Fe-Mn Oxides Research Articles

Effect of pH, Temperature, and Salinity Levels on Heavy Metal Fraction in Lake Sediments.

Heavy metals (HMs) in aquatic environments are characterized by high toxicity, a propensity for bioaccumulation, and non-degradability, and pose significant risks to biological communities. Previous studies of HMs in lakes have shown that the physical and chemical characteristics of the lake water may control both the migration of HMs in the sediments and the concentration of heavy metals in the lake water. In fact, the change in aquatic environments changes the heavy metal fraction in the sediment, which controls the release of HMs. In this paper, we investigated the effects of the pH, temperature, and salinity levels of overlying water on the chemical fraction of Cu and Zn in Wuliangsuhai Lake surface sediments. The results show that lower water pH and higher water salinity and temperature could increase Cu and Zn release from the sediment. An increase in pH led to changes in the speciation of solid fractions of Zn, namely increases in the residual fraction and decreases in the organic matter and sulfide, whereas acid-extractable and Fe-Mn oxide fractions remained largely the same. Increases in temperature and salinity led to opposite changes in the speciation of solid fractions, namely decreases in the residual fraction and increases in the organic matter and sulfide and Fe-Mn oxide fractions, whereas acid-extractable fractions remained largely the same. The effect of pH, temperature, and salinity on Cu fractions in the solids was much smaller. According to the ratio of the secondary phase to the primary phase (RSP), acidic, high-temperature, and high-salt conditions increase the release risks of Zn. Changes in water temperature have the greatest influence on the risk of Zn and Cu release from sediments, followed by the influence of salinity changes.

Enhancing long-term stability in oxygen evolution through in-situ etching of phase segregation Fe-Mn oxide

Phase segregation, induced by the dynamic evolution of the electrode surface during operation, impacts the stability of catalysts involved in the energy conversion process, specifically in the oxygen evolution reaction (OER). To address this issue, we propose an innovative electrochemical etching method for the in-situ elimination of the surface phase segregation in FeMn layered double oxides (FeMn LDO). The Mn-rich structure on the FeMn LDO surface, which undergoes a transition process from Mn3O4 to MnO4−, can be eliminated during the etching process, thereby restoring the OER performance of the catalyst. The resultant electrode shows a low overpotential of 245 mV at 10 mA cm−2 and robust durability of 1250 h at 100 mA cm−2, marking one of the highest stabilities among transition-metal based OER catalysts. Our insights into the electrode surface evolution provide valuable guidance for designing stable electrode materials.

SEQUENTIAL EXTRACTION OF SELECTED HEAVY METALS IN THE SOILS OF ABUJA, NIGERIA

Speciation of selected heavy metals in Abuja metropolitan soil samples was investigated using a sequential extraction analytical technique. Flame atomic absorption spectrometer was used for instrumental analysis. Metals were bound in six operational phases, in the sequential extraction method. Pb, Mn and Cd speciate more in exchangeable, As and Ni speciate more in bound to carbonate, Cu and Fe speciate more in bound to Fe-Mn oxide, Cr and Zn speciate more in organically bound while Al speciate more in residual in urban soil samples. In sub-urban samples, Pb and Cd speciate more in exchangeable and bound to Fe-Mn oxide, Cu speciate more in exchangeable, Al speciate more in bound to Fe-Mn oxide, Fe and Al speciate more in residual, Ni and As speciate more in bound to carbonate, Zn speciate more in organically bound and Cr speciate more in exchangeable and organically bound. Asokoro Forest (control) has most of the metals as non-residuals except Al and As which speciate more in residual phase. Sequence of ionic mobility in decreasing order for Abuja urban soils is as follows: Zn>Cu>Fe>Al>Mn>>As>Ni>Cr>Cd>Pb and in sub-urban soil samples is: Zn>Cu>Fe>Al>Mn>>Ni>As>Pb>Cd>Cr. From the results, it can be deduced that Zn is the ion with highest speciation. This portends danger to Abuja metropolis due to Zn phytoxicity which hinders photosynthesis in plants, thereby increasing the amount of CO2 giving rise to global warming. This requires that relevant authorities should enforce reduction of the activities that lead to abundance of Zn in Abuja soils.

Iron biogeochemical redox cycling dominantly controls cadmium availability in acidic paddy soils

Periodic redox condition changes in acidic paddy soils substantially induce the biogeochemical redox cycling, and consequently affect Cd availability. However, the underlying biogeochemical mechanisms of the complicated redox processes in paddy soil remain poorly understood. Thus, we investigated the dynamics of Cd fractions under anoxic (0–40 days) and oxic (40–55 days) conditions. The available Cd content was evaluated using the diffusive gradients in thin film (DGT) technique, and the results show it decreased from 6.3 μg L–1 to below 0.1 μg L–1 under anoxic conditions, but rapidly increased to 13.5 μg L–1 under oxic conditions. Both sequential extraction procedures and X-ray absorption spectroscopy (XAS) analyses found that majority of available Cd transformed to organic matter complex and Fe-Mn oxides fractions, rather than bounded with sulfides. The soil chemical properties further evaluated, and the correlation analysis and principal component analysis results suggested that the key factors in soils for the available Cd was the SO42–, pH, and surface site concentration. The reduction of SO42– could generate sulfides which may precipitate with dissolved Cd. The biogeochemical redox cycling of Fe/N/S determined the changes of soil pH and consequently influenced adsorption behavior of Cd. The breakdown of the soil aggregations changed the surface site concentration, which may affect the immobilization of Cd. A process-based kinetic model was established, and it found that iron biogeochemical redox cycling dominated the changes of soil pH, and thereby contributed to majority Cd retention by Fe-Mn oxides (34.4 %) and organic matter (33.7 %). In addition, sulfur biogeochemical redox cycling only contributed to 13.6 % of the total Cd contents, because of relatively low Cd solubility in contaminated soils and the competition with other cations for limited sulfides. The findings provide robust targets for interpreting the iron and sulfur biogeochemical processes for Cd availability and would be helpful for developing the precise and effective remediation strategies in Cd-contaminated soils.

CFD modelling of a chemical looping combustion system − Exploring the potential of natural oxygen carriers

Research advancements in Carbon Capture technology has allowed for Chemical Looping Combustion (CLC) to emerge as a promising technique which can be feasibly implemented into existing power plant infrastructures. In this study, a 120 kWth interconnected Dual Circulating Fluidized Bed (DCFB) reactor has been studied, which uses methane fuel and NiO/Al2O3 particles as oxygen carrier. Two-dimensional transient CFD simulations have been conducted for the DCFB – CLC system using an Eulerian – Eulerian model coupled with heterogeneous reactions and the results have been compared to existing literature. Using the same methodology, two natural ore potential oxygen carriers in Pakistan: Hematite (Fe-based) and Hausmannite (Mn-based) have been evaluated for the same pilot scale apparatus. The fuel conversion and combustion efficiencies have been evaluated for the oxygen carrier particles and have been compared with the original system. The results show that Fe ore provides lesser combustion efficiency as compared to NiO, whereas Mn ore exhibits extremely high reactivity. In retrospect, the use of a mixed (Fe-Mn) oxide oxygen carrier can be considered as a viable option.

Nickel, chromium, and cobalt in soils developed on nickel laterites near an abandoned mining area in southern Czech Republic

Geochemical anomalies are gaining importance due to the Europe's renewed prospecting activities for technologically critical metals, such as nickel (Ni) and cobalt (Co). In this context, soils developed on Ni laterites near old open pit mining and exploration works near Křemže in southern Czech Republic were investigated using multi-method approach to assess the distribution, solid speciation, and (bio)availability of the trace metals, with a particular focus on Ni, chromium (Cr), and Co. The total concentrations of metals in the studied soils (Ni: 170–4950 mg/kg, Cr: 56–1190 mg/kg, Co: 14–424 mg/kg) exceeded the median world regulatory guideline values (Ni: 112 mg/kg; Cr: 250 mg/kg; Co: 50 mg/kg) as well as the Czech concentration limits for agricultural soils for most of the samples. The concentration of metals in the soil profiles generally increased as a function of depth with surface horizons in agricultural plots homogenized by ploughing. The effect of a former open pit mine (already closed for ca 80 years) on the vertical distribution of metallic elements has not been demonstrated. The extractable metals were relatively low (extraction efficiency order: water < DTPA < EDTA). The mean EDTA-extractable values corresponded to 4.2 % Nitot, 8.6 % Cotot, and only 0.14 % Crtot. This contrasting metal availability is strictly related to the metal speciation in the solid phase. The primary minerals (olivine, clinopyroxene) are highly weathered to secondary phyllosilicates (lizardite, talc) and Fe oxyhydroxides and Mn oxides, all representing important carriers for Ni. Cobalt was exclusively hosted by Mn oxides, and the less mobile Cr was mainly bound in insoluble phases, likely spinel-family oxides. Despite the relatively low metal availability, elevated concentrations of Ni in the crop biomass (86 mg/kg) collected in the agricultural area suggest a metal uptake from the soil, which should be further investigated in detail.

Chemical fractionation and mobility of Cd, Mn, Ni, and Pb in farmland soils near a ceramics company.

Soil contamination due to industrial activity in ceramics production is of concern because of the risk of heavy metal pollution. Successive extraction was used to measure and identify the concentrations of Cd, Mn, Ni, and Pb in farming soils near a ceramics company in Nigeria. Furthermore, soil pH and particle size analyses were determined. The concentration of Pb was the highest, followed by that of Ni, Mn, and Cd (lowest), and the mean level of Cd exceeded the regulatory allowed limit of 1.4mgkg-1. The order of the metals' mobility factors was as follows: Cd > Mn > Ni, Pb. While the Fe-Mn oxide phase had 37% (Mn) and 20 to 83% (Ni), the residual fraction had approximately 30% (Cd) and 19 to 50% (Pb). Soil pollution evaluation was performed using enrichment factor (EF), contamination factor (CF), pollution load index (PLI), and geoaccumulation index (Igeo). Values of EF indicated significant enrichment for all metals, as the EF mean values for Cd, Ni, and Pb in soil were > 1.5. Total EF is of the order Cd > Pb > Ni > Mn. CF results revealed moderate to very high contamination (CF < 1: 3 ≤ CF ≥ 6). Similarly, the PLI indicated moderately to severely polluted soil. The order is 100m > 200m > 300m > 400m. The Igeo ranged from 1.46 to 2.76 (Cd), 0.07 to 1.62 (Ni), and 0.05 to 2.81 (Pb). The PCA, CA, and EF analyses suggest that the metals are a consequence of anthropogenic activities.

High-efficiency remediation of Hg and Cd co-contaminated paddy soils by Fe–Mn oxide modified biochar and its microbial community responses

Fe–Mn oxide modified biochar (FMBC) was produced to explore its potential for remediation of Hg–Cd contaminated paddy soils. The results showed that the application of FMBC decreased the contents of bioavailable Hg and Cd by 41.49–81.85% and 19.47–33.02% in contrast to CK, while the amount of labile organic carbon (C) fractions and C-pool management index (CPMI) was increased under BC and FMBC treated soils, indicating the enhancement of soil C storage and nutrient cycling function. Dry weight of different parts of Oryza sativa L. was enhanced after the addition of BC and FMBC, and the contents of Fe and Mn in root iron–manganese plaques (IMP) were 1.46–2.06 and 6.72–19.35 times higher than those of the control groups. Hg and Cd contents in brown rice under the FMBC treatments were significantly reduced by 18.32–71.16% and 59.52–72.11% compared with the control. FMBC addition altered the composition and metabolism function of soil bacterial communities, especially increasing the abundance of keystone phyla, including Firmicutes, Proteobacteria and Actinobacteria. Partial least squares path modelling (PLSPM) revealed that the contents of Na2S2O3–Hg, DTPA–Cd and IMP were the key indicators affecting Hg and Cd accumulation in rice grains. These results demonstrate the simultaneous value of FMBC in remediation of Hg and Cd combined pollution and restoring soil fertility and biological productivity.Graphical

Hydrological dynamics and manganese mineralization in the wake of the Sturtian glaciation

The Cryogenian Sturtian and Marinoan glaciations stand as the most extreme climate events in Earth history. Intriguingly, large-scale Mn carbonates characterize the nonglacial interlude of this period in South China. The formation mechanism of Mn carbonates and the potential correlation underlying this temporal association remain elusive. Here, we present an integrated petrographic and geochemical study of drill core materials intercepting the Mn-bearing Datangpo Formation. Rare earth element patterns of these Mn carbonates exhibit positive Ce anomalies and a lack of Y anomalies, which differ from those of modern seawater but resemble marine Mn-Fe oxides. These features, combined with negative carbonate carbon isotope compositions (δ13Ccarb as light as −9.9 ‰ VPDB), indicate the presence of oxide precursors and the incorporation of light carbon during Mn-carbonate precipitation. Phosphate oxygen isotope ratios (δ18Op) of HCl-extractable apatite reveal a ∼4 ‰ difference in the average δ18Op between Mn-rich and Mn-poor rocks. We propose that the more positive δ18Op of Mn-rich samples may result from the dominance of phosphate released by reductive dissolution of metal oxides or a heavier oxygen isotope signal of surrounding waters with which isotopic equilibrium has been reached. We further illustrate how marine invasions into coastal anoxic basins could have triggered the formation of Mn oxides and highlight the role of glaciation–deglaciation in the development of giant Mn deposits.

Boosting organics degradation via sulfite activation by Fe/Mn@CF composite electrode: Performance and mechanism

Sulfite has been proven to promote advanced oxidation processes (AOPs) to achieve low-cost and efficient degradation of contaminants, serving as an alternative to persulfate. In this study, a novel composite Fe/Mn@carbon felt (CF) electrode was successfully constructed to remove carbamazepine (CBZ). The capacity of the Fe/Mn@CF anode to activate sulfite was evaluated under various electrode preparation conditions and operating parameters. Results clearly indicated that the complete removal of CBZ was achieved in Fe/Mn@CF anode activated sulfite system under the specific conditions including Na2SO4 electrolyte concentration of 50 mM, sulfite dosage of 1 mM, initial pH of 7, and current density of 1 mA/cm2. The capacity of Fe/Mn@CF anode for sulfite activation was further presented by its excellent reusability and stability in terms of CBZ removal and metal ion release. Both radical and non-radical pathways were significantly contributed to the CBZ removal, including OH, SO4·-, O2·-, 1O2, and other reasons. Density functional theory (DFT) calculations demonstrated that Fe-Mn bimetals effectively promoted sulfite activation, with the electric field further boosting the process of Fe-Mn valence cycle and oxidation. Overall, the novel Fe/Mn@CF activated sulfite system exhibited outstanding performance and had great potential for sustainable use in removing organics.

Redox-mediated changes in the release dynamics of lead (Pb) and bacterial community composition in a biochar amended soil contaminated with metal halide perovskite solar panel waste

This study explored the redox-mediated changes in a lead (Pb) contaminated soil (900 mg/kg) due to the addition of solar cell powder (SC) and investigated the impact of biochar derived from soft wood pellet (SWP) and oil seed rape straw (OSR) (5% w/w) on Pb immobilization using an automated biogeochemical microcosm system. The redox potential (Eh) of the untreated (control; SC) and biochar treated soils (SC + SWP and SC + OSR) ranged from −151 mV to +493 mV. In SC, the dissolved Pb concentrations were higher under oxic (up to 2.29 mg L−1) conditions than reducing (0.13 mg L−1) conditions. The addition of SWP and OSR to soil immobilized Pb, decreased dissolved concentration, which could be possibly due to the increase of pH, co-precipitation of Pb with FeMn (hydro)oxides and pyromorphite, and complexation with biochar surface functional groups. The ability and efficiency of OSR for Pb immobilization were higher than SWP, owing to the higher pH and density of surface functional groups of OSR than SWP. Biochar enhanced the relative abundance of Proteobacteria irrespective of Eh changes, while the relative abundance of Bacteroidota increased under oxidizing conditions. Overall, we found that both OSR and SWP immobilized Pb in solar panel waste contaminated soil under both oxidizing and reducing redox conditions which may mitigate the potential risk of Pb contamination.

Enhanced bioremediation of hexavalent chromium via Stenotrophomonas acidaminiphila 4–1 assisted with agricultural wastes-derived biochar

Chromium (Cr) contamination in soil poses high toxicity risks to organisms. In this study, a Cr(VI)-resistant strain was isolated from oil-contaminated soil and designated as Stenotrophomonas acidaminiphila 4–1. The optimal removal efficiency of Cr(VI) (67.4 %) was achieved by employing the response surface methodology, with a glucose concentration of 6.1 %, soil moisture content of 31 %, inoculation dose of 4.5 mL, and initial Cr(VI) concentration of 0.2 mg·g−1. The strain 4–1 was immobilized in biochar derived from the pyrolysis of agricultural waste, including corn straw, loofah, and reed straw. In the loofah biochar-4–1 group, the removal efficiency of Cr(VI) was 74.94 % when the initial concentration of Cr(VI) was 0.2 mg·g−1. The biochar-immobilized strain 4–1 exhibited superior removal efficiency and tolerance towards Cr(VI) compared to the single free strain 4–1.The FT-IR results revealed that the surface functional groups of reed straw biochar exhibited a higher abundance compared to those of corn straw biochar and loofah biochar. The predominant form of Cr(VI) in untreated soil was found to be residual form, while the proportion of Fe-Mn oxides form increased from 7.9 % to 18.8 % within a span of 14 days. Notably, loofah biochar-4–1 exhibited the ability to convert unstable chromium species into stable forms within the soil. This work offers a specific instructive method to for remediating Cr polluted sites.

Metal partitioning in sediments and risk assessment of a ramsar site-Cochin estuary, South West India

Geochemical partitioning of sediment bound metals in Cochin estuary were determined by sequential extraction to unravel the processes controlling their distribution, mobility and contamination status. Most of the metals recorded higher content at residual and exchangeable fractions. Abundance of Cd, Zn and Mn in bioavailable form (promoted by surface adsorption on fine grained sediments) was sourced to industrial operations, municipal sewage and agriculture effluents. Pyrite formation effectively controls the fraction distribution of redox sensitive elements- Mn and Fe. Scavenging by Fe-Mn oxide was dominant process regulating the accretion of metals -Zn, Ni, Cr, Co, Cd, Mn whereas organic matter complexation facilitate the accumulation of the metals-Mn, Co, Cu and Zn. Contamination due to Zn and Cd was substantiated by enrichment factor (range for Zn: 4.42–57.22; range for Cd: 0.02–0.37), contamination factor (range for Zn: 0.51–22.19; range for Cd: 3.30–60.67 and geoaccumulation index (range for Zn: 0.10–4.45; range for Cd: 0.66–12.18). Elevated PLI (Range: 0.19–1.58) indicated metal inputs from anthropogenic activities. Potential ecological risk values >40 implied that Cd, Zn and Pb can induce risk to the ecosystem.

Experimental Behavior of Solar Still Using Mixed Oxides Mn-Fe/Silicone Resin Composite as Selective Solar Absorber

In this research, the optical properties of a black pigment of mixed Mn-Fe oxides synthesized by the precipitation method dispersed in silicone resin at different concentrations for use as a solar absorber in a two-slope passive solar still were evaluated. The transmittance of different thicknesses of float glass with 0.1% Fe2O3 was also studied for use as a condenser in the construction of the solar still. Regarding the pigments, the absorbance and spectral emittance were evaluated, the floated. With the above information, both the absorbent surface and the condensers were optimized to propose the best design of the solar still. The novel hybrid material used as a selective coating in the still, which corresponds to 2.3% Mn-Fe mixed oxides, exhibited a high solar absorbance of 91.82% and a relatively low infrared thermal emission of less than 57.22%, as well as good stability to the corrosive and hot environment of the solar still, in addition to great durability over time and in real operating conditions. The float glass with the highest transmittance corresponds to a thickness of 3 mm and an average transmittance of 82.57%. The built prototype was characterized by obtaining the temperature profiles of the absorber and condensers, thermal efficiency, production and water quality. The prototype has a thermal efficiency of 29.6%, requiring only energy from the sun for its operation. The water produced by this device becomes an option for human use and consumption in accordance with current official standards, allowing supply in communities that do not have access to drinking water but have access to seawater or waters with high hardness.

Investigation on YSZ- and SiO2-Doped Mn-Fe Oxide Granules Based on Drop Technique for Thermochemical Energy Storage.

The Mn-Fe oxide material possesses the advantages of abundant availability, low cost, and non-toxicity as an energy storage material, particularly addressing the limitation of sluggish reoxidation kinetics observed in pure manganese oxide. However, scaling up the thermal energy storage (TCES) system poses challenges to the stability of the reactivities and mechanical strength of materials over long-term cycles, necessitating their resolution. In this study, Mn-Fe granules were fabricated with a diameter of approximately 2 mm using the feasible and scalable drop technique, and the effects of Y2O3-stabilized ZrO2 (YSZ) and SiO2 doping, at various doping ratios ranging from 1-20 wt%, were investigated on both the anti-sintering behavior and mechanical strength. In a thermal gravimetric analyzer, the redox reaction tests showed that both the dopants led to an enhancement in the reoxidation rates when the doping ratios were in an appropriate range, while they also brought about a decrease in the reduction rate and energy storage density. In a packed-bed reactor, the results of five consecutive redox tests showed a similar pattern to that in a thermal gravimetric analyzer. Additionally, the doping led to the stable reduction/oxidation reaction rates during the cyclic tests. In the subsequent 120 cyclic tests, the Si-doped granules exhibited volume expansion with a decreased crushing strength, whereas the YSZ-doped granules experienced drastic shrinkage with an increase in the crushing strength. The 1 wt% Si and 2 wt% Si presented the best synthetic performance, which resulted from the milder sintering effects during the long-term cyclic tests.

Application of iron-manganese oxide fillers in bioretention facility: Enhanced removal of antibiotics and conventional contaminants

Bioretention facilities are common source reduction facilities, but traditional fillers are not effective in reducing emerging contaminants such as antibiotics. Although Fe-Mn oxides have been extensively explored, their removal of emerging contaminants and application in the sponge city have not yet been addressed. Therefore, this study aims to address this limitation by developing Fe-Mn oxide fillers. In this research, the optimal preparation conditions (Fe/Mn mole ratio, polyvinyl alcohol (PVA) concentration, and filler particle size) and influencing factors (filler dosage, initial pollutant concentration, pH, temperature, and co-existing ions) were investigated using a typical antibiotic, norfloxacin (NOR), as the target contaminant. The removal mechanism of NOR was investigated by SEM, FTIR, and XPS characterizations. Subsequently, the fillers were applied to bioretention facilities with different filling modes (layered and mixed) to evaluate their effectiveness in removing NOR and conventional pollutants at different recurrence periods, drought periods, and pollutant influent concentrations. The study indicated that Fe-Mn oxide filler (Fe/Mn mole ratio of 4:1, PVA concentration of 7 %, particle size of 4 mm) could remove more than 70 % of NOR (1–20 mg/L). The NOR removal by Fe-Mn oxide filler involved adsorption and redox reactions. Notably, bioretention facilities using Fe-Mn oxide fillers have shown varying degrees of improvement in the removal of NOR and conventional pollutants compared to conventional ones. This study contributes to the application of Fe-Mn oxide filler in bioretention facilities, thus playing a crucial role in mitigating antibiotic pollution in stormwater runoff.

Experimental Behavior of Solar Still Using Mixed Oxides Mn-Fe/Silicona Resin Composite as Selective Solar Absorber

The optical properties of a black pigment of mixed Mn-Fe oxides synthesized by the precipitation method, dispersed in silicone resin in different concentrations as well as different thicknesses of float glass with 0.1% of Fe2O3 for use in the construction of a two-slope passive solar still. Regarding the pigments, the spectral absorbance and emittance were evaluated, the x-ray diffraction patterns were obtained to know their crystalline structure and their morphology was studied through surface profilometry, in addition the spectral transmittance for the different samples of float glass was evaluated. With the previous information, both the absorbing surface and the condensers were optimized to propose the best design of the solar still. The hybrid material used as a selective coating in the still, which corresponds to 2.3% Mn-Fe mixed oxides, exhibited a high solar absorbance of 91.82% and a relatively low infrared thermal emission, less than 57.22%, as well as good stability to the corrosive and hot environment of the solar still, in addition to great durability over time, real operating conditions. The float glass with the highest transmittance corresponds to a thickness of 3 mm and an average transmittance of 82.57%. The built prototype was characterized by obtaining the temperature profiles of the absorber, water column and condensers, thermal efficiency, production and water quality. The prototype has a thermal efficiency of 27%, requiring only energy from the sun for its operation and the product water is distilled water, free of salts, of great potential value for human use and consumption in accordance with current official standards.

A bio-adsorbent of Fe-Mn oxides@SiO2 NPs from brown rice husk ash: ultrasonic-assisted synthesis and its application for cobalt removal from industrial wastewater

ABSTRACT In the present study, SiO2 NPs (nanoparticles) were designed and synthesised from brown rice husk ash with the assistance of ultrasonic waves. The synthesised SiO2 NPs with high purity were modified using Fe-Mn oxides. The adsorption ability of SiO2 NPs and Fe-Mn oxides@SiO2 hybrid nanomaterials has been investigated for cobalt removal from wastewater. The characteristics of prepared adsorbents were determined using different techniques of identification. The pseudo-second-order model could describe well the effect of contact time. The Langmuir model described the equilibrium manner of the process well, and one gram of Fe-Mn oxides@SiO2 could attract 284.24 mg of cobalt at saturation state. The thermodynamic parameters show the exothermic and spontaneity of the adsorption process. The electrostatic interaction, physical adsorption in meso-macropores, and complexation reaction are the involved mechanisms. The regeneration of prepared adsorbent was investigated at 4 adsorption/desorption cycles in the continuous process. Synthesised hybrid nanomaterial can remove 70.5% cobalt and reduce 61% COD of the actual effluent from the Petrochemical wastewater.

Preparation of iron composite filler for PRB technology and its application in the removal of toxic metals(loids) from groundwater

Iron-based materials have garnered significant research interest due to their high surface reactivity, exhibiting potential for remediating metal(loid)s in groundwater. However, agglomeration and blockage limit its long-term and stability performance in application in permeable reactive barrier (PRB) technology. In this study, three innovative and low-cost iron composite fillers were prepared using a mass-producible impregnation method and applied as fillers for PRB. Static sorption and dynamic column experiments were conducted to assess the long-term performance of these composites to remediate multiple toxic metals(loids) contaminated groundwater. The results showed that the iron composite fillers had the excellent adsorption capacities for Co(II), Cu(II), Cr(VI) and As(III) from simulated contaminated groundwater even under the interference of Fe(III) and Mn(II). The pH of the influent favored the adsorption of toxic metals(loids) by the iron composite fillers in the order of 3.00＞5.00＞8.00＞7.00＞9.00＞6.00. The overall adsorption process was more consistent with the quasi-secondary kinetic equation. The corresponding constant values of Cr, Co, Cu, and As on CZ were 0.022, 0.093, 0.756, and 0.342 h−1, respectively. And that of CP-I and CP-II were 0.004, 0.022, 0.001, 0.126, 0.008, 0.041, 0.001, and 0.154 h−1, respectively. The specific surface area of the composite zeolite (Na92Al92Si100O384) and composite pumice was 48.185 m2/g and 0.63 m2/g, respectively. The dynamic column experiment was run steadily for 40 days, during which the average removal rates of toxic metals(loids) were above 95% and approximate 20 times its own volume of contaminated water was purified. FeO(OH) on composite zeolite and Fe3O4 on composite pumice played a dominant role in the removal of toxic metals(loids). The toxic metals(loids) adsorbed in the PRB were mainly in a stable phase of residual fraction and Fe-Mn oxide fraction, making them less likely to cause secondary pollution problems.

Comparative study of chemical speciation and leaching feature of typical heavy metals in coarse and fine slags from the entrained-flow coal gasification

ABSTRACT The dissimilarity in chemical speciation and release properties of heavy metals will result in varying levels of environmental hazards and potential applications of coal gasification coarse and fine slags. The distribution, chemical speciation, leaching features, and potential environmental risks of heavy metals (Cr, Cu, Cd, Zn, Pb, and Mn) in coarse and fine slags from different coal gasification processes were revealed and compared by the sequential chemical extraction method, Horizontal vibration method, and pH-dependent leaching experiments. The results show that Cr (516.78 mg/kg) in coarse slag, Zn (348.50 mg/kg) and Pb (214.78 mg/kg) in fine slag are highly enriched and the content exceeds the screening value, indicating the need for better management during stockpiling and landfilling. The distribution of Cr, Cu, Pb, and Mn in residual state, Zn in Fe-Mn oxide bound state, and Cd in unstable bound state is the highest in both coarse slag and fine slag. The leaching toxicity of heavy metals (HMs) does not exceed the standard, but the leachate is classified as Level V surface water or groundwater quality due to the leaching concentration of Pb exceeding 0.1 mg/L. Furthermore, leaching of Cr, Zn, Cd, and Pb in fine slag is much more dependent on pH compared to coarse slag, and the concentrations of Zn and Pb exceed emission standards at pH < 3.0. The high concentration of heavy metals caught on the surface of fine slag is more harmful to the environment. The properties of HMs in the slags and pH of the application environment must be comprehensively considered before coal gasification slag disposal, especially fine slag.