultaneous removal of As and Mn at 2.0 mA/cm2 produced a volume of sludge 3.3 times greater than at 0.5 mA/cm2. Lastly, high As (99 %) and variable Mn (40–57 %) removal efficiencies were obtained after Elow and Ehigh treatment, with potential positive effect of the presence of Ca2+ and Cl- on the removal of As, while SO42- may have negatively affected the removal of Mn. After ECG treatment, no addition of toxicity to D. magna was observed for Elow and Ehigh. The outcomes of this study may provide promising insights for the application of ECG for simultaneous removal of metal(loid)s from contaminated mine water.

Sulfide-modified magnetic titanium dioxide microparticles for the adsorption and solid-phase extraction of toxic metals in aqueous samples

In this work, sulfide-modified magnetic titanium dioxide microparticles (magnetic TiO2-µPs@S) were synthesized and studied for adsorption-based removal and extraction of Cd(II), Co(II), Cu(II), Mn(II), and Ni(II) ions in aqueous solutions before FAAS analysis. The magnetic TiO2-µPs@S was well characterized by UV-vis, FTIR, XRD, SEM, and EDS techniques, and the material was well functionalized, pure, and had a slightly rod-like morphology. Under optimized conditions, initial concentration of 10 mg/L, sample solution pH of 7, adsorbent dose of 0.5 g/L, agitation speed of 200 rpm, and contact time of 45 min, the magnetic TiO2-µPs@S exhibited an adsorption capacity of 24.0, 34.9, 37.6, 38.5, and 27.9 mg/g for Cd(II), Co(II), Cu(II), Mn(II), and Ni(II), respectively. Then after, the desorption experiment was conducted using 5 mL of 0.2 M HNO3 as an eluting solvent. The method showed excellent linearity (R 2 ≥ 0.998) in 0.05–10 mg/L concentration range. The limits of detection and quantification of the developed method were found to be in the range of 0.14–0.81 and 0.47–2.73 µg/L, consecutively, indicating high sensitivity of the proposed method, and <3% RSD was obtained. Furthermore, its practical applicability was assessed on tap water, lake water, and wastewater samples, and satisfactory percent recovery values, 84.5–114%, were acquired. These results indicate the potential applicability of the developed method. In general, the magnetic TiO2-µPs@S can be used as an effective adsorbent for removing heavy metals, and the adsorbent-based solid-phase extraction can be considered a promising technique for extracting and enriching heavy metals from aqueous solutions.

Biochar supported nanoscale zerovalent iron-calcium alginate composite for simultaneous removal of Mn(II) and Cr(VI) from wastewater: Sorption performance and mechanisms

Heavy metal pollution in water caused by industrial activities has become a global environmental issue. Among them, manganese mining and smelting activities have caused the combined pollution of Cr(VI) and Mn(II) in water, posing a serious ecotoxicological risk to ecological environments and human health. To efficiently remove Cr(VI) and Mn(II) from wastewater, a novel biochar supported nanoscale zerovalent iron-calcium alginate composite (CA/nZVI/RSBC) was synthesized by liquid-phase reduction and calcium alginate embedding methods. The adsorption performance and mechanisms of Cr(VI) and Mn(II) by CA/nZVI/RSBC were investigated. The maximum adsorption capacities of Cr(VI) and Mn(II) onto CA/nZVI/RSBC fitted by the Langmuir model were 5.38 and 39.78 mg/g, respectively, which were much higher than the pristine biochar. The iron release from CA/nZVI/RSBC was comparatively lower than that of nZVI/RSBC. Mn(II) presence enhanced the reduction of Cr(VI) by CA/nZVI/RSBC. The results of XRD, XPS, and site energy distribution analysis indicated that redox was the predominant mechanism of Cr(VI) adsorption, while electrostatic attraction dominated Mn(II) adsorption. This study provides a novel alternative way for the simultaneous removal of Cr(VI) and Mn(II) in wastewater.

Development of novel biopolymer membranes by electrospinning as potential adsorbents for toxic metal ions removal from aqueous solution

This work aims to develop novel biomembranes based on PLA, PBS, or their blend and composites, with the Cloisite® 20A nanoclay, as adsorptive materials for metal ions removal. To obtain a membrane with good morphology and thinner diameter of the fibers, a series of nonwoven mats were prepared by electrospinning. To improve the adsorption performance of the electrospun membranes, thermal and acid modifications were carried out in the nanoclay before the electrospinning process, and the final electrospun membranes were applied in the removal of Cr(VI), Cu(II), Cd(II), Zn(II), Ni(II), and Mn(II) ions present in a multi-metal solution. The PBS/PLA/C20A (80/10/10) membrane obtained with an injection flow rate of 3 mL/h, needle tip-to-collector distance of 15 cm, and voltage of 20 kV were selected for the synthesis of the adsorptive membranes, which has the best morphology due to the small average diameter of the fiber and bead-free structures. The characterization techniques (TGA, BET, helium pycnometry, RMN, and DMA) results proved that the addition of PLA and nanoclay resulted in the formation of a material more resistant and with high porosity and specific surface area than the neat PBS. It can be seen that the membranes prepared with the nanoclay after thermal modification showed high metal removal efficiency than the mats designed with the raw nanoclay and after acid modification. It was also possible to conclude that PBS and PLA present the capacity to gradually release organic carbon compounds, which can be used directly as electron donors for Cr(VI) reduction.

Manganese cycling and transport in boreal estuaries impacted by acidic Mn-rich drainage

As critical transition zones between the land and the sea, estuaries are not only hotspots of hydrogeochemical and microbial processes/reactions, but also play a vital role in processing and transferring terrestrial fluxes of metals and nutrients to the sea. This study focused on three estuaries in the Gulf of Bothnia. All of them experience frequent inputs of acidic and Mn/metal-rich creek waters due to flushing of acid sulfate soils that are widespread in the creekś catchments. Analyzing existing long-termwaterchemistrydata revealed a strong seasonal variation of Mn loads, with the highest values in spring (after snow melt) and autumn (after heavy rains). We sampled surface waters, suspended particulate matter (SPM), and sediments from the estuarine mixing zones and determined the loads and solid-phase speciation of Mn as well as the composition and metabolic potentials of microbial communities. The results showed that the removal, cycling, and lateral transport of Mn were governed by similar phases and processes in the three estuaries. Manganese X-ray absorption spectroscopy data of the SPM suggested that the removal of Mn was regulated by silicates (e.g., biotite), organically complexed Mn(II), and MnOx (dominated by groutite and phyllomanganates). While the fractional amounts of silicate-bound Mn(II) were overall low and constant throughout the estuaries, MnOx was strongly correlated with the Mn loadings of the SPM and thus the main vector for the removal of Mn in the central and outer parts of the estuaries, along with organically complexed Mn(II). Down estuary, both the fractional amounts and average Mn oxidation state of the MnOx phases increased with (i) the total Mn loads on the SPM samples and (ii) the relative abundances of several potential Mn-oxidizing bacteria (Flavobacterium, Caulobacter, Mycobacterium, and Pedobacter) in the surface waters. These features collectively suggested that the oxidation of Mn, probably mediated by the potential Mn-oxidizing microorganisms, became more extensive and complete towards the central and outer parts of the estuaries. At two sites in the central parts of one estuary, abundant phyllomanganates occurred in the surface sediments, but were converted to surface-sorbed Mn(II) phases at deeper layers (>3–4 cm). The occurrence of phyllomanganates may have suppressed the reduction of sulfate in the surface sediments, pushing down the methane sulfate transition zone that is typically shallow in estuarine sediments. At the outermost site in the estuary, deposited MnOx were reduced immediately at the water–sediment interface and converted most likely to Mn carbonate. The mobile Mn species produced by the Mn reduction processes (e.g., aqueous Mn(II) and ligand complexed Mn(III)) could partly diffuse into the overlying waters and, together with the estuarine Mn loads carried by the surface waters, transfer large amounts of reactive Mn into open coastal areas and subsequently contribute to Mn shuttling and inter-linked biogeochemical processes over the seafloor. Given the widespread occurrence of acid sulfate soils and other sulfidic geological materials on many coastal plains worldwide, the identified Mn attenuation and transport mechanisms are relevant for many estuaries globally.

A DFT study on removal of Mn and V from wastewater using chitosan/graphene oxide composite as adsorbent

Metals tend to accumulate in the environment, leading to carcinogenic effects. Chitosan (Cs) has gathered significant research interest for its exceptional metal-binding properties and cost-effectiveness in heavy metal removal. To enhance chitosan adsorption capacity, it has been combined with graphene oxide, forming a chitosan-graphene oxide composite through hydrogen bonding. Various biopolymers have interacted with these metals, effectively removing them from wastewater via adsorption processes. In this study, the Cs/GO composite has been utilized for extracting metals from aquatic environments. The Cs/GO-M interaction and complex stability have been analyzed using ground-level DFT at the B3LYP/LANL2DZ level of theory. The study has demonstrated the selectivity of both Mn and V towards the composite, successfully extracting them from wastewater. Analyses of band gap energy, adsorption energy, electrophilicity, and reactivity indices have revealed that vanadium exhibited higher adsorption affinity towards Cs/GO than Manganese. Furthermore, in interactions with metals Mn and V have reduced the band gap to 0.1986 eV and 0.1940 eV, respectively. The Cs/GO composite has displayed substantial stability in aqueous media, suggesting its potential as a promising adsorbent for effluent and toxic metal removal.

Rapid start-up of the biofilter for simultaneous manganese and ammonia removal at low temperature: Effects of phosphate and copper

In low-temperature environments, low nutrients such as inorganic salts limiting microbial proliferation further extended the start-up period of biofilters for drinking water treatment. This study explored the ammonia and manganese (Mn) removal performance and the relevant mechanisms under single and combined PO43− at 30 μg/L and Cu2+ at 10 μg/L. The start-up periods of R0 (control), R1 (Cu2+ single), R2 (PO43− single) and R3 (combined Cu2+ and PO43−) were 98, 82, 32 and 24 days, respectively. PO43− increased the concentration of extracellular polymeric substances (EPS) by stimulating cellular metabolism, which promoted the formation of biofilm. Additionally, the combined Cu2+ and PO43− significantly promoted the ammonia monooxygenase (AMO) and nitrite oxidoreductase (NXR) activities, which further facilitated the removal of ammonia. The combined Cu2+ and PO43− accelerated the conversion of NH4+-N to NO2−-N and NO2−-N to NO3−-N processes thereby reducing the inhibition of Mn removal by NH4+-N and NO2−-N, and the kinetics of biological manganese oxidation showed that the combined Cu2+ and PO43− increased the rate of Mn removal, which both promoted the Mn removal in the biofilters. Furthermore, the combined Cu2+ and PO43− supported the proliferation of functional microorganisms. In summary, the synergistic effect of Cu2+ and PO43− enhanced the Mn and ammonia removal performance and achieved rapid start-up of the biofilter at low temperatures.

Effect of Fe(II) on manganese removal in biofilters: Microbial community, formation of manganese oxide and related mechanisms

In this study, different concentrations of Fe(II) (0, 1.00, 7.00 mg/L) were introduced to investigate the effect on the removal of Mn(II) in the biofilter. Fe(II) significantly inhibited the removal of Mn and prolonged the start-up of biofilters, the start-up periods for the biofilters with different Fe(II) concentrations (0, 1.00 and 7.00 mg/L) were 24, 30 and 46 days, respectively. The study showed that Fe(II) and the Fe(III) oxyhydroxides generated from Fe(II) oxidation inhibited the removal of Mn(II) by affecting the proliferation of manganese-oxidizing bacteria (MnOB) and the activity of manganese oxides (MnOx) in the biofilter. On day 20, the total MnOB genera proportions were 13.44 %, 13.35 % and 20.09 % with different Fe(II) concentrations (0, 1.00, 7.00 mg/L), respectively. The addition of Fe(II) significantly impeded the proliferation of Pseudomonas, Acinetobacter and Arthrobacter, but enhanced the proliferation of Hyphomicrobium and Sphingopyxis. On day 60, the abundance of total MnOB was reduced obviously in three biofilters (6.95 %, 6.44 % and 9.76 %). This indicated that the biological oxidation of Mn dominates during the initial operation stage of the filter layer, while the chemical auto-catalytic oxidation of active MnOx dominates in the later stages. The contribution of Mn removal by biological oxidation was positively correlated with the abundance of MnOB, and batch experiments confirmed this conclusion. Moreover, the addition of Fe(II) reduced MnOx activity by suppressing the production of high-reactivity intermediate-Mn(III), and Fe(III) oxyhydroxides hindered the formation of mature MnOx films on the surface of the filter media.

In-depth study of the removal of Mn(II) by Fe(VI) treatment and the profound influence of NOM on floc formation and properties

The presence of manganese(II) in drinking water sources poses a significant treatment difficulty for water utilities, thus necessitating the development of effective removal strategies. Treatment by Fe(VI), a combined oxidant and coagulant, has been identified as a potential green solution; however, its effectiveness is hampered by natural organic matter (NOM), and this underlying mechanism is not fully understood. Here, we investigated the inhibitory effect of three different types of NOM, representing terrestrial, aquatic, and microbial origins, on Mn(II) removal and floc growth during Fe(VI) coagulation. Results revealed that Fe(VI) coagulation effectively removes Mn(II), but NOM could inhibit its effectiveness by competing in oxidation reactions, forming NOM-Fe complexes, and altering floc aggregation. Humic acid was found to exhibit the strongest inhibition due to its unsaturated heterocyclic species that strongly bond to flocs and react with Fe(VI). For the first time, this study has presented a comprehensive elucidation of the atomic-level structure of Fe(VI) hydrolysis products by employing Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS). Results demonstrated that NOM strengthened single-corner and double-corner coordination between FeO6 octahedrons that were consumed by Mn(II), resulting in an increased contribution of γ-FeOOH in the core-shell structure (γ-FeOOH shell and γ-F2O3 core), thereby inhibiting coagulation effects. Furthermore, NOM impeded the formation of stable manganite, resulting in more low-valence Mn(III) being incorporated in the form of an unstable intermediate. These findings provide a deeper understanding of the complex interplay between Fe coagulants, heavy metal pollution, and NOM in water treatment and offer insight into the limitations of Fe(VI) in practical applications.

Evading the refining-induced trade-off between performance enhancement and alloy composition deviation in Fe-based amorphous alloys

Understanding the slag-metal reactions in Fe-based amorphous alloys is of paramount importance to evade the refining-induced trade-off between performance enhancement and alloy composition deviation. In this study, the B2O3 and B2O3–CaO slags refining-induced alloy composition deviation was theoretically and experimentally verified in Fe83Si2B12P3 (at.%) amorphous alloy, and a quaternary SiO2–B2O3–CaO–Al2O3 slag suitable for FeSiBP amorphous alloy was designed after the careful calculation of slag-metal equilibrium, slag viscosity and melting point. After refining with simple B2O3 and B2O3–CaO slags, the enrichment of B element and depletion of Si element in the FeSiBP amorphous alloy was confirmed due to the oxidation of constituent Si element and the reduction of B2O3 in the slag. The refining-induced alloy composition deviation can be effectively alleviated by using our designed slags, and the 20%SiO2–55%B2O3–10%CaO–15%Al2O3 (wt.%) slag is effective in removing the impurities and enhancing the glass-forming ability (GFA). In terms of the removal of impurities, the high activity of B2O3 in slag is crucial for the oxidation and removal of Mn, Al, Ti impurities. These results are quite vital for the design of refining slags suitable for Fe-based amorphous alloys and pave the way for the large-scale production of high-performance soft magnetic materials.

Treatment of wastewater containing thallium(I) by long-term operated manganese sand filter: Synergistic action of MnOx and MnOM

The long-term and stable removal of thallium (Tl) from industrial wastewater generated by mining and smelting operations remains challenging. While sand filters are commonly applied for the simultaneous removal of Mn(II) and other heavy metals, they have limited efficacy in treating Tl-contaminated wastewater. To address this gap, we operated a lab-scale Mn sand filter (MF) without added microorganisms to investigate the efficiency and mechanisms of Mn(II) and Tl(I) removal. Trends in effluent Mn(II) and Tl(I) concentrations indicated three operational stages: start-up, developing and maturation. Over time, the removal efficiency of Tl(I) gradually improved, plateauing at approximately 80 % eventually. Throughout operation, Tl(I) was sequestrated via surface complexation and ion exchange. Besides, enrichment of Sphingobium and other typical manganese oxidizing microorganisms (MnOM) during operation facilitated Mn(II) and Tl(I) oxidation and sequestration by generating biogenic manganese oxides (BioMnOx). Additionally, the accurate control of water quality and operating conditions during operation could also enhance removal efficiency. In summary, physicochemical actions of Mn oxides and biochemical actions of microorganisms synergistically contributed to the sequestration of Mn(II) and Tl(I). These findings provided a novel and sustainable method for the long-term and stable treatment of industrial wastewater containing thallium.

Improving conventional household greensand treatment for efficient Mn(II) removal from drinking water

Geogenic contaminants pose a global threat to ensuring access to safe drinking water. Manganese (Mn) is a naturally-occurring redox-active element which in its reduced form, Mn(II), is a widespread groundwater contaminant. Prolonged consumption of water containing high levels of Mn has been linked to adverse effects on memory, attention, motor skills, and nervous system function, particularly in vulnerable groups including pregnant individuals and young children. In addition, Mn can lead to aesthetic issues such as altered taste, clogging, and damage to plumbing systems. While Mn has historically been regulated as an aesthetic concern, a mounting body of evidence linking health issues to Mn exposure through drinking water has heightened the challenges of using groundwater to meet drinking water needs. Recently, Health Canada established a health guideline which set a maximum acceptable concentration for total Mn in drinking water of 120 μg/L. Greensand (GS) filters are commonly used in conventional drinking water treatment systems for Mn(II) removal due to their cost-effectiveness and high exchange capacity. However, under certain conditions conventional GS systems may have a low Mn(II) removal efficiency (Galangashi et al. 2021) and encounter challenges related to Mn leaching (Outram et al. 2018), resulting in failure to meet health-related standards. Furthermore, GS filters typically undergo regeneration using potassium permanganate (KMnO4), a mild oxidant that results in the release of additional Mn waste byproducts during the regeneration of the filter. Recent research suggests that Mn-containing materials can effectively activate peroxymonosulfate (PMS) and produce reactive oxygen species (ROS) that facilitate contaminant degradation. This study aims to investigate whether PMS may be used to improve greensand treatment systems and enhance Mn(II) removal from drinking water. Batch experiments were performed to test the Mn(II) removal efficiency across a range of PMS concentrations (0-500 μM) and GS mass (0.1-3 g). Aqueous Mn concentrations were measured over time using inductively coupled plasma optical emission spectrometry (ICP-OES). Solid-phase reaction products were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The mechanisms of Mn oxidation were identified by quenching experiments and electron paramagnetic resonance (EPR) spectroscopy. The activation of PMS by greensand significantly increased the removal efficiency of Mn(II) compared to the conventional method (e.g., 96.83(±3.77)% at PMS = 500 µM vs. 5.77(±11.1)% at PMS = 0 µM). Our results attribute the mechanism underlying increased Mn removal in our improved treatment method to advanced oxidation processes that involve free radicals (e.g., hydroxyl radical (·OH) and sulfate radical (SO4·-)) and non-free radical pathways, with Mn oxides as the main oxidation products. This study provides a new treatment method for more efficient Mn(II) removal while simultaneously reducing Mn wastes produced during the regeneration cycle which allows for a more sustainable and holistic management of invaluable groundwater resources.

Characterization and properties of manganese oxide film coated clinoptilolite as filter material in fixed-bed columns for removal of Mn(II) from aqueous solution

A new filter material, manganese oxide film coated clinoptilolite (MOFCC), was characterized and introduced to explore the effect in treating high concentration of manganese (1.71–2.12 mg L−1) from aqueous solution in fixed-bed column. Adsorption behavior of Mn(II) can be approximately described with the Langmuir isotherm. During the continuous 30 days filtration experiment, the removal rate of Mn(II) has maintained to be above 95.51%, the accumulated removal amount (806.42 mg) is much higher than the theoretical adsorption capacity (89.71 mg), which indicated that the removal of manganese by MOFCC includes both adsorption and auto-catalytic oxidation process, and it does not require a start-up period. SEM, EDS, XPS, XRD, ZETA potential and BET analyses were used to observe the surface properties of MOFCC. The manganese oxide film of MOFCC exhibits in clusters, apparently on occupied surface, the main component of the manganese oxide film is (Na0.7Ca0.3)Mn7O14·2.8H2O, the specific surface area of MOFCC is 38.76 m2 g−1, and the pore size is concentrated in the range of 3–40 nm, within the mesoporous range mesopores. pHpzc (point of zero charge) value is about 2.36. The characteristics of MOFCC make it an excellent manganese removal filter material for water treatment plant. Therefore, there is a long-term practical significance to develop new system for deep removal of manganese based on MOFCC.

Competitive Mn(II) removal occurs in Lysinibacillus sp. MHQ-1 through microbially-induced carbonate precipitation (MICP) and indirect Mn(II) oxidation

Biological Mn(II) removal usually involves adsorption and precipitation of Mn(II) in the form of various minerals. Manganese oxides (MnOx) formation through the activity of Mn(II) oxidation bacteria (MnOB) contributes to the majority of Mn(II) removal. However, whether other bacterial-mediated pathway could couple or competitive with Mn(II) oxidation during Mn(II) removal is scarcely reported. In this study, we reported a competitive Mn(II) removal occurred in nutrient-rich condition during the indirect Mn(II) oxidation of Lysinibacillus sp. MHQ-1, i.e., microbially-induced carbonate precipitation (MICP). In the presence of 1 mM Mn(II), 39.4% of free Mn(II) converted to MnCO3(s) quickly within 100 h, and then 11.6% of initial Mn(II) slowly oxidized to MnOx within 442 h. The urease activity assay and the genome sequencing confirmed the existence of urease and the absence of Mn(II)-oxidizing enzymes in the genome of strain MHQ-1. The urease catalyzed the formation of carbonate ion that reacts with Mn(II) and the formed ammonia raises the pH to initiate indirect Mn(II) oxidation. Genome survey suggests the urease widely exists in various Mn(II)-oxidizing bacteria (MnOB), emphasizing the importance to reconsider the composition, stability and environmental effects of biological Mn(II) removal products in nutrient-rich environment.

The treatment of As(III)-contaminated water by using granular Fe-Mn-Cu composite oxide: Removing As(III) via the oxidation-adsorption process and handling the release of manganese ions

It is a challenge to obtain an outstanding removal performance for the treatment of As(III)-contaminated water without the risk of secondary pollution. In this study, a novel granular adsorbent of Fe-Mn-Cu composite oxide (GFMCO) was fabricated by the redox-precipitation method. Batch adsorption experiments were conducted to investigate the adsorption behavior of As(III) onto GFMCO, including adsorption isotherms, adsorption kinetics, the influences of pH and competing anions, and reuse performance. The adsorption equilibrium of As by GFMCO could be achieved within 12 h. As(III) can be effectively oxidized to As(V) and adsorbed by GFMCO with a theoretical maximum As adsorption capacity of 72.88 mg/g. The As removal performance remained stable within a wide pH range of 3–9. Phosphate and silicate anions inhibited As removal, whereas chloride ions, sulfate anions, calcium ions, and magnesium ions had little effect. In addition, GFMCO could be successfully regenerated and reused with almost no loss in adsorption capacity during four consecutive cycles. Moreover, the GFMCO-packed column used as an adsorption reactor could produce approximately 969 bed volumes of treated water with the effluent arsenic concentration below 10 μg/l. Although divalent manganese ions (Mn(II)) were released from the GFMCO-packed column, efficient Mn(II) removal could be achieved with the combination of sodium hypochlorite dosing and the manganese sand filtration. Overall, this work provides a promising adsorbent for As(III) removal with satisfactory efficiency and good security.

Mechanism of Mn(II) removal by the cake layer containing biogenic manganese oxides in a flow-through mode: Biological or chemical catalysis?

Biogenic manganese oxides (BioMnOx) can effectively remove Mn(II) from drinking water. In the gravity-driven membrane (GDM) system for Mn(II)-containing water treatment, both BioMnOx and Mn(II)-oxidizing bacteria (MnOB) present in the cake layer, and their role in Mn(II) oxidation is still controversial. To address this issue, in this study, we naturally formed a cake layer containing BioMnOx and MnOB using the GDM process and identified the different roles of BioMnOx and MnOB in the removal of Mn(II). The experimental results showed that the BioMnOx accounted for a major proportion of the cake layer of GDM, and it played a principal role in the removal of Mn(II) through the combination of adsorption and catalytic oxidation. However, this removal efficiency would be continuously reduced in the absence of MnOB, while stabilized in the presence of MnOB. XPS analysis revealed that the proportion of Mn(III) and Mn(IV) in BioMnOx with MnOB reached 64.1% and 35.8%, respectively, while BioMnOx without MnOB did not contain Mn(IV). These findings suggest that BioMnOx may be the primary catalyst for Mn(II) oxidation, but its long-term activity is dependent on MnOB, which can maintain the catalytic activity by 1) producing new BioMnOx and 2) sustaining the high valence state of MnOx.

Towards Using MMO Anodes in Zinc Electrorefining: Mn Removal by Simulated Plant Off-Gas

Implementing mixed metal oxide (MMO) anodes in zinc electrowinning is highly desired due to the considerable reduction in electrical energy consumption. However, the presence of manganese in the electrolyte is a major obstacle for implementing MMO anodes in the zinc cell houses. In this work, we explore the possibility of using plant off-gas, containing SO2, to remove manganese. A SO2/air gas mixture with different SO2 and O2 concentrations was therefore used for the oxidative precipitation of manganese. It was shown that the manganese oxidation reaction is highly pH-dependent. Calcium hydroxide was used to control the pH during the process. Different operating parameters, i.e., pH, SO2/air ratio, reaction time, and effect of cobalt as a reaction catalyst, were investigated. Optimal conditions for manganese removal were reported. Under the optimal conditions, the manganese concentration decreased from 1 g L−1 to less than 1 mg L−1 within 30 min. Precipitates were characterized using EDS, XRF, and XPS techniques and showed coprecipitation of manganese, zinc, gypsum, and cobalt.

Performance Assessment of Wood Ash and Bone Char for Manganese Treatment in Acid Mine Drainage

Developing efficient methods for Mn separation is the most challenging in exploring innovative and sustainable acid mine drainage (AMD) treatments. The availability and capacity of certain waste materials for Mn removal warrant further exploration of their performance regarding the effect of process factors. This study addressed the influence of AMD chemistry (initial pH and concentrations of Mn, sulfate, and Fe), the solid/solution ratio, and the contact time on Mn separation by wood ash (WA) and bone char (BC). At an equivalent dose, WA displayed higher neutralization and Mn removal capacity over the initial pH range of 2.5–6.0 due to lime, dicalcium silicate, and fairchildite dissolution. On the other hand, at optimal doses, Mn separation by BC was faster, it was less affected by coexisting sulfate and Fe(II) species, and the carbonated hydroxyapatite structure of BC remained preserved. Efficient removal of Mn was feasible only at final pH values ≥ 9.0 in all systems with WA and at pH 6.0–6.4 using BC. These conclusions were confirmed by treating actual AMD with variable doses of both materials. The water-leaching potential of toxic elements from the AMD/BC treatment residue complied with the limits for inert waste. In contrast, the residue of AMD/WA treatment leached non-toxic quantities of Cr and substantial amounts of Al due to high residual alkalinity. To minimize the amount of secondary waste generated by BC application, its use emerges particularly beneficial after AMD neutralization in the finishing step intended for Mn removal.