Cr Concentration Research Articles

Assessment of potentially toxic element contamination in wetland sediments of Boracay Island, Philippines

Boracay Island, Philippines, famous for its white sand beaches, has wetlands increasingly threatened by human activities. This study evaluated the ecological state of Boracay Island's wetlands and assessed the consequences of anthropogenic activities on sediment quality. Results showed that sediments from Wetland Nos. 3 and 4 have higher concentrations of potentially toxic elements (PTEs) than Wetland No. 1. Comparative analysis with other Southeast Asian wetlands revealed that Boracay's sediments contain the highest average values of As, Cd, Cu, Ni, Zn. Enrichment factor values suggest that the moderate enrichment of Cd, Cr, Cu, Mo, Pb, and Zn in the wetland sediments can be attributed to anthropogenic activities on the island. Elevated concentrations of Cr, Cu, and Zn above interim sediment quality guidelines indicate occasional adverse biological effects on aquatic biota. These findings provide a crucial baseline for future pollution monitoring and highlight the need for ongoing conservation efforts in Boracay's wetlands.

Understanding Stacking Fault Tetrahedron Formation in FCC Stainless Steel: A Fusion of Transmission Electron Microscopy, Molecular Dynamics, and Machine Learning

The stacking fault tetrahedron (SFT) formation displays a pronounced size effect, progressing from vacancy equilateral triangular plate to perfect SFT, and eventually to truncated SFT, as demonstrated in numerous irradiated face-centered cubic metals. However, the presence of distinct SFT structures in F321 stainless steel has not been reported. This study explored the SFT formation mechanism in irradiated F321 stainless steel using transmission electron microscopy (TEM), molecular dynamics (MD) simulations, and machine learning. SFTs, Frank loops, and Lomer-Cottrell locks were found to be widely generated in the irradiated F321 steel. The critical size for truncated and perfect SFTs was determined using MD simulations; the results were consistent with the theoretical predictions. Additionally, the twin boundaries observed through TEM, which were attributed to the elevated tensile stress near the boundaries, facilitated the formation of perfect SFTs. Moreover, interstitial Frank loops also facilitated the formation of perfect SFTs. This study also explored the influence of variations in Ni and Cr concentrations on the critical size n1 for the transition from vacancy plates to perfect SFTs and n2 for the transition from perfect SFTs to truncated SFTs, using a combination of MD and machine learning methods. As the Ni concentration increased and the Cr concentration decreased, n1 and n2 increased; conversely, the critical sizes decreased when the Ni concentration decreased and the Cr concentration increased. These insights reveal the systematic mechanism of SFT formation under varied conditions, offering new perspectives for understanding the nano-defects in F321 stainless steel.

Heavy metal migration and enrichment in desulfurization wastewater during low-temperature triple effect evaporation process

Zero discharge of desulfurization wastewater from coal-fired power plants has become important. Desulfurization wastewater and gypsum from different stages of the low-temperature triple-effect evaporation process of a coal-fired power plant were collected and investigated. The results showed that after low-temperature triple-effect evaporation, the concentrations of Na+, Mg2+, K+, and Cl− in the desulfurization wastewater increased by 7.91, 7.15, 8.49, and 8.35 times, respectively. With the progress of low-temperature triple effect evaporation process, the concentrations of As, Cd, Co, Cr, Cu, Mn, Se, and Zn in the wastewater after the triple effects were 5.85, 75.44, 1.28, 2.34, 13.66, 5.58, 8.59, and 4.35 times higher than those in the raw wastewater. Mn and Se exceeded the emission limits by 40 and 10 times, respectively. After triple-effect evaporation, the concentrations of As, Cd, Co, Cr, Cu, Pb, Se, and Zn in gypsum decreased to 46%, 26%, 66%, 41%, 35%, 97%, 39%, and 51% of the raw gypsum, respectively. Compared with that of other metal sulfates, the solubility of PbSO4 was extremely low under low-temperature conditions, and some PbSO4 precipitated during the triple-effect evaporation process, leading to a gradual decrease in the Pb concentration in the liquid phase. The mercury compounds in gypsum after the first and second effects were the same as those in raw gypsum, both of which were HgS and HgO. After third effect, the mercury compound in gypsum also included HgSO4. In addition, owing to the promoting effect of the pH of desulfurization wastewater approaching 5.50 on the generation of HgS, the proportion of HgS gradually increased, and the proportion of HgO gradually decreased from the raw gypsum to the third effect gypsum. Therefore, the stability of the mercury compounds in gypsum was enhanced. It can provide a good reference for the migration and enrichment of heavy metals in the low-temperature triple-effect evaporation process, which is beneficial for the clean production and efficient utilization of coal.

Metal concentration in honeybees along an urbanization gradient in Central Mexico

Urbanization is rapidly increasing worldwide, leading to rising levels of pollution, one of the major drivers of environmental change; yet little is known about the relationship between urbanization intensity and pollution levels in pollinator taxa. Toxic metals are among the most common contaminants in urban environments, but few data exist on their presence in the flora and fauna of cities in Latin America, one of the world's most urbanized and biologically diverse regions. In this study, we used an urban-rural gradient approach to analyze the relationship between the concentrations of eleven metals present in adult honeybees (Apis mellifera) and the degree of urbanization within twelve landscapes in the metropolitan area of Pachuca, Hidalgo, which forms part of the megalopolis of Mexico City. Metal concentrations were compared with previously reported values contrasting honeybees from urban and rural areas after standardizing urbanization levels among published reports. The concentrations of Ag, Cr, Cu, and Zn in honeybees increased significantly with the degree of urbanization. Urbanization was not found to influence the levels of Al, Ba, Cd, Mn, and Sr in honeybees. The maximum concentrations of six metals in our urban sites (Al, Ba, Cd, Cu, Mn, and Sr) were higher than the maximum values reported for bees in other urban areas. The concentrations of two metals measured in our study (Cr and Zn) were within the range of values previously published for urban areas. Compared to other studies, we did not detect Pb in the body of honeybees. We conclude that the concentrations of Ag, Cr, Cu, and Zn present in honeybees are a quantitative reflection of the degree of urbanization in central Mexico. Our results highlight the need to monitor metal emission sources in this and other areas and investigate their effects on bees and other pollinator taxa.

Compositional-geochemical characterization and multi-element pollution and risk assessment of potentially toxic elements in the urban landfill soil

Urban areas are characterized by the presence of various pollution sources including landfills. During the recent decade, urban landfills were investigated as a source of pollution by potentially toxic elements and potential deposits for landfill mining. The contents of Cr, V, Ti, Ca, K, Mo, Zr, Sr, Rb, As, Zn, Cu, Co, Fe, Mn, Pb, Ba in soils of Vanadzor city landfill site (VL) were determined using the X-ray fluorescence spectrometer to assess multi-element pollution and ecological risk and to identify potentially toxic elements geochemical associations through the application of compositional data analysis. The results showed that Cr, Mo, Zn, Cu, and Pb displayed significant values (>100%) of coefficient of variation suggesting their anthropogenic origin. Moreover, these elements, except Cr, displayed outliers and extreme values in the same sampling sites located directly on the reclaimed part of the landfill. The median contents of Zn, Pb, Cu, Cr, Cd, and As exceeded the global median values by 8.2, 9.8, 19.0, 4.6, 6.1, and 4.5 times, respectively. The multi-element pollution assessment showed that an extremely hazardous level of pollution was observed on the reclaimed part of the VL. From this site, a trend of decrease in the pollution level was observed in the eastern and western directions. In contrast, an allowable level of pollution was observed in the northern part - toward the direction of the above-located hill. The VL was found to be in an inferior ecological condition (a very high level of potential ecological risk was observed), which might also have a negative impact on the ecosystems located in its vicinity. The hierarchical clustering has revealed that the studied elements are grouped in two geochemical associations: a naturally formed - Co, Fe, V, Ti, Mn, Sr, Zr, Rb, K, Ba, As; and an anthropogenic one - Zn, Pb, Cu, Ca.

Heavy metals in commonly consumed rice grains in Bangladesh and associated probabilistic human health risks

Food contamination by heavy metals is a concerning issue worldwide. The presence of elevated levels of heavy metals in commonly consumed rice has emerged as a critical issue in ensuring food safety. This research encompassed the collection of 44 rice samples, representing seven distinct varieties, through a randomized sampling approach across various retail markets within Dhaka city. The investigation of heavy metal content (including Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Hg, and Pb) within the rice samples was carried out employing Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The findings disclosed substantial disparities in heavy metal concentrations among the different rice varieties. Notably, the concentrations of Cr (0.99 mg/kg), Fe (8.35 mg/kg), Pb (0.49 mg/kg), and Co (0.02 mg/kg) were observed to exceed the established maximum permissible limits. This contamination of the rice varieties may stem from either natural processes or human activities. Utilizing these metal concentrations, this study employed Monte-Carlo simulation to calculate health risk and probabilistic health risk. The Target Hazard Quotients (THQs) for Cr, Fe, and As exceeded the threshold of 1 in each rice variety, particularly in Amon and Lal Biroi in Mymensingh, Najirshail in Bogra, 28 in Sherpur and Kushtia, Miniket in Bogra and Rajshahi, and lastly, paijam in Rangpur and Tangail. Furthermore, the Hazard Index (HI) exceeded 1 in all rice varieties, implying that the consumption of these selected rice grains may have a substantial impact on overall food quality and its potential health consequences. Both carcinogenic risk and probabilistic risk for As, Ni, Cd, Cr, and Pb were found to surpass the threshold levels and safe limits, respectively. This suggests that individuals who have regularly consumed these rice varieties may face a heightened probability of developing cancer in the future, as predicted. According to sensitivity analysis, metal concentration and food ingestion rate (FIR) are the most relevant components that contribute to the significant impact of carcinogenic health hazards. Finally, the study concluded that heavy metal intake from food poses a risk to human health, necessitating the effective monitoring based on each geographic location and identify the source of this heavy metal to limit its exposure.

Chromium uptake and its impact on antioxidant level, photosynthetic machinery, and related gene expression in Brassica napus cultivars.

The development of heavy metals, particularly chromium (Cr)-tolerant crop cultivars, is hampered due to lack of understanding of the mechanisms behind Cr stress tolerance. In this study, two Brassica napus cultivars, ZS758 and ZD622, were compared for Cr stress resistance by using the chlorophyll a fluorescence technique and biochemical characteristics. In both cultivars, Cr stress dramatically decreased PSII and PSI efficiency, biomass accumulation, and antioxidant enzyme levels. Although, cultivar ZS758 showed reduction in oxidative stress by decreasing the production of reactive oxygen species (ROS) in terms of reduced H2O2 and MDA content and increased enzymatic activities of key antioxidants enzymes including SOD, APX, CAT, and POD activities that play a crucial role in the regulation of numerous transcriptional pathways involved in oxidative stress responses. Higher non-photochemical quenching (NPQ) and QY were found in tolerant ZS758 cultivar under Cr stress, indicating that tolerant cultivar had a greater capacity to preserve PSII activity under Cr stress by enhancing heat dissipation as a photo-protective component of NPQ. Lower PSI activity and electron transfer from PSII were confirmed by lower PSI efficiency and higher donor end limitation of PSI in both rapeseed cultivars. The Cr concentration was greater in the ZD622 as compared to ZS758, which affected the mineral nutrients profile and damaged the cellular ultrastructure and related gene expression levels. However, current study suggest that cultivar ZS758 is more resistant to Cr stress than ZD622 due to improved metabolism and structural integrity and Cr stress tolerance that is linked with the increased PSII activity, NPQ, and antioxidant potential; these physiological characteristics can be exploited to select cultivars for Cr stress tolerance.

Immobilization of Pb, Cd, and Cr in contaminated soil around mining areas using Mg/Al LDH-zeolite and evaluation of maize growth

Abstract This study conducted simultaneous adsorption of Pb, Cd, and Cr ions using Mg/Al LDH-zeolite on contaminated soils from lead-zinc and tin mining areas. The optimal conditions were a 3% adsorbent-to-soil ratio, a 30-day incubation period, and 70% soil moisture. Characterization of the materials revealed that Mg/Al LDH-zeolite has superior physicochemical properties to natural zeolite, with a higher surface area and better adsorption capacity. Results indicated significant reductions in exchangeable heavy metal content: in lead-zinc mining area soil, exchangeable Pb decreased from 139.79 mg kg−1 to 10.95 mg kg−1, Cd−1 from 1.518 mg kg−1 to 0.533 mg kg−1, and Cr from 2.636 mg kg−1 to 0.461 mg/kg using Mg/Al LDH-zeolite. In tin mining area soil, exchangeable Pb decreased from 583.97 mg kg−1 to 48.22 mg kg−1, Cd−1 from 0.498 mg kg−1 to 0.122 mg kg−1, and Cr from 106.095 mg kg−1 to 38.038 mg/kg. Maize cultivation on post-adsorption soil showed improved growth performance, with plants exhibiting increased height and ear and reduced heavy metal accumulation in roots, shoots, and grains. Pb, Cd, and Cr concentrations in maize roots decreased significantly, with Pb reducing to 0.113 mg kg−1 in the lead-zinc area and 0.203 mg kg−1 in the tin area, Cd reducing to 0.061 mg kg−1 and 0.037 mg kg−1, respectively, and Cr reducing to 0.036 mg kg−1 and 0.243 mg kg−1 respectively. Mg/Al LDH-zeolite consistently demonstrated higher efficiency in reducing the bioavailability and translocation of heavy metals in maize tissues, confirming its potential as an effective adsorbent for soil remediation. Key mechanisms, including adsorption, surface complexation, ion exchange, precipitation, and structural incorporation, reduce metal mobility and bioavailability.

Passive behavior of TNB intermetallic and Inconel 625 in electrochemical machining

The TNB alloy, a novel lightweight material, shows great potential for application in crucial aero-engine parts. This paper reveals the passive behavior of TNB alloy in electrochemical machining (ECM), Inconel 625 alloy was used for comparison. The polarization curve shows that TNB and Inconel 625 alloys have obvious passivation phenomenon at the passivation potential. Research reveals that the passive film structure of TNB alloy comprises a compact layer (about 7 nm) and a loose layer (about 13 nm), with significantly higher corrosion resistance in the compact layer compared to the loose layer. In contrast, the passive film structure of Inconel 625 alloy is a single layer with a thickness of approximately 11 nm. It was also found that the passive film composition for TNB alloy is TiO2, Al2O3, and Nb2O5. The composition of passive film for Inconel 625 alloy is NiO, Ni(OH)2, Cr2O3, MoO3, Nb2O5, FeO, and Fe2O3, and the content of Ni and Cr is high. TNB alloys exhibit uneven and loose lamellar morphology at low current densities, but can reach Ra 0.15 μm at greater than 15 A/cm2. There are always some disordered carbides rich in Nb and Mo on the surface of Inconel 625 alloy. Quantitative models were developed for both alloys to describe their electrochemical dissolution behavior.

Distribution and contamination of trace elements in surface sediments of the Yellow River Estuary and Laizhou Bay, China

Abstract This study analyzed trace elements (Cu, Pb, Zn, Cr, Cd, As, and Hg) in 42 surface sediment samples collected from the Yellow River Estuary and Laizhou Bay to characterize their spatial distributions and pollution statuses. Determination of trace elements was carried out by ICP-MS for Cu, Pb, Zn, Cr, and Cd, and by AFS for As and Hg. The results showed that the average concentrations for Cu, Pb, Zn, Cr, Cd, As, and Hg were 13.21 mg kg−1, 10 .61 mg kg−1, 21 .03 mg kg−1, 24 .41 mg kg−1, 0.14 mg kg−1, 6.47 mg kg−1, and 14.15 μg kg−1, respectively. All the trace elements were classified in the first-class sediment according to the Chinese national standard ‘Marine Sediment Quality’. The higher concentrations and pollution levels were found in the eastern Yellow River estuary which due to inputs from the Yellow River, and northeastern Laizhou Bay which could be attributed to the impacts of human activities at Longkou Port. This study has important scientific value for further understanding the source-sink effects of pollutants and regional environmental effects of heavy metals.

Characterization of Cr(VI)-reducing indigenous bacteria from a long-term tannery waste-contaminated soil

This paper investigated the Cr (VI) detoxification potential of 4 novel bacterial strains isolated from a long-term tannery waste-contaminated soil. Molecular techniques were used to identify the bacterial strains using 16 S rDNA gene sequencing. The Cr (VI) detoxification capacity of the bacteria was determined by 1,5-diphenylcarbazide (DPC) methods. The identified bacterial strains were Bacillus subterraneus MMKT-10, Klebsiella quasivariicola MMKT-15, Acinetobacter seohaensis MMKT-19, and Staphylococcus saprophyticus MMKT-25. All the strains showed maximum tolerance concentration (MTC) of Cr (VI) up to 4000 mg/L. However, in terms of Cr(VI) reduction rate, K. quasivariicola can be considered the most efficient, reducing the two preliminary Cr(VI) concentrations (10 and 20 mg/L) at 15 and 18 h, respectively, while the rest of the strains needed 30 h to reduce the same concentrations from the culture medium. The favorable temperature for Cr(VI) detoxification ranged from 30–40 °C. However, 100 % Cr (VI) reduction was achieved by all the strains at 35 0C. Interestingly, all the bacterial strains reduced a significant amount of Cr (VI) at 50 0C, indicative of their thermotolerant nature. The ideal pH for Cr (VI) reduction was 7 for B. subterraneus MMKT-10 and K. quasivariicola MMKT-15, whereas it was 8 for Acinetobacter seohaensis MMKT-19 and Staphylococcus saprophyticus MMKT-25. The indigenous bacterial strains isolated in this study could be one of the promising candidates for the detoxification of Cr (VI) contaminated sites.

Sediment evaluation indices point to cadmium and selenium contamination: A simultaneous analysis of potentially toxic elements in the water and sediment along the upper and middle Awash River, Ethiopia

This study presents a simultaneous analysis of potentially toxic elements (PTEs) in the water and sediment of the upper and middle Awash River for the first time. We used standard field and laboratory procedures, sediment assessment indices and guidelines, and multivariate statistical methods to analyze PTEs and assess their possible sources. Water and sediment samples were collected from nine sampling sites, and PTEs were analyzed using the Inductively Coupled Plasma Optical Emission Spectrometer. The PTEs concentrations arranged in descending order in water were Fe>Mn>B>Zn>Cr>Ni>Pb>Cu, ranging between 4.14 ± 2.093 mg L 1 and 0.074 ± 0.016 mg L 1. The level of PTEs in the sediment varied between 24,493.6 ± 16,640.3 mg kg-1 and 0.4 ± 0.2 mg kg-1 and follows the order: Fe>Mn>Cr>Zn>Pb>Ni>B>Se>Co>Cu>Cd>Hg>As. The river-mouth of the upper Awash had the highest concentrations of Mn, Ni, Cr, and Cu in water and Fe, Mn, Cr, Ni, Pb, Co, Se, Cu, Cd, and AS in the sediment. Contamination factor, enrichment factor, and geo-accumulation index showed a very high level of contamination of Se and Cd. The ecological risk index, Nemerow pollution index, and pollution load index also indicated a high ecological risk and pollution by PTEs in the river. The levels of Fe, Pb, Ni, Mn, B, and Cr in the water surpassed Ethiopian/WHO's drinking water guidelines, while the levels of Cd, Hg, and Cr in the sediment exceeded Canadian/Ontario's probable/severe effect levels. This study revealed the presence of ecological degradation at the downstream sites of the upper and middle Awash. The most likely sources of contaminants were identified as small-scale agricultural pollution, residential and commercial waste from towns like Addis Ababa, Merti, and Metehara, and the inflow of Lake Beseka. We recommend an integrated management plan for the Awash River to ensure sustainable use of the water, guarantee the well-being of wildlife, and reduce public health risks.

Size distribution, sources and chemistry of ultrafine particles at Barcelona-El Prat Airport, Spain

The rapid expansion of the aviation sector raises concerns about air quality impacts within and around airports. Ultrafine particles (UFP, diameter < 100 nm) are of particular concern due to their potential adverse health effects. In this study, particle number concentrations (PNC), particle number size distribution (PNSD), and other ancillary pollutants such as particulate matter (PM), nitrogen oxides (NOX), black carbon (BC), sulfur dioxide (SO2), ozone (O3), carbon monoxide (CO) and benzene, as well as organic markers and trace elements (in quasi-UFP) were measured at Barcelona-El Prat Airport (80 m and 250 m from the main taxiway and runway). Comparisons were made with an urban background (UB) location, and source apportionment of PNSD was performed using Positive Matrix Factorization (PMF). PNC inside the airport was nine-fold higher than the UB, and fifteen-fold higher when considering only nucleation mode particles (< 25 nm). Six sources contributing to PNC were identified inside the airport: Taxiing (48.7 %; mode diameter = 17 nm), Industrial/Shipping (7.4 %; mode diameter = 35 nm), Diesel (3.9 %; mode diameter = 64 nm), Regional recirculation (1.1 %; mode diameter = 100 nm), Photonucleation (16.6 %; mode diameter = 13 nm) and Takeoff (18.5 %; mode diameter = 23 nm). Due to the measurement location and prevailing wind patterns, no significant contributions from landings were detected. Chemical analysis of quasi-UFP collected on Electrical Low-Pressure Impactor (ELPI + ) filters (stages 2 to 6: 17–165 nm) revealed higher concentrations (> 2-fold) of Fe, Al, Cr, Cu, Mo, Mn, Pb, Ti, and Sb at the airport compared to the UB, with Al exhibiting the most pronounced disparity. Generally, PAH levels were low at both sites, although concentrations were higher at the airport relative to the UB. Overall, this study provides a comprehensive understanding of UFP within a major European airport, identifying the different sources contributing to PNC and PNSD.

Understanding the role of alloying elements Cr, Ni in erosion–corrosion process of nuclear grade austenitic stainless steel 304 L by total reflection X-ray fluorescence

Stainless steel (SS) has gained an indispensable position as one of the most widely used industrial material. In nuclear industry, it is one of the technologically most important structural materials used in pressure tube, containment vessel and reprocessing-related applications. In fact, SS 304 L is the workhorse material of the reprocessing plant which faces the hostile conditions of acid, temperature as well as high radiation dose. These conditions can affect the erosion-corrosion behavior of the material and can lead to poor mechanical properties. This also affects the life of the reactor components. In the present study, a systematic work has been carried out to develop an in-depth understanding of the Corrosion Rates (CRs) with respect to the loss of major and minor elements from SS into the corrosive nitric acid medium using Total reflection X-Ray Fluorescence (TXRF). The effect of acid molarity as well as temperature, on the erosion-corrosion behavior of SS304L was studied. The TXRF studies have revealed that the CR was maximum in 2 M HNO3 and minimum in 8 M, showing that as the nitric acid molarity has an important role to play in the corrosion and as the molarity increases, the passivation of SS 304 L also increases. This observation was further corroborated with the concentrations of Fe, Cr and Ni, which had leached into the nitric acid medium. The role of alloying elements, Cr and Ni, in the passivation of SS was also studied. The effect of temperature showed that at 45 °C, the rate of corrosion was minimum, as compared to at 25 °C and 90 °C which reveals that the formation of chromium oxide passive layer was thermodynamically most favorable at this temperature.

Comprehensive analysis of nutritive and toxic metal contents in canned tuna: Implications for safety and consumer health

Ca, Mg, K, Na, Fe, Cu, Mn, Zn, Ni, Cr, As, Cd, Pb and Hg levels of canned tuna fish marketed in Turkey were determined by inductively coupled plasma mass spectrometry. Ca content ranged from 80 to 2930 mg/kg, Mg from 900 to 1910 mg/kg, Na from 5930 to 12130 mg/kg, and K from 6930 to 44340 mg/kg. Fe (4.73–27.34 mg/kg), Cu (0.21 and 0.98 mg/kg), Mn (0.12–0.44 mg/kg), Zn (32–45 mg/kg), Ni (0.88–2.06 mg/kg) and Cr (0.03–0.11 mg/kg) contents of the canned foods did not exceed the provisional tolerable weekly intake limit. Cd was detected in two groups (C4=0.02 mg/kg, C18=0.15 mg/kg), while Pb was found in one group (C10=0.48 mg/kg). As content ranged from 0.27 to 1.75 mg/kg in all groups. Most of the tuna cans contained Hg between 0.046 and 0.099 mg/kg, but the highest concentration was found in sample C4 (0.81 mg/kg). Based on the increased lifetime cancer risk findings, the consumption limits of Group 4 and Group 14 should be limited to around 60 g/week (less for children). As a result of the findings that were obtained from this study careful observations should be followed up for the safer consumption of canned tuna.

Citric acid functionalized chitosan hydrogel beads for enhanced Cr(VI) removal: Experimental assessment and COMSOL modelling of adsorption in a fixed-bed system

Chitosan hydrogel beads (CHB) and cross-linked CHB functionalized with tricarboxylic citric acid (CA-GLA-CHB) were synthesized and used for the removal of Cr(VI) from aqueous solutions in batch and dynamic adsorption systems. Applicability of COMSOL Multiphysics software as a tool for predictive modelling of column dynamics using a minimum set of experimental parameters was tested and compared with experimental results. Batch experiments demonstrated that CA-GLA-CHB showed almost 20% higher adsorption capacity and wider operational pH range compared to non-functionalized CHB. In a dynamic system, CA-GLA-CHB was used as column packing material and the column dynamics was investigated at different conditions. The breakthrough and exhaustion time of the column increased with an increase in bed height and a decrease in feed flow rate and initial Cr(VI) concentration. Computational modeling by COMSOL software with implemented Advection-Dispersion-Reaction (ADR) equation was used to simulate breakthrough curves for the applied dynamic system in order to validate the possibility of its application for process design in the scaled-up fixed-bed column systems for wastewater treatment. The simulated breakthrough curves of Cr(VI) adsorption matched well with the experimental, thus proving that COMSOL Multiphysics software can be used for scaling-up fixed-bed column systems packed with low-cost and effective CA-GLA-CHB bioadsorbent.

The PDINH decorated NH2-UiO-67 MOF for promoted photocatalytic Cr(VI) reduction: Performance, and mechanism

A series of composite materials comprising NH₂-UiO-67 metal-organic framework (MOF) and highly π-conjugated 3,4,9,10-perylenetetracarboxylic diimide (PDINH) was synthesized via a facile ball-milling process. These hetero-conjugated MOFs, denoted as PNU-67(X) with varying amounts of PDINH (X = 0.5 %, 1 %, 2 %, and 3 % wt), were evaluated for their photoreduction of Cr(VI) to Cr(III) under visible light irradiation. Systematic investigations revealed a direct correlation between increasing PDINH content and enhancing the conductivity of the MOFs. Additionally, the incorporation of PDINH motifs significantly improved CO₂ capture capability by increasing charge transfer, charge separation, and light absorption. To elucidate the impact of various factors on the photocatalytic performance of PNU-67(3) in Cr(VI) remediation, a comprehensive study was conducted. These factors included pH, initial Cr(VI) concentration, catalyst dosage, scavengers, and scavenger concentration. Notably, PNU-67(3) (5 mg/L) demonstrated 100 % photoreduction efficiency within 35 min, highlighting its potential application in catalyst loading and efficiency compared to other reported UiO-type MOFs. Furthermore, the composites exhibited exceptional stability and reproducibility throughout multiple experimental cycles. Overall, this research presents a promising avenue for constructing heterojunction photocatalysts by integrating MOFs and organic PDINH molecules, offering a viable solution for wastewater remediation.

A study on microstructure evolution of MCrAlY coatings after thermal aging in Te environment

The effects of thermal exposure on tellurium (Te) diffusion behavior in MCrAlY coatings were investigated at 800 °C in Te vapor. The results showed that the diffusion depth of Te in MCrAlY coatings gradually increased with the exposure time, and the dense Cr3Te4 layer formed on the coating surface in the initial stage was no longer continuous, especially under aging conditions with higher Te concentration. The high Cr content of the coating promoted the solid phase transition of the surface reaction product from Cr3Te4 to Cr7Te8, and resulting in the formation of large α-Cr phase either within or beneath the reaction layer during long aging processes. As a result of this phase transition, excess Te atoms were released from Cr3Te4 and continued to diffuse into the coating. Te did not exhibit obvious intergranular diffusion characteristics within the coating. When it encountered Y, it was captured by Y and formed a YTe phase. After aging for 3000 h, Te was distributed throughout the coating, and numerous voids were formed at the interface between the coating and the substrate. These two factors deteriorated the plasticity and adhesion of the coating. Results from molten salt corrosion tests indicated that the high content of Cr and Al in the coating, as well as high densities of grain boundaries providing diffusion pathways, reduced the corrosion resistance of the coating to molten salt.

Synergistic removal of malachite green and Cr(Ⅵ) using ethylenediamine disuccinic acid functionalized silica gel

As common industrial raw materials, malachite green (MG) and Cr(Ⅵ) generally coexist in waste liquids discharged from the paper printing, leather, and textile industries, causing serious harm to humans and the environment. Therefore, developing an effective method for the synergistic removal of MG and Cr(Ⅵ) from aquatic environments is of great research value. In this work, the non-homogeneous Fenton-like catalysts, namely, EDDS-Silica and EDDS-Co2+-Silica were successfully prepared using ethylenediamine disuccinic acid (EDDS) and silica gel (Silica) as raw materials, and a non-homogeneous Fenton-like catalytic method was developed for the efficient and synergistic removal of MG and Cr(Ⅵ) from wastewater. EDDS-Silica and EDDS-Co2+-Silica were analyzed using Fourier infrared spectroscopy and X-ray photoelectron spectroscopy to determine their structural composition and elemental contents. The catalytic degradation and removal effects of these materials in an MG single-waste system were also investigated. The results demonstrated that the incorporation of both materials can overcome the limitation of the conventional Fenton reaction, which is its applicability to acidic environments only. Moreover, EDDS-Co2+-Silica showed better degradation effects on MG than EDDS-Silica. Quantitative calculations based on density functional theory were used to predict the optimal coordination forms between Co2+and EDDS-Silica as well as the MG structure. The lowest unoccupied and highest occupied molecular orbitals of the catalysts were then used to predict the active sites on which MG tends to capture or release electrons during the degradation reaction. The optimal conditions for the synergistic removal of MG and Cr(Ⅵ) from a binary system using EDDS-Co2+-Silica were further investigated under different influencing factors. The results showed that EDDS-Co2+-Silica still had excellent catalytic effect on the degradation rate of MG in the range of pH 3-7, and the optimal conditions were as follows: solution pH, 7; degradation time, 1 h; temperature, 25 ℃; H2O2 concentration, 20 mmol/L; and the initial mass concentration of Cr(Ⅵ), 25 mg/L. Under the above conditions, the degradation rate was increased from 87.25% to 96.67% compared with that in the MG monosystem. Obvious enhancements in degradation effect and efficiency confirmed that the incorporation of EDDS-Co2+-Silica was favorable for the synergistic removal of MG and Cr(Ⅵ) in the binary system. Strongly oxidizing Cr(Ⅵ) can participate in the Fenton reaction, thus promoting MG degradation over a wide pH range. Thus, a positive synergistic effect exists between MG and Cr(Ⅵ). Considering that a large number of metal ions remained in the solution after the degradation reaction, EDDS-Silica was added to the degradation solution, and adsorption experiments were performed for 4 h at 30 ℃to adsorb and remove Cr and Fe via the strong chelating property of EDDS. The total residual mass concentrations of Cr and Fe were 4.96 and 1.02 mg/L, respectively, which meet national emission standards. These findings indicate that EDDS-Silica has good effects on the removal of residual metal ions after the nonhomogeneous Fenton reaction. As heterogeneous Fenton-like catalysts, the aminopolycarboxylic acid-modified materials proposed in this study can simultaneously promote the Fenton reaction and remove residual metal ions, thereby effectively removing MG and Cr(Ⅵ) from the binary system while ensuring that the content of residual metal ions in the system meets environmental emission standards. This study has broad application prospects in dye degradation and heavy-metal-ion wastewater treatment, and provides a reference value and theoretical basis for the development of other similar ligand-modified materials.

Optimizing chromium removal from synthetic wastewater via electrocoagulation process with a natural coagulant (blended of eggshell powder and lime) using response surface methodology

The presence of chromium (Cr) in synthetic wastewater has become a serious environmental issue. Therefore, main aim of this work was to investigate Cr removal from synthetic wastewater via electrocoagulation (EC) with a natural coagulant using aluminum electrodes. The central composite design (CCD) of the response surface methodology (RSM) method was used to optimized the operating variables of solution pH (5-9), initial Cr concentration (225-475 mgL-1), reaction time (30-40 min), and applied current (0.35-0.55 A). The ANOVA results clearly shows that the quadratic model (p < 0.0001) was sufficient to the best predicting of the removal performance of Cr (R2 = 0.9994 for electrode distance of 0.5 cm and 0.9924 for 1 cm). The maximum removal (99.836% for electrode distance of 0.5 cm, and 98.175% for 1 cm) of Cr was achieved with optimized conditions of solution pH 7.053, initial Cr concentration 337.795 mgL-1, reaction time 37.148 min, and applied current of 0.505 A. From this finding, it was proved that the EC process assisted with natural coagulant is an efficient, and cost-effective method for the removal of Cr from synthetic wastewater.