High Metal Content Research Articles

Detoxification pathways of multiple metals from intensive copper production by indigenous ureolytic microbes coupled with soil nitrogen transformation

The ubiquitous ureolytic microbes were potential to clean up toxic heavy metals from environment. Their responses and detoxification mechanisms are largely unknown for multiple metals in field soils. In this study, high-throughput sequencing of the urease-encoding genes and deep learning from bioinformatic analysis were conducted for identifying ureolytic prokaryote-related processes throughout China. The passive adsorption of heavy metals onto cell walls or cell surfaces was mainly performed by G+ ureolytic bacteria in soils located in the large-scale smelting areas with slightly high Hg and low Cu/Zn/Ni contents. For the large-scale smelting areas with the highest Cr and lowest Cu/As contents, the Cr(VI) was reduced to Cr(III) by G– ureolytic bacteria and then accumulated in their periplasmic spaces or cell surfaces. The G– ureolytic bacteria detoxified high contents of multiple metals by intracellular antioxidant defense mechanisms and extracellular urease-induced (co)precipitation in the medium-scale smelting areas, consistent with high urease activities and ureolytic microbial diversity. In addition, this large-scale field work verified that toxic metals stimulated the bacterial hydrolysis of urea as soil nitrogen fertilizers and depressed the bacterial fixation of nitrogen from air. Simultaneously, the heavy metals used nitrate-N and nitrite-N as alternative electron acceptors, driving the soil denitrification processes.

Multi-Omics Uncover the Mechanism of Wheat under Heavy Metal Stress.

Environmental pollution of heavy metals has received growing attention in recent years. Heavy metals such as cadmium, lead and mercury can cause physiological and morphological disturbances which adversely affect the growth and quality of crops. Wheat (Triticum aestivum L.) can accumulate high contents of heavy metals in its edible parts. Understanding wheat response to heavy metal stress and its management in decreasing heavy metal uptake and accumulation may help to improve its growth and grain quality. Very recently, emerging advances in heavy metal toxicity and phytoremediation methods to reduce heavy metal pollution have been made in wheat. Especially, the molecular mechanisms of wheat under heavy metal stress are increasingly being recognized. In this review, we focus on the recently described epigenomics, transcriptomics, proteomics, metabolomics, ionomics and multi-omics combination, as well as functional genes uncovering heavy metal stress in wheat. The findings in this review provide some insights into challenges and future recommendations for wheat under heavy metal stress.

Diversity, heavy metals, and antibiotic resistance in culturable heterotrophic bacteria isolated from former lead-silver-zinc mine heap in Tarnowskie Gory (Silesia, Poland).

Mine tailings represent a great environmental concern due to their high contents of heavy metals. Cultivation analysis of microbiota of Tarnowskie Góry (Poland) mine tailing showed the occurrence of bacteria with colony-forming units as low as 5.7 × 104 per one gram of dried substrate. Among 110 bacterial isolates identified by a combination of MALDI-TOF mass spectrometry and 16S rRNA gene sequencing, phylum Actinobacteria was dominant, followed by Firmicutes and Proteobacteria. Extremely high levels of heavy-metal resistance were observed in Arthrobacter spp., particularly for zinc (500mg/L), lead (1500mg/L), and cadmium (1000mg/L). On the other hand, Staphylococcus spp. showed high tolerance to several antibiotics tested, especially ampicillin, partly due to blaZ gene presence. Due to the occurrence of antibiotic-resistant bacteria, mine tailings are not the cause of heavy-metal contamination only, but also a source of antibiotic-resistant bacteria and thus may represent a serious risk for public health.

A Review of On-Line Measurement Methods of Alkali Metal Emissions from Combustion by Passive Spontaneous Emission Spectroscopy

This article reviews the principles and applications of passive spontaneous emission spectroscopy (SES) for the quantitative determination of alkali metal concentrations emitted from combustion processes. The combustion of fuels that contain a high alkali metal content (Na and/or K) is challenging, as alkali metals reduce the slag formation temperature and induce fouling, causing combustion facilities to shutdown prematurely. The in situ on-line quantification of alkali metals is, thus, a critical measure to control combustion processes, preventing slagging and fouling from occurring. This review shows that several SES systems, developed by the Huazhong University of Science and Technology (HUST), are inexpensive, portable, and useful for measuring the alkali metal content, and have been applied for biomass combustion as well as coal and municipal solid waste combustion, from laboratory-scale settings (20 kW) to industrial facilities (300 MW). Compared with other research, the SES system from HUST has successfully quantified the emitted alkali metal concentrations during combustion. This review also highlights the challenges of the SES system and recommends further work to improve it for further applications.

Soil heavy metal contamination in the vicinity of the abandoned Zeïda mine in the Upper Moulouya Basin, Morocco. Implications for airborne dust pollution under semi-arid climatic conditions

For thirteen years, the Zeïda mine was one of Morocco's biggest lead reserves. The mining activities produced a huge volume of waste stored as tailings and subjected to meteoric agents. To better understand the impact of the past mining activity on the soil ecosystem in the vicinity of the abandoned mine, several physical and chemical analysis were done to identify the level of soil contamination. A total of 27 surface soil samples were collected from a depth of about 0–20 cm from crop areas and analysed for Pb, Zn, Cu, Co, Cd, and As total concentrations (aqua regia extraction) using the ICP-MS method. Results showed that soils have high to medium levels of metal concentrations, especially close to the tailings, compared to the non-contaminated soil sample taken as a geochemical background reference. Analysis of physicochemical parameters (pH, electrical conductivity, total calcium, phosphorus, potassium, and organic matter) has shown high alkalinity levels related to carbonates, varying organic matter content, and electrical conductivity values ranging from 4.12 to 1466 μS/cm. Most of the studied soils share the same mineralogical composition that includes: carbonates (Calcite and Dolomite), Quartz, Orthoclase, and Muscovite. Lead mineral phases (cerussite and wulfenite) have been found in 3 samples (ZAM17, ZAM18, and ZAM21). The Illite and the Kaolinite are the main clay minerals. Descriptive and multivariate statistics were carried out to investigate the distribution of the studied metals. Comparing the obtained results with International Standard Limits (ISL), soils especially those close to the mine tailings show high heavy metals content. Pb, Zn, Cu, As, and Cd contents in Zeïda soils are usually linked to anthropogenic origins. Results have shown correlation values between As, Cu, and Cd and Pb and Zn indicating that they come from the same origin and react similarly throughout transport.

Elemental and boron isotopic variations in tourmaline in two-mica granite from the Cuona area, Tibet: Insights into the evolution of leucogranitic melt

Two-mica granite is the most common magmatic rock type in the Himalayan leucogranite belt, which has close relationship with rare metal mineralization. Its genesis is generally attributed to magmatic differentiation. In recent years, the mineral geochemical compositions are increasingly used to study magmatic differentiation, which are significant for deciphering the melt evolution and element migration processes. In this study, in-situ major and trace element and boron isotope compositions for tourmalines from two-mica granites in the Cuona and Cuonadong leucogranites in the Cuona area are conducted to determine microscopic changes in mineral assemblages and geochemical compositions. Analytical results show that the tourmalines in the Cuonadong leucogranite were crystallized earlier relative to the tourmalines in the Cuona leucogranite during magmatic differentiation. The volatile contents have a genetic relationship with incompatible elements in tourmaline, which is possibly responsible for the formation of tourmaline zonation and the enrichment of Sr, Zn, and Pb during magmatic differentiation. The B isotopic composition of tourmaline in the Cuona area suggests that the granitic magma was dominantly derived from the partial melting of the metasedimentary source rocks. Their B isotope variations likely resulted from fluid exsolution during B-rich melt evolution. High rare metal contents in tourmalines indicate that the two-mica granites in the Cuona area may have great mineralization potential.

High-performance pinecone-like MOF derivative electromagnetic wave-absorbing composite via in situ anisotropic-oriented growth

Designing multihierarchical electromagnetic wave-absorbing composite with multiphase, multieffective, and multidimensional properties is an effective way to improve absorption performance. Metal–organic frameworks (MOFs) have a high metal content and a stable carbon framework. By adjusting the metal type, organic ligand type, and precursor ratio during the preparation process, MOF materials with different morphologies can be synthesized and transferred into multihierarchical electromagnetic wave-absorbing composites via in situ pyrolysis. Herein, based on the Kirkendall diffusion effect, an in situ anisotropic-oriented growth strategy was advanced during the pyrolysis of Prussian blue, and a new magnetic carbon composite (γ-Fe2O3 @N-rGO/MWCNT) was prepared. The composite has a multihierarchical structure consisting of pinecone-like nanoflowers and a porous carbon framework. The nanoflowers are core-shell structures with γ-Fe2O3 magnetic nanoparticles as cores and nitrogen-doped reduced graphene oxides as shells interspersed in a porous carbon framework that includes intertwined multiwalled carbon nanotubes and amorphous carbon. The minimum reflection loss (RLmin) of the samples can reach up to − 59.2 dB at 5.51 GHz. The in situ anisotropic-oriented growth strategy used in this work shows great promise for the preparation of a variety of multihierarchical structure nanocomposite electromagnetic wave-absorbing materials with abundant absorption effects.

Use of sewage sludge biochar as a catalyst in production of biodiesel through thermally induced transesterification

Sewage sludge (SS) is a residual/semi-solid material produced from industrial and municipal wastewater treatment processes. SS contains a high content of lipids and earth alkaline metals that can be used as catalysts for various chemical applications; however, its valorization has rarely been the focus of research. This study demonstrates that SS could be a promising raw material for biodiesel production and a biochar catalyst to promote the reaction kinetics of alkylation. Thermally induced transesterification of the SS extract (SSE) was performed in comparison with the conventional homogeneous reaction. SS biochar was fabricated via pyrolysis. The highest yield (33.5 wt.% per SSE) of biodiesel production was achieved in 1 min of reaction at 305 °C via thermally induced transesterification in the presence of SS biochar, while the yield of biodiesel from (trans)esterification with 5 wt.% H2SO4 was less than 1% even after 24 h. The reaction kinetics (< 1 min) of thermally induced transesterification was extraordinarily faster than that of conventional transesterification (3–24 h). The porous structure and high content of alkaline species in the SS biochar expedited the reaction kinetics. Consequently, the integrated/hybridized process for thermally induced transesterification and pyrolysis of the solid residue of SS was experimentally proved for the valorization of SS in this study. Considering that SS is being disposed of as a waste material and generates toxic chemicals in the environment, its valorization into value-added biodiesel and a catalyst could be an environmentally benign and sustainable technique.Graphical

Results of micrometallographic analysis of metalworking tools in graves of metallurgists in Moravia/Czech Republic

AbstractThe number of finds relating to metalworking, without evidence of mining and processing facilities, is very limited. In Final Eneolith graves of specialized metallurgists that have occurred, they contain a metal‐founding or metalsmithing toolkit, whose origins were from eastern Europe (the Maykop, Yamnaya Culture). Such metallurgical tools may have reached central Europe as part of the so‐called Yamnaya Package before the onset of the Bee Beaker Culture (BBC); and unlike the Pontic region, these two types of metallurgy separated here. There are found an accumulation of metallurgists' graves in Moravia, where the complete metalworking toolkit is deposited in a predefined place in richly furnished male graves with a distinctive funerary architecture that exhibit a clear relationship to the grave goods.EDX‐analysis detected a high content of metals (Cu, Ag, Au, Au–Ag alloy) on all working surfaces of stone tools, grinders, and boar tusks used for the final treatment of their metal products. This makes us believe that the used artefacts were laid as symbolical objects in the graves of these craftsmen who perfectly knew these advanced technologies. Due to their knowledge, their social significance gradually rose and finally reached the level of social elites, who were usually buried in a spectacular manner, including the quantity of grave goods (Überausstattung) and the pars pro toto deposition in one part of the finds.

Impacts of utilizing swine lagoon sludge as a composting ingredient

Lagoon sludge, a byproduct of swine operations in the Southeast United States, poses a management challenge due to its high mineral and metal content. Composting is a low-cost, scalable technology for manure management. However, limited information is available on composting swine lagoon sludge in terms of recipes, greenhouse gas emissions and end-product quality. Moreover, due to its high Zn and Cu content, high inclusion of sludge in composting recipes can potentially inhibit the process. To address these knowledge gaps, in-vessel aerated composting (0.4 m3each) was carried out to evaluate impacts of sludge inclusion, at 10% (Low Sludge, LS-Recipe) and 20% (High sludge, HS-Recipe) wet mass-basis, on composting process and end-product quality. Comparable maximum temperatures (74 ± 2.7 °C, 74.9 ± 2.9 °C), and organic matter loss were observed in both recipes. Similarly, sludge inclusion ratio had no significant impact on cumulative GHG emissions. The global warming potential (20-year GWP) for swine lagoon sludge composting using LS and HS recipes was observed to be 241.9 (±13.3) and 229.9 (±8.7) kg CO2-e/tDM respectively. Both recipes lost 24–28% of initial carbon (C) and 4–15% of nitrogen (N) respectively. Composting and curing did not change water-extractable (WE) phosphorus (P) concentrations while WE Zn and Cu concentrations decreased by 67–74% and 55–59% respectively in both recipes. End compost was stable (respiration rates <2 mgCO2-C/g OM/day) with germination index >93 for both recipes.

Effects of lignocellulosic biomass type on the economics of hydrothermal treatment of digested sludge for solid fuel and soil amendment applications

Digested sludge is a waste stream from anaerobic digestion (AD) in wastewater treatment plants. Hydrothermal treatment (HTT) of sludge mixed with lignocellulosic biomass is an attractive approach to improve sludge dewaterability and generate value-added products. However, process economics has not been well understood. In this study, firstly, the effect of biomass type on the energy properties of hydrochars was studied. Secondly, two scenarios were simulated to evaluate the effects of biomass type on the economics (processing 50,000 tonnes of sludge per year) of HTT of digested sludge for solid fuel and soil amendment applications. The two HTT scenarios included sludge alone and sludge-biomass mixtures (four cases for four biomass feedstocks) at 180 °C for 60 min. In both scenarios, HTT liquids were returned to existing AD facilities for biomethane production to offset the energy cost of the HTT process. The results showed that the higher heating value significantly increased from 16.0–17.0 MJ kg−1 in the sludge alone case to 18.0–23.0 MJ kg−1 in sludge–biomass mixtures (except for rice husk). With the use of saved transport cost as a revenue source, HTT of sludge–biomass led to a net present value (NPV) range of AU$ 9.9–20.3 million (20 years) and an internal rate of return (IRR) range of 25.0 %–45.2 % for solid fuel application of resulting hydrochar compared to an NPV of AU$ 18.4 million and an IRR of 55.0 % from HTT of sludge alone scenario. HTT of sludge-biomass led to a NPV range of AU$ 4.5–14.5 million and an IRR range of 17.2 %–35.7 % for soil amendment application while the hydrochar from HTT of sludge alone was not recommended for soil application due to the high contents of heavy metals. This study provides useful and critical information for process scale-up and commercialization for integration into wastewater treatment plants.

Preparation of highly dispersed lignite-char-supported cobalt catalyst for stably steam reforming of biomass tar at low temperature

The removal of generated tar during the biomass gasification is a serious issue. Catalytic tar cracking is one of the most efficient methods to reduce tar deposition while many common tar cracking catalysts suffer problems of serious carbon deposition and active metal sintering, especially at low temperatures. Therefore, developing catalysts with both high activity and stability is critical. In this work, we aim to prepare catalysts with a high active metal contents, a small metal particle size and a high dispersion to contribute to the highly efficient tar removal at relatively low temperatures. By adjusting the type and the concentration of the Co precursor solution when lignite is used as the carbon precursor, we prepared a series of catalysts which were then applied for both activity and stability test of the steam reforming of model tar and biomass tar. The results show that Co0.15-C2H3O2− prepared with a 0.15 M solution of Co(C2H3O2)2·4H2O achieves a Co content of about 16.0 wt% with an average particle size of about 3.77 nm and a relatively high metallic Co dispersion. For steam reforming of toluene, the catalyst achieves an almost 100 % toluene conversion at 400 °C and exhibits a high stability in the 100 h test. Moreover, Co0.15-C2H3O2−, which produces approximately 283.8 mL.gcorncob−1.gcat−1.h−1 H2 catalytically, is also active and stable in biomass tar cracking. The catalyst prepared in the present study by using the economic and simple ion-exchange method also has a well-dispersed nano-metal-loaded structure and can efficiently remove the tar at a low temperature with a high stability, which will contribute to the industrial application in the future.

Understanding the demetallization of nitrogen-rich hydrothermal liquefaction biocrudes by FTICR mass spectrometry: Recalcitrant effect of metalloporphyrins and basic nitrogenates

Higher metallic content in nitrogen-rich hydrothermal liquefaction (HTL) biocrudes is a bottleneck during downstream hydroprocessing, which is necessary for producing drop-in biofuels from urban residues and algal feedstocks. Therefore, this work explores a non-catalytic pathway for effective demetallization of nitrogen-rich HTL biocrudes obtained from sewage sludge and cyanobacteria (generally referred as Spirulina algae). Herein, we utilized five different organic/inorganic acids and comprehensively documented the effect of acid washing on basic nitrogen containing compounds (NCCs), oxygenates and organometallics. HTL biocrudes before and after acid washing were characterized by Fourier transform ion cyclotron resonance (FTICR) mass spectrometry (MS). FTICR MS showed the presence of iron porphyrins in cyanobacteria biocrude, whereas no sign of metalloporphyrins was observed in sludge biocrude. Moreover, cyanobacteria biocrude mostly contains basic NCCs (N1 and N2 species), whereas sludge biocrude apart from basic NCCs mostly contain fatty acids (O2 and O4 species). Due to the presence and absence of metalloporphyrins, acid washing (0.1 M H2SO4) showed ineffective demetallization (3.2 %) for cyanobacteria and effective demetallization 89.2 % for sludge biocrude. For cyanobacteria, 66.3 % demetallization was achieved at 10 M H2SO4 which not only degrades the biocrude but also accounts for 35 % organic loss. However, O1-O4 species in sludge biocrude represent acidic groups such as carboxyl groups; thereby, 20.1 % organic loss is encountered even at 0.1 M H2SO4. For both biocrudes denitrogenation via acid washing remains unfeasible due to high organic loss. Present results indicate that a priori information about organometallics, NCCs, and oxygenates in a given biocrude could provide guidance to select and further optimize the demetallization process.

Migration characteristics and ecological risk assessment of heavy metals in ash from sewage sludge co-combustion in coal-fired power plants

Co-combustion in coal-fired power plants is one of the main methods to dispose of municipal sewage sludge (MSS). The high heavy metals content of MSS increases the ecological risk of ash from the coal and MSS co-combustion. In response to this problem, the three types of fly ash or bottom ash from MSS co-combustion in the three coal-fired power plants were sampled. The properties of fly ash and bottom ash were analyzed in terms of ash composition, particle size distribution, heavy metals content and leaching characteristics. The potential ecological risks were evaluated using the ecological risk index assessment method. The results showed that the co-combustion of MSS had no significant effect on the ash composition order and heavy metals content order. However, the total content of Cu, Mn, Pb and Zn, Hg in the co-combustion ash was higher than that in the coal-fired ash without sludge blending but did not exceed the risk screening value for soil heavy metal contamination of residential land. Heavy metals showed significant enrichment in fly ash and dilution in bottom ash. The leaching concentrations of Cr and Ni were several times the limit value. The potential ecological risk levels of fly ash and bottom ash were moderate risk and high risk respectively. Cr and Hg were the main contributors to potential ecological risks. The contents of Cr, Hg and Ni need to be paid attention to in the subsequent utilization of coal ash mixed with co-combustion of sewage sludge.

Soil Quality Assessment from Areas of Great Mining Interest Using the Grey Clustering Method

Mining is one of the most important activities in Peru, although controversial because it is currently highly criticized for generating environmental liabilities that mostly contain a high content of metals which contaminate the different environmental components such as water. , soil, air, biodiversity and social among others, for the study and analysis of the soil in a specific area we will use the grey clustering methodology, which determines, based on the grey systems and it should be noted that for this analysis it was also used as a reference the parameters defined by the Kelley Directives, a clustering coefficient through various calculations and with these define the level of soil contamination in 5 sectors located in the communities of Michiquillay and La Encañada. With the calculated grey clustering coefficients, it was determined that, of the five sectors, only the Michiquillay sector presents a slight level of contamination, and the other sectors are in uncontaminated soils, at least for the parameters that were selected. Mining activity, the authorities in charge of measuring the environmental impact in the sector, can proceed to investigate and infract if the permitted limits are exceeded and these have not been correctly remedied. The results of this study could be an important contribution for the analysis of soil contamination and the impact on the same of future mining projects that are developed in Michiquillay and La Encañada communities studied, how much the natural conditions of the soils have changed after the operation of the mine. Keywords—Grey Clustering, Grey Systems, Mining Activities, Soil Quality.

High metal content of highly accreting quasars: Analysis of an extended sample

Context. We present an analysis of UV spectra of quasars at intermediate redshifts believed to belong to the extreme Population A (xA), aimed to estimate the chemical abundances of the broad line emitting gas. We follow the approach described in a previous work, extending the sample to 42 sources. Aim. Our aim is to test the robustness of the analysis carried out previously, as well as to confirm the two most intriguing results of this investigation: evidence of very high solar metallicities and a deviation of the relative abundance of elements with respect to solar values. Methods. The basis of our analysis are multicomponent fits in three regions of the spectra centered at 1900, 1550, and 1400 Å in order to deblend the broad components of AlIIIλ1860, C III]λ1909, CIVλ1549, He IIλ1640, and SiIVλ1397+OIV]λ1402 and their blue excess. Results. By comparing the observed flux ratios of these components with the same ratios predicted by the photoionization code CLOUDY, we found that the virialized gas (broad components) presents a metallicity (Z) higher than 10 Z⊙. For nonvirialized clouds, we derived a lower limit to the metallicity around ∼5 Z⊙ under the assumption of chemical composition proportional to the solar one, confirming the previous results. We especially relied on the ratios between metal lines and He IIλ1640. This allowed us to confirm systematic differences in the solar-scaled metallicity derived from the lines of Aluminum and Silicon, and of Carbon, with the first being a factor ≈2 higher. Conclusions. For luminous quasars accreting at high rates, high Z values are likely, but Z-scaled values are affected by the possible pollution due to highly-enriched gas associated with the circumnuclear star formation. The high-Z values suggest a complex process involving nuclear and circumnuclear star formation and an interaction between nuclear compact objects and an accretion disk, possibly with the formation of accretion-modified stars.

Phenomena and mechanism of slagging and corrosion in energy use of coal with a high content of salts

Purpose. Determination of the main mechanisms of slagging and corrosion of heating surfaces when using coal or other raw materials with a high content of alkali and alkaline earth metals. Experimental determination of mineral phases of ash residues of burning composite raw materials with the participation of salty coal and the influence of component composition on the formation of refractory compounds. Methodology. Critical analysis and generalization of achievements in the developed theories of slagging and corrosion of surfaces during the combustion of problematic carbon raw materials (salty coal, biomass, some wastes, etc.). Determination of the main approaches to the problem of using coal with a high pollution factor. Selection of objects of experimental study on composite raw materials, including coal of different degrees of metamorphism and salinity. Identification of minerals of ash residues of individual fuels and their blends using X-ray phase analysis (X-ray diffraction). Semi-quantitative phase analysis of diffractograms was performed using MATCH! software. Findings. Modern views on the causes of slagging and corrosion processes during the combustion of fuel with a high salt content are highlighted. It has been determined that the process of intensive slagging is associated with a certain ratio of sodium, calcium and iron compounds. The composition and features of the mineral phases of ash residues of composite fuel with the participation of salty coal are experimentally established. The influence of the content of components on the formation of certain mineral phases of mixed ash was determined. Originality. For the first time, the prospects of using two-component blended fuel with the participation of Ukrainian salty coal have been studied. The analysis of minerals in ash residues of salty coal and its blends was carried out. It has been determined that the main part of Na in ash of salty coal of the Bohdanivske deposit in the Northern Donbas is in the form of sulfates and silicates. For the first time, the composition and ways of formation of new refractory mineral compounds in the ash formed during the combustion of composite fuel from coal of different metamorphism and salinity have been established. Practical value. Based on the analysis of literary sources and conducted studies, the dependence of the ash composition on the minerals of the initial fuel and on the ratio of various components in the blends was determined. The proposed approach has a predictive power, as it allows predicting the formation of the main refractory ash minerals. The expediency and prospects of involving salty coal in the fuel base of Ukraine as a component of blended fuels are shown.

Nickel-Doped Carbon Dots as an Efficient and Stable Electrocatalyst for Urea Oxidation.

Urea is a typical contaminant present in wastewater which may cause severe environmental problems. Electrochemical catalytic oxidation of urea has emerged as an efficient approach to solve this problem. Nevertheless, the current nickel-based catalysts (e.g., nickel hydroxide/sulfides) feature a high metal content. It not only lowers the utilization efficiency of nickel but also causes secondary pollution to the environment. Here, nickel-doped carbon dots (Ni-CDs) with an excellent and stable catalytic activity for the electrocatalytic urea oxidation reaction (UOR) are reported. Specifically, carbon dots (CDs) with abundant functional groups are synthesized by a one-pot hydrothermal method and then Ni-CDs with a very low metal content (1.1 at%) are prepared. The Ni2+ sites by coordination with carboxylic groups on the CDs provide excellent electrocatalytic activity and excellent durability for the UOR, as demonstrated by an anodic current density of 100mA cm-2 at a potential of 1.38V (vs RHE) and similar experimental results in practical application. To the best of knowledge, this is the first report of CDs-based materials applied for the UOR, which opens an important new area of applicability for CDs as well as broadens the scope of the materials for electrochemical catalysis of urea.

Land Use Based Distribution Pattern, Fractionation forms and Health Risk Assessment of Heavy Metals in Mining-affected Soils of Western Ghat of Goa, India

Goa is a biodiversity hotspot and a major iron ore producer state in India. The study investigated heavy metal (HM) distribution pattern, fractionation forms under different land use types near an iron mining including health risks associated with different exposure pathways. Georeferenced 38 soil surface samples, 8 soil profile samples and 6 plant samples were collected from three land use types- agriculture cropland, fallow land and natural vegetation. Collected samples were analyzed for HM contamination in inductively coupled plasma atomic emission spectrophotometer (ICPAES). The mean total HM concentration in surface soil exceeded the background value. Weak acid soluble fraction % of metals posed no to medium risk values. Fallow land had higher metal content in surface soil. Principal component (PC) analysis showed Pb, Cd and Cr metals were more associated with mining activity. Vertical distribution pattern of HM accumulation in soil profiles showed a drastic reduction in HM concentration below plough layer in fallow land indicating anthropogenic sources of origin. Hazard index (HI) in the descending order were Cd&gt; Cr &gt;Pb. Non-carcinogenic HI value were considerably higher than safe level. Higher organic carbon (OC) and clay content in soil had a tendency to accumulate ample HM in unavailable form due to chelation effect. Soils had higher pool of unavailable residual HM as compared to available. Overall the land uses are in medium risk category and site specific management is requisite of the time to maintain the balance of this fragile ecosystem with anthropogenic activities in long run.

Development of biomass-fired circulating fluidized bed boiler with high steam parameters based on theoretical analysis and industrial practices

Further improvement of steam parameters is essential to developing biomass-fired circulating fluidized bed (CFB) boiler technology, which necessitates solving severe slagging, fouling, agglomeration, and corrosion problems caused by the high content of alkali metals and chlorine in biomass fuels. Studies indicate that by arranging the high-temperature heating surfaces inside the furnace, the slagging and corrosion of the surface can be effectively lightened through the continuous wash and cleaning by solid circulating ash. Meanwhile, the ash fouling on the convective heating surface can be mitigated by applying in-line tube bundles with large intercept, small tube diameter, and parallel flow design. In addition, the significant improvement of circulating loop performance can not only alleviate the bed agglomeration but also help increase the boiler efficiency, decrease slagging on the heating surface, and reduce the NOx emission. Series biomass-fired CFB boilers with high steam parameters have been successfully established based on these technical routes, including one 125 MW super-high pressure boiler with the largest capacity and the highest steam parameters in Asia. Lone-term operational data from four commercial CFB boilers show that they can operate stably within a wide range of load ratios, from 30% to 105%, and continuous operation time can last more than half a year. Moreover, the boiler efficiency can reach up to 90%–93.5%, and the NOx and SO2 emissions can be stably controlled lower than the ultra-low emission standard in China. The variation of some operation parameters with boiler load was also discussed in this work.