Metal Fractions Research Articles

Appraisal of Heavy Metal Risk Hazards of Eisenia fetida-Mediated Steel Slag Vermicompost on Oryza sativa L.: Insights from Agro-Scale Inspection and Machine Learning Analytics

The steel industry drives world economic growth, yet it generates heavy metal-rich steel slag, which jeopardizes the environment. The utilization of vermi-technology is essential for the sustainable transformation of toxic steel waste slag (SW) into organic amendments, although field-scale use of vermiprocessed SW remains unexplored. To bridge the gap, this study evaluated the efficacy of vermiprocessed SW as an organic supplement for rice field cultivation, focusing on heavy metal (HM) bioavailability, human health risk, and yield in comparison to raw slag and NPK fertilizer. The results indicated a considerable decrease in the bioavailable fraction of heavy metals in T4 (1:1 SW vermicompost 50% + 50% fertilizer). In treatments, T9 (100% SW) and T10 (50% SW + 50% fertilizer) (FIAM) free ion activity modeling confirmed grain absorption of HMs, and the FIAM HQ values indicated the health risk for the direct application of steel slag waste on the field. The risk factor evaluation of HMs’ presence in treatments T9 and T10 established the possible cancer risk for living beings. Similarly, machine learning models like SOBOL sensitivity analysis and artificial neural networks revealed potential threats associated with HMs on different treatments, respectively. The correlation coefficient revealed the negative effects of bioavailable HMs on various soil microbial and enzymatic properties. Moreover, the abundant yield of rice was attributed to the combination treatment (1:1 50% + NPK 50%), which paved the way for an alternative agronomic approach based on the utilization of vermicomposted steel waste slag.

Rice husk biochar resuscitates the microecological functions of heavy–metal contaminated soil after washing by enriching functional bacteria

Biochar has great potential for simultaneously improving soil ecological functions and eliminating environmental pollutants. However, studies on this strategy in the restoration of ecological functions in chelator–washed soil are lacking, and the effect of biochar on the structure, functions, and microbial interactions of washed soil microbiomes are unclear. Hence, the effect of rice husk biochar (RHB, 2 %) on the physicochemical properties, heavy metal fractions, and microbial community structure of glutamate–N, N–diacetic acid (GLDA)– and ethylenediaminetetraacetic acid (EDTA)– washed remediated soil were investigated. Results showed that the RHB addition restored the washed soil physical structure (pores and agglomerates) and meanwhile, the soil colloidal sheet sweeps increased by 20.49 % and 102.07 % in the z–axis, respectively. Additionally, RHB significantly increased washed soil pH (P < 0.05) and alkaline phosphatase and urease activities, while decreased acid phosphatase and glucosidase activities. The Observed–species and Shannon index were significantly higher in soil treated by RHB combined with GLDA and EDTA than those treated with GLDA and EDTA alone (P < 0.05). GLDA washing coupled RHB treatment enriched key bacterial groups such as MND1, Chelativorans, and Ellin6067, while EDTA washing coupled RHB treatment enriched Sreroidobacter, Micromonospora, and Reyranella, that both related to C–, N–, and P– cycles. Importantly, RHB addition could enrich functional bacteria by increasing bacterial resistance, including glucose metabolic homeostasis and metal ion resistance. The observed enrichment of functional bacteria provided evidence for the enhancement of soil nutrient cycles, indicative of improved soil functions by combination of chelator washing and biochar amended.

Heavy metals in homestead soil: Metal fraction contents, bioaccessibility, and risk assessment

Rapid urbanization in China has led to the disappearance of countless villages and the transformation of homestead land into cultivated land or grassland. The quality of homestead soil (HS) plays a pivotal role in land-use conversion and reuse strategies, so the current state of heavy metal pollution in HS deserves attention. This study determined the fraction contents, bioaccessibility, risks, and affecting factors of Hg, As, Cd, Pb, Cu, and Zn in HS by comparing them with soil in cultivated land (CS), grassland (GS), homestead-converted cultivated land (HCS), and homestead-converted grassland (HGS). Results demonstrate that the contents of the six metals exceed background values, especially for Cd and Hg, resulting in significant pollution and elevated ecological risk. Distinct from the dominant residual fraction of other metals, the extractable fraction of Cd shows the highest proportion, which also contributes most to the high values of the Risk Assessment Code and extreme pollution conditions in HS, GS, and CS. Moreover, pH shows predominantly negative relations with the effective available and potentially available contents, while the effects of organic carbon fractions are notably the opposite. Furthermore, CS and GS suggest higher non-carcinogenic and carcinogenic risks than in the converted soil. This study indicates that HS has a lower metal accumulation risk compared with cultivated land and grassland, and homestead conversion seems to restrict the bioaccessibility of metals in soil.

The succession of microbial community and distribution resistance gene in response to enrichment cultivation derived from a long-term toxic metal(loid)s polluted soil

Microbial communities as the most important and active component of soil play a crucial role in the geochemical cycling of toxic metal(loid)s in the Pb and Zn smelting site soils. However, the relationships between soil microbial communities and the fractions of toxic metal(loid)s and the succession of soil microbial community and functions after enrichment cultivation have rarely been analyzed. In this study, the diversity and composition of microbial communities in soils before and after enrichment cultivation were investigated by high-throughput sequencing. And the co-occurrence relationships between soil microbial community after enrichment cultivation and MRGs genes were also analyzed through the BacMet database. Results showed that the dominant genus in the soils was Lactobacillus and Stenotrophomonas. The soil microbial community exhibited a notable correlation with Cd, Pb, and As, among which Cd exerted the most profound impact. Alishewanella, Pseudomonas, Massilia and Roseibacillus were significantly correlated with the fraction of Cd. After enrichment cultivation, the number of genera decrease to 96. And the dominant genus changed to Acinetobacter, Bacillus, Comamonas, Lysobacter, and Pseudoxanthomonas. High abundance of metal resistance genes (MRGs) including zntA, fpvA, zipB, cadA, czcA, czcB, czcC, zntA, arsR, pstS and pstB was found in the microbial community after enrichment cultivation. The potential host genus for MRGs was Acinetobacter, Comamonas, Lysinibacillus, Azotobacter, Bacillus, Lysobacter, Cupriavidus, Pseudoxanthomonas, and Thermomonas. Additionally, these microbial community after enrichment cultivation possessing pathways of bacterial chemotaxis and two-component systems was enabled them to adapt to the polluted environment. These observations provided potential guidance for microbe isolation and the development of strategies for the bioremediation of toxic metal(loid)s polluted soils.

Effects of Ageing on Surface Properties of Biochar and Bioavailability of Heavy Metals in Soil

This study aims to explore the effects of biochar ageing on its surface properties and the bioavailability of heavy metals in soil. The biochar was subjected to chemical oxidation/dry–wet cycles (CDWs), chemical oxidation/freeze–thaw cycles (CFTs), and natural ageing (NT) to analyze changes in the elemental composition, pH, specific surface area, pore volume, and surface functional groups. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were applied to characterize the functional groups and microstructure, and the BCR sequential extraction method was employed to demonstrate the fractionation distribution of Cu, Cd, and Pb. The results showed that the CDWs and CFTs treatments significantly reduced the carbon content of the biochar (with a maximum reduction to 47.70%), increased the oxygen content (up to 49.17%), and notably increased the specific surface area and pore volume. The pH decreased significantly from 9.91 to 4.92 and 4.99 for the CDWs and the CFTs, respectively. The FTIR analysis indicated notable changes in hydroxyl and carboxyl functional groups, and the SEM revealed severe microstructural damage in biochar after the CDWs and CFTs treatments. The heavy metal fractionation analysis indicated that exchangeable Cu, Cd, and Pb significantly increased after the CDWs treatment, reaching 31.40%, 5.25%, and 6.79%, respectively. In conclusion, biochar ageing significantly affects its physicochemical properties and increases the bioavailability of heavy metals, raising concerns about its long-term remediation effectiveness.

Response of bacterial and fungal communities in natural biofilms to bioavailable heavy metals in a mining-affected river

Biofilms, known as “microbial skin” in rivers, respond to rapid and sensitive environmental changes. However, the ecological response mechanisms of bacterial and fungal communities in river biofilms toward heavy metal pollution (HMP) remains poorly understood. This study focused on the key driving factors of bacterial and fungal community diversity and composition and their ecological response mechanisms within periphytic biofilms of Asia's largest Pb–Zn mining area. The diversity, dominant bacterial taxa, and bacteria structure in biofilms were influenced by biologically available heavy metal (HM) fractions, with Ni-F3 (17.96 %) and Pb-F4 (16.27 %) as the main factors affecting the bacterial community structure. Fungal community structure and α-diversity were more susceptible to physicochemical parameters (pH and nutrient elements). Partial least squares path modeling revealed that environmental factors influencing bacterial and fungal communities in biofilms were ranked as water quality > metal fractions > total metals. Dispersal limitation was the most critical ecological process in bacterial (56.9 %) and fungal (73.4 %) assembly. The proportion of heterogeneous selection by bacteria (39.5 %) was higher than that of fungus (26.2 %), which increased with increasing HMP. Bacterial communities had a higher migration rate (0.48) and ecological drift proportion (3.6 %), making them more prone to escape environmental stress. Fungal communities exhibited more keystone species, larger niche width (23.24 ± 13.04 vs. 9.72 ± 5.48), higher organization level, and a more stable co-occurrence network than bacterial communities, which enabled them to better adapt to high environmental pollution levels. These findings expanded the understanding of the spatiotemporal dynamics of microbial communities within biofilms in HM-polluted watersheds and provided new insights into the ecological responses of microbial communities to HMP.

Chemical Fractions and Magnetic Simulation Based on Machine Learning for Trace Metals in a Sedimentary Column of Lake Taihu

In this study, the chemical fractions (CFs) of trace metal (TMs) and multiple magnetic parameters were analysed in the sedimentary column from the centre of Lake Taihu. The sedimentary column, measuring 53 cm in length, was dated using 210Pb and 137Cs to be 124 years old. Surface layers of the column were found to contain significantly higher concentrations of Cd, Co, Cu, Pb, Sb, Ti, and Zn than the middle and bottom layers. The sedimentary core contained a substantial amount of ferrimagnetic minerals. Most of the TMs were present in the residual state, except for Mn and Pb. The chemical fractions of Cd exhibited the most significant variation with depth. The pollution load index (PLI) indicated moderate TMs pollution levels in the region, whereas the risk assessment code (RAC) classified Mn as being heavily polluted. Multiple linear regression (MLR) and random forest (RF), support vector machine (SVM), and XGBoost (1.7.7.1) machine learning models were used to simulate the RAC and total concentration of TMs, using physical and chemical indicators and magnetic parameters of the sediments as input variables. The MLR model outperformed RF, SVM, and XGBoost in simulating the CFs and total concentrations of most TMs in the sedimentary column, with R2 up to 0.668 and 0.87. The SHapley Additive exPlanations (SHAP) method reveals that χarm/χ is the dominant factor influencing the RAC of As in the XGBoost models. For the RAC of Co and Cu in RF models, C% and N% exhibit greater contributions.

Optical and thermoplasmonic properties of core (AuxAg1- x)- shell (Au) nanostructures

The optical and thermoplasmonic properties of bimetallic nanoparticles (NPs) offer a wide range of possibilities for designing functional materials and innovative nanotechnological devices. Their exploration is generating increasing interest in experimental and theoretical scientific research. The combination of noble metals such as gold (Au) and silver (Ag) within the same nanostructure, in the form of an alloy or core/shell arrangement, presents several advantages and potential applications. In this paper, the finite element method (FEM) is used to study the optical response and nanoscale heat generation capability of bimetallic core/shell nanospheres composed of a mixed alloy (AuxAg1−x)-core and an Au-shell. First, we studied the surface plasmon resonance (SPR) properties by generating absorption spectra. Our results show that the position and amplitude of the SPR peak of these nanospheres are strongly influenced by the fractions of Au and Ag metals composing the core, as well as by the Au-shell thickness. In particular, the SPR-peak position can be adjusted between 535nm and 1085nm depending on the composition and structure of these NPs. Secondly, we studied the ability of these NPs to convert absorbed light into heat when exposed to either a continuous wave (cw) laser or a femtosecond pulsed (fs-pulsed) laser. The results demonstrate the ability to control the temperature generated by these NPs based on the core composition, Au-shell thickness, illumination intensity, and the type of illumination (cw or fs-pulsed). In particular, under fs-pulsed illumination, the internal temperature of the NPs is significantly higher than under cw illumination. These findings are crucial for the use of these alloy-core and Au-shell nanoparticles in various thermoplasmonic applications.

Cosmogenic radionuclides in meteorites from the Otway Massif blue ice area, Antarctica: An unusual, well‐preserved H5 chondrite strewn field

AbstractThe US Antarctic Search for Meteorites (ANSMET) discovered a dense cluster of 88 ordinary chondrites with a total mass of more than 100 kg on a blue ice area (BIA) of 1.6 × 0.3 km2 near the Otway Massif, Grosvenor Mountains, Antarctica. The larger masses (weighing up to 29 kg) were found at one end of an oval‐shaped pattern and the smaller masses (50–200 g) at the other end. We measured concentrations of the cosmogenic radionuclides 10Be (half‐life—1.36 × 106 year) and 36Cl (3.01 × 105 year) in the metal fraction of 17 H chondrites, including 14 fragments of this cluster, to verify the hypothesis that this meteorite cluster on the Otway Massif BIA represents a meteorite strewn field produced by the atmospheric breakup of a single meteoroid. The 10Be and 36Cl concentrations confirm that 10 out of 14 H chondrites from different locations within this small area are paired fragments of the same meteorite fall, while the four other H chondrites represent two additional—smaller—falls. The radionuclides suggest a pre‐atmospheric mass of 200–400 kg for the large pairing group, suggesting that 25%–50% of the meteoroid survived atmospheric entry. Based on the distribution of the paired H chondrites and evidence of their common cosmic‐ray exposure history in space, we conclude that most of the 88 meteorites within this small area represent a meteorite strewn field. The small size of the strewn field suggests that the meteoroid entered at a steep angle (&gt;60°), while the low amount of fusion crust on most meteorite surfaces most likely indicates atmospheric break up at low altitude, while additional fragmentation of a large surviving fragment may have occurred during impact on the ice. This well‐documented strewn field provides a good opportunity to apply model simulations of the atmospheric fragmentation of this object as a function of entry angle, velocity, and meteoroid strength. Cosmogenic 14C analyses in two members of the Otway Massif pairing group yield a terrestrial age of 15.5 ± 1.5 kyr, which represents the time elapsed since this meteorite fell on Earth. The excellent preservation of an Antarctic meteorite strewn field suggests that the Otway Massif BIA represents a relatively stagnant blue ice field.

Contamination, fraction, and source apportionment of heavy metals in sediment of an industrialized urban river in China

In this study, we conducted an analysis of the heavy metal concentrations, health risk assessment, fraction and source interpretation in surface and core sediments from main stream of the Pearl River and Pearl River Estuary (RRE) area. Results showed that the higher deposited heavy metal concentrations in sediments occur at the Pearl River. The concentrations of heavy metals in surface sediments from the studied locations are in a descending order: Zn > Cr > Cu > Ni > Pb > Cd. Regarding chemical fractions, Cd showed the highest proportion of acid soluble fraction (F1) among all studied heavy metals. The high mobility of Cd poses a significant threat to water bodies and the surrounding environment. The potential ecological risk index (RI) showed the Pearl River sediments exhibited significantly higher values than the estuary sediments. Cd was found to be the primary contributor to potential ecological risk, accounting for 74% of RI. The health risk assessment showed the total hazard index (HI) for child was exceeded 1 mainly driven by Zn, indicating that the child population was at risk of non-carcinogenic effects. Besides, unacceptable carcinogenic risk in both Pearl River and estuary area were observed for children. The positive matrix factorization (PMF) model was used to ascertain sources of six heavy metals and apportion their contributions in sediments. The results showed that the source contributions of natural, industrial, and mixed sources from coal combustion and traffic emissions accounted for 39.81%, 34.10%, 26.10%.

Source, bioavailability, and toxicity of metals in modern fjord sediments, west Spitsbergen, and their influence on sediment-associated biota

Metal contamination in the Arctic region has increased over the years despite its remote and isolated location. Thus, to evaluate the bioavailable fractions of various metals and their effects on sediment-associated biota, the surface sediments from the fjords were analyzed for bulk concentration of metals and their speciation in different fractions. Metals concentrations were higher in the inner fjord region and decreased towards the outer fjord, supported by the terrigenous influence (TI%) calculated. Cr and Pb showed higher excess values attributed to their additional source other than the catchment rocks. So, to assess the metal-related ecological risk, the bulk concentration of metals was compared with Arctic sediment quality guidelines (ASQGs). Cr, Cd, and Pb concentrations were high, indicating potential adverse biological effects in the study. To avoid the risk of overestimation, metal speciation was conducted, showing that overall metal concentrations were higher in the residual fraction; however, higher concentrations of Mn in labile phases pose a moderate risk to the sediment-associated biota. Additionally, the population density of foraminifera in the sediments was calculated to assess the influence of bioavailable metal on benthic foraminifera. It was found that the presence of metals in bioavailable fractions affected the abundance of the foraminifera. However, no morphological abnormalities were observed in the species.

Hazard reduction of heavy metals by co-pyrolysis of modified vermiculite with paper mill sludge/municipal solid waste: Characterization, risk and reaction mechanism study in pyrolytic environment

The increasing volume of paper mill sludge (PM) and municipal solid waste (MW) poses environmental problems associated with heavy metals. Co-pyrolysis of PM/MW with additives effectively reduces the risk of heavy metal contamination. In this study, co-modified vermiculite (LMV) was prepared using the modification methods of intercalation-exfoliation, Mg2+ impregnation, and thermal activation. PM and MW were mixed at different doping ratios, and a non-doping experiment was performed to compare the pyrolysis processes and the retention rates for different heavy metals (Zn, Cr, Cu, Cd, and Pb), as well as the potential ecological risks, and the form distribution of the heavy metals. The addition of LMV reduced the risk posed by heavy metals. In the absence of doping, a higher pyrolysis temperature is conducive to an increase in the oxidizable and residual fractions of heavy metals without higher retention rates. Among these heavy metals, Zn, Cr, and Cu had higher retention rates and low risks, whereas Cd had a relatively high risk with low retention rates. Simulations showed that there was a transfer of the Mulliken charge after the reaction, indicating that all the heavy metals can interact with O, Al, and Si in the LMV; this reaction mainly occurs around the No. 17 O atom of the LMV. The monomers, oxides, and chlorides of Zn/Cr/Cu exhibited better adsorption on vermiculite compared to that of Pb/Cd.

A comparative study on the slow pyrolysis of Miscanthus (Miscanthus×giganteus Greef et Deu.) cultivated on agricultural and contaminated soils: Assessment of distribution of final products

This study aims to investigate the slow pyrolysis behavior of uncontaminated (MSC-I - reference) and heavy metals contaminated (MSC-R) samples with heavy metals from the tailings of a Pb-Zn-Cu flotation mine, consisting of whole stems of Miscanthus. Physicochemical properties of raw materials were investigated through instrumental characterization techniques (Atomic Absorption Spectrometry (AAS), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy, and X-ray diffraction (XRD)), while the pyrolysis process was monitored by simultaneous thermal analysis techniques (thermogravimetry (TG) – derivative thermogravimetry (DTG)), coupled with Mass spectrometry (MS), for evolved gas analysis. After determination of the lignocellulose content (cellulose, hemicellulose, and lignin) and extractive of the MSC-I and MSC-R samples, it was found that Pb, Zn, Fe, and Mn in MSC-R lead to very fast decomposition of extractive fraction, which facilitates their distribution in formed bio-char, together with lignin char-participation, acting catalytically. It was established that a much greater fraction of extractives decomposition products and non-volatile heavy metals are incorporated in MSC-R bio-char increasing its yield (23 %), compared to MSC-I bio-char yield (21.5 %). It was identified that MSC-R has increased production of H2, CO, and CO2, while decreased production of CH4, influenced by Fe (Fe has a significant positive effect on CO2 evaluation during MSC-R pyrolysis, enhancing decarboxylation process). It was established that CH4 reforming reactions catalyzed by iron additionally affect methane reduction, and increase production of H2, compared to the reference sample. Isoconversional kinetic analysis showed that pyrolysis reactions profile was strongly conditioned by the presence of heavy metals, such as Cd, Pb, and Zn, because they affect the modification of biomass lignocellulosic structure. Also, it was found that small amounts of Cd present in MSC-R can increase pyrolysis activation energy of three pseudo-components, and inhibit their deoxygenation, thus increasing yield of bio-char.

New magnetic proxies to reveal source and bioavailability of heavy metals in contaminated soils

Environmental magnetism plays an important role in monitoring heavy metal pollution, but most studies are confined to indicating only the levels of heavy metals using magnetic parameters. This study established new magnetic proxies for accurately depicting the sources and bioavailability of heavy metals in contaminated soils. We observed different relationships between χ and SIRM in the soils contaminated by non-ferrous metal smelting compared to those polluted by coal combustion and steel smelting. Furthermore, we found that the soft magnetic components (IRMsoft) in the soils were mainly controlled by the non-ferrous metal smelting activities, while the hard magnetic components (HIRM) might be affected by the iron erosion. These new magnetic proxies enriched the source composition spectrum and improved the accuracy of the source apportionment analyses (principal component analysis and positive matrix factorization), yielding a result that was comparable to that by Pb isotope fingerprinting. We also found strong relationships between magnetic parameters (especially IRMsoft) and bioavailable fractions of heavy metals, indicating that magnetic measurement may be a powerful tool for monitoring the bioavailability of heavy metals. This study expands the application fields of magnetism in environmental science research.

End-of-life options for printed electronics in municipal solid waste streams: a review of the challenges, opportunities, and sustainability implications

Abstract Although printed electronics (PE) are a more sustainable option than conventional electronics, proper treatment of PE in their end-of-life phase is crucial to decrease their overall environmental impacts and ensure the materials specifically the metal fraction of PE are recovered. Thus, to investigate the state of the art regarding the research and development of material recovery from PE, this study performed a literature review process. It concluded that the majority of the observed articles rather not mention specifically what is recycling option for recycling the PE or introduced a novel recycling method for the metal ink. Only a marginal fraction of the articles covered proper recycling methods for the metal fraction of PE. Then based on the literature review process, this study investigates the suitability of the current waste management system to recover different fractions of PE products.

Evaluation of heavy metal speciation in waters of Hirakud reservoir: a Ramsar site in India.

The growing concern of aquatic heavy metal (HM) pollution is dependent on the toxic nature of its bio-available form. Thus, bio-availability is guided by the HM fractionation in water. This study was therefore conducted to evaluate the spatial impact on physicochemical fractionation of HM (Zn, Mn, Cu, and Fe) in the waters of the Hirakud reservoir in India. Speciation along different pores using a filtration technique was adopted to fractionate the HMs in water samples. The result suggests that the water of the study area is polluted with Cu (0.22-0.35mg/L), Mn (0.15-0.23mg/L), and Fe (1.90-3.10mg/L) that have crossed their permissible limits while Zn (0.17-0.97mg/L) was within the permissible standard. When studied for physical partitioning, the right dyke was comparatively more polluted than the left dyke. While the water samples were dominated by the dissolved fraction of heavy metals, it was construed that a large proportion of the HMs are in bio-available form. Further, a distinct impact of spatial variation on metal fractionation was also evident in the study with PCA revealing site-specific behaviour. Therefore, it can be concluded that multiple anthropogenic activities lead to the distribution and fractionation of HMs in water.

Contrasting metal bioaccumulation in marine benthic invertebrate groups in polluted harbor sediments

This study examined the sediment metal fractions and availability to infer bioaccumulation in marine harbor benthic organisms. Total metals were analyzed using atomic absorption spectrometry and inductively coupled plasma-optical emission spectrometry for chemical fractions and organisms. The results showed similar metal concentrations and distribution driven by rivers and harbor pollution. We found significant differences in metal accumulation in marine benthic groups, highest in scavenger species. Their metal concentrations in decreasing order were 1.97–4568, 0.10–1260, 1.64–159, and 0.105–112 μg g−1 dw for hermit crabs, forams, bivalves, and polychaetes. Moreover, certain organisms, such as tusk shells, sea pens, bivalves, forams, and isopods, may exhibit selective metal accumulation. Biota-sediment accumulation factors (>1) were highest for essential metals like Cu, Zn, and Mn, while toxic metals like As, Cr, Co, and Ni increased. This concurrent assessment provides more comprehensive data for metal bioaccumulation in marine benthic ecosystems.

Exploiting Deep Eutectic Solvents in LiFePO4 Battery Recycling: From Cathode Leaching to Resynthesis

Nowadays, the increasing demand for electronic devices and electric vehicles influences the request for Lithium-Ion Batteries (LIBs), which are worldwide the most exploited electrochemical energy storage systems for portable devices and are expected to completely dominate also the sector of transportation soon. In particular, the use of LIBs with ordered-olivine structure LiFePO4 (LFP) cathodes stands out ever since their invention in 1997, being a valid solution in terms of durability, reliability, and safety, essential characteristics in the electric mobility application combined with the benefit of low content of critical raw materials, CRMs. Considering that the average life of LFP cathodes is about 5-8 years, the management of these materials as waste becomes essential: the growing number and volumes of LIBs that are currently produced is inevitably intended to correspond to the number of LIBs that will reach the end of their life, becoming waste that are accumulating, posing a staggering danger. [1,2] An also important consideration concerns the conditions required to synthesize LFP for electrochemical purposes, as it is necessary to coat the surface with conductive species, controlling the morphology and reducing the particle size, thus complicating the synthesis and making it economically more impactful. [3]In such a context, recycling combines the necessity to produce new LIBs with the need to cope with the increase in batteries’ waste accumulation: this can limit the disposal of waste batteries into landfills, thus decreasing the inevitable hazardous environmental consequences, while reducing the demand for new mining, re-assigning value to raw materials, in an attempt to minimize the costs that would be required to synthesize pristine LFP-based cathodes. Today, recycling is already implemented at the industrial level, exploiting the pyrometallurgy approach, which involves thermal treatments at very high temperatures (>1000°C) allowing for the recovery of only a fraction of valuable metals; nevertheless, this approach has a strong environmental impact due to the high energy demand and high carbon footprint. The hydrometallurgical approach is also employed, exploiting the leaching process with strong inorganic acids; however, this brings problematic issues, because producing such acids is itself a polluting process, and acidic wastewater management is a demanding problem. Moreover, today these processes involve the recycling of the most diffused cathode, LiCoO2, Li(Ni/Mn/Co)O2, LiMn2O4, and the sustainability of recycling relies on the possibility to recover valuable CRMs such as Co and Ni.In the proposed work we are currently investigating the degradation properties of Deep Eutectic Solvents (DESs), cheap and greener mixtures of compounds forming a eutectic system, liquid at room temperature. [4] In particular, the focus is on the leaching of LFP with a DES obtained by mixing different molar ratios of hydrogen bond acceptor and various hydrogen bond donors, in order to assess the best combination to leach the elements out of LFP structure. The key point of such approach is the design of a degradation system that can enable the conditions for the direct re-synthesis of new LFP material. Indeed, here the sustainability of the process cannot be driven by the recovery of CRMs, thus must rely on the close-loop recycling scheme. For this reason, we specifically designed DES compositions that allow for this process.The proposed DESs, which have been easily prepared at mild heating conditions, have been investigated through different techniques; the results obtained on the chemical-physical characterization (via FTIR spectroscopy, Solid-State NMR, viscosity, thermal analysis) will be presented. Among the different DESs, those with the best combination of properties (e.g. low viscosity, high thermal stability) have been explored for the leaching of LFP cathode. The leaching process has been optimized with respect to the temperature, duration, and cathode-to-DES ratio for different DESs, and the leaching yields have been evaluated through ICP-OES analysis. The obtained leached solution has been considered as the starting point for a sol-gel-like synthesis of new LFP material, finally characterized through XRD, TGA, ICP-OES, and SEM-EDX analysis. Tuning the parameters of the synthesis (temperature and duration of the heat treatment, ratio between LFP mass and conductive species to realize the coating) enables to control the morphology and the dimension of the synthesized particles, to find the best condition for the electrochemical application. The electrochemical performances of the resynthesized materials will also be presented.[1] Sun et al., J. Alloys Compd., 818 (2020)[2] Lv et al. ACS Sustain. Chem. Eng., 6 (2018)[3] Yuan et al., Energy Environ. Sci, 4 (2010)[4] Zhu et al., Resour. Conserv. Recycl., 188 (2023)

Copper leaching from ultrasonically treated milled waste printed circuit boards: investigation of parameters optimization and kinetics.

Waste printed circuit boards (WPCBs) encompass abundant metals (gold, silver, and copper), along with other harmful materials including brominated epoxy resins, plastics, and heavy metals (lead, mercury, and cadmium). Direct burning and landfilling of WPCBs may cause severe health issues and impair the environment. Therefore, sustainable treatment of WPCBs is necessary to recover valuable metals and remove hazardous materials before disposal. The present work investigates the separation of copper-rich metallic fractions from the WPCBs by the combination of hammer milling and ultrasonic irradiation. Initially, discarded mobile phone PCBs are pre-processed and shortened into 1 × 1 cm2. Downscaled WPCBs are fed into the hammer mill to obtain the fine ground powder. The Powdered WPCBs are further processed through ultrasonic treatment to acquire metal-rich fraction. XRD, SEM-EDS, and ICP/AAS analysis revealed that the current technique can efficiently separate the metal-rich fraction without using toxic solvents. Results show the enhancement of copper fraction from 42.73 to 87 wt. % after ultrasonic treatment of WPCBs ground powder. Further, nitric acid leaching has been implemented to metal-rich fractions, and the parameters have been optimized for copper leaching with the assistance of response surface methodology (RSM) of the design of experiments (DOE). Quantitative dissolution (98.96%) of copper occurred using 3.5M nitric acid within 3h at 30°C with 50 GPL pulp density and 500rpm agitation speed. Finally, the kinetics of the leaching process were studied to conform the kinetics model. Moreover, the activation energy for diffusion (19.075kJ/mole) and reaction kinetics model (13.29kJ/mole) has also been calculated. The low energy consumption due to room temperature pre-treatment and effective leaching ensures the industrial feasibility of the proposed process.

Chemical fractionation of heavy metals and zinc isotope source identification in sediments of the Huangpu River, Shanghai, China

BackgroundThe Huangpu River serves as a vital water source for around 24 million individuals residing in the metropolitan area of Shanghai. Despite this, elevated levels of heavy metals persist in the sediments of the river, with their chemical fractionation and sources remaining inadequately understood.ResultsTo improve the management of heavy metal contamination, sequential extractions and zinc (Zn) isotopic compositions were utilized to evaluate pollution levels in the Huangpu River. The findings reveal that the majority of heavy metals in the river sediments are present in residual fractions, constituting an average of 67.5% for Cd, 57.6% for Cu, 60.6% for Ni, 56.2% for Pb, and 74.4% for Cr, with the exception of Zn (33.8%). Furthermore, a substantial portion of Zn, exceeding 66%, was found in acid-exchangeable, reducible, and oxidizable fractions, indicating a high potential for Zn release into aquatic ecosystems.ConclusionFurther analysis of Zn isotopes pinpointed traffic emissions, including exhaust fumes and tire wear particles (account for ~ 34.0%), along with anthropogenic emissions and fertilizer (~ 31.7%), as the major culprits behind this contamination. These findings highlight the critical need for stricter regulations to control heavy metal contamination from traffic and domestic sources within the Huangpu River basin.