Thallium isotopic fractionation in soils from a historic HgTl mining area: New insights on thallium geochemistry.

Thallium (Tl), a highly toxic heavy metal, which may pose significant environmental threats due to extensive discharge from anthropogenic activities. It is crucial to understand geochemical behavior of Tl in soils for initiating proper measures for Tl pollution control. For this purpose, transport behavior of Tl and its dominant factors in soils collected from a typically Tl-enriched depth profile, surrounding a historical tailing dump near an independent HgTl mine area in China, were investigated by using Tl isotope compositions. Results showed that an overall enrichment of Tl (48.68-375.21 mg/kg) was accompanied with As elevation (135.00-619.00 mg/kg) in the whole depth profile, and Tl and As exhibited co-migration behavior with Fe, S, K, and Rb. Geochemical fractionation of Tl unveiled by sequential extraction further indicated that Mn-/Fe-bearing minerals and clay minerals act as main hosts of Tl in the studied soils. Thallium isotopic composition and its fractionation pattern further revealed that the major contributors to high Tl levels in the depth profile were tailing and lorandite minerals, with mean contribution rate of 51.99 % and 42.47 %, respectively. These findings facilitate the understanding of Tl transport behavior in highly contaminated environment, providing valuable insights for developing new technologies in mining waste treatment and historical mine reclamation.

Pb isotopic fingerprinting of uranium pollution: New insight on uranium transport in stream-river sediments.

Uranium mill tailings (UMT) present a significant environmental concern due to high levels of radioactive and toxic elements, including uranium (U), thorium (Th), and lead (Pb), which can pose serious health risks to aquatic ecosystems. While Pb isotopic tracers have been widely utilized in environmental studies to identify elemental sources and geological processes, their application in U geochemistry remains relatively limited. In this study, we investigate the distribution and migration of U in stream-river sediments surrounding a decommissioned U hydrometallurgical area, employing Pb isotopes as tracers. Our findings reveal significant enrichment and ecological risk of U, Pb, and Th in the sediments. Uranium predominantly associates with quartz and silicate minerals, and its dispersion process is influenced by continuous leaching and precipitation cycles of typical U-bearing minerals. Furthermore, we establish a compelling positive relationship (r2 = 0.97) between 208Pb/207Pb and 206Pb/207Pb in the stream-river sediments and sediment derived from UMT. Application of a binary Pb mixing model indicates that anthropogenic hydrometallurgical activities contribute to 2.5-62.7% of the stream-river sediments. Notably, these values are lower than the 6.6-89.6% recorded about 10 years ago, prior to the decommissioning of the U hydrometallurgical activity. Our results underscore the continued risk of U pollution dispersion even after decommission, highlighting the long-term environmental impact of UMT.

MnFe2O4-biochar decreases bioavailable fractions of thallium in highly acidic soils from pyrite mining area.

The prevalence of toxic element thallium (Tl) in soils is of increasing concern as a hidden hazard in agricultural systems and food chains. In the present work, pure biochar (as a comparison) and jacobsite (MnFe2O4)-biochar composite (MFBC) were evaluated for their immobilization effects in Tl-polluted agricultural soils (Tl: ∼10 mg/kg). Overall, MFBC exhibited an efficient effect on Tl immobilization, and the effect was strengthened with the increase of amendment ratio. After being amended by MFBC for 15 and 30 days, the labile fraction of Tl in soil decreased from 1.55 to 0.97 mg/kg, and from 1.51 to 0.88 mg/kg, respectively. In addition, pH (3.05) of the highly acidic soil increased to a maximum of 3.97 after the immobilization process. Since the weak acid extractable and oxidizable Tl were the preponderantly mitigated fractions and displayed a negative correlation with pH, it can be inferred that pH may serve as one of the most critical factors in regulating the Tl immobilization process in MFBC-amended acidic soils. This study indicated a great potential of jacobsite-biochar amendment in stabilization and immobilization of Tl in highly acidic and Tl-polluted agricultural soils; and it would bring considerable environmental benefit to these Tl-contaminated sites whose occurrence has significantly increased in recent decades near the pyrite or other sulfide ore mining and smelting area elsewhere.

Applying thallium isotopic compositions as novel and sensitive proxy for Tl(I)/Tl(III) transformation and source apportionment.

Thallium is a rare metal known for its highly toxic nature. Recent research has indicated that the precise determination of Tl isotopic compositions using Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP MS) provides new opportunities for understanding Tl geochemical behavior. While isotopic fractionation of Tl derived from anthropogenic activities (e.g., mining, smelting) have been reported, there is limited information regarding Tl influenced by both natural weathering processes and anthropogenic origins. Herein, we investigated, for the first time, the Tl isotopic compositions in soils across a representative Tl-rich depth profile from the Lanmuchang (LMC) quicksilver mine (southwest China) in the low-temperature metallogenesis zone. The results showed significant variations in Tl isotope signatures (ε205Tl) among different soil layers, ranging from -0.23 to 3.79, with heavier isotope-205Tl enrichment observed in the bottom layers of the profile (ε205Tl = 2.18-3.79). This enrichment of 205Tl was not solely correlated with the degree of soil weathering but was also partially associated with oxidation of Tl(I) by Fe (hydr)oxide minerals. Quantitative calculation using ε205Tl vs. 1/Tl data further indicated that the Tl enrichment across the soil depth profile was predominantly derived from anthropogenic origins. All these findings highlight that the robustness and reliability of Tl isotopes as a proxy for identifying both anthropogenic and geogenic sources, as well as tracing chemical alterations and redox-controlled mineralogical processes of Tl in soils. The nascent application of Tl isotopes herein not only offers valuable insights into the behavior of Tl in surface environments, but also establishes a framework for source apportionment in soils under similar circumstances.

High-efficiency removal of arsenic(III) from wastewater using combined copper ferrite@biochar and persulfate.

Arsenic (As) is a potentially toxic element with variable valence states. Due to high toxicity and bioaccumulation, As can pose a severe threat to the quality of the ecology as well as human health. In this work, As(III) in water was effectively removed by biochar-supported copper ferrite magnetic composite with persulfate. The copper ferrite@biochar composite exhibited higher catalytic activity than copper ferrite and biochar. The removal of As(III) could reach 99.8% within 1 h under the conditions of initial As(III) concentration at 10 mg/L, initial pH at 2-6, and equilibrium pH at 10. The maximum adsorption capacity of As(III) by copper ferrite@biochar-persulfate was 88.9 mg/g, achieving superior performance than mostly reported the metal oxide adsorbents. By means of a variety of characterization techniques, it was found that ∙OH acted as the main free radical for removing As(III) in the copper ferrite@biochar-persulfate system and the major mechanisms were oxidation and complexation. As a natural fibre biomass waste-derived adsorbent, ferrite@biochar presented a high catalytic efficiency and easy magnetic separation for As(III) removal. This study highlights the great potential of copper ferrite@biochar-persulfate application in As(III) wastewater treatment.

A novel application of thallium isotopes in tracing metal(loid)s migration and related sources in contaminated paddy soils.

Thallium (Tl) is a highly toxic heavy metal, which is harmful to plants and animals even in trace amounts. Migration behaviors of Tl in paddy soils system remain largely unknown. Herein, Tl isotopic compositions have been employed for the first time to explore Tl transfer and pathway in paddy soil system. The results showed considerably large Tl isotopic variations (ε205Tl = -0.99 ± 0.45 ~ 24.57 ± 0.27), which may result from interconversion between Tl(I) and Tl(III) under alternative redox conditions in the paddy system. Overall higher ε205Tl values of paddy soils in the deeper layers were probably attributed to abundant presence of Fe/Mn (hydr)oxides and occasionally extreme redox conditions during alternative dry-wet process which oxidized Tl(I) to Tl(III). A ternary mixing model using Tl isotopic compositions further disclosed that industrial waste contributed predominantly to Tl contamination in the studied soil, with an average contribution rate of 73.23%. All these findings indicate that Tl isotopes can be used as an efficient tracer for fingerprinting Tl pathway in complicated scenarios even under varied redox conditions, providing significant prospect in diverse environmental applications.

Thallium adsorption on three iron (hydr)oxides and Tl isotopic fractionation induced by adsorption on ferrihydrite.

Thallium (Tl) is an extraordinarily toxic metal, which is usually present with Tl(I) and highly mobile in aquatic environment. Limited knowledge is available on the adsorption and isotopic variations of Tl(I) to Fe-(hydr)oxides. Herein, the adsorption behavior and mechanism of Tl(I) on representative Fe-(hydr)oxides, i.e. goethite, hematite, and ferrihydrite, were comparatively investigated kineticly and isothermally, additional to crystal structure modelling and Tl isotope composition (205Tl/203Tl). The results showed that ferrihydrite exhibited overall higher Tl(I) adsorption capacity (1.11-10.86 mg/kg) than goethite (0.21-1.83 mg/kg) and hematite (0.14-2.35 mg/kg), and adsorption by the three prevalent Fe-minerals presented strong pH and ionic strength dependence. The magnitude of Tl isotopic fractionation during Tl(I) adsorption to ferrihydrite (αsolid-solution ≈ 1.00022-1.00037) was smaller than previously observed fractionation between Mn oxides and aqueous Tl(I) (αsolid-solution ≈ 1.0002-1.0015). The notable difference is likely that whether oxidation of Tl(I) occurred during Tl adsorption to the mineral surfaces. This study found a small but detectable Tl isotopic fractionation during Tl(I) adsorption to ferrihydrite and heavier Tl isotope was slightly preferentially adsorbed on surface of ferrihydrite, which was attributed to the formation of inner-sphere complex between Tl and ≡Fe-OH. The findings offer a new understanding of the migration and fate of 205Tl/203Tl during Tl(I) adsorption to Fe (hydr)oxides.

Sustainable management and recycling of food waste anaerobic digestate: A review.

Anaerobic digestion (AD) is a widely used technology to valorise food waste for biogas production yet a considerable amount of digestate remains under-utilised. Sustainable management and recycling of the nutrient-rich food waste anaerobic digestate (FWD) is highly desirable for closing resource loop and actualising circular economy. This work reviews the distinct properties of FWD and the existing treatment technologies. FWD shows great prospects as a nutrient source for microalgal cultivation and biofuel production. Emerging technologies such as thermal conversion (e.g., pyrolysis and hydrothermal treatment) of FWD into value-added products such as functionalised biochar/hydrochar with diverse applications would be attractive and warrant further research investigation. Integrated AD with subsequent valorisation facilities is highly encouraged to achieve complete utilisation of resources and reduce carbon emissions.

A critical review on performance indicators for evaluating soil biota and soil health of biochar-amended soils.

Amendment of soil with biochar has been widely investigated for soil quality improvement in terms of biotic and abiotic functionalities. The performance of biochar-based amendment varies according to the site characteristics, biochar properties, and soil management targets. There is no existing review that summarizes a broad range of performance indicators to evaluate the health of biochar-amended soil. Based on the latest studies on soil amendment with biochar, this review critically analyzes the soil health indicators that reveal the potential impact of biochar amendment with respect to physicochemical properties, biological properties, and overall soil quality. It is found that soil pH, soil aggregate stability, and soil organic matter are the basic indicators that could influence most of the soil functions, which should be prioritized for measurement. Relevant functional indicators (e.g., erosion rate, crop productivity, and ecotoxicity) should be selected based on the soil management targets of biochar application in agricultural soils. With this review, it is expected that target-oriented performance indicators can be selected in future studies for field-relevant evaluation of soil amendment by biochar under different situations. Therefore, a more cost-effective and purpose-driven assessment protocol for biochar-amended soils can be devised by using relevant measurable attributes suggested in this review.

Valorization of humins from food waste biorefinery for synthesis of biochar-supported Lewis acid catalysts.

To close the carbon loop of biomass waste valorization, it is imperative to utilize the unavoidable by-products such as humins, a carbonaceous residue with complex and heterogeneous composition. In this study, starch-rich rice waste was effectively converted into value-added chemicals (e.g., 5-hydroxymethylfurfural) under microwave heating at 160 °C using AlCl3 as the catalyst. The solid by-products, i.e., humins, were then valorized as a raw material for fabricating biochar-supported Lewis acid catalysts. The humins were collected and pretreated by AlCl3 as the impregnation agent, followed by carbonization. Detailed characterization revealed several AlO species on the biochar surface plausibly in the amorphous state. The oxygen-containing functional groups of humins might serve as anchoring sites for the Al species during impregnation. The humins-derived biochars exhibited good catalytic activity toward glucose-to-fructose isomerization, a common biorefinery reaction catalyzed by Lewis acids. A fructose yield of up to 14 Cmol% could be achieved under microwave heating at 160 °C for 20 min in water as the greenest solvent. Such catalytic performance was comparable with the previously reported Al-based catalysts derived from wood waste and graphene/graphitic oxide. This study herein highlights humins as a low-cost alternative source of carbon for the preparation of renewable solid catalysts, proposing a novel practice for recycling by-products from food waste valorization to foster circular economy and sustainable development.

A cross-region analysis of commercial food waste recycling behaviour.

To tackle the crisis associated with the rising commercial food waste generation, it is imperative to comprehend how corporates' recycling behaviour is influenced by different industry structures and economies. This study aims to fill in the information gap that various factors might be affecting corporates' recycling behaviour in two different economies due to environmental inequality by comparing upper-middle-income region (Malaysia) and high-income region (Hong Kong), respectively. A questionnaire survey regarding food waste management according to the Theory of Planned Behaviour was conducted with representatives coming from diverse industries of the hotel, food and beverage, and property management. The questionnaire responses were evaluated based on quantitative structural equation modelling and correlation analysis. The analysis results showed that the model fit the data well, explaining 78% of the variance in recycling behaviour. The findings demonstrated that the most substantial factor on individual's recycling intention by Malaysian commercial food waste generators was perceived behavioural control, and logistics and management incentives. Subjective norms demonstrated significant and adverse effects on the behaviour of food waste recycling. The variable of administrative incentives and corporate support presented strong positive correlations with moral attitudes as well as logistics and management incentives. Hotel industries from both Hong Kong and Malaysia have a higher acceptance level on human resources regarding food waste recycling. In comparison, food and beverage industries from both regions have a lower acceptance level. These findings could enrich our knowledge of the concerns in establishing regional policy strategies to encourage economic behavioural changes for sustainable development.

A review on the valorisation of food waste as a nutrient source and soil amendment.

Valorisation of food waste offers an economical and environmental opportunity, which can reduce the problems of its conventional disposal. Food waste is commonly disposed of in landfills or incinerated, causing many environmental, social, and economic issues. Large amounts of food waste are produced in the food supply chain of agriculture: production, post-harvest, distribution (transport), processing, and consumption. Food waste can be valorised into a range of products, including biofertilisers, bioplastics, biofuels, chemicals, and nutraceuticals. Conversion of food waste into these products can reduce the demand of fossil-derived products, which have historically contributed to large amounts of pollution. The variety of food chain suppliers offers a wide range of feedstocks that can be physically, chemically, or biologically altered to form an array of biofertilisers and soil amendments. Composting and anaerobic digestion are the main large-scale conversion methods used today to valorise food waste products to biofertilisers and soil amendments. However, emerging conversion methods such as dehydration, biochar production, and chemical hydrolysis have promising characteristics, which can be utilised in agriculture as well as for soil remediation. Valorising food waste into biofertilisers and soil amendments has great potential to combat land degradation in agricultural areas. Biofertilisers are rich in nutrients that can reduce the dependability of using conventional mineral fertilisers. Food waste products, unlike mineral fertilisers, can also be used as soil amendments to improve productivity. These characteristics of food wastes assist in the remediation of contaminated soils. This paper reviews the volume of food waste within the food chain and types of food waste feedstocks that can be valorised into various products, including the conversion methods. Unintended consequences of the utilisation of food waste as biofertilisers and soil-amendment products resulting from their relatively low concentrations of trace element nutrients and presence of potentially toxic elements are also evaluated.

Ball milling as a mechanochemical technology for fabrication of novel biochar nanomaterials.

Mechanochemical synthesis of nano-biochar by ball-milling technology is gaining attention for the sake of its low-cost and eco-friendly nature. Ball milling as a non-/less-solvent technology can propel environmental sustainability and waste valorization into engineered biochar for advanced applications. Scalable production of biochar nanomaterials with superior properties (e.g., 400-500 m2 g-1 surface area and 0.5-1000 nm pore sizes) enables diverse applications in the field of energy and environment. This review critically evaluates the synthesis, characterization, and application of ball-milled biochar nanomaterials based on the latest findings. Limitations such as feedstock selection, process optimization, product homogeneity and reusability, environmental risks, and sustainability assessment remain challenging for further studies. This work highlights the recent advances on mechanochemical biochar technology and offer insights into opportunities and future prospects related to sustainable and facile synthesis of biochar-based novel materials for achieving sustainable development goals.

Microplastics as pollutants in agricultural soils.

Microplastics (MPs) as emerging persistent pollutants have been a growing global concern. Although MPs are extensively studied in aquatic systems, their presence and fate in agricultural systems are not fully understood. In the agricultural soils, major causes of MPs pollution include application of biosolids and compost, wastewater irrigation, mulching film, polymer-based fertilizers and pesticides, and atmospheric deposition. The fate and dispersion of MPs in the soil environment are mainly associated with the soil characteristics, cultivation practices, and diversity of soil biota. Although there is emerging pollution of MPs in the soil environment, no standardized detection and quantification techniques are available. This study comprehensively reviews the sources, fate, and dispersion of MPs in the soil environment, discusses the interactions and effects of MPs on soil biota, and highlights the recent advancements in detection and quantification methods of MPs. The prospects for future research include biomagnification potency, cytotoxic effects on human/animals, nonlinear behavior in the soil environment, standardized analytical methods, best management practices, and global policies in the agricultural industry for the sake of sustainable development.

Biorenewable hydrogen production through biomass gasification: A review and future prospects.

Hydrogen is recognized as one of the cleanest energy carriers, which can be produced from renewable biomass as a promising feedstock to achieve sustainable bioeconomy. Thermochemical technologies (e.g., gasification and pyrolysis) are the main routes for hydrogen production from biomass. Although biomass gasification, including steam gasification and supercritical water gasification, shows a high potential in field-scale applications, the selectivity and efficiency of hydrogen production need improvement to secure cost-effective industrial applications with high atom economy. This article reviews the two main-stream biomass-to-hydrogen technologies and discusses the significance of operating conditions and considerations in the catalytic system design. Challenges and prospects of hydrogen production via biomass gasification are explored to advise on the critical information gaps that require future investigations.

Sustainable food waste management towards circular bioeconomy: Policy review, limitations and opportunities.

Research attention is increasingly drawn on constructing a circular bioeconomy and enhancing the value of material flows. Circular bioeconomy aims to achieve sustainable consumption and production with reduction of greenhouse gas emission. This study identifies research gaps on how circular bioeconomy can be achieved through sustainable food waste management by comparing the similarities and differences in concepts of bioeconomy and circular economy, reviewing the benefits and limitations of the existing policies, and evaluating the global situations of food waste and its management on household and commercial basis to promote circular bioeconomy. Future development on food waste management is expected to capitalise on the multi-functionality of products, boundary and allocation in a circular system, and trade-off between food waste and resources. With future technological advances, food waste management in circular bioeconomy policy can facilitate the accomplishment of sustainable development goals.

Potentially toxic elements in solid waste streams: Fate and management approaches.

Solid wastes containing potentially toxic elements (PTEs) are widely generated around the globe. Critical concerns have been raised over their impacts on human health and the environment, especially for the exposure to PTEs during the transfer and disposal of the wastes. It is important to devise highly-efficient and cost-effective treatment technologies for the removal or immobilisation of PTEs in solid wastes. However, there is an inadequate overview of the global flow of PTEs-contaminated solid wastes in terms of geographical distribution patterns, which is vital information for decision making in sustainable waste management. Moreover, in view of the scarcity of resources and the call for a circular economy, there is a pressing need to recover materials (e.g., precious metals and rare earth elements) from waste streams and this is a more sustainable and environmentally friendly practice compared with ore mining. Therefore, this article aims to give a thorough overview to the global flow of PTEs and the recovery of waste materials. This review first summarises PTEs content in various types of solid wastes; then, toxic metal(loid)s, radioactive elements, and rare earth elements are critically reviewed, with respect to their patterns of transport transformation and risks in the changing environment. Different treatments for the management of these contaminated solid wastes are discussed. Based on an improved understanding of the dynamics of metal(loid) fates and a review of existing management options, new scientific insights are provided for future research in the development of high-performance and sustainable treatment technologies for PTEs in solid wastes.

Plenty of room for carbon on the ground: Potential applications of biochar for stormwater treatment.

Low impact development (LID) systems are increasingly used to manage stormwater, but they have limited capacity to treat stormwater-a resource to supplement existing water supply in water-stressed urban areas. To enhance their pollutant removal capacity, infiltration-based LID systems can be augmented with natural or engineered geomedia that meet the following criteria: they should be economical, readily available, and have capacity to remove a wide range of stormwater pollutants in conditions expected during intermittent infiltration of stormwater. Biochar, a carbonaceous porous co-product of waste biomass pyrolysis/gasification, meets all these criteria. Biochar can adsorb pollutants, improve water-retention capacity of soil, retain and slowly release nutrients for plant uptake, and help sustain microbiota in soil and plants atop; all these attributes could help improve removal of contaminants in stormwater treatment systems. This article discusses contaminant removal mechanisms by biochar, summarizes specific biochar properties that enhance targeted contaminants removal from stormwater, and identifies challenges and opportunities to retrofit biochar in LID to optimize stormwater treatment.

Production of 5-hydroxymethylfurfural from starch-rich food waste catalyzed by sulfonated biochar.

Sulfonated biochar derived from forestry wood waste was employed for the catalytic conversion of starch-rich food waste (e.g., bread) into 5-hydroxymethylfurfural (HMF). Chemical and physical properties of catalyst were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area, and elemental analysis. The conversion of HMF was investigated via controlling the reaction parameters such as catalyst loading, temperature, and reaction time. Under the optimum reaction conditions the HMF yield of 30.4 Cmol% (i.e., 22 wt% of bread waste) was achieved in the mixture of dimethylsulfoxide (DMSO)/deionized-water (DIW) at 180 °C in 20 min. The effectiveness of sulfonated biochar catalyst was positively correlated to the density of strong/weak Brønsted acidity (SO3H, COOH, and OH groups) and inversely correlated to humins content on the surface. With regeneration process, sulfonated biochar catalyst displayed excellent recyclability for comparable HMF yield from bread waste over five cycles.

A review of biochar-based catalysts for chemical synthesis, biofuel production, and pollution control.

This review addresses the use of biochar as a green and versatile catalyst support for emerging high-end applications beyond soil remediation, including chemical synthesis and biodiesel production from biomass, and pollutant degradation in the environment. Their catalytic performances are comparable or even superior to the conventional resin-, silica-, or carbon-based catalysts, owing to the favourable intrinsic features of biochar (various functional groups, intricate network of structures, etc.). Yet, distinctive active sites are needed for different applications. It is highlighted that the active site accessibility for substrates critically determines the performance, which is associated with the biochar physicochemical characteristics (-SO3H site density, pore size distribution, surface area, etc.). They show varying significance depending on the catalytic sites on biochar, which may be controlled via novel pre-/post-synthesis modifications. This review elucidates the links among catalytic performances, physicochemical properties, and pyrolysis/modification-induced features, advising the tailored production of application-oriented biochar-based catalyst in the future.