Soluble Metal Research Articles

Cathodic catalyst from lemon peel-based hydrogel for application in a SCMFC

In this investigation, a hydrogel has been prepared with the filling of lemon peel powder (LP) at three different concentrations of 1, 1.5, and 2 g (CS-PF/LP1, CS-PF/LP1.5, and CS-PF/LP2), in a mixture of phenol formaldehyde resin and chitosan, and they are pyrolyzed at 700°C to get soluble metal and nitrogen-doped carbon as cathode catalysts for oxygen reduction reaction (ORR). Several analytical characterization results confirmed the presence of inherent metallic content (or soluble metal) in the LP power. Among the three, CS-PF/LP1 provides the maximum surface area of 259.38 m2g-1, which is confirmed by the BET analysis. Additionally, the highest conductivity and catalytic activity of CS-PF/LP1 are also confirmed by electrochemical analysis. Thus, CS-PF/LP1 was selected to be used in a single-chamber microbial fuel cell (SCMFC) as a cathode catalyst. A maximum power density of 170.67 mWm-2 is obtained for CS-PF/LP1 which is 5.70 times higher than the base catalyst (without LP). Therefore, the present work uses LP, a waste material to develop a porous carbon material that can be used as an efficient cathode catalyst using solely the soluble metals of LP, for ORR in SCMFC for efficient power generation.

CHEMICAL AND MICROBIOLOGICAL DIVERSITY DETECTED IN WATER BODIES IN THE MUNICIPALITY OF BARCARENA/PA, AMAZONIA, BRAZIL

Population growth linked to greater exploitation of nature compromises the quality of water, which is considered a limited natural resource and is vitally important for the survival of living organisms and directly influences the economy, leisure, culture and the social environment. This study evaluated the physicochemical, toxicological and microbiological parameters of rivers and streams in the municipality of Barcarena, State of PA, Amazonia, Brazil. We collected 58 samples in the period from 2021 to 2022. The average values ​​verified were above the limits allowed by Brazilian legislation (CONAMA 357/2005) for true color (µ = 218.09 ± 223.843), BOD (µ = 31.30 ± 64.992) and Escherichia coli (µ = 1243.76 ± 2838.743) in stream samples when compared to those from the river, demonstrating that there are statistical differences in these parameters between these two environments. We also analyzed traces of 10 toxic metals (Al, B, Ba, Be, Cd, Co, Cr, Cu, Li, Pb). The average levels of these pollutants ranged from 0 (<LD) to 1,504 mg/L. The highest concentration was found for Aluminum, which ranged from 0.003 to 1.504 mg/L with an average of 0.275 ± 0.289 mg/L. The greatest concentration similarity (75.16%) of these soluble metals was observed between the Pará river and the Dendê stream. Therefore, the studied area presents contamination of aquatic ecosystems due to mining activity, which has caused serious impacts on the remaining communities on the banks of the municipality's rivers that cross the Municipality of Barcarena-Pa.

Ultrasound-Assisted Community Bureau of Reference (BCR) Procedure for Heavy Metal Removal in Sewage Sludge

Sewage sludge (SS) resulting from wastewater treatment plants (WWTP) is commonly applied worldwide as a fertilizer in agriculture. This can be done following a rigorous analysis of the sewage sludge composition. Due to its toxic potential, heavy metal ion content is one of the key parameters to test when evaluating SS sample usage as fertilizer. The distribution of metals present in SS samples produced by five municipal WWTPs in Romania was studied. To obtain information regarding metal distribution in SS, a modified ultrasound-assisted extraction procedure of the Community Bureau of Reference (BCR) was employed for As, Cd, Cr, Cu, Mo, Ni, Pb, Zn, and Co quantitation. Concentrations of these metals were measured using ICP-EOS spectrometry. Method extraction accuracy was verified using CRM-483 certified reference material. Results show that extraction efficiency was lowest for the exchangeable fraction for all studied metals. The detected ion metals were found distributed in fractions (F) 2 and 3, which are unavailable for plants and groundwater under natural environmental conditions. One noteworthy finding was that using ultrapure water for the leachate test resulted in low metal solubility, indicating slight metal desorption in real environmental samples. Furthermore, maize stalk bio-adsorbent was used to minimize metal ion content in WWTP leachate samples produced by the storage of SS in terms of metal ion adsorption.

The Effects of Model Insoluble Copper Compounds in a Sedimentary Environment on Denitrifying Anaerobic Methane Oxidation (DAMO) Enrichment

The contribution of denitrifying anaerobic methane oxidation (DAMO) as a methane sink across different habitats, especially those affected by anthropogenic activities, remains unclear. Mining and industrial and domestic use of metals/metal-containing compounds can all cause metal contamination in freshwater ecosystems. Precipitation of metal ions often limits their toxicity to local microorganisms, yet microbial activity may also cause the redissolution of various precipitates. In contrast to most other studies that apply soluble metal compounds, this study investigated the responses of enriched DAMO culture to model insoluble copper compounds, malachite and covellite, in simulated sedimentary environments. Copper ≤ 0.22 µm from covellite appeared to cause immediate inhibition in 10 h. Long-term tests (54 days) showed that apparent methane consumption was less impacted by various levels of malachite and covellite than soluble copper. However, the medium-/high-level malachite and covellite caused a 46.6–77.4% decline in denitrification and also induced significant death of the representative DAMO microorganisms. Some enriched species, such as Methylobacter tundripaludum, may have conducted DAMO or they may have oxidized methane aerobically using oxygen released by DAMO bacteria. Quantitative polymerase chain reaction analysis suggests that Candidatus Methanoperedens spp. were less affected by covellite as compared to malachite while Candidatus Methylomirabilis spp. responded similarly to the two compounds. Under the stress induced by copper, DAMO archaea, Planctomycetes spp. or Phenylobacterium spp. synthesized PHA/PHB-like compounds, rendering incomplete methane oxidation. Overall, the findings suggest that while DAMO activity may persist in ecosystems previously exposed to copper pollution, long-term methane abatement capability may be impaired due to a shift of the microbial community or the inhibition of representative DAMO microorganisms.

Numerical simulation of a base metal deposit related to a fossil geothermal system

Fossil and active geothermal systems that produce ore deposits are sites of complex physicochemical processes and a favorable combination of factors related to the amount of metal-bearing fluid that flows through the system, ore fluid metal concentrations, depositional efficiency, and the duration of ore deposition. Of all these factors, the length of the mineralizing event is one of the least understood aspects of ore genesis.We used fluid inclusion data, chemical compositions of base metal sulfides, and fluid flow rates to constrain a reactive-transport model of a fossil geothermal system - the Patricia Zn-Pb-Ag deposit in northern Chile. The Patricia deposit consists of quartz and base metal sulfide veins of hydrothermal origin with structural control, hosted in a volcanic succession with intense propylitic alteration. The fluid inclusions are liquid-rich, with homogenization temperatures ranging from 250 to 150 °C and salinities between 22 and 1 wt% NaCl equiv., with an early fluid mixing trend and no evidence of boiling in the system. Sulfide mineralogy indicates intermediate sulfidation conditions.To identify the most relevant geochemical and transport parameters controlling the formation of this fossil geothermal system >1000 simulations were performed using the reactive-transport code TOUGHREACT. The paragenesis of the deposit is mimicked by a model of successive stages of fluid circulation consistent with the observed mineral assemblage distribution, the fluid inclusion data, and the estimated resources in the deposit.The entire geothermal activity of the system was modeled considering 10,000 years of fluid-rock interaction, with periods of circulation of metal-barren fluids followed by metal-rich fluids driving the ore formation. In the initial model, base metal solubility with predominant chloride complexing suggests that the most efficient ore-forming mechanism for the Patricia deposit was the result of the interaction of two different fluids, one fluid transporting metals and another fluid transporting reduced sulfur, mixing in a rock volume of high permeability. Mass balance estimations with this model give a period of 3500 to 5000 years for the ore stage duration in which all the ore resources of the Patricia deposit could have been precipitated by fluid mixing.In a second model, the previous estimates for the duration of the main ore stage were used to simulate the fluid-rock interaction during the ore stage for 3500 years. The results indicated the importance of the permeability of the host rock enhanced by fractures to concentrate the volume of the mineralization and the role of the hydrothermal alteration assemblage in controlling the circulating fluid acidity. A higher efficiency in forming sulfide minerals appears to coincide with pH values ranging from 5.1 to 5.3.The results of both models are validated by replicating the system evolution, reproducing the same mineral alteration assemblage, the expected base metal resource distribution, and similar amounts of ore resources to those of the Patricia deposit: a total of 52,602 tons of lead and 157,731 tons of zinc. The models indicate that the hydrothermal event might be two times longer than the ore stage.

Enhancing the Phytoremediation of Heavy Metals by Plant Growth Promoting Rhizobacteria (PGPR) Consortium: A Narrative Review.

Heavy metal pollution has become a significant concern as the world continues to industrialize, urbanize, and modernize. Heavy metal pollutants impede the growth and metabolism of plants. The bioaccumulation of heavy metals in plants may create chlorophyll antagonism, oxidative stress, underdeveloped plant growth, and reduced photosynthetic system. Finding practical solutions to protect the environment and plants from the toxic effects of heavy metals is essential for long-term sustainable development. The direct use of suitable living plants for eliminating and degrading metal pollutants from ecosystems is known as phytoremediation. Phytoremediation is a novel and promising way to remove toxic heavy metals. Plant growth-promoting rhizobacteria (PGPR) can colonize plant roots and help promote their growth. Numerous variables, such as plant biomass yield, resistance to metal toxicity, and heavy metal solubility in the soil, affect the rate of phytoremediation. Phytoremediation using the PGPR consortium can speed up the process and increase the rate of heavy metal detoxification. The PGPR consortium has significantly increased the biological accumulation of various nutrients and heavy metals. This review sheds light on the mechanisms that allow plants to uptake and sequester toxic heavy metals to improve soil detoxification. The present review aids the understanding of eco-physiological mechanisms that drive plant-microbe interactions in the heavy metal-stressed environment.

Breaking Barriers in Chalcogenide Perovskite Synthesis: A Generalized Framework for Fabrication of BaMS3 (M═Ti, Zr, Hf) Materials

AbstractChalcogenide perovskites have garnered increasing attention as stable, non‐toxic alternatives to lead halide perovskites. However, their conventional synthesis at high temperatures (>1000 °C) has hindered widespread adoption. Recent studies have developed low‐to‐moderate temperature synthesis methods (<600 °C) using reactive precursors, yet a comprehensive understanding of the pivotal factors affecting reproducibility and repeatability remains elusive. This study delineates the critical factors in the low‐temperature synthesis of BaMS3 (M═Zr, Hf, Ti) compounds and presents a generalized framework. Innovative approaches are developed for synthesizing BaMS3 compounds using this framework involving organometallics for solution deposition. The molecular precursor routes, employing metal acetylacetonates to generate soluble metal–sulfur bonded complexes and metal–organic compounds to produce soluble metal‐thiolate, metal‐isothiocyanate, and metal‐trithiocarbonate species, are demonstrated to yield carbon‐free BaMS3. These methods have achieved the most contiguous films of BaZrS3 and BaHfS3 using solution deposition to date. Furthermore, a hybrid solution processing method involving stacking sputter‐deposited Zr and solution‐deposited BaS layers is employed to synthesize a contiguous, oxygen‐free BaZrS3 film. The diffuse reflectance measurements indicate a direct bandgap of ≈ 1.85 eV for the BaZrS3 films and ≈ 2.1 eV for the BaHfS3 film under investigation.

Stabilization of clay soil using alkali-activated sewage sludge

This study investigates the innovative reuse of sewage sludge with eco-friendly alkaline solutes to improve clayey soil without conventional cementitious binders. The unconfined compressive strength (UCS) was the main criterion to assess the quality and effectiveness of the proposed solutions, as this test was performed to measure the strength of the stabilized clay by varying binders’ dosages and curing times. Moreover, the direct shear test (DST) was used to investigate the Mohr-Coulomb parameters of the treated soil. Microstructure observations of the natural and treated soil were conducted using scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and FTIR. Furthermore, toxicity characteristic leaching procedure (TCLP) tests were performed on the treated soil to investigate the leachability of metals. According to the results, using 2.5% of sewage sludge activated by NaOH and Na2SiO3 increases the UCS values from 176 kPa to 1.46 MPa after 7 d and 56 d of curing, respectively. The results of the DST indicate that sewage sludge as a precursor increases cohesion and enhances frictional resistance, thereby improving the Mohr-Coulomb parameters of the stabilized soil. The SEM micrographs show that alkali-activated sewage sludge increases the integrity and reduces the cavity volumes in the stabilized soil. Moreover, TCLP tests revealed that the solubility of metals in the treated soil alkali-activated by sewage sludge significantly decreased. This study suggests that using sewage sludge can replace cement and lime in ground improvement, improve the circular economy, and reduce the carbon footprint of construction projects.

Influence of Electrolyte Molarity and Applied Voltage on the Purification of Ferronickel by Electrolysis Method

The current advancements in the automotive industry highlight the critical need for electric vehicles, which require a reliable supply of nickel for battery production. A potential nickel source is Ferronickel's local content, which can be used as a secondary resource. However, research on converting smelted Ferronickel into electrolytic nickel is still limited. This study aims to examine the effects of electrolyte molarity and applied voltage during the electrolysis process for refining Ferronickel. The molarities of HCl employed in this research are 0.1, 0.25, 0.5, 0.75, and 1 M for 2 hours. Additionally, the molarities of HCl are set at 2, 3, and 4 M for 6 hours. Further experiments were performed using varying voltages of 1, 2, 4, 6, and 8 V while keeping the solution concentration constant at 1 M and maintaining an electrolysis duration of 2 hours. The electrolysis solution was subsequently analyzed using the AAS (atomic absorption spectrophotometry) test. The results indicated that higher molarity levels were associated with increased current, resulting in faster reaction rates and greater solubilization of nickel metal. The Ni concentration rose with higher molarity, increasing from 76.50 mg/L in .25 M HCl to 91.88 mg/L in 1 M HCl. In contrast, the Fe concentration remained nearly constant across various molarity levels, ranging from 11.81 mg/L in .25 M HCl to 11.95 mg/L in 1 M HCl, suggesting a minimal influence of molarity below 1 M. Fe exhibited a strong positive correlation with increasing electrolyte molarity, showing a significant rise in concentration from 49.06 g/L at 2 M to 90.17 g/L at 4 M. Ni showed a more modest response to elevated molarity, with concentrations increasing from 11.95 g/L at 2 M to 22.70 g/L at 4 M. The Ni concentration increased with the applied voltage up to 6 V, reaching 95.57 mg/L, but then decreased to 77.67 mg/L at 8 V, indicating that the optimum voltage is 6 V. The Fe concentration displayed slight fluctuations but remained relatively stable across different voltage levels, measuring 11.81 mg/L at 1 V and 12.28 mg/L at 8 V, indicating that the applied voltage does not significantly influence Fe concentration in the solution.

An Overview of the Soil Acidity Causes in Ethiopia, Consequences, and Mitigation Strategies

Soil acidity is a serious land degradation problem and worldwide danger, impacting approximately 50% of the world's arable soils and limiting agricultural yield. Soil acidification is a complicated series of events that lead to the production of acidic soil. In its widest sense, it can be defined as the total of natural and human processes that reduce the pH of soil solutions. Soil acidity affects around 43% of agricultural land in Ethiopia's humid and sub humid highlands. The main objective of this seminar is to highlight different literatures on the concepts of soil acidity and to give a wealth of knowledge on the causes of soil acidity, the effects it has on agricultural production, and management strategies for reducing soil acidity and raising crop yield. Acid soils in western Ethiopia are mostly caused by topsoil erosion caused by heavy rains and high temperatures. This results in the loss of organic matter and the leaching of exchangeable basic cations (Ca<sup>2+</sup>, Mg<sup>2+</sup>, Na<sup>+</sup>, and K<sup>+</sup>). Because ammonium-based fertilizers are easily converted to nitrate and hydrogen ions in the soil, they play a significant role in acidification. One of the reasons of soil acidity is inefficient nitrogen usage, which is followed by alkalinity exports in crops. Soil acidity in Ethiopian highlands is mostly caused by the clearance of crop residues, continuous crop harvest without sufficient fertilization, cation removal, and usage of acid-forming inorganic fertilizers. Acid soil reduces nutrient availability and produces Al and Mn toxicity. In addition to these effects, soil acidity may rapidly degrade soil physicochemical qualities such as organic carbon (OC), cation exchange capacity (CEC), soil structure, porosity, and texture. Liming, the use of organic materials as ISFM, and the adoption of crop types that are resistant to Al toxicity are all alternatives for correcting acid soils. Liming can minimize toxicity by lowering concentrations, improving the availability of plant nutrients like P, Ca, Mg, and K in the soil, and reducing heavy metal solubility and leaching. Application of organic matter has a liming impact because of its abundance in alkaline cations (such Ca, Mg, and K) that were released from OM during mineralization. The pH of the soil is raised by soil organic matter, which helps with soil acidity supplements.

Antisolvent crystallization of rare earth sulfate hydrates: Thermodynamics, kinetics and impact of iron

The thermodynamics and kinetics of ethanol antisolvent crystallization of rare earths from sulfate solutions has been explored, with a view towards separating the rare earths as part of a NdFeB magnet recycling process. The solubility of single and binary metal (Nd, Pr, Fe) phases in aqueous ethanol solutions has been determined. The impact of Fe and Pr on the crystallization of Nd is evaluated, the oxidation kinetics of Fe(II) to Fe(III) quantified, and the influence of Fe oxidation state on the thermodynamics and kinetics of crystallization investigated. Oxidation to Fe(III) is slow, with a half life of approx. 600 h. For pure Nd, the solubility of the obtained, stable sulphate octahydrate decreases exponentially with increased molar organic:aqueous (O/A) ratio, and is well described by the OLI model until O/A=0.2. Pr crystallizes as an isostructural octahydrate with similar solubility. Fe(II) precipitates as a mixed solid phase, with a solubility approximately 40 times higher than the rare earths at O/A=0.2. Fe(III) solutions exhibit liquid–liquid phase separation without precipitation at all evaluated concentrations. Nd and Pr coprecipitate together in proportion to their relative concentrations, with Pr precipitating at concentrations well below its pure component solubility. Fe(II) does not precipitate with Nd at O/A≤0.2 even at high concentration, with significant precipitation as separate particles at higher O/A for all concentrations. The crystallization kinetics and the morphology of the Nd phase is affected by the Fe oxidation state. The work highlights the potential of antisolvent crystallization for selective and efficient separation of REE from Fe.

Transition metals in alkaline Lost City vent fluids are sufficient for early-life metabolisms

Despite the importance of alkaline seafloor hydrothermal vents in broadening our understanding of deep-sea hydrothermal ecosystems, little is known about the mobility and concentrations of micronutrient transition metals in these environments. Here, we present new analyses of micronutrient transition metal concentrations in vent fluids from the iconic Lost City Hydrothermal Field (LCHF) and report concentrations of Fe = 2.9–18.3 µmol/kg, Zn = 1.30–5.86 µmol/kg, Cu = 0.43–5.06 µmol/kg, Ni = 86.4–556 nmol/kg, Mn = 8.3–274 nmol/kg, V = 25.9–127 nmol/kg, Mo = 24–94 nmol/kg, Co = 8.0–135 nmol/kg, W = 4.8–16 nmol/kg, and Cd = 1.7–4.5 nmol/kg. We additionally present results of a hydrothermal lherzolite alteration experiment conducted at 300 °C, 500 bar. Transition metal concentrations and major chemical parameters of experimental reaction fluids are broadly similar to LCHF vent fluids, indicating that transition metal concentrations in LCHF vent fluids, and alkaline hydrothermal fluids more generally, reflect metal solubility controlled by underlying rock-buffered hydrothermal reactions.Concentrations of Ni and Mo are especially noteworthy because of their recognized importance for biological methanogenesis (Ni) and nitrogen fixation (Mo). When compared with known biological thresholds, our findings indicate that Ni concentrations in LCHF vent fluids are sufficient to support the robust methane-metabolizing microbial communities observed in the immediate vicinity of LCHF vents and suggest that Ni availability influences the spatial distribution of LCHF methanogens. Furthermore, our laboratory hydrothermal experiments demonstrate that Mo concentrations of similar magnitude to those observed in LCHF vent fluids (and also modern seawater) can be obtained by hydrothermal alteration of ultramafic rocks with Mo-free (Na, Ca) Cl aqueous solution. Thus, we conclude that alkaline hydrothermal fluids were likely similarly enriched in Mo prior to oxidation of the Earth’s atmosphere and ocean, providing localized Mo-rich geochemical environments capable of supporting Mo-dependent nitrogen fixation at currently recognized threshold concentrations.

Evaluating a process‐guided deep learning approach for predicting dissolved oxygen in streams

AbstractDissolved oxygen (DO) is a critical water quality constituent that governs habitat suitability for aquatic biota, biogeochemical reactions and solubility of metals in streams. Recently introduced high‐frequency sensors have increased our ability to measure DO, but we still lack the capacity to understand and predict DO concentrations at high spatial resolutions or in unmonitored locations. Machine learning (ML) has been a commonly used approach for modelling DO, however, conventional ML models have no representation of the limnological processes governing DO dynamics. Here we implement and evaluate two process‐guided deep learning (PGDL) approaches for predicting daily minimum, mean and maximum DO concentrations in rivers from the Delaware River Basin, USA. In both cases, a multi‐task approach was taken in which the PGDL models predicted stream metabolism and gas exchange rates in addition to the DO concentrations themselves. Our results showed that for these sites, the PGDL approaches did not improve upon baseline predictions in temporal and spatially similar holdout experiments. One of the approaches did, however, improve predictions when applied to spatially dissimilar sites. Although this particular PGDL approach did not improve predictive accuracy in most cases, our results suggest that process guidance, perhaps a more constrained approach, could benefit a data‐driven DO model.

Synthesis of metal powders via reduction of carbonates in self-stirred autoclave

Abstract Commercial carbonates were used as the metal sources for synthesis of metal powders, and a self-stirred autoclave device was proposed to accelerate the complete reduction of carbonates. Fluent software was employed to simulate the system and analyze the distribution of the solution and particles in the autoclave, Ni and Cu powders were synthesized to verify the experiment’s feasibility. Results indicate that sufficient mixing of reactants, solvents, and intermediate products is maintained in the improved self-stirred autoclave throughout the reaction process, facilitating the full reduction of carbonates and enhancing the uniformity of metal powders. Additionally, because basic carbonates can neutralize the hydrogen ions produced by the reduction reaction, and thus Ni powders can be synthesized without NaOH added, which is beneficial for controlling particle morphology and saving reaction time. Well-dispersed Ni and Cu powders were synthesized via the present route, which is possible to promote the reduction preparation of ultrafine metal powders for other insoluble and slightly soluble metal salts.

Influence of sources and atmospheric processes on metal solubility in PM2.5 in urban Guangzhou, South China

Water-soluble metals exert a significant influence on human and ecosystem health. In this study, a comprehensive investigation was undertaken to elucidate the solubilities of metals in PM2.5 and potential influencing factors during the dry season of 2019–2020 in urban Guangzhou, South China. The observed average solubility was <20 % for Al, Fe, Sn, and Ti; 20–40 % for V, Cr, Sb, Pb, and Ni; 40–60 % for Ba and Cu; and 60–80 % for Zn, As, Se, Cd, and Mn. Metals (Al, Ti, and Fe) originated from crustal sources (e.g., soil dust) have much lower solubilities than those (Mn, Zn, As, Se, Cd, and Ba) from fossil fuel combustion sources (e.g., traffic emission, coal combustion), suggesting the dominant role the metal sources played on solubility. Enhanced solubilities of Cu, As, Se, Cd, Sn, Sb, and Pb were associated with aerosol acidity, while those of V, Cr, Mn, Ni, Zn, and Ba were linked to organic acid complexation. For the three crustal metals, the solubilities of Al and Ti primarily depended on aerosol acidity, whereas the solubility of Fe depended on both aerosol acidity under pH < 2 conditions and organic acid complexation under pH > 2 conditions. These findings underscore the primary influence of inherent properties of the metals on their solubility and reveal the varying impacts of atmospheric physicochemical processes, with changes in their solubilities being <10 % for Cd, Sn, Sb, and Pb, 10–20 % for Cu, Cr, Mn, Ni, and Ba, and 20–30 % for As, Se, and Zn.

Unraveling the Potentials of Extremophiles in Bioextraction of Valuable Metals from Industrial Solid Wastes: An Overview

The continuous dumping of industrial solid wastes into the immediate environment is incommodious since these waste materials cause pollution and serious hazards to human health. In addition, these solid wastes are complex and consist of toxic chemical substances, heavy metals, and valuable metals, hence warranting treatment before disposal. Bioleaching is a green and sustainable technology for the solubilization and mobilization of metals from solid matrices. The leaching efficacy is contingent on the types and physiology of the organisms, the elemental content of the solid wastes, and the presence of appropriate bioprocess parameters at optimum conditions. Extremophilic microbes, including thermophiles, acidophiles, alkaliphiles, and halophiles, are recognized as excellent biological agents for the efficient bioextraction of metals from industrial solid wastes due to their aptitude for survival under harsh bioleaching conditions. Therefore, this review provides insights into the employability of extremophilic microorganisms as a biofactory for the recovery of valuable metals from various industrial solid wastes. More so, it discusses the sustainability of the bioleaching technique in terms of its life cycle assessment (LCA) and techno-economic analysis.

Positive Effect of Biochar Application on Soil Properties: Solubility and Speciation of Heavy Metals in Non-Acidic Contaminated Soils near a Steel Metallurgical Plant in Southeastern Europe

Neutral and slightly alkaline arable soils from the vicinity of the former and the biggest metallurgical plant in southeastern Europe were analyzed for the status of the water soluble pool of heavy metals in 1–20% w/w biochar (BC)-amended contaminated soils. Heavy metal solubility was monitored over a 6-month period. The metals (Fe, Mn, Cu, Zn, Cd, Pb and Ba) exhibited significant relationships between each other and exceeded the maximum permissible concentrations (MPC) in surface waters for domestic and drinking purposes. In most of the investigated sites and BC treatments, metal concentrations decreased with time due to the transfer to more resistant soil pools. Cation exchange capacity, exchangeable Ca and pH increased after BC application, while electrical conductivity decreased. BC amendment led to the prevalence of humic acids (HAs) over fulvic acids (FAs) and increased the fraction of refractory organic carbon. The share of metal–organic complexes increased for the metals Zn, Cd, Mn and Ba in the BC-amended soils, and the share of free Me2+ species decreased. This trend was especially pronounced in the soils with the lowest pH of 6.4–6.9. In addition to improving soil physicochemical and ecochemical properties, biochar application contributed to metal species in solutions that were less mobile and bioavailable.

Ecofriendly synthesized Zeolite 4A for the treatment of a multi-cationic contaminant-based effluent: Central composite design (CCD) statistical approach

One of the key aspects of futureproofing the sustainability of life on earth lies in the protection of the hydrosphere, particularly from soluble heavy metal ion pollutants. In the current study, the central composite design and optimization of the ion-exchange process have been carried out for the simultaneous removal of selected cations; Cd2+, Cu2+, and Zn2+ cations using synthesized zeolite 4A. X-ray diffraction analysis confirmed the formation of zeolite 4A. The Brunauer-Emmett-Teller (BET) surface area of the synthesized zeolite was 32 m2/g. Results mainly indicate that there is a strong relationship between the experimental data and central composite design-based models of ion removal efficiency with R2 > 0.9 and the lack of fit less than 0.1 %. All the selected ion exchange parameters (time, dosage, pH, and temperature) were found to be statistically significant, with a p-value less than 0.05.For the complete simultaneous removal of selected cations, the optimal zeolite dosage, pH, and contact time are 1.2 g/100 cm3, 6, and 3 h. The optimal temperature ranges from 25 to 27 °C. The initial concentration of each selected cation is 450 mg/L. The ion exchange is in good agreement with the Freundlich and Langmuir isotherm models. Based on the Langmuir isotherm model, the maximum Cd2+, Cu2+, and Zn2+ uptake capacity values of zeolite are 103, 99.89, and 82.08 mg/g, respectively. In this study, it has been mainly inferred that CCD can be considered a useful tool for the modeling and optimization of zeolite ion exchange applications.

Geochip 5.0 insights into the association between bioleaching of heavy metals from contaminated sediment and functional genes expressed in consortiums.

The heavy metal contamination in river and lake sediments endangers aquatic ecosystems. Herein, the feasibility of applying different exogenous mesophile consortiums in bioleaching multiple heavy metal-contaminated sediments from Xiangjiang River was investigated, and a comprehensive functional gene array (GeoChip 5.0) was used to analyze the functional gene expression to reveal the intrinsic association between metal solubilization efficiency and consortium structure. Among four consortiums, the Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans consortium had the highest solubilization efficiencies of Cu, Pb, Zn, and Cd after 15days, reaching 50.33, 29.93, 47.49, and 79.65%, while Cu, Pb, and Hg had the highest solubilization efficiencies after 30days, reaching 63.67, 45.33, and 52.07%. Geochip analysis revealed that 31,346 genes involved in different biogeochemical processes had been detected, and the systems of 15days had lower proportions of unique genes than those of 30days. Samples from the same stage had more genes overlapping with each other than those from different stages. Plentiful metal-resistant and organic remediation genes were also detected, which means the metal detoxification and organic pollutant degradation had happened with the bioleaching process. The Mantel test revealed that Pb, Zn, As, Cd, and Hg solubilized from sediment influenced the structure of expressed microbial functional genes during bioleaching. This work employed GeoChip to demonstrate the intrinsic association between functional gene expression of mesophile consortiums and the bioleaching efficiency of heavy metal-contaminated sediment, and it provides a good reference for future microbial consortium design and remediation of river and lake sediments.

Enhanced Phytoremediation of Heavy Metals By Soil-applied Organic And Inorganic Amendments: Heavy Metal Phytoavailability, Accumulation, And Metal Recovery

ABSTRACT Phytoremediation, an eco-friendly and cost-effective technique for remediating heavy metal-contaminated soils, can be significantly enhanced through the application of soil amendments. This study investigates the impact of Foliar spraying of both organic (fulvic acid, auxin, Compost, and coconut coir) and inorganic (sulfur) amendments on the phytoavailability, accumulation, and recovery of heavy metals: Arsenic-As, Mercury-Hg, Cadmium-Cd and Lead-Pb in contaminated soils. Field experiment was conducted using hyperaccumulator plant species; T. capensis and H. psittacorum with varying amendment treatments to assess their effectiveness in improving phytoremediation outcomes. The results demonstrate that specific amendments significantly increase heavy metal uptake and translocation within plants by altering soil pH, cation exchange capacity, and microbial activity, thus enhancing metal solubility and bioavailability. Furthermore, the study evaluates the potential of these amendments to not only facilitate metal recovery but also to restore soil health and fertility. The findings underscore the potential of tailored amendment strategies in optimizing phytoremediation processes, offering a sustainable solution for heavy metal remediation in polluted environments.