Metal Leaching Research Articles

Interactions between microplastics and heavy metals in leachate: Implications for landfill stabilization process

The emission of microplastics and heavy metals in landfills has attracted widespread attention for its stabilization process. Microplastics have become carriers of heavy metals due to their adsorption properties, affecting their environmental behavior. However, the effects of landfill stabilization on the interaction between microplastics and heavy metals in leachate are ambiguous. This work explored the abundance characteristics of microplastics and heavy metals in leachate from 10 landfills in Beijing. Overall, the average abundance of microplastics was 196.3 items/L, dominated by small particle size (20–50 µm) and film microplastics. The levels of Cr and As were much higher than other heavy metals. The average abundance of microplastics and polymer types tended to decrease as the landfill stabilization proceeded, and the surface composition of microplastics became more complex. Statistical analysis revealed that the correlations between microplastics and heavy metals in the leachate of landfill stabilization presented significant parabolic characteristics, and Cr and As were more susceptible to landfill stabilization with significant positive correlation with a wide range of microplastics such as 20–30 µm. These results were intended to provide a scientific basis for the treatment and disposal of waste leachate and the synergistic prevention and control of new and traditional pollutants.

The promoting effect of Fe on the immobilization of heavy metals in MSWI FA–lead–zinc tailings-based backfill materials under field application: Dynamic simulation leaching and immobilization mechanisms

Currently, research on solid waste-based backfill materials containing municipal solid waste incineration fly ash (MSWI FA) was primarily concentrated at the laboratory stage, with insufficient studies on their leaching safety and heavy metal immobilization mechanisms under field application. This study demonstrated that MLBM (Binder weight ratio: MSWI FA: steel slag (SS): blast furnace slag (BFS): flue gas desulfurized gypsum (FGDG): coal fly ash (CFA) = 10 %:33.6 %:33.6 %:12.8 %:20 %; binder-to-lead–zinc tailings (LZT) ratio was 1:8; mass concentration was 60 %) exhibited excellent leaching safety in actual backfilling. The study found that MLBM posed no risk of heavy metal and anion leaching under various leaching standards. Furthermore, MLBM showed no risk of harmful element leaching within a simulated percolation period of 100 years. The release mechanisms of Pb, As, Zn, and Cr in MLBM were diffusion, diffusion, flushing, and dissolution, respectively. The immobilization efficiency of Pb, Zn, Cr, As, Cl−, and SO42− positively correlated with the pH value (pH>7.5). The immobilization mechanism included: 1) Formation of insoluble heavy metal compounds. In the MLBM system (The pH ranged from 7.89 to 8.87), Fe(III) (Fe(OH)3(aq) and Fe(OH)4−) contributed to the immobilization of Pb2+ and SO42− and oxidized As(III) (H2AsO3−) and Cr(III) (Cr(OH)3(aq)), forming As(V) (HAsO42−) and Cr(VI) (CrO42−), respectively. 2) Adsorption. The negatively charged surface of C–(A)–S–H gel could immobilize Zn2+ and Pb2+ through adsorption, and the ionic forms of Pb(II) and Zn(II) were PbOH+ and ZnOH+, respectively. This study provided theoretical support for the leaching safety and immobilization mechanisms of solid waste-based backfill materials containing MSWI FA in field applications.

Quantitative and mechanistic elucidation of the reactive oxygen species for effective sulfamethoxazole removal in heterogeneous peroxymonosulfate activated by MOFs-derived cladding structure CoZn/NC@UiO

In cobalt-based catalyst/peroxymonosulfate (PMS) systems, the key issues are the leaching of metals and the stability of catalysts. In this study, a NH2-UiO-66 cladded CoZn/NC catalyst was synthesized for efficient degradation of sulfamethoxazole (SMX) using activated PMS. The removal efficiency of SMX could achieve 100% within 30 min. The leaching of Co2+ was inhibited to 0.05 ppm and the anti-interference and cyclic stability of the catalyst were enhanced by the NH2-UiO-66 shell. In addition, the quenching experiment, electron paramagnetic resonance (EPR) technique and probe experiment were used to analyze the reactive oxygen species (ROSs) qualitatively and quantitatively. The findings demonstrated that singlet oxygen (1O2) had the highest steady-state and cumulative concentration. However, 1O2 could only participate in the degradation of SMX through single electron transfer or addition reaction, resulting in a lower second-order rate constant of the SMX reaction with 1O2. Sulfate radical (SO4·-) contributed the most to the degradation of SMX due to the high reactivity of the sulfonamide structure in SMX to SO4·-. Finally, possible pathways for SMX degradation were proposed. The two primary mechanisms of SMX degradation were S-N cleavage and amino hydroxylation/oxidation. The toxicity of most of the intermediates was less than that of SMX through ecological structure–activity relationship analysis. Overall, a novel approach to synthesize low leaching and efficient cobalt based catalyst was put forward, and the activation mechanism of PMS was also revealed.

Efficiency of metal(loid) phytostabilization by white lupin (Lupinus albus L.), common vetch (Vicia sativa L.), and buckwheat (Fagopyrum esculentum Moench).

Erosion and leaching of metal(loid)s from contaminated sites can spread pollution to adjacent ecosystems and be a source of toxicity for living organisms. Phytostabilization consists of selecting plant species accumulating little or no metal(loid)s in aerial parts to establish a vegetation cover and thus to stabilize the contaminants in the soil. Seeds of white lupin, common vetch, and buckwheat were sown in greenhouse on soils from former French mines (Pontgibaud and Vaulry) contaminated with metal(loid)s including high concentrations of As and Pb (772 to 1064 and 121 to 12,340mgkg-1, respectively). After 3weeks of exposure, the growth of white lupin was less affected than that of the 2 other species probably because metal(loid) concentrations in roots and aerial parts of lupins were lower (5-20 times less Pb in lupin leaves on Pontgibaud soil and 5-10 times less As in lupin leaves on Vaulry soil than in vetch and buckwheat). To limit oxidation and/or scavenge metal(loid)s, white lupin increased the content of proline and total phenolic compounds (TPC) in leaves and roots by a factor 2 whereas buckwheat stimulated the production of TPC by a factor 1.5-2, and non-protein thiols (NPT) by factors around 1.75 in leaves and 6-12 in roots. Vetch accumulated more proline than white lupin but less NPT than buckwheat and less TPC than the 2 other plant species. The level of oxidation was however higher than in control plants for the 3 species indicating that defense mechanisms were not completely effective. Overall, our results showed that white lupin was the best species for phytostabilization but amendments should be tested to improve its tolerance to metal(loid)s.

Recycling valuable metals from spent cathode material by in-situ thermal reduction combined with electrochemical leaching

In-situ thermal reduction is a promising technology that realizes the reduction of high-valence metals in spent lithium-ion batteries (LIBs) through its reductive substances. However, the subsequent simple acid leaching cannot adapt to all thermal reduction products, especially elemental Ni and Co, resulting in low leaching efficiency and high acid consumption. In this work, in-situ thermal reduction combined with electrochemical-enhanced leaching technology was provided for extracting valuable metals from spent LIBs with minimum chemical consumption. Results show that after thermal reduction, the layered structure of LiNi1/3Co1/3Mn1/3O2 was fully broken, yielding acid-soluble components including Ni, Co, NiO, CoO, MnO, Li2CO3, and LiAlO2, all achieved without external reductants. During the electrochemical leaching, the acidic solution produced by water electrolysis and electrochemical oxidation synergistically promoted the leaching of valuable metals, and finally, 99.02 % Li, 96.34 % Ni, 98.28 % Co and 99.24 % Mn were leached from the roasted cathode product. Compared with traditional acid leaching, the proposed electrochemical method has advantages in the dissolution of elemental Ni and Co. Moreover, the whole process does not consume any external acids or bases, and there is no emission of waste acid. The findings of this work help to reduce reagent consumption in the spent LIBs recycling process and provide an effective, adaptable, and green method for leaching thermal reduction products.

A CASE STUDY OF IMPLEMENTATION OF CIRCULAR ECONOMY PRINCIPLES TO WASTE MANAGEMENT: INTEGRATED TREATMENT OF CHEESE WHEY AND HI-TECH WASTE

In a global context characterized by severe environmental problems and increasing resource scarcity, waste represents both a challenge and an opportunity. This study aims to demonstrate with a real case the potential for optimizing the waste valorization action attainable through the synergic application of different treatments to residues of equally different nature and origin. In particular, bio-chemical (dark fermentation), chemical-physical (selective leaching) and thermo-chemical (hydrothermal carbonization) treatments were applied for the integrated valorization of whey from sheep cheese production and Hi-Tech waste (discarded electrical and electronic equipment). The treatments were applied at a laboratory scale on real samples of these residues. The organic acids used for selective leaching of valuable metals from Hi-Tech waste were obtained by dark fermentation of the cheese whey, while hydrothermal carbonization was used to convert the waste from previous stages into hydrochar feasible as solid fuel or soil improver. The dark fermentation tests have highlighted the possibility of recovering ≈ 100 g of organic acids from 1 L of whey; furthermore, it is also possible to recover bio-hydrogen depending on the operating conditions applied and the type of targeted organic acids. The leaching tests have demonstrated how the organic acids from whey fermentation have selective and quantitative mobilization capacities comparable to those of the same acids available on the market. The carbonization tests produced carbon-enriched hydrochar with promising fuel properties, as well as process waters suitable for anaerobic digestion with methane production. The results of the project led to the filing of an international patent.

Environmental Impact of Waste Treatment and Synchronous Hydrogen Production: Based on Life Cycle Assessment Method.

Based on the life cycle assessment methodology, this study systematically analyzes the energy utilization of environmental waste through photocatalytic treatment and simultaneous hydrogen production. Using 10,000 tons of organic wastewater as the functional unit, the study evaluates the material consumption, energy utilization, and environmental impact potential of the photocatalytic waste synchronous hydrogen production system (specifically, the synchronous hydrogen production process of 4-NP wastewater with CDs/CdS/CNU). The findings indicate that potential environmental impacts from the photochemical treatment of environmental waste and synchronous hydrogen production primarily manifest in freshwater ecological toxicity, marine ecological toxicity, terrestrial ecological toxicity, and non-carcinogenic toxicity to humans. These ecological impacts stem from the catalyst's adsorption and metal leaching during the photo-degradation and hydrogen production processes of environmental waste. By implementing reasonable modifications and morphological refinements to the catalyst, these effects can be mitigated while achieving enhanced efficiency in environmental waste processing and simultaneous hydrogen production. The research outcomes provide valuable insights for advancing sustainable development in green technology for environmental waste treatment and energy utilization.

Determination of Some Element’s Migrants in Aqueous Simulant from Plastic Food Contact Products by Inductively Coupled Plasma Mass Spectrometer

Various chemicals present at different stages in the food supply chain can lead to the leaching of heavy metals. These metals can accumulate in the human body through the consumption of contaminated food. Consequently, it is necessary to validate an analytical technique for the quantification chemical that could contaminate food. This study presents a rapid, straightforward, and efficient analytical method for the direct quantification of some potentially toxic elements in aqueous simulants from plastic food contact products using an inductively coupled mass spectrometer (ICP-MS). The method’s validation encompassed the study of the estimated detection limits, practical quantification limits, linearity, accuracy, and measurement uncertainty of aluminium (Al), antimony (Sb), arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni), and zinc (Zn) under optimized ICP-MS conditions. The estimated detection limits ranged from 7.5 × 10−4 to 0.074 mg/kg, while practical quantification limits spanned from 0.02 to 0.8 mg/kg. The average recoveries ± standard deviations at different spiking levels were varied between 85.7 ± 1.51 and 115.6 ± 0.88% with coefficients of variation between 0.42 and 5.85%. The method trueness was verified by using references materials (test material in aqueous acetic acid) purchased from Food Chemistry Proficiency Testing and Analysis (FAPAS) yielding satisfactory results within acceptable recovery and Z-score values. The method precision, in terms of relative standard deviation (RSD), was being below 4.22%. The method uncertainty expressed as expanded uncertainty of all validated elements was found to be ≤ 21.9%. Validated method was employed to determine specific elements in aqueous simulants of thirty commercial plastic food packaging samples, representing three distinct types of plastic polymers. The results showed that the mean concentrations, in mg/kg, were as follows: 2.04 (Al), 0.02 (As), 0.02 (Cd), 0.02 (Co), 0.06 (Cr), 0.41 (Cu), 1.55 (Fe), 0.09 (Mn), 0.15 (Ni), 0.07 (Pb), 0.05 (Sb), and 0.81 (Zn). Furthermore, 30% of analyzed samples exceeding the maximum permissible limits of Al for plastic materials and articles intended to come into contact with food.

Self-supporting CoFe2O4 nanoparticles on 2D g-C3N4/2D loofah activated carbon mediated peroxymonosulfate activation for tetracycline degradation

For antibiotic contaminants, biomass have been regarded as one of the most resource of functional carbonaceous materials due to its biocompatibility, biodegradability, and good adsorption/degradation performance. Herein, a self-supporting CoFe2O4 nanoparticles on 2D g-C3N4/2D loofah activated carbon (CoFe2O4/g-C3N4/BC) is successfully synthesized by simple hydrothermal method using loofah as carbon source and melamine as nitrogen source. The obtained CoFe2O4/g-C3N4/BC materials have a stable hierarchical sandwich structure with macroporous and mesoporous and a large surface area (189.52 m2/g), which can be used as an adsorbent/catalyst for the adsorption/degradation of organic pollutants. With these beneficial properties, the CoFe2O4/g-C3N4/BC material mediated peroxymonosulfate activation exhibits superior catalytic activity in the degradation of organic pollutants under ambient conditions. A model pollutant tetracycline (TC) can be rapidly degraded by 94.97 % within 25 min. The degradation efficiency was sustained at 88.21 % even after five operational cycles, with the cobalt metal leaching rate consistently below 50 μg/L. The inhibition experiment indicates that the main active species in the CoFe2O4/g-C3N4/BC + PMS system are SO4•−, HO• and 1O2, and the degradation of TC is achieved by the synergistic effect of free radical and non-radical pathways. This study provides a new perspective on the treatment of antibiotic wastewater via the sulfate radicals based-advanced oxidation processes (SR-AOPs).

Separation of valuable metals from low nickel matte to prepare NiCo2O4 materials: Optimization of oxidative leaching process and improvement of electrochemical properties of materials

The economical and efficient utilization of intermediate low nickel matte has become an important goal of nickel smelting industry. In this work, an innovative process of oxidative leaching of valuable metal from low nickel matte to prepare NiCo2O4 materials was proposed based on the materials utilization of mineral. The addition method and speed of ammonium persulfate in the oxidative leaching process was investigated to improve the extraction of valuable metals. The key factors affecting the leaching of valuable metals and the optimum leaching condition were determined by orthogonal experiments, and the extraction of Ni, Cu, and Co was 92.3 %, 97.1 % and 96.6 %, respectively. The leaching mechanism was clarified and the advantages of the leaching process were compared and analyzed. The kinetics of oxidative leaching process was studied by timing sampling method, and the control model, activation energy and kinetic equation of Ni, Cu and Co leaching were determined by analyzing the data with unreactive shrinkage model. The effects of Ni:Co ratio and calcination temperature of precursor on the properties of NiCo2O4 were investigated using the leaching solution removing iron and copper as raw materials. The NiCo2O4 material with the Ni:Co ratio of 1:2 prepared by calcining precursor at 750 ℃ for 3 h has a specific capacitance of 864F/g when the current density is 1 A/g. The prepared NiCo2O4 materials show good capacitance performance and has potential to be used as capacitor electrodes. This work combines metal extraction with product materialization, which is expected to help the metallurgical industry effectively shorten the industrial production process and reduce production costs.

Nitrogen Forms and Heavy Metals Leachability Following Biosolids Application to Sandy Soil.

Nitrogen Forms and Heavy Metals Leachability Following Biosolids Application to Sandy Soil.

Oil-based drilling cutting pyrolysis residues-recycled fine powder sintered ceramsite: Basic properties, microsintering mechanism, lightweight concrete application and heavy metals solidification

Oil-based Drilling Cutting Pyrolysis Residue (ODPR) is a waste produced during oilfield drilling using oil-based mud. Recycled Fine Powder (RFP) consists of particles less than 0.16 mm, crushed and sieved from waste concrete. China's solid waste is characterized by high production, low utilization rates, and high pollution levels. This study explores the feasibility of preparing ceramsite from ODPR and RFP. By examining the effects of varying temperatures and proportions on the macroscopic and microscopic properties of ODPR-RFP ceramsite (ORC), the optimal process was determined: ODPR: RFP = 7:3, 2 % borax flux, 10 minutes ball milling, 1200℃ sintering temperature, and 30 minutes insulation. The resulting ORC, with a bulk density of 1120 kg/m³, cylinder compression strength of 10.50 MPa, and water absorption rate of 7.8 %, meets the "Lightweight aggregates and its test methods (GT/B17431.2)" standard. Batch production of ORC products of various sizes was conducted to evaluate their practical application in LC30 lightweight aggregate concrete. Replacing the aggregate in lightweight concrete with ORC yielded a concrete with excellent mixing performance, reaching a maximum strength of 31.2 MPa after 7d and 44.8 MPa after 28d. The damage pattern of ORC lightweight concrete is characterized by longitudinal splitting, with varied crack initiation and expansion paths. In the interfacial transition zone of ORC concrete, the ORC form a strong bond with the cement mortar, enhancing the strength of the lightweight concrete. Additionally, the leaching of heavy metals (HMs) from the ORC was examined to assess potential environmental pollution. The results indicated that preparing ORC from these two types of solid waste can effectively immobilize HMs, with a solidification rate of up to 92.10 %. Pb with high content is mainly solidified in the form of solid solution to form (Ba, Pb) SO4. The ecological risk assessment method for HMs shows that using this solid waste and process to prepare ORC does not pose HMs risks and is an environmentally friendly building material.

Study on hydration and heavy metal leaching of washed MSWI FA as a green cementitious material

Despite municipal solid waste incineration fly ash (MSWI FA) being classified as hazardous waste, there is a consensus on its significant potential for resource utilization. The high content of soluble chlorides in MSWI FA not only limits its co-disposal in cement kilns but also hinders its application in the field of construction materials. The research aimed to investigate the viability of MSWI FA as a binding material in the construction engineering field. Through examining the impact of liquid/solid ratio and pH levels on the chemical composition of MSWI FA during the washing procedure, the study delved into the mechanisms affecting hydration and the characteristics of heavy metal contamination before and after washing pretreatment. The results indicate the feasibility of developing MSWI FA into construction engineering materials. The liquid/solid ratio is a significant factor affecting the removal of chlorides, with an optimal ratio of 30. pH plays a crucial role in the mineral composition during the water-washing process of MSWI FA. An acidic environment can remove a higher proportion of chlorides, while an alkaline environment can form more calcium salts. The compressive strength of pure MSWI FA at 28 days is 3.92 MPa, which can be increased by 0.99 MPa after washing. The washed MSWI FA not only exhibits heightened reactivity but also demonstrates reduced leaching concentrations of heavy metals, and its leaching toxicity was much lower than the safe landfill threshold. Therefore, MSWI FA, after washing, is a very promising alternative material for construction engineering.

An in-depth Analysis of Soil Quality and Heavy Metal Contamination in the vicinity of the Visakhapatnam Municipal Solid Waste Dumpsite

The study conducts a comprehensive analysis of soil quality and heavy metal contamination in the vicinity of the Visakhapatnam Municipal Solid Waste Dumpsite, with a focus on the Gajuwaka municipality. The research addresses the escalating global concerns arising from improper waste disposal practices and their environmental repercussions. The Gajuwaka dumpsite, receiving diverse waste types, poses significant threats due to the leaching of heavy metals into the soil, impacting environmental components and human health. The study employs a robust experimental methodology involving soil sampling, metal extraction and Atomic absorption spectroscopy for elemental analysis. Waste characterization reveals the predominant presence of organic fractions and inert materials in the dumpsite. Seasonal physicochemical analysis of soil samples indicates variations in pH, moisture content, soil texture, organic matter and nutrient availability. Metal content generally decreases during the post-monsoon period. Phytotoxicity analysis of selected plant species demonstrates their capacity to accumulate heavy metals, particularly lead. The study emphasizes the urgent need for effective waste management practices, continuous soil monitoring and community engagement to mitigate environmental and health risks associated with waste dumping sites. The findings underscore the critical importance of sustainable waste management and environmental health. The study contributes valuable insights into the complex challenges posed by improper waste disposal practices and provides a foundation for the development of comprehensive strategies aimed at addressing environmental concerns.

Investigation of hydrohalic acids as lixiviants for the leaching of cathode metals from spent lithium-ion batteries

The exploration of alternative energy sources is inextricably linked with energy storage considerations. Current high density energy storage options on the market rely heavily on lithium (Li)-based technologies. A projected increase in energy storage technology demand has sounded the alarm on a need to develop suitable approaches for the recovery of the various constituent metals from spent Li-ion batteries (LIBs). This, coupled with urgent consideration for the environment has necessitated the investigation of various LIB metal recovery techniques. In this work, we explore the novel application of the hydrohalic acids, hydrobromic (HBr) and hydroiodic (HI) acid, as lixiviants in a series of leaching experimental investigations on LIB cathode powder. A methodology for battery disassembly and cell cathode material recovery is presented leading up to the metal leaching. Our results indicate that the lixiviants can be utilized in the absence of a reducing agent which is typically present in conventional LIB leaching systems. The highest recoveries of the constituent metals, Co, Li, Mn and Ni in the HI system were 92.9 %, 93.6 %, 93.1 % and 94.5 % respectively, at an operating temperature of 60 ℃ and with a 1.5 M HI concentration. The HBr system achieved metal recoveries of 90.6 %, 89.1 %, 83.1 % and 96.4 % for Co, Li, Mn and Ni respectively, at 60 ℃ and using 2 M HBr. Kinetic studies showed that the leaching mechanism for both acids follow a chemical reaction-controlled model.

Assessment of the environmental impacts of utilizing coal ashes and OPC for soil stabilization applications: Leachate analysis in response to rainfall interaction

The construction industry is a leading sector for coal ashes utilization, including in cement manufacturing and soil stabilization applications. In soil stabilization, coal ashes, alongside Ordinary Portland Cement (OPC), are the most commonly used materials. However, the environmental impact of coal ashes, particularly the leaching of heavy metals from stabilized soil when exposed to rainfall, remains underexplored. There is a notable gap in assessing the environmental impacts of this utilization, particularly when the stabilized soil interacts with rainfall in real-world scenarios. Therefore, this study aimed to contribute to filling this gap. Accordingly, in this study, peat soil was stabilized by using fly ash, bottom ash, and OPC. The characterization of soil mixture materials, including physicochemical and engineering properties, was established and studied first. Following the environmental impact, simulations were conducted using a column to study soil leachate under different conditions and seasons (dry and wet) in response to its interaction with rainfall. The leachate was analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to measure the concentrations of heavy metals, including copper (Cu), aluminum (Al), manganese (Mn), iron (Fe), and zinc (Zn). Additionally, Ion Chromatography (IC) was employed to determine the concentrations of major anions, including fluoride (F⁻), chloride (Cl⁻), nitrate (NO₃⁻), phosphate (PO₄³⁻), and sulfate (SO₄²⁻). The findings revealed the complex interaction of the chemical stabilization processes and environmental factors with the leaching behavior of heavy metals and anions, highlighting the significant impact of stabilization on leaching patterns. To conclude, this study provides a valuable contribution to understanding the environmental and engineering implications of utilizing coal ashes in soil stabilization.

Utilization of cow bone waste and calcium oxide for the solidification and stabilization of MSWI fly ash: Towards sustainable practices

The quest for sustainable waste management practices has catalysed the development of innovative approaches to transform waste into resourceful products. This study explores the effectiveness of cow bone waste and calcium oxide (CaO) as agents in the stabilization/solidification (S/S) process of Municipal Solid Waste Incineration (MSWI) fly ash derived from two distinct cities employing both grate-type and circulating fluidized bed incinerators in China. Employing a robust experimental framework, the research evaluated the stabilization efficacy for heavy metals, monitored the progression of pH, and quantified the compressive strength of the treated MSWI fly ash. Moreover, it conducted risk assessment and economic analyses. Incorporating CBW and CaO into the MSWI fly ash from grate-type incinerators significantly enhanced the Pb stabilization efficiency, achieving up to 99.7 % when adding 31 % CBW and 7 % CaO. This treatment resulted in the leaching of other heavy metals, which were also below the standard landfill limits. In the circulating fluidized bed incinerator fly ash, the leaching concentrations of heavy metals in the treated samples were reduced by up to 98.6 % for Cd and 64.4 % for Ni.Additionally, an increase in CaO content was found to substantially improve the compressive strength of the solidified samples across all tested curing periods (7, 14, and 28 days). The optimal compressive strength result, observed at 28 days, reached 1.2 MPa, compared to the raw fly ash, which exhibited only 0.77 MPa when adding just 9 % CaO. This highlights CaO's critical role in enhancing the mechanical integrity of the treated MSWI fly ash. The study concludes that strategically calibrated ratios of cow bone waste and CaO attenuate the environmental hazard presented by MSWI fly ash and bolster its mechanical attributes, thereby repurposing the waste into a viable material for construction.

A Review of Catalyst Integration in Hydrothermal Gasification

Industrial scale-up of hydrothermal supercritical water gasification process requires catalytic integration to reduce the high operational temperatures and pressures to enhance controlled chemical reaction pathways, product yields, and overall process economics. There is greater literature disparity in consensus on what is the best catalyst and reactor design for hydrothermal gasification. This arises from the limited research on catalysis in continuous flow hydrothermal systems and rudimentary lab-scale experimentation on simple biomasses. This review summarizes the literature status of catalytic hydrothermal processing, especially for continuous gasification and in situ catalyst handling. The rationale for using low and high temperatures during catalytic hydrothermal processing is highlighted. The role of homogeneous and heterogeneous catalysts in hydrothermal gasification is presented. In addition, the rationale behind certain designs and component selection for catalytic investigations in continuous hydrothermal conversion is highlighted. Furthermore, the effect of different classes of catalysts on the reactor and reactions are elaborated. Overall, design and infrastructural challenges such as plugging, corrosion, agglomeration of the catalysts, catalyst metal leaching, and practical assessment of catalyst integration towards enhancement of process economics still present open questions. Therefore, strategies for catalytic configuration in continuous hydrothermal process must be evaluated on a system-by-system basis depending on the feedstock and experimental goals.

Evaluation of leaching parameters for dissolving Ni and Co from chromite overburden using acidophilic bacterial consortium

ABSTRACT The chromite mine of Sukinda Valley located in the Indian state Odisha produces a large amount of overburden during the mining of chromite ore. The overburden waste contains different valuable metals with very low concentrations. Its environmental metal leaching contaminates nearby water resources, which creates serious chaos in the local communities. However, the presence of Ni-oxide in the overburden makes it the only Ni resources of India. Therefore, an experimental attempt was made to evaluate the possibility of Ni recovery from the overburden. The physico-chemical analysis of the overburden sample showed that it contains 0.89 and 0.031% (w/w) of Ni and Co, respectively, which remain embedded within the goethite matrix. Bioleaching may be suitably applied to it. Therefore, bioleaching of Ni and Co from the overburden sample was conducted using an acidophilic bacterial consortium. Effect of leaching parameters like contact time, initial pH, temperature, Fe(II) addition, and pulp density was evaluated. Bioleaching of the overburden sample using the acidophiles was found to be effective. Further, all the leaching parameters showed positive effect on the bioleaching efficiency.

Efficient peroxydisulfate activation with γ-Al2O3-C-MIL-100(Fe) framework for sulfamethazine degradation: Enhanced oxidant utilization and reduced metal leaching

Low degradation efficiency and significant transition metal leaching are two challenges in persulfate activation systems based on metal-organic frameworks (MOFs) for organic pollutant degradation. Here, the challenges were solved by designing and synthesizing a micron-sized core-shell material, γ-Al2O3-C-MIL-100(Fe) (γACM), by coating the γ-Al2O3 core with carbon (γ-Al2O3-C) and futher modifying with MIL-100(Fe). Testing γACM with sulfamethazine (SMZ) demonstrated its outstanding peroxydisulfate (PDS) activation, achieving 92.5 % SMZ removal within 20 min at a low oxidant/pollutant ratio. Fe leaching from γACM was effectively inhibited, with only 3.59 % Fe lost after three recycles. The system showed adaptability across a wide pH range, and usability in sewage effluent, indicating promise for practical application. The hydrophobicity of γ-Al2O3-C, the coordinatively unsaturated sites in MIL-100(Fe), and the strong bounding of MIL-100(Fe) on γ-Al2O3-C ensured the effective SMZ gather, PDS activation, and Fe stability respectively, which led to the excellent performances of γACM.