Metal Leaching Research Articles

Screening of variables affecting the selective leaching of valuable metals from waste motherboards' PCBs.

The presence of valuable and hazardous metals in waste printed circuit boards, especially, motherboards, makes their recovery necessary as implies great economic and environmental advantages and develops urban mining processes. Hence, this research is focused on the selective leaching of Cu, Pb, and Sn as base metals using nitric acid and hydrochloric acid and Au, Ag, and Pd as precious metals using thiourea and sodium thiosulfate from waste motherboards' PCBs in a sequential eco-friendly two-stage process. Previously, thiourea and sodium thiosulfate were used as leaching agents to investigate their applicability for the leaching of metals from PCBs in a single-stage process. Screening experimental design was applied to screen the variables affecting the leaching process in order to evaluate their impact on the recovery of metals and select the significant factors. The results demonstrated that base and precious metals can be leached appropriately in two consecutive stages compared to a single-stage process. Nitric acid was found to be a much more efficient agent to leach Cu and Pb in comparison with hydrochloric acid which was more suitable for the leaching of Sn. In the case of precious metals, higher amounts of Au were leached using thiourea, whereas sodium thiosulfate was able to leach more Pd. Roughly similar results were obtained for the leaching of Ag using these leaching agents. Nitric acid concentration, average particle size, temperature, and leaching time were found to be significant to maximize the leaching of Cu and Pb and minimize that for Au, Ag, and Pd in the first stage. Initial pH was the only variable influencing the second stage, in particular, Au leaching by thiourea.

Atomically dispersed cobalt activator with nitrogen and sulfur co-coordination for high-efficiency Fenton-like catalysis: Insights into density-dependent activity and mechanisms

Atomically dispersed metal activators (ADMAs) have demonstrated unique advantages in environmental remediation, but how to controllably regulate the active site density and electronic structure of ADMAs to further enhance activation efficiency remains challenging. Here, we introduce a sulfur-atom-doping approach that allows the fine-tuning of atomic Co site content and electronic structure, enabling exploration of density-dependent activation performance of ADMAs for peroxymonosulfate (PMS)-based Fenton-like catalysis. Our investigation reveals a direct correlation between activation capacity and single-Co-site density. The optimal SNC@CoSA-0.05 activator with densely populated Co–N3S1 sites (10.1 wt%) displays exceptional efficacy in eliminating Rhodamine B, with specific activity of 31.0 min−1 g−1 L, outperforming most previously published activators. Moreover, SNC@CoSA-0.05 showed a remarkedly reduced metal leaching (47.4 μg L−1) than its nanocluster counterpart (194 μg L−1) at pH 3.2. Experimental and theoretical analyses unveiled that coordinated sulfur actively modulates the electronic structure of the central Co atom, enhancing the adsorption and activation of PMS, thereby improving decontamination efficiency. Mechanistic studies further elucidate the predominant electron-transfer regime involved in oxidizing micropollutants by SNC@CoSA-0.05/PMS, with Co(IV)=O, •OH, and SO4•− being the auxiliary oxidizing species. This study not only offers a method for concurrent adjustment of active site density and electronic structure in ADMAs but also sheds light on the activation mechanisms of atomic metal sites.

Biogeochemical impact of historical submarine mine tailings on benthic ecosystems in the Repparfjord (Northern Norway)

Historical copper mine tailings deposited in the Repparfjord, Northern Norway, provided new insight into the biogeochemical impact of submarine tailings disposals on high-latitude coastal ecosystems. The submarine tailings disposal in the Repparfjord represents a product of mining activities between 1972 and 1979. Their environmental impact has been extensively studied during the last decade, but geochemistry of the sediment pore water, which is crucial to assess and monitor the in-situ metal leaching and bioavailability, has never been analysed. The actual impact on the benthic fauna remains poorly known. Therefore, this study couples the pore water chemistry and the foraminiferal analysis obtained from selected sediment cores (gravity core, multicore, box cores) to examine metal stability and the past and current status of the foraminifera community. We measured down-core sulfate and trace metal concentrations and Eh-Ph and applied the Shannon index, the AZTI's Marine Biotic Index (F-AMBI) index and the foraminiferal abnormality index. This study confirms the ongoing leaching of Cu from the underlying mine tailings and release across the sediment-water interface. Leaching of Ni, Zn and Pb have been attributed to weathering of natural bedrock lithologies. The original benthic foraminiferal community disappeared almost entirely during the disposal period, and now it is dominated by stress-tolerant and opportunistic species like Bulimina marginata and Spiroplectammina biformis. Anyhow, against previous assumptions, the community composition changed, while the overall diversity and abnormalities (FAI) shell formation is unaffected by elevated Cu concentrations.

Carp-inspired self-regulating marine antifouling coating: Featuring robust controlled release of eugenol and high-efficiency self-healing performance

The practical application of low surface energy polydimethylsiloxane (PDMS) in marine antifouling is significantly limited due to its inadequate static antifouling capability. Herein, integrating a strategy inspired by carps to release antifouling agents with the fouling release properties of low surface energy materials, an innovative self-regulating marine antifouling coating (named PDMS-Pun-x) was developed, which demonstrates remarkable robust ability of controlled release of eugenol and efficient self-healing performance. Under seawater, the coating regulates its inherent hydrophilicity and the content of the surface anti-fouling agent to obtain the ability of controlled releasing eugenol. Compared with other self-renewal coatings, there proves non-heavy metal leaching and no internal self-hydrolysis existing. Moreover, based on the synergistic action of disulfide bonds and hydrogen bonds, the coating demonstrated a notable self-healing performance, with a self-healing rate of 94.06%. Additionally, the substrate of PDMS modified with polyurea provides the coating with excellent resistance against corrosion. This study introduces a highly promising approach towards the advancement of environmentally-friendly and durable marine antifouling coatings.

Green synthesis of ZnFe2O4@BC nanocrystals using pomelo peel waste for photo‐Fenton degradation of dye under visible light

AbstractIn this study, an economical ZnFe2O4@BC composite was successfully synthesized using pomelo peel biochar through a simple one‐pot thermal‐calcination roasting method. The combination of biochar and ZnFe2O4 was confirmed by FTIR, XRD, Raman, TEM, and XPS analysis, confirming that the successful insertion of carbon into the oxygen sites of the ZnFe2O4 lattice, forming C−O bonds. The incorporation of biochar resulted in a high specific surface area, providing more active sites for catalytic reactions, enhancing electron transport, effectively separating electron‐hole pairs, increasing light capturing capacity, and restraining the leaching of metals. The Zn vacancy acted as an electron acceptor, promoting electron transfer in the catalyst by reducing the lowest unoccupied orbital position. Additionally, various reaction parameters such as solution pH, iron content, catalyst dosage, and H2O2 volume were investigated to elucidate their effects on the degradation performance. This study proposes a novel method for synthesizing carbon‐coated metal oxide semiconductors, which shows great potential for environmental and energy‐related applications.

Bimetallic FeCo nanoparticles embedded N-rich porous ZIF-derived carbon as highly active heterogeneous Fenton catalyst for degradation of tetracycline and organic dyes

Peroxymonosulfate (PMS) based advanced oxidation process (AOP) is used for the degradation of the organic molecules due to ease of reactive oxygen species (ROS) generation through activation. In this study, bimetallic FeCo nanoparticles (NPs) supported on N-doped porous carbons are prepared for the first time by in-situ co-precipitation of metal ions in ZIF-67 followed by carbonization. The prepared nanocomposite, denoted as Fe(x)Co@N-CZ-67, is used to activate PMS for Fenton-like degradations of tetracycline (TC) and dyes. The results reveal that about 96% of TC is degraded by Fe(0.4)Co@N-CZ-67 in 4 min. The catalyst can also degrade three organic dyes, namely methylene blue, neutral red and methyl orange with outstanding reaction rates of 1.75, 1.80 and 2.62 min−1, respectively. The excellent catalytic activities of the catalysts can be ascribed to the synergistic effects between Fe and Co that enhance the electron transfer rate, uniform dispersion of NPs, presence of N in support, and generation of surface PMS complexes with high oxidation activity. Based on the quench experiments, SO4•–, •OH, O2•− and 1O2 are determined to be the ROS responsible for degradations organic molecules. Fe(x)Co@N-CZ-67 shows excellent catalytic activity over ten consecutive cycles with negligible metal leaching and remarkable structural stability.

Application of iron tailings in the coagulation of landfill leachate by bipolar membrane electrodialysis

Landfill leachate contains large amounts of non-biodegradable organic matter. The recalcitrant substances become more concentrated following the treatment using a combination of biological methods and nanofiltration. In this study, the nanofiltration concentrated landfill leachate (NCLL) was subjected to coagulation treatment using the bipolar membrane electrodialysis (BMED) process with iron tailings. The H+ required for metal leaching and OH− for coagulation are supplemented by water dissociation. The pH value of the NCLL played an important role for coagulation and the suitable pH value was 4. As the resource of the coagulant, a certain amount of iron tailing is needed. The energy consumption (EC) for chemical oxygen demand (COD) removal was about 0.70 kW h/g COD with 10 g tailing. Pretreating the tailing with 0.2 mol/L HNO3 could enhance the coagulation process, resulting in a COD removal ratio of 67.3% within 4 h. Increasing the current density improved the COD removal rate, but consumed more electricity. Employing more treatment units is a viable approach to reduce EC. It decreased to 0.045 kW h/g COD when two treatment units connected together. Humic like acids and fulvic like acids present in the NCLL have been effectively removed. This study provides a way of ‘treating the wastes with wastes’ for NCLL treatment.

Reduction of the environmental and health consequences of cigarette butt recycling by removal of toxic and carcinogenic compounds from its leachate.

Cigarette butt is a hazardous waste, and its management faces many challenges. The generation of leachate containing many pollutants including heavy metals is one of the limitations of recycling cigarette butts. The aim of this study was to reduce organic compounds and heavy metals in leachate resulting from cigarette butt recycling in an electrocoagulation reactor. For this purpose, two samples, including freshly smoked cigarette butts and littered cigarette butts, were processed and the treatment of leachate resulting from them was studied in an electrocoagulation reactor. The efficiency of leachate treatment was investigated in the treatment time of 10-40min and current intensity of 20-100mA. The results showed that the minimum reduction of chemical oxygen demand and turbidity was 25.3% and 33.4%, respectively. Increasing the current intensity and treatment time increased the efficiency of removing turbidity and chemical oxygen demand up to 47.1% and 41.2%, respectively, in optimum conditions. The reduction of nickel, chromium, cadmium, and lead in the lowest current density and minimum treatment time was more than 90%, which increased to more than 99% with the increase of the current density and treatment time. The use of electrocoagulation is a suitable solution to reduce heavy metals in leachate resulting from cigarette butt recycling, while the proper reduction of organic compounds in this type of leachate requires further treatment processes.

Sludge‐based geopolymer materials: A review

AbstractSludge refers to the solid waste produced after sewage treatment. Unreasonable disposal of sludge can cause environmental pollution. Nonetheless, the sludge contains large amounts of silica‐aluminate, which has pozzolanic activity by treatment, and the sludge can be used as a sustainable building material. The previous studies have recommended that it is reasonable to produce geopolymers, that is, a green low‐carbon cementitious material with excellent mechanical and durability properties, from sludge. This article provides an overview of recent advancements in the study of sludge‐based geopolymer. It delves into the mechanisms behind alkali‐activated geopolymer, examines the feasibility of preparing geopolymer from sludge, and discusses various preparation methods. Additionally, it elaborates on the impact of incorporating different auxiliary materials on sludge‐based geopolymer. The comprehensive performance of sludge‐based geopolymer, encompassing mechanical properties, durability, and setting time, is thoroughly summarized. An environmental assessment is conducted, evaluating heavy metal leaching and the lifecycle of sludge‐based geopolymer. Finally, we briefly discuss some problems in the current research and development trends in the future on sludge‐based geopolymer. The aim of this article is to provide comprehensive support and guidance for both the research and practical engineering applications of sludge‐based geopolymer.

Ultrasound-assisted sustainable recycling of valuable metals from spent Li-ion batteries via optimisation using response surface methodology

In this study, the use of response surface methodology was proposed to optimise a novel green leaching process for recovering Li and Co from spent lithium-ion batteries (LIBs), assisted by ultrasonic irradiation and gluconic acid. This work investigated various parameters such as temperature, time, gluconic acid concentration, and ultrasound power (US power). To enhance the interpretability and optimisation of experimental data on metal leaching, the central composed design (CCD) was utilised to establish a predictive model. A statistical analysis using the analysis of variance (ANOVA) test was conducted to validate the quadratic model and determine the significant operating parameters, indicated by p-values (< 0.05). The model exhibited Adj R2 values of 0.98 for Li leaching and 0.96 for Co leaching, respectively. To confirm the results, additional characterisations of the solid residues were performed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transformation infrared spectrometer (FT-IR/NIR). The leach liquor was subjected to precipitation and crystallisation methods to recover Li and Co. The purity of Li2CO3 and Co3O4 was confirmed to be ≥ 99% and ≥ 98.8%, respectively, through ICP-OES analysis. Finally, the recovered Li2CO3 and Co3O4 were utilised in a 1:1 molar ratio for regenerating new LiCoO2 cathode materials using a solid-state method. The resulting cathode materials exhibited high purity (≥ 99.43%) as confirmed by ICP-OES analysis. The obtained results demonstrate that ultrasound irradiation significantly enhanced the dissolution of metal oxides within the mixture. Furthermore, gluconic acid exhibited a dual function, acting as both an oxidising and reducing agent. Consequently, this process presents a promising and sustainable alternative for recycling valuable metals from spent LIBs.

Cobalt nanoparticles embedded in carbon nanotubes with high specific surface area activate peroxymonosulfate to degrade ciprofloxacin

Advanced oxidation method based on sulfate radical (SO4−) are increasingly used to degrade organic pollutants. However, high-efficient and stable catalysts are still needed at this stage. In this study, nitrogen-doped carbon nanotubes coated cobalt nanoparticles (Co@NCNTs) were prepared by a simple and rapid pyrolysis method and employed as a high performance peroxymonosulfate (PMS) activator for degradation of the antibiotic ciprofloxacin (CIP). The Co@NCNTs/PMS system achieved 100 % removal of CIP in 40 min with low metal leaching. The effects of Co@NCNTs on PMS activation under different experimental conditions were investigated. The catalyst maintained excellent catalytic activity in the presence of different anions and humic acids and in a wide pH range (4–9). SO4– was identified as the active substance primarily responsible for removing CIP. The possible degradation pathway of CIP was proposed by analyzing the degradation intermediates of CIP. This work provides a high-performance catalyst to activate PMS for the removal of antibiotic with low metal leaching.

Metal recovery from spent lithium-ion batteries cathode materials: Comparative study of sugar-based reductants

Sugars and sugar-rich agricultural by-products are cheaper and eco-friendly alternatives to conventional reductants used in recovering metals from spent lithium-ion batteries. Still, they are rarely used due to a poor understanding of their performance and reaction chemistry. In this study, two hypotheses bearing on the role of chemistry and influence of non-sugary organic compounds (impurities) on the performance of sugars, namely: glucose, fructose and sucrose, and a parent sugar-rich agro-industrial by-product – molasses, as reductants in the leaching of Li, Co, Mn and Ni from spent lithium-ion battery cathode material were tested. Statistical analysis using ANOVA revealed that the performance of the sugars and molasses are similar with >85% Mn, >88% Ni, >88%Co and >98% Li leached at 90 °C and 60 min. This shows that the presence of non-sugar organic compounds does not hamper the performance of the sugars-based reductants. The performance of the sugars relies more on temperature than chemistry. Furthermore, evaluation of the oxidation pathway hints at a potential inhibition of secondary oxidation reactions at lower temperatures. This study provides statistically validated proof that the performance of sugarcane molasses, even at lower concentration, is equipollent to the pure sugars in the leaching of critical metals from spent lithium-ion batteries.

Влияние кучного выщелачивания золотосодержащего сырья на окружающую среду

The issue of rational use of metal-containing raw materials goes hand in hand with the problem of minimization of environmental hazards caused by new technologies, which hampers the development of metal leaching, including gold leaching. The objective of this paper is the increase the mineral reserves of gold-mining enterprises via the application of leaching technology in stacks on the condition of minimization of damage to the natural environment. The results of the study of the impact of heap leaching complex on the surrounding ecosystems are provided based on the example of the stack of the «Kazakhaltyn» mine (the Republic of Kazakhstan), formed by tails of enrichment. The technological scheme of gold leaching and the parameters of its implementation, considering the minimization of consequences potentially hazardous for ecosystems, have been recommended. The calculation of parameters of hypothetically hazardous impact of gold leaching processes is provided for a stack of 6 m height; the time of leaching is 90 days; for four sorption stages, the coefficient of through-extraction of gold is 0.65. The specifics of the version of technology implying the use of recycled water supply to prevent contact with the environment are described. The processes of leaching affecting the environment and the preventive measures have been systematized. It has been demonstrated that emergencies are local, whereas sodium cyanide under the impact of atmospheric air and solar energy reacts with the generation of volatile short-lived hydrogen cyanide. It has been proved that the process of demetallization of mining and processing tails in the stack is a measure of environmental protection; it is not more hazardous than the traditional technology of handling processing tails. Such demetallization process is worth spreading.

Ce/Fe bimetallic MOF derivatives in situ modified bulk carbon aerogel composite cathode for efficient heterogeneous electro-fenton degradation of chloramphenicol

In this study, we utilized a Ce-modified iron-based metal-organic framework derivative to in situ modify bulk CA (Ce/Fe@C-CA) as a bifunctional composite cathode to degrade chloramphenicol (CAP) in the heterogeneous electro-Fenton (EF) process. The composite cathode exhibited satisfactory CAP degradation efficiency, wide pH adaptability (2–9) and low metal leaching. Under the appropriate conditions (pH = 5, current density = 6 mA/cm2), 94.89% of CAP degradation efficiency was obtained within 60 min. The introduction of Ce increased the oxygen vacancy content, enhanced the cathodic electrochemical activity, promoted the production of a variety of reactive oxygen species and participates in the degradation of CAP, of which ·OH and 1O2 were dominant. Meanwhile, the electron transfer and synergistic catalysis between Ce and Fe promoted the regeneration of the metal active site, which was beneficial to improve the reuse stability of the Ce/Fe@C-CA cathode. The degradation pathway of CAP was obtained by DFT calculations and UPLC-MS/MS detection. This study not only proposed a novel bifunctional electro-Fenton cathode, but also provided a effective strategy for the treatment of actual pharmaceutical wastewater.

H2 production based on a ternary mixture of commercial CuO-NiO-TiO2 in a solar pilot plant

Glycerol is a by-product in biodiesel production (in the range of g·L−1), so its photoreforming by photocatalysis is a way of valorising it. TiO2 in photocatalysis has been widely studied, although its efficiency is limited by the high energy band gap, and the electron-hole recombination. Its combination with different semiconductors should improve charge separation, extending also the absorption from UV to visible light. Cu and Ni oxides are two of the most efficient low-cost transition metal oxide catalysts. Experiments were carried out in a 25 L pilot plant connected to a compound parabolic solar collector. Different combinations of the three semiconductors, based on the concentration of each metal on TiO2 (Me, 5%, 7.2% and 10%) were evaluated. Evonik P25-TiO2, CuO and NiO were combined by mechanical mixing. Hydrogen was quantified by a micro gas chromatograph, and copper and nickel leaching by ICP-MS. The best hydrogen production (0.060 mMol kJ−1) was attained with a proportion of 10:1 of TiO2:MeO, that corresponds to a total metal concentration of 7.2 wt%, being Cu and Ni in the same proportion. Metal content in solution increased as the reaction progressed, but Ni lixiviation of <0.012 mg L−1 was not significant. Significant Cu leaching (>1 mg L−1) was observed. This article presents novel results, in a solar pilot plant, for determining which ternary mixture can give better results, as well as metal leaching into water. Handling relevant volume of water in anoxic conditions can help to understand the application of this technology for the production of hydrogen.

Study on the hydration characteristics of steel slag cement

The direct use of stainless steel slag in cement presents potential weaknesses in terms of strength and the risk of cracking, which limits its large-scale utilization. Therefore, it was crucial to explore the use of stainless steel slag in clinker cement. In this study, the hydration characteristics of stainless steel slag cement (SS) and ordinary Portland cement (OPC) were compared and analyzed using isothermal calorimetry, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG-DTG), scanning electron microscopy (SEM), and heavy metal leaching tests. The study investigated the hydration heat, compressive strength at curing ages of 1d, 3d, 5d, 7d, and 28d, hydration products, and safety aspects of SS and OPC. Results showed that the optimum calcination temperature of stainless steel slag cement (SC) and Portland cement (PC) are 1350℃ and the holding time is 2 h. The clinker composition of the two is similar. The main minerals are dicalcium silicate (C2S), tricalcium silicate (C3S), tricalcium aluminate (C3A) and aluminum ferrite tetracalcium (C4AF). Compared with OPC, SS shows a delayed heat release peak during hydration. SS exhibited a delayed exothermic peak in the heat release during hydration compared to OPC. Furthermore, during the stable hydration period, SS produced more calcium aluminate-type solid solution, tightly encapsulating the crystal surface, and exhibited lower heat release. With an increase in curing age, the contents of acicular ettringite (AFt), C-S-H gel, and hexagonal calcium hydroxide (CH) gradually increased in both SS and OPC. Due to higher contents of C4AF, C3S, and C2S in SS, it produced more AFt and C-S-H than OPC. The compressive strength of both SS and OPC increased with curing age, reaching 55.4 MPa and 42.4 MPa at 28 days, meeting the requirements of the national standard (GB/T 21372-2008) in terms of initial and final setting times and f-CaO content. Additionally, heavy metal leaching and soluble Cr6+ tests indicated that their use is safe.

Crystallization, microstructural evolution, heavy metals migration, and solidification mechanism of blast furnace slag glass-ceramics

In recent years, researchers have prepared glass-ceramics using a mixture of multiple solid waste materials, which is an effective and resourceful way to use and store solid waste. However, solid waste usually contains multiple heavy metals, which presents challenges during the mixing and co-solidification processes. In this study, high-performance glass-ceramics with low leaching were prepared from blast furnace slag (BFS). The synergistic curing mechanism of BFS glass-ceramics for heavy metals Cr, Mn, Cu, Zn, Ni, and Co was investigated in detail, as well as the migration pattern and storage state of heavy metals under different heat treatment stages and different Cr contents. The results show that the increases in temperature and Cr2O3 content contribute to the incorporation of heavy metals into the crystal lattice and promote crystal growth. Excessive crystallization of spinel causes aggregation, which further curtails the leaching of heavy metals. The leaching concentration of heavy metals mainly depends on the heavy metal content in the glass network and the degree of network polymerization. Thus, spinel acts as a crystal core for the solidification of heavy metals, while augite and glass phases act as a double barrier to physically encapsulate them, which is effective for the storage of a wide range of heavy metals. Furthermore, the physical and chemical properties of BFS glass-ceramics are consistent with the Chinese industry standard “Glass-ceramics plate for industrial application” (JC/T 2097-2011). This study provides important theoretical support for the synergistic solidification of multiple heavy metals in glass-ceramics, as well as insights into the preparation of glass-ceramics by mixing BFS with other solid wastes.

Developing and understanding Leaching-Resistant cobalt nanoparticles via N/P incorporation for liquid phase hydroformylation

The ultimate target in heterogeneous catalysis is the achievement of robust, resilient and highly efficient materials capable of resisting industrial reaction conditions. Pursuing that goal in liquid-phase hydroformylation poses a unique challenge due to carbon monoxide-induced metal carbonyl species formation, which is directly related to the formation of active homogeneous catalysts by metal leaching. Herein, supported heteroatom-incorporated (P and N) Co nanoparticles were developed to enhance the resistance compared with bare Co nanoparticles. The samples underwent characterization using operando XPS, XAS and HR electron microscopy. Overall, P- and N-doped catalysts increased reusability and suppressed leaching. Among the studied catalysts, the one with N as a dopant, CoNx@NC, presents excellent catalytic results for a Co-based catalyst, with a 94% conversion and a selectivity to aldehydes of 80% in only 7.5 h. Even under milder conditions, this catalyst outperformed existing benchmarks in Turnover Numbers (TON) and productivity. In addition, computational simulations provided atomistic insights, shedding light on the remarkable resistance of small Co clusters interacting with N-doped carbon patches.

Engineering the Co(II)/Co(III) Redox Cycle and Coδ+ Species Shuttle for Nitrate-to-Ammonia Conversion.

Electroreduction of waste nitrate to valuable ammonia offers a green solution for environmental restoration and energy storage. However, the electrochemical self-reconstruction of catalysts remains a huge challenge in terms of maintaining their stability, achieving the desired active sites, and managing metal leaching. Herein, we present an electrical pulse-driven Co surface reconstruction-coupled Coδ+ shuttle strategy for the precise in situ regulation of the Co(II)/Co(III) redox cycle on the Co-based working electrode and guiding the dissolution and redeposition of Co-based particles on the counter electrode. As result, the ammonia synthesis performance and stability are significantly promoted while cathodic hydrogen evolution and anodic ammonia oxidation in a membrane-free configuration are effectively blocked. A high rate of ammonia production of 1.4 ± 0.03 mmol cm-2 h-1 is achieved at -0.8 V in a pulsed system, and the corresponding nitrate-to-ammonia Faraday efficiency is 91.7 ± 1.0%. This work holds promise for the regulation of catalyst reactivity and selectivity by engineering in situ controllable structural and chemical transformations.

Preparation of geopolymer based on municipal solid waste incineration fly ash-phosphorus slag and its function for solidification of heavy metals

Municipal solid waste incineration fly ash (MSWIFA) contains potential contaminants and needs to be efficiently solidified/stablized and so should be managed properly. To achieve this goal, alkali-activated MSWIFA and phosphorus slag (PS) based geopolymer solidified bodies were investigated. Therefore, the mechanical properties of the solidified body, heavy metal leaching characteristics, heavy metal chemical forms, and heavy metal solidification/stabilization mechanisms were also analyzed. The results show that: The addition of an appropriate amount of PS can promote the strength development of a solidified body. When the mass ratio of MSWIFA to PS is 7:3, the strength of the solidified body reaches 22.8 MPa at 90d curing age, which is 5.3 times higher than that of the unmodified material. The MSWIFA/PS immobilized Zn 99.9 %, Pb 99.4 % and Cd 99.8 % in 60 day leaching tests. Meanwhile, PS can significantly increase the proportion of chemically stabilized forms of heavy metals in the solidified body. PS affects on the hydration process of the solidified body. When the mass fraction of PS doping was 30 %, the main hydration products of the solidified body were calcium silicate hydrate (C-S-H) and calcium alumina (AFt). When the mass fraction of PS is 50 %, the main hydration products are calcium aluminosilicate hydrate (C-A-S-H), sodium aluminosilicate hydrate (N-A-S-H), and AFt. These hydration products have good solidification effects on heavy metals. Therefore, it can be concluded that the MSWIFA/PS solidified body is an environmentally friendly and efficient binder.