Hexavalent Chromium Compounds Research Articles

A review on the environment friendly electroplating of Cr (III) & Cr (VI)

Chromium plating process is the most effective way of protecting the base material against hostile environment or improving surface properties of base material. There are several problems with traditional chrome plating. Traditional process uses toxic acid baths and may cause various health conditions. The baths employed contain chromic acid in which the chromium is in the hexavalent state. Hexavalent chromium has been proved to have toxic, mutagenic and cancerogenic effects for human health. As a result, In Europe, the implementation of the reach initiative will increase fees on companies still using Cr (VI) in 2017 and will require action plans to phase out Cr (VI) in the future. This has left the plating industry in a very delicate position with dark future prospects unless new solutions that are both effective and environmentally friendly are discovered. Superchrome Physical Vapor Deposition coating ahead of looming industry regulatory actions that will drive towards the removal of hazardous hexavalent chromium compounds. These new sputtered chromium coatings do not require a protective paint top coat to pass exterior automotive trim specifications. Visually the chromium coatings match those of electroplated decorative chromium in color and appearance.

Технологические решения и опыт промышленной переработки жидких хромсодержащих отходов

Analysis of the list of liquid wastes of hazard classes I and II in the Federal Classification Catalog of waste (FCCW) showed that one of the most common wastes is wastewater, waste technological solutions containing chromium ions(III, VI). This type of waste accounts for up to 15% of the total amount of liquid technogenic waste of hazard classes I and II, formed as a result of the activities of electroplating and chemical enterprises. Hexavalent chromium compounds belong to the class of toxic, extremely dangerous substances, the maximum permissible concentration (MPC) in the water of drinking water bodies for chromium (VI) is 0.05 mg/L. A feature of this type of waste is the increased salt background characteristic of electrolytes used in electroplating industries. The article presents experimental data, as well as basic technological solutions for the neutralization of chromium-containing wastewater and waste technological solutions. A technological scheme containing four main stages is proposed: reduction of hexavalent chromium, isolation of trivalent chromium from aqueous solutions, separation of accompanying compounds of heavy and non-ferrous metals, filtration post-treatment of the solution. Experimental studies have shown that, depending on the ionic composition of the medium, the efficiency of isolation of trivalent chromium compounds from aqueous solutions by electroflotation varies from 8 to 95%. The introduction of an anionic flocculant makes it possible to increase the degree of extraction to 99% or more.

Bismuth dichalcogenide-exfoliated Bi2Se3 nanosheets: A novel approach for hexavalent chromium and azo compound photocatalysis

A promising approach for the photocatalytic degradation of hexavalent chromium [Cr(VI)] and azo compounds in wastewater involves utilizing exfoliated nanosheets derived from bismuth dichalcogenide crystals, specifically Bi2Se3. In this study, we synthesized Bi2Se3 nanosheets through a straightforward sonication method using N, N-Dimethylformamide as the solvent. The resulting Bi2Se3 nanosheets displayed substantial surface areas, layered sheet structures resembling rocks, and exhibited single crystalline characteristics, featuring an optical bandgap of 5.30 eV and a lattice spacing of 0.505 nm. Photocatalytic assessments employing methyl orange (MO) and Cr(VI) as model pollutants demonstrated remarkable efficiency, achieving degradation rates of up to 81.2% within 240 min and 88.4% within 60 min, respectively, under visible light exposure. Both reactions adhered to pseudo-first-order kinetics, with kinetic constants (k) of 0.0038 min−1 for MO and 0.007 min−1 for Cr(VI). The underlying photocatalytic mechanism involved the transfer of electrons from the Bi2Se3 nanosheets to the pollutants adsorbed on their surface, resulting in the efficient detoxification of wastewater. This investigation underscores the potential of exfoliated Bi2Se3 nanosheets as exceptionally effective and environmentally sustainable photocatalysts for the remediation of wastewater contaminated with Cr(VI) and MO, making significant contributions to the field of environmental remediation. This research not only provides insights into the novel utilization of Bi2Se3 nanosheets but also addresses urgent environmental issues, indicating its potential significance in promoting sustainable wastewater treatment methods.

Optical monitoring of adsorption of chromium (VI) molecular anions, molecules and clusters on carbon nanomaterials

Search for efficient adsorbent materials for removal of hexavalent chromium compounds from environment is a topical technological problem. In this paper, the possibility of optical monitoring of the adsorption of chromium (VI) molecular compounds on the surface of carbon nanomaterials (CNM) is examined. Theoretical calculations of optical absorption spectra of CrO42- anions and molecular clusters of such anions with metals, n*K2CrO4 (n = 1, 2, 4) and MIICrO4 (MII = Zn, Cd, Pb) adsorbed on the surfaces of bare and doped carbon nanotubes and graphene are carried out by TD-DFT method. Results of calculations are compared with experimental data on optical transmission, diffuse reflection and photoluminescence of specially prepared samples containing chromate molecular compounds and particles adsorbed on CNM.It is shown that adsorption of CrO42- anions by CNM can be detected by the appearance of characteristic bands in diffuse reflectance spectra in 310–380 nm region. Nanoparticles of K2CrO4 crystal adsorbed on CNM reveal an additional luminescence band in 600–700 nm region, and it can be utilized in the monitoring of such adsorption. The effect of CNM surface on optical spectra of chromium (VI) molecular compounds is analyzed in terms of splitting of excited electronic states of quasi-tetrahedral CrO42- anions.

THE ROLE OF SULFUR-CONTAINING AMINO ACIDS IN THE PREVENTIVE NUTRITION OF WORKERS IN CONTACT WITH CHROMIUM

In the world, a large number of workers are exposed to fumes, mists and dusts containing Chromium and its compounds. One of the ways to prevent chromium intoxication is the enrichment of food rations with substances that have antioxidant and complexing ability. Attention is focused on the recommendations on the use of sulfur-containing amino acids and sulfur-rich proteins in the composition of food products for the prevention of intoxication in workers who come into contact with chromium in production. The mechanism of reduction of hexavalent chromium compounds by cysteine was considered. It has been shown that the process of reduction of chromates with cysteine is accompanied by the oxidation of cysteine to cystine and subsequent complexation with trivalent chromium. The structure of chromium III cystinate was confirmed by IR and electron spectroscopy and elemental analysis. It has been established that in the formed chelate complex [Cr(SNO2C3H6)6Cr], chromium (III) has a bond with cystine through the amino and carboxyl groups, LD50 is 2100 mg/kg and is less toxic than inorganic chromium (III) salts. The article analyzes protein raw materials rich in cysteine, which can be recommended to satisfy the daily requirement of cysteine, or to reduce chromium intoxication of workers working in a work area with a high content of chromium salts.

Kinetics and Mechanism of Electrochemical Reactions Occurring during the Chromium Electrodeposition from Electrolytes Based on Cr(III) Compounds: A Literature Review

A literature review was conducted to examine the current understanding of the kinetics and mechanism of electrochemical reactions occurring during the electrodeposition of chromium coatings from electrolytes based on trivalent chromium compounds. The research in this scientific field is crucial, as it addresses the pressing need for an alternative to chromium plating processes that rely on solutions containing highly toxic and harmful hexavalent chromium compounds. Numerous literature data on the kinetics and mechanism of the stepwise reduction process of Cr(III) complex ions were analyzed. The influence of various additives and surfactants on the reaction kinetics of the stepwise reduction of trivalent chromium ions was considered. Special attention was given to the kinetics of the stepwise discharge of trivalent chromium ions in ionic liquids and deep eutectic solvents.

MECHANISMS OF ADAPTATION PERICLASE-SPINEL REFRACTORIES TO THERMAL SHOCKS

In the group of periclase spinel refractories, the dynamics of demand for magnesite-chromite and chromium-magnesite refractories, which contain MgCr2O4 – magnesia-chromium spinel – in their phase composition, is changing, due to the environmental hazard of any hexavalent chromium compounds. These reasons stimulate the search for alternative refractories to replace chromium-containing ones. Periclase-spinel refractories of the MgO – MgAl2O4 system are poorly wetted by cement clinker melt and the lining made of them does not gain a garnish (coating), which is a mandatory technical requirement. It was necessary to develop a new type of periclase-spinel refractories based on more multicomponent oxide systems. At the same time, the task of ensuring their high heat resistance should be solved. Thus, the study of the mechanisms of adaptation of materials of the MgO – Al2O3 – FeO – TiO2 system, which counteract thermal stresses in refractories, is relevant. A new periclase-spinel refractory material has been developed, the phase composition of which is modified by a FeO- and TiO2-containing pre-synthesized additive. Refractories made of the developed material meet the technical requirements that determine operational reliability when used for lining high-temperature zones of rotary kilns for firing Portland cement clinker. The thermal resistance of a material is determined by its ability to withstand thermal stresses caused by the involuntary expansion/contraction of individual structural blocks of the material and causing its breakdown and subsequent destruction. Some mechanisms of adaptation are demonstrated and discussed based on the results of the analysis of X-ray and electron microscopic studies. Some of the discussed mechanisms are unconventional for the technological practice of refractory nonmetallic materials and complement the toolkit of materials scientists. The achieved results and some technological methods of ensuring thermal stability have signs of universality and can be used for various types of heterophase refractory nonmetallic materials

Cold-curing mixtures based on biopolymer lignin complex for casting production in single and small-series conditions

<abstract> <p>This study proves that lignin-based biopolymer materials can be employed as starting materials for the synthesis of novel casting binders that fulfill the current level of characteristics. The optimal concentration of the binder in the mixture was experimentally determined to be 5.8%–6.2%. It has been demonstrated in practice that the employment of ammonium salts as a technical lignosulfonate (TLS) modifier can result in the provision of cold (room temperature) curing of a mixture based on them. It was proposed to use as a technological additive that boosts the strength characteristics of a mixture of substances carboxymethyl cellulose (CMC). In a variety of adhesive materials, it is utilized as an active polymer base. The concentration limits for using CMC in the mixture are set at 0.15%–0.25%. To improve the moldability of the combination, it was suggested that kaolin clay be used as a plasticizing addition. The concentration limits for using a plasticizing additive are set at 3.5%–4.0%. The produced mixture was compared to the analog of the alpha-set method in a comparative analysis. It was discovered that the proposed composition is less expensive, more environmentally friendly, and enables the production of high-quality castings. In terms of physical, mechanical, and technological properties, the created composition of the cold curing mixture is not inferior to analogs from the alpha-set method. For the first time, a biopolymer-based binder system containing technical lignosulfonate with the addition of ammonium sulfate and carboxymethyl cellulose was used in the production of cast iron castings on the case of a cylinder casting weighing 18.3 kg from gray cast iron grade SCh20. Thus, it has been proved possible for the first time to replace phenol-based resin binders with products based on natural polymer combinations. For the first time, a cold-hardening mixture based on technological lignosulfonates has been developed without using hardeners made of very hazardous and cancer-causing hexavalent chromium compounds. But is achieved through a combination of specialized additives, including kaolin clay to ensure the mixture can be manufactured, ammonium sulfate to ensure the mixture cures, and carboxymethyl cellulose to enhance the strength properties of the binder composition. The study's importance stems from the substitution of biopolymer natural materials for costly and environmentally harmful binders based on phenolic resins. This development's execution serves as an illustration of how green technology can be used in the foundry sector. Reducing the amount of resin used in foundry manufacturing and substituting it with biopolymer binders based on technological lignosulfonates results in lower product costs as well as the preservation of the environment. Using lignin products judiciously can reduce environmental harm by using technical lignosulfonates, or compounds based on technical lignin. The combination is concentrated on businesses with single and small-scale manufacturing because it is presumable that this is merely the beginning of the investigation. This study confirms the viability of creating a cold-hardening combination based on technical lignosulfonates in practical applications and supports this with the castings produced, using the creation of a gray cast iron cylinder casting as an example.</p> </abstract>

Sensitivity of Zea mays and Soil Microorganisms to the Toxic Effect of Chromium (VI).

Chromium is used in many settings, and hence, it can easily enter the natural environment. It exists in several oxidation states. In soil, depending on its oxidation-reduction potential, it can occur in bivalent, trivalent or hexavalent forms. Hexavalent chromium compounds are cancerogenic to humans. The aim of this study was to determine the effect of Cr(VI) on the structure of bacteria and fungi in soil, to find out how this effect is modified by humic acids and to determine the response of Zea mays to this form of chromium. A pot experiment was conducted to answer the above questions. Zea mays was sown in natural soil and soil polluted with Cr(VI) in an amount of 60 mg kg-1 d.m. Both soils were treated with humic acids in the form of HumiAgra preparation. The ecophysiological and genetic diversity of bacteria and fungi was assayed in soil under maize (not sown with Zea mays). In addition, the following were determined: yield of maize, greenness index, index of tolerance to chromium, translocation index and accumulation of chromium in the plant. It has been determined that Cr(VI) significantly distorts the growth and development of Zea mays, while humic acids completely neutralize its toxic effect on the plant. This element had an adverse effect on the development of bacteria of the genera Cellulosimicrobium, Kaistobacter, Rhodanobacter, Rhodoplanes and Nocardioides and fungi of the genera Chaetomium and Humicola. Soil contamination with Cr(VI) significantly diminished the genetic diversity and richness of bacteria and the ecophysiological diversity of fungi. The negative impact of Cr(VI) on the diversity of bacteria and fungi was mollified by Zea mays and the application of humic acids.

Epigenetic alterations of CXCL5 in Cr(VI)-induced carcinogenesis.

Chronic exposure to hexavalent chromium compounds [Cr(VI)] is associated with an increased risk of cancers, but the molecular mechanisms remain to be elucidated. In this study, we found that CXCL5 levels in peripheral blood monocytes (PBMCs) and plasma from workers with occupational exposure to Cr(VI) were dramatically upregulated compared to non-exposure healthy subjects, and plasma C-X-C Motif Chemokine Ligand 5 (CXCL5) CXCL5 levels were positively correlated with Cr concentrations in subjects' toenails. Zinc chromate exposed mice showed higher levels of CXCL5 and its receptor CXCR2 in lung tissues, and in PBMCs. Similar CXCL5 upregulation was evident in Cr(VI)-induced transformed (Cr-T) cells with long-term Cr(VI) treatment. Mechanistic studies showed that elevated CXCL5 expression levels were regulated by Cr(VI)-induced histone modifications and DNA hypomethylation, and that the c-Myc/p300 complex was a key upstream regulator of histone H3 acetylation. CXCL5 overexpression promoted Cr(VI)-induced the epithelial to mesenchyme transition (EMT) by upregulating zinc finger E-box binding homeobox 1 (ZEB1) to promote tumor development. Our findings identify a novel mechanism by which CXCL5 is upregulated and promotes EMT and carcinogenesis upon chronic Cr(VI) exposure. Our work also implies that CXCL5 mRNA and protein levels will elevate in PBMCs and serum after occupational Cr(VI) exposure, which may be a potential target and biomarker for cancer prevention and health surveillance among populations exposed to Cr(VI).

Influence of carboxylic acids on the performance of trivalent chromium electrolytes for the deposition of functional coatings

As a direct consequence of the restrictions on the use of hexavalent chromium compounds, the demand for a suitable replacement has arisen. In this work the electrodeposition of thick chromium layers (>1 µm) from a trivalent electrolyte is investigated with the aim to identify an electrolyte composition for the deposition of hard functional coatings. These layers can be used to surface finish tribological components experiencing high wear rates or mechanical stress in applications such as coating printing cylinders, feed rollers or piston rods. The influence of different carboxylic acids (malonic acid, malic acid, glycolic acid) on the deposition has been studied. The effect of current density on the current efficiency was investigated using in-situ microgravimetry. For a technical application the electrolyte containing malonic acid was the most promising one and was further investigated regarding the properties of the deposits, such as surface morphology, crack formation, composition, thickness and hardness, aiming at properties as close as possible to those of hexavalent chromium. In comparison to hexavalent chromium, the layer of trivalent chromium showed the same properties in terms of crack formation, hardness and layer thickness (> 1 µm).

Dissimilatory reduction of sulfate, nitrate and nitrite ions by bacteria Desulfovibrio sp. under the influence of potassium dichromate

In the process of anaerobic respiration, sulfate reducing bacteria, besides sulfates, can use other electron acceptors: nitrates, nitrites, oxidized forms of heavy metals, in particular, hexavalent chromium, which are harmful for organisms. Selection of pollutant-resistant stains of this kind of bacteria isolated from technogenically altered ecotopes, capable of reductive transformation of various nature pollutants, is an especially relevant task for the creation of new effective remediation biotechnologies. The purpose of this work was to investigate the regularities of usage of sulfate, nitrate or nitrite ions by bacteria of the Desulfovibrio genus, isolated from Yavorivske Lake, at conditions of simultaneous presence in the medium of another electron acceptor – Cr(VI), to establish a succession of electron acceptors’ reduction by investigated sulfidogenic bacteria and to evaluate the efficiency of their possible application in technologies of complex purification of the environment from metal, sulfur and nitrogen compounds. Bacteria were grown under anaerobic conditions for 10 days in Kravtsov-Sorokin medium without Mohr’s salt. To study the efficiency of sulfate, nitrate, or nitrite ions’ reduction at simultaneous presence in the medium of Cr(VI), bacteria were sown in media with Na2SO4×10H2O, NaNO3, NaNO2 or K2Cr2O7 to final SO42–, NO3–, NO2– or Cr(VI) concentration in the medium of 3.47 (concentration of SO42– in medium of standard composition) or 1.74, 3.47, 5.21, 6.94, 10.41 mM. Biomass was determined turbidimetrically, and the concentrations of sulfate, nitrate, nitrite, ammonium ions, hydrogen sulfide, Cr(VI), Cr(ІІІ) in cultural liquid were determined by spectrophotometric method. It has been established that Cr(VI) inhibits the biomass accumulation, sulfate ions’ reduction and hydrogen sulfide production by Desulfovibrio sp. after simultaneous introduction into the medium of 3.47 mM SO42– and 1.74–10.41 mM Cr(VI). In the medium with the same initial content (3.47 mM) of SO42– and Cr(VI), bacteria reduced 2.1–2.3 times more Cr(VI) than sulfate ions with Cr(III) production at concentrations up to 2.2 times higher than hydrogen sulfide. It has been shown that K2Cr2O7 inhibits the biomass accumulation, the nitrate ions reduction and the ammonium ions production by bacteria after simultaneous addition into the medium of 3.47 mM NO3– and 1.74–10.41 mM Cr(VI) or 1.74–10.41 mM NO3– and 3.47 mM Cr(VI). In the medium with the same initial content (3.47 mM) of NO3– and Cr(VI) bacteria reduced 1.1–1.3 times more nitrate ions than Cr(VI) with the production of ammonium ions at concentrations up to 1.3 times higher than that of Cr(III). It has been established that K2Cr2O7 inhibits the biomass accumulation, the nitrite ions’ reduction and the ammonium ions’ production by bacteria after simultaneous addition into the medium of 3.47 mM NO2– and 1.74–10.41 mM Cr(VI) or 1.74–10.41 mM NO2– and 3.47 mM Cr(VI). In the medium with the same initial content (3.47 mM) NO2– and Cr(VI) the reduction of Cr(VI) by bacteria practically did not differ from the reduction of nitrite ions (was only slightly lower – up to 1.1 times), almost the same concentrations of trivalent chromium and ammonium ions in the cultural liquid were detected. The processes of nitrate and nitride reduction, carried out by bacteria of Desulfovibrio genus, were revealed to be less sensitive to the negative influence of sodium dichromate, as compared with the process of sulfate ions’ reduction, which in the medium with 3.47 mM SO42– and 1.74–10.41 mM Cr(VІ) decreased by 3.2–4.6 times as compared with this process in the medium with only Na2SO4×10H2O. The investigated strains of bacteria are adapted to high concentrations of toxic pollutants (up to 10.41 mM) and therefore are promising for application in technologies of complex environment purification from hexavalent chromium, sulfur and nitrogen compounds.

Nephroprotective Efficacy of Selenium and Zinc Against Potassium Dichromate-Induced Renal Toxicity in Pregnant Wistar Albino Rats.

Hexavalent chromium (CrVI) compounds are potent toxicants commonly used in numerous industries. Thus, potential toxic effects and health hazards are of high relevance. Selenium (Se) and zinc (Zn) are known for their antioxidant and chemoprotective properties. However, little is known about their protective effects against CrVI-induced renal damage during pregnancy. In this context, the present study aimed to investigate the protective efficacy of these two essential elements against potassium dichromate-induced nephrotoxicity in pregnant Wistar Albino rats. Female rats were divided into control and four treated groups of six each receiving subcutaneously on the 3rd day of pregnancy, K2Cr2O7 (10mg/kg, s.c. single dose) alone, or in association with Se (0.3mg/kg, s.c. single dose), ZnCl2 (20mg/kg, s.c. single dose) or both of them simultaneously. The nephrotoxic effects were monitored by the evaluation of plasma renal parameters, oxidative stress biomarkers, DNA damage, and renal Cr content. The obtained results showed that K2Cr2O7 disturbed renal biochemical markers, induced oxidative stress and DNA fragmentation in kidney tissues, and altered renal histoarchitecture. The co-administration of Se and/or ZnCl2 has exhibited pronounced chelative, antioxidant, and genoprotective effects against K2Cr2O7-induced renal damage and attenuated partially the histopathological alterations. These results suggest that Se and Zn can be used as efficient nephroprotective agents against K2Cr2O7-induced toxicity in pregnant Wistar Albino rats.

[Antigenotoxicity of the soy isoflavone genistein in mice exposed to carcinogenic hexavalent chromium compounds].

Introduction: the consumption of antioxidant-rich foods such as soy isoflavones may be an alternative in the protection and modulation against metal-induced genotoxicity with carcinogenic potential associated with oxidative stress. Objective: to evaluate the antigenotoxic effects of soy isoflavone genistein in mice exposed to carcinogenic compounds of hexavalent chromium (Cr[VI]). Material and method: twenty-five male Hsd:ICR mice were divided into five groups treated as follows: a) vehicle 1 (sterile distilled water, intraperitoneally); b) vehicle 2 (corn oil for fat-soluble compounds, orally); c) 15 mg/kg of genistein, orally; d) 20 mg/kg of CrO3, intraperitoneally; and e) 15 mg/kg of genistein four hours before the application of 20 mg/kg of CrO3. Evaluations of micronuclei (MN), apoptosis, ratio of polychromatic/normochromatic erythrocytes (EPC/ENC) and cell viability in peripheral blood obtained at 0, 24, 48 and 72 hours were performed. Results: the treatment with genistein reduced MN when administered prior to treatment with CrO3, the effect being greater at 48 hours (reduction of 84 %). Cell viability was reduced with genistein and CrO3 treatments alone, the effect being greater in the latter. Conclusions: genistein effectively blocked the genotoxic action of CrO3. The fact that MN and apoptosis were reduced in the group treated with genistein and CrO3 suggests that genistein could have inhibited the oxidative damage of Cr(VI) since, as there were no cells with damage, the apoptotic pathways were not activated.

Removal of chromium (VI) ions from aqueous solutions

The object of the research is the flotoextraction of chromium (VI) ions from model and real waste waters. Hexavalent chromium compounds pose a serious hazard to surface and ground waters and can have mutagenic and carcinogenic effects on living organisms. The study of the process of flotoextraction as a method of purifying waste water from heavy metals using the example of chromium (VI) ions is an important task. The paper considers flotoextraction of chromium (VI) ions using a cationic surfactant – hexadecylpyridinium chloride and butyl alcohol as the organic phase. The dependences of the process efficiency on the presence of a cationic surfactant, the flotoextraction time, the type of organic extractant, the nature of the collector and the surfactant: Cr molar ratio, the initial concentration of pollutants, and the pH of the initial solution were obtained. Certain rational conditions for flotation allow removing 98–99.6 % of pollutants. The method was tested on real wastewater. The importance of this study is emphasized by the fact that flotoextraction has a number of features and advantages. In particular, the possibility of multiple concentration of pollutant ions in small volumes of an organic solvent and the possibility of its further regeneration. In this case, a much smaller amount of an organic solvent is used and the process is not limited by the distribution constant (compared to the extraction method). Flotoextraction is also characterized by the absence of foam (compared to the flotation method) and the absence of large amounts of wet sludge (compared to the reagent method). The proposed method provides a sufficient level of chromium ions removal from wastewater, and can also be used in systems for local wastewater treatment with the subsequent return of water to the technological process. This will ensure a reduction in costs for the consumption of water resources, discharge of wastewater into water bodies, and also limit the ingress of harmful substances into the environment.  

Characterization of the Reduction Mechanism of Chromium(III) By in Situ Microgravimetry and Volumetric Determination of Hydrogen

Processes for chromium electrodeposition based on hexavalent chromium compounds are more and more restricted by governmental laws1 due to the toxic and carcinogenic nature of Cr(VI) compounds. The most promising alternatives to replace hexavalent chromium solutions are trivalent chromium electrolytes considering process management, quality of the deposits and cost issues.2 However, many of these electrolytes suffer from low current efficiencies and reduced process stability compared to hexavalent chromium electrolytes. Organic additives are used to reduce the overvoltage of Cr(III) reduction and, hence, reach an acceptable current efficiency.3 In order to improve performance and reliability of the deposition process, a profound knowledge of the deposition mechanism and the effect of additives is crucial.In this work the stepwise reduction process of Cr(III) to metallic chromium is investigated by gravimetric and volumetric in-situ methods under variation of current density. Electrochemical quartz crystal microbalance (EQCM) was used to quantify the mass of deposited chromium metal.4 The amount of evolved hydrogen gas was determined with a gas burette in combination with a purpose-built setup for collecting the gas. Based on the results, the partial current densities of the two reduction steps of Cr(III) and the hydrogen evolution were calculated. A shift in the ratio of the partial current densities and an increased current efficiency of metal deposition was observed after the addition of saccharin, which is used as additive in chromium electrolytes for decorative applications.5 A mechanism on the mode of action of saccharin during chromium electrodeposition is proposed. European Chemicals Agency, Authorisation List, EC No. 215-607-8, 231-801-5, 231-889-5, 231-906-6, 232-140-5, 232-143-1, 234-190-3, 236-881-5. Z. X. Zeng, A. M. Liang, and J. Y. Zhang, Recent Pat. Mater. Sci., 2 (1), 50-57 (2009). D. Del Pianta, J. Frayret, C. Gleyzes, C. Cugnet, J. C. Dupin, and I. Le Hecho, Electrochim. Acta, 284, 234-241 (2018). M. Leimbach, C. Tschaar, U. Schmidt, and A. Bund, Electrochim. Acta, 270, 104-109 (2018). R. Katirci, Int. J. Surf. Sci. Eng., 10 (1), 73-85 (2016).

High-temperature stability and leaching kinetics of the hexavalent chromium compound, chrome-hauyne (Ca4Al6CrO16)

Cr-refractories usually contain Cr(III) compounds that can convert into carcinogenic Cr(VI) compounds such as CaCrO4 and Ca4Al6CrO16 under alkaline and oxygen-rich conditions. Literature provides insight into the characteristics, thermal stability, and aqueous solubility of CaCrO4, while there is hardly any data available on Ca4Al6CrO16. The present paper comprehensively studied high-temperature stability and leaching kinetics and other characteristics of Ca4Al6CrO16 by using high-temperature XRD, TG-DSC, XPS, Raman, and TRGS 613. XPS confirmed that chromium in Ca4Al6CrO16 is present in the +6 oxidation state. Ca4Al6CrO16 is thermally stable up to 1500 °C in the air but decomposes in nitrogen above 1258 °C to form the Cr3+-containing phases CaCr2O4 and Ca6Al4Cr2O15. The Ksp of Ca4Al6CrO16 in deionized water is 1.0381 × 10−22, 4.5723 × 10−21 and 2.3489 × 10−20 at 12, 25, and 40 °C, respectively. The leaching process of Ca4Al6CrO16 is chemical reaction controlled, with an apparent activation energy of 58.78 kJ/mol.

Increased urine chromium concentrations in a worker exposed to lead chromate due to medicinal herb intake

Background: Hexavalent chromium compounds are sensitizers of the skin and lung. Chronic exposure to hexavalent chromium compounds is associated with respiratory effects and ulceration and perforation of the nasal septum. Such compounds are also considered carcinogens of the lung and nasal and paranasal sinus. Objectives: To demonstrate the importance of studying occupational and non-occupational exposure when assessing the concentration of substances in the urine. Case study: A study was conducted of environmental chromium concentrations in the workplace. In addition, an occupational medical examination was performed, recording activities inside and outside the workplace, eating habits, blood lead and urine chromium at the beginning and end of the workday. Results: One worker exposed to lead chromate presented high chromium concentrations in urine (up to 62 µg/l before the working day and 52 µg/l at the end of the working day). Environmental chromium concentrations in the workplace were below 0.25 µg/m3. In view of the results, a full study was conducted of the patient’s habits outside work. He reported having bought a kilo of a medicinal herb infusion at a street market three weeks previously. The concentration of total chromium in the prepared infusion was 12000 µg/l. The patient stopped consuming the medicinal herb. Subsequently, the urine chromium analysis was below 0.5 µg/l. Discussion and Conclusions: This case is interesting because it demonstrates that the consumption of medicinal herbs can interfere with biological monitoring of workers exposed to hexavalent chromium compounds. This may give rise to confusion and can also create legal problems for companies and workers. It is important to provide advice to workers and to investigate their habits outside work, especially when there is a discrepancy between environmental and biological values. In this case, the increase in urinary chromium is due to the consumption of medicinal herbs.

Hexavalent chromium promotes differential binding of CTCF to its cognate sites in Euchromatin

ABSTRACT Hexavalent chromium compounds are well-established respiratory carcinogens to which humans are commonly exposed in industrial and occupational settings. In addition, natural and anthropogenic sources of these compounds contribute to the exposure of global populations through multiple routes, including dermal, ingestion and inhalation that elevate the risk of cancer by largely unresolved mechanisms. Cr(VI) has genotoxic properties that include ternary adduct formation with DNA, increases in DNA damage, mostly by double-strand break formation, and altered transcriptional responses. Our previous work using ATAC-seq showed that CTCF motifs were enriched in Cr(VI)-dependent differentially accessible chromatin, suggesting that CTCF, a key transcription factor responsible for the regulation of the transcriptome, might be a chromium target. To test this hypothesis, we investigated the effect of Cr(VI) treatment on the binding of CTCF to its cognate sites and ensuing changes in transcription-related histone modifications. Differentially bound CTCF sites were enriched by Cr(VI) treatment within transcription-related regions, specifically transcription start sites and upstream genic regions. Functional annotation of the affected genes highlighted biological processes previously associated with Cr(VI) exposure. Notably, we found that differentially bound CTCF sites proximal to the promoters of this subset of genes were frequently associated with the active histone marks H3K27ac, H3K4me3, and H3K36me3, in agreement with the concept that Cr(VI) targets CTCF in euchromatic regions of the genome. Our results support the conclusion that Cr(VI) treatment promotes the differential binding of CTCF to its cognate sites in genes near transcription-active boundaries, targeting these genes for dysregulation.

Chromium Electroplating from Cr(III) in Deep Eutectic Solvents

Hard chromium coatings are often used to improve the wear and corrosion resistance of different tools and components. Often electrolytes based on hexavalent chromium compounds, which are highly oxidative and carcinogenic, are still used to plate hard chromium layers. A key challenge is the development of an alternative baths free of Cr(VI). Such an alternative could be chromium coatings from a Cr(III)-based electrolyte.Over the last years alternative electrolytes besides water were studied for electroplating. One of these alternatives are the deep eutectic solvents, DES, of which ethaline is a prominent candidate. It is 1:2 molar ratio mixture of choline chloride and ethylene glycol. This DES show good solubility for various metal salts. The electrochemical potential window of most DES is typically in the range of 3 V. Ethaline has excellent physical and chemical properties, such as: it is stable under ambient conditions, easy to prepare and handle, cheap (manufactured on the M tons scale globally) and biodegradable (used as a B-vitamin in animal food), requires no additional registration for process applications, it has good conductivity and low viscosity.This paper will discuss the electroplating of Cr layers from ethaline on steel substrates. Different concentrations of CrCl3 × 6 H2O in the DES were investigated. The influence of LiCl, NaCl, KCl, formic acid and oxalic acid in the electrolyte as well as the influence of temperature were also investigated. Furthermore, the role of deposition technique (direct current or pulsed current) and of the hydrodynamic conditions on the quality of the chromium layers were evaluated.The electrodeposition of some µm thick and adherent chromium films was proved to be possible from ethaline. The hardness of the deposited Cr layers was up to 2500 N/mm2, depending on the process parameters.