High Chromium Content Research Articles

Effective removal of hexavalent chromium from water by sustainable nano-scaled waste avocado seeds: adsorption isotherm, thermodynamics, kinetics, and error function

In the current investigation, an efficient low-cost nano-scaled material was prepared from waste avocado seeds (NASs) and employed as a sustainable nanosorbent for removal of hexavalent chromium ions. The adsorption and surface characteristics with respect to the availability of functional groups, basic component elements, and structural properties of NASs were achieved by different techniques. Analysis of NASs referred to the presence of carbon and oxygen contents providing 97.21%. The NASs particles were homogenously identified and ranged between 18.68 and 19.05 nm. The impact of various affecting adsorption parameters on hexavalent chromium ions removal was elaborated and optimized at pH 2.0, NASs dose 10 mg, contact time 30 min, and temperature 25 °C by the batch adsorption assay. Fifteen linear and nonlinear modeling tests were applied to evaluate the adsorption isotherms and arranged in the following fitting order: Tempkin < BET < Dubinin-Radushkevich < Generalized < Halsey ˂ Flory–Huggins < Freundlich < Harkins–Jura ˂ Langmuir for linear formulas and Weber-van Vliet < Langmuir < Generalized < Radke–Prausnitz (II) < Radke–Prausnitz (III) < Fritz-Schlunder IV < Baudu < Multilayer < Fritz-Schlunder V < Toth for nonlinear formulas with 2 to 5 parameters. Linear and nonlinear pseudo-second-order models, intraparticle diffusion, and Elovich models were also scrutinized, and both pore diffusion and film were similarly involved in the rate-limiting step. The values of ΔS° (0.21 kJ/mol), ΔH° (− 41.02 kJ/mol) and ΔG° (− 28.30 to − 19.97 kJ/mol) at high concentration of hexavalent chromium (50 mg L−1) and a temperature range of 20–60 °C reflected the disordering, spontaneously exothermic adsorption process. The activation energy (Ea) was also confirmed to include the diffusion process at the activation energy in the rate-limiting step. The potential application of NASs in hexavalent chromium removal from wastewater, seawater, and tap water as real aqueous matrices referred to excellent percentage removal values in the range from 98.44 to 98.86%. Based on the outlined results, one can deduce that excellent performance and efficiency for removal of high hexavalent chromium concentration at high temperature, low nanosorbent mass, and low pH from different aqueous matrices were accomplished by the evaluated NAS nanosorbent. Accordingly, the investigated NAS nanosorbent is recommended to apply in high stress industrial and wastewater treatment plants.

Growth Kinetics, Microstructure Evolution, and Some Mechanical Properties of Boride Layers Produced on X165CrV12 Tool Steel

The powder-pack boriding technique with an open retort was used to form borided layers on X165CrV12 tool steel. The process was carried out at 1123, 1173, and 1223 K for 3, 6, and 9 h. As a result of boriding the high-chromium substrate, the produced layers consisted of three zones: an outer FeB layer, an inner Fe2B layer, and a transition zone, below which the substrate material was present. Depending on the applied parameters of boriding, the total thickness of the borided layers ranged from 12.45 to 78.76 µm. The increased temperature, as well as longer duration, was accompanied by an increase in the thickness of the FeB zone and the total layer thickness. The integral diffusion model was utilized to kinetically describe the time evolution of the thickness of the FeB and (FeB + Fe2B) layers grown on the surface of powder-pack borided X165CrV12 steel. The activation energy of boron for the FeB phase was lower than that for the Fe2B phase. This suggested that the FeB phase could be formed before the Fe2B phase appeared in the microstructure. The high chromium concentration in X165CrV12 steel led to the formation of chromium borides in the borided layer, which increased the hardness (21.88 ± 1.35 GPa for FeB zone, 17.45 ± 1.20 GPa for Fe2B zone) and Young's modulus (386.27 ± 27.04 GPa for FeB zone, 339.75 ± 17.44 GPa for Fe2B zone). The presence of the transition zone resulted from the accumulation of chromium and carbon atoms at the interface between the tips of Fe2B needles and the substrate material. The presence of hard iron and chromium borides provided significant improvement in the wear resistance of X165CrV12 steel. The powder-pack borided steel was characterized by a four times lower mass wear intensity factor and nine times lower ratio of mass loss to the length or wear path compared to the non-borided material.

Capacitive deionization of high concentrations of hexavalent chromium using nickel–ferric-layered double hydroxide/molybdenum disulfide asymmetric electrode

To decontaminate wastewater affected by high concentrations of aqueous hexavalent chromium (Cr(VI)) and improve the capability of layered double hydroxide (LDH) as an electrode in the capacitive deionization (CDI) process, nickel–ferric-LDH (NiFe-LDH) and NiFe-LDH/molybdenum disulfide (NiFe/MoS2) were synthesized using a hydrothermal method. Characterization results indicated that the flower-like cluster framework of MoS2 was decorated with the NiFe-LDH. Addition of MoS2 improved the conductivity, capacitance reversibility, charge efficiency, coulombic efficiency, and stability of NiFe/MoS2. The CDI performance of aqueous Cr(VI) was evaluated using NiFe/MoS2 and activated carbon as the anode and cathode, respectively. The process reached equilibrium within 240 min. The deionization capacity and removal ratio for Cr(VI) (100 mg/L, 100 mL) were 49.71 mg/g and 99.42 %, respectively, at 1.2 V and 20 mL/min. The isothermal data were accurately described using the Langmuir model, and the theoretical maximum deionization capacity of NiFe/MoS2 for Cr(VI) was 106.2 mg/g. The interaction mechanisms included electrostatic attraction, surface complexation, and reduction. These findings indicate that NiFe/MoS2 has feasible applications in practical wastewater treatment for Cr(VI) removal.

A Decarbonization Approach for FeCr Production.

In this study, the reducing smelting of chromite concentrates by EAF-assisted metallothermic method was investigated. The effect of AlPowder and AlDross addition amount, time, and the ratio of flux addition on the produced metal and slag compositions and metal recovery were investigated. It was seen that ferrochrome can be produced from fine-grained chromite concentrate by this method. As a result of EAF-assisted semi-pilot metallothermic smelting, the highest chromium content in produced alloys was 59.5 wt. %, while the highest chromium recovery from chromite concentrate to alloys was 76.7 wt. % in these experiments.Graphical Abstract

Study on Potential Causes of Defects Following Heat and Thermochemical (Carburising) Treatments of Linear Bearings

Abstract Guide rings and rolling bodies are mainly made of alloy steel with a high chromium content, heat treated, as well as of carburising steel. The efforts to improve the standard of quality of bearing steels are determined by the interest of continuously increasing the adhesion of constructive types. These steels are recommended for large bearings which operate under shock and vibration conditions. Thermochemical treatments are followed by quenching and tempering heat treatments. However, undesirable defects occur sometimes on the surface of the carburised layer and solutions are constantly being sought to identify the causes thereof.

Migration characteristics of chromium and organic compounds released from waste leather fragments in soil under rainfall

The environmental issues caused by chrome-tanned leather could not be overlooked, and the high concentration of chromium (Cr) in the waste leather fragments was a major factor in limiting its resource utilization. Few studies have reported the contamination of soil and groundwater by discarded leather fragments. Soil column and static leaching experiments were conductive to exploring the release and transport of organic compounds and Cr from waste leather fragments with various types and sizes. The findings revealed that the 1 cm2-sized leather fragments of cowhide released more organic compounds into the leachate than the pigskin with same size, whereas leather fragments of the pigskin released more Cr than those of the cowhide, and this phenomenon was more prominent under rainfall condition at pH 4.68 than at pH 5.86. The Cr concentration increased at first and then decreased in the leachate, while the concentrations of soluble protein (SP), free amino acid (FAA), and total organic carbon (TOC) increased with the leaching event. After leaching, the concentrations of SP and FAA in each soil layer were nearly three times higher in the leather treatment groups than in the leather absent groups. Cr(III) was the primary species existed in the deep soil layer. The impact of leather fragment type and size on the release of Cr and organic compounds into soil was assessed, which helped to guide waste leather fragment reuse, landfill procedures, and impermeability measure design.

Secondary Structures on the Friction Surface of Diamond-like Coating

Peculiarities of the formation of secondary structures on the surface of a diamond-like coating are studied on the example of a friction contact between a steel ball and a diamond-like coating. The friction surface was examined in various areas; the zone of wear products (the boundary of the friction track) and the original surface outside the friction area. It is shown that secondary structures with a high content of iron, nickel, manganese, chromium, and oxygen are characteristic of areas with the highest wear resistance. Such secondary structures are formed because of the intense interaction of the diamond-like coating with the steel of the ball during dry friction.

Dislocation nucleation mechanisms during nanoindentation of concentrated FeNiCr alloys: unveiling the effects of Cr through molecular simulations

Fe-based alloys with high chromium and nickel concentrations are very attractive for efficient energy production in extreme operating conditions. We perform molecular dynamics (MD) simulations of nanoindentation on fcc FeNiCr multicomponent materials. Equiatomic FeNi, Fe55Ni19Cr26, and Fe74Ni8Cr18 are tested by using established interatomic potentials and similar conditions, for the elucidation of key dislocation nucleation mechanisms and interactions. Generally, we find that the presence of Cr in these alloys reduces the mobility of prismatic dislocation loops, and increases their area, regardless of crystallographic orientation. Dislocation nucleation and evolution is tracked during mechanical testing as a function of nanoindentation strain and Kocks–Mecking continuum modeling displays good agreement with MD findings. Furthermore, the analysis of geometrically necessary dislocations (GNDs) is consistent with the Ma–Clarke’s model at depths lower than 1.5 nm. The presence of Cr leads to a decrease of the GND density with respect to Cr-less FeNi samples, thus we find that Cr is critically responsible of increasing these alloys’ hardness. Post-indentation impression maps indicate that Ni–Fe–Cr compositions display strain localization and hardening due to high Cr concentration.

The Effect of Leonardite on Chromium Toxicity and Growth of Cordes Rose

High concentrations of chromium in the soil have a toxic effect on the living organisms in the soil ecosystem. If chromium, which is not an absolute essential element, accumulates in plants, it causes structural changes, causing a decrease in plant growth and also high toxicity due to its accumulation in biomass. Use of plants to remove chromium (Cr) from contaminated soils, it is an environmentally efficient, cost-effective, modern, applicable technique. The different species of plant and ornamental plants are used in this technique. In this study, the Kordes shrub rose used in landscaping in our province, Cr phytoremediation capacity was evaluated by growing at contaminated soil with Cr. In the study, the different doses of Cr (0, 50, 100, 500, 1000 mg kg-1) have been applied in Cr+3 and Cr+6 forms. In addition, two doses (0% and 3%) of leonardite were added to the pots to determine the effect on the developmental status of the plants and Cr uptake. In the study, plant height, number of branches, number of flowers, flower diameter, stem diameter, flower yield values and total wet and dry weight values at the end of the experiment were determined. At the end of the experiment, it was observed that generally developmental status of the plants was adversely affected at high Cr doses. Especially at 500 and 1000 mg kg-1 application doses was observed that the plants could not withstand Cr toxicity in a short time. It has been observed that plants treated with leonardite were healthier than those without. According to the data obtained at the end of the study, it was determined that the resistance of plant to high doses of Cr was low, but it showed better growth at 50 and 100 mg kg-1 doses.

Study of the Passivation Film on S32750 Super-Duplex Stainless Steel Exposed in a Simulated Marine Atmosphere

The corrosion behavior and passivation mechanism of S32750 super-duplex stainless steel exposed in a simulated marine atmosphere were studied using electrochemical methods, XPS and SEM. Passivation and local corrosion occurred on the metal surface when S32750 SDSS was exposed in the simulated marine atmospheric environment. The passivation film is composed of two chromium-enriched layers. The outer layer is a very thin film at the metal/atmosphere interface of the specimen surface with higher chromium content, whereas the chromium in the inner layer seems a little depleted. The outer and inner layers had similar Fe components, and Fe3+ oxide/hydroxide was the primary oxide in the film. The outer layer contains CrO3, whereas the inner layer has Cr3+ as its primary oxide. Pitting occurred when exposure time exceeded 24 d, and the Cr content of the specimen decreased. Therefore, S32750 SDSS exposed for 24 d exhibited the best corrosion resistance.

GEOPHAGIC CLAY PREDOMINANCE AND ITS POSSIBLE HEALTH IMPLICATIONS IN THE SOUTH-EAST REGION OF NIGERIA

Geophagy has been a common practice especially in the Southern part of Nigeria and some parts of the world at large. They are earthy/clay materials eaten as food supplements and also adopted for medical purposes. Hence, they are bound to contain trace metal contents that may be harmful to human health which is a great cause for concern among health workers in this modern age. Therefore, geophagic clays from Amawom- Ikwanoin Abia province, South-eastern Nigeria were examined and evaluated for their heavy metal concentration to deduce their quality and possible health implication that is associated with their consumption. Edible clay from south eastern Nigeria was analysed with X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Inductively Couple Plasma Mass-Spectrometry (ICP-MS) revealing quartz (SiO2), kaolinite (Al2Si2O5(OH)4, goethite (FeOH) and pyrite (FeS2) as the predominant minerals while SEM revealed clay flaky structure specifying an alumino-silicate with sulfur and carbon as impurities. The clay’s pH ranges between 3.36 and 4.57, E.C from 52-399 μs/cm revealed its high acidity and signified high ionic contents in the edible clays. The soil Organic Carbon 0.1-5.83% may possibly indicate absorption and retention of contaminants. High concentrations ppm for Cu(19.91), Pb(13.15), Zn(18.4), Ni(5.8), As(9.15) and Hg(126.0) in the clay exceeded the WHO and USEPA recommended dietary intake by humans signifying its likely toxicity. Other associated carcinogenic and non-carcinogenic diseases that could be connected to the high concentrations of mercury, chromium, arsenic, lead and nickel in the edible clay structure which may likely camouflage the taunt and healing properties of kaolinite include renal, respiratory, cardiovascular, gastrointestinal, hepatic, immune, reproductive and dermal systems. For this reason, continuous ingestion of edible clay may lead to bio-accumulation of mercury, chromium, arsenic, lead and nickel in the inhabitants of Amawom, hence, posing serious health challenges that may lead to death.

Improving oxidation resistance of porous FeAl-based intermetallics with high boron/yttrium alloying

The coalloying with high contents of chromium (Cr), boron (B) and yttrium (Y) for porous B2-structured FeAl intermetallics fabricated through reactive synthesis was conducted. The oxidation behaviors of porous FeAl-based materials were investigated by evaluating the pore-structure evolution, oxidation kinetics and oxide-scale configuration. The results show that with the coalloying of high contents of Cr, B and Y, the oxidation mass gains of porous FeAl materials at 600−800 °C are significantly reduced. The combination of B enriched on the surface of oxide scales and Y located at the scale−metal interface promotes the formation of thin protective nodular α-Al2O3 oxide scales. It is indicated that introducing relatively high contents of reactive elements such as B and Y can benefit the selective growth of α-Al2O3 scales at relatively low temperatures without pre-treatment.

Safe bioremediation of chromium by Pseudomonas isolated from industrial waste water and detection of genes responsible for its degradation

Isolation of microorganisms capable of reducing toxic chromium (VI) into less toxic chromium (III) has been given attention due to their significance in bioremediation of the contaminated sites. Five isolates out of the twelve isolates were selected according to their abilities to grow in the presence of high concentration of chromium. From the five bacterial isolates, isolates FAYP2 and FAYP3 were selected according to their higher reduction percent of toxic chromium (VI) into chromium (III) and their reduction percent was 60% and 70% respectively. The isolates FAYP2 and FAYP3 were identified as Pseudomonas aeruginosa and Pseudomonas zhadogens, respectively, based on morphological and biochemical characterization and confirmed by molecular sequence analyses of amplified 16S rRNA genes with accession numbers OMO10239 and OMO019074. The results reveal that P. aeruginosa FAYP2 and P. zhadogens FAYP3 can be used for the bioremediation of wastewater effluent containing hexavalent chromium.

Simulation of the operation of two-roll screw piercing of steels of the 13Cr type

The development of new offshore oil and gas fields is impossible when using pipes made of carbon and low-alloy steel grades, due to their inability to effectively withstand an aggressive environment. Therefore, the urgent task of pipe manufacturers is to develop and master the technology of mass production of seamless pipes from martensitic steels with a high chromium content. This article discusses the peculiarities of the technology for the production of seamless pipes from steel grades of the 13Cr type when piercing a billet on a two-roll screw rolling mill with a non-driven guide tool - a ruler. The results of physical modeling at the MISIS laboratory screw rolling mill are presented. To identify the features of the piercing during physical modeling, the elongation coefficient was changed (due to the use of piercing mill mandrels of different diameters and due to a change in the thickness of the sleeve wall), the feed angle was varied, and the workpieces were pierced at different temperatures. In addition, for a comparative analysis, steel 45 was pierced. During the research, the machine time of the piercing and the force on the roll of the piercing mill were recorded. Underrolls were obtained, on which the pitch of the sleeve was measured, and the area of the contact surface of the pierced metal with the rolls was also determined. The energypower parameters of the piercing were evaluated at various settings of the piercing semi-industrial mill "MISiS -130D". To compare the obtained force values, the piercing process was simulated in the QForm software package. As the material of the billet workpiece, the material C.20Сr13 was chosen with deformation resistance characteristics obtained from the results of testing samples on the Gleeble System 3800.

Arsenic and chromium resistance mechanisms in the Micrococcus luteus group

High arsenic and chromium concentrations are currently receiving attention because of their negative effects on the environment and human health. Microorganisms inhabiting contaminated environments have developed resistance mechanisms against the toxicity of these pollutants. Indeed, members of the bacterial genus Micrococcus have been isolated from different toxic-metal-contaminated environments. However, knowledge concerning the resistance mechanisms of Micrococcus to arsenic and chromium, isolated from contaminated sites, remains scarce. In response, the aim was to examine strains of Micrococcus luteus (An24, Mh, NE2TL6, and NE2TTS4) from the endosphere and soil of two different sites in Mexico contaminated with heavy metals in order to observe any differences in the resistance mechanisms by M. luteus group. The strains were resistant to arsenic (As 3+ , As 5+ ), chromate, dichromate, cobalt, copper, nickel, and zinc. Genome analysis indicated that the heavy metal-resistant strains could be assigned to the M. luteus group ( M. luteus NCTC 2665 T and M. endophyticus JCM 16951 T ), which had more heavy metal-resistant genes (transporters, chaperones, and enzymes) compared to the type strains of the M. luteus group. The bacteria were able to biotransform arsenic (As 3+ and As 5+ ) through a carbon-source-dependent mechanism. The As 5+ was potentially carried out in the cytoplasm through the thioredoxin-dependent pathway, which may be coupled with biosorption. A qualitative analysis of organic acids (OAs) picked up a change in the OA profile that was metal-depending (arsenic or chromium). Our findings on the genome and phenotype tests suggest that the four studied strains of the M. luteus group had developed resistance mechanisms that may have enabled their survival in contaminated sites in Mexico.

Failure analysis of corrosion products formed during CO2 pre-corrosion of X70 and 3Cr steels: Effect of oxygen contamination

This study investigates the impact of oxygen contamination on corrosion products formed during CO2 pre-corrosion of X70 and 3Cr steels. The results show that O2 promotes the generation of Fe2O3, γ-FeOOH and Fe3O4 and the degradation of original FeCO3, accelerating the corrosion process. The pores on the original surface and the hydrolysis of Cr(OH)3 lead the general corrosion rate of 3Cr steel to be much higher than that of X70 steel in the first 24 h. Cr’s self-repairing can mitigate the corrosion failure of 3Cr steel, and thus the general corrosion rate of 3Cr after 24 h is lower than that of X70. However, this self-repairing effect is quite less than the destructive effect of oxygen. Therefore, in the actual oil and gas production process, it is recommended to use deoxygenation treatment, anti-oxidation corrosion inhibitor and steel with high chromium content.

Degradation of phthalic acid by anodic oxidation in acidic aqueous solutions with high chromium content using boron-doped diamond anode

Mineralization of phthalic acid, a highly refractory organic pollutant was studied by an anodic oxidation process with boron-doped diamond (BDD) anode in a highly acidic chromium medium. Synthetic solutions were composed of Cr(III)/Cr(VI), sulfate, sulfuric acid, and phthalic acid (initial form potassium hydrogen phthalate, KHP). Degradation/mineralization of KHP was carried out by hydroxyl radicals produced on the anode and sulfate radicals generated from the sulfate ions present in the medium. To find appropriate operating conditions, the effects of cathode type, current density, electrolysis time, and presence of Cr(VI)-Cr(III) were investigated. Thereafter, the effect of current density, amount of Cr(VI)-Cr(III) in solution, and electrolysis time on KHP mineralization was realized by using response surface methodology and central composite design. The most effective TOC removal rate was found as 94.8% in the case of 0.675% Cr(VI) and 3.825% Cr(III) content by mass at 80 mA cm−2 of current density and 360 min of electrolysis time, despite a high initial TOC content of 9400 mg L−1. As a result, the organic content of the wastewater was removed by electro-persulfate process via the catalytic effect of Cr species. Additionally, the use of BDD anode avoided metal ion pollution that could dissolve from different anode materials like PbO2 and affect the chromium recovery efficiency.

Heavy metals in leathers, artificial leathers, and textiles in the context of quality and safety of use

The article presents research findings on the content of arsenic, cadmium, chromium, copper, lead, and zinc in extracts from leathers, artificial leathers intended for footwear components, and textiles. After extracting the metals using an artificial acidic sweat solution, their contents were quantitatively determined by atomic absorption spectrometry. In the cotton textiles, the metal contents were in accordance with the OEKO-TEX limits, while regarding the artificial leathers, only the acrylic knit fur had a too high chromium content (1.1 mg/kg) as compared with the requirements of the STANDARD 100 by OEKO-TEX for products intended for children (< 1.0 mg/kg). The chromium content in lining and upper leather (> 228.0 mg/kg) exceeds the limits for children’s products (< 2.0 mg/kg), but also the less restrictive ones for other products (< 200.0 mg/kg). Regarding the other metals, the leathers met the OEKO-TEX requirements. Approved materials may have elevated heavy metal contents, as demonstrated for chromium. The presence of heavy metals in too large amounts in products is a serious problem due to their allergenic and toxic effect. Therefore, action should be taken aimed at more effective detection and elimination of such products from markets and at reducing the use of chemicals containing harmful metals in manufacturing processes.

Distribution of Heavy Metals in the Commune of Coronel, Chile

Anthropogenic activities often produce different emanations, some of them excessive, producing contamination of the soil, water, and/or air. This article analyzes soil conditions in Coronel, Chile, a commune with a large industrial presence, identifying the sources emitting potentially toxic elements, the degree of soil contamination, and the carcinogenic and non-carcinogenic risks in the area. Ninety-four samples in the study area were analyzed using different methods. Three factors were identified through a principal component analysis (PCA) that explain 83.27% of the variability of the elements. Four factors were identified through the positive matrix factorization (PMF) model, making it possible to identify the polluting sources according to the pattern of elements they contain. The sources of these factors were then identified. The most common elements in the soil with a particularly high degree of contamination are nickel, vanadium, and chromium, the latter of which being the element that poses the greatest carcinogenic and non-carcinogenic risk to children and adults. Additionally, the highest concentrations of chromium and vanadium were identified near industrial areas of the commune.

Hydrogeochemical, Geophysical and Geological Assessment of the Recharge Zone of Guarani Aquifer System in Alegrete, southern Brazil

The state of Rio Grande do Sul has a huge part of the Guarani Aquifer, having a recharge area in its central and western region and, therefore, this investigation was focused on the city of Alegrete. There is no annual plan for water resources in the state and, hence, it is required to evaluate the hydrogeochemical, geophysical and geological characteristics where the aquifer has its recharge regions. Thus, some data were acquired, having chemical analysis of the water in different wells (mostly in rural areas) and refraction seismic and geoelectrical surveys. In addition, the geological information was obtained from the public database SIAGAS (Sistema de Informações de Águas Subterrâneas – ground water information system). Then, different maps of chemical parameters and a Piper diagram were made. Moreover, the refraction seismic and geoelectrical data were processed and interpreted, concatenating these results with the geological data obtained from the SIAGAS wells, mapping the different formations and static levels of the aquifer. A high concentration of lead, chromium and cadmium along with phosphate was found. Additionally, by means of geophysical surveys, a line was pointed out as a possible aquifer, which could be used for human, agropastoral or industrial activities after treatments of altered values.