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The nano-Sulphonated Poly (glycidyl methacrylate)-Hexamethyl Pararosaniline Chloride (Crystal Violet; CV) composite (CV-SPGMA) has been developed as a novel adsorbent for treatment of Dichromate and Permanganate Contaminated Waste Water for the first time. The innovative adsorbent has been developed by adsorption of CV dye from wastewater using nano-Sulphonated Poly (glycidyl methacrylate) (SPGMA) particles. The study investigated the impact of various adsorption parameters. The CV content was observed to be linearly increased by variations in the concentration of CV up to 200 mg/L where maximum content obtained; 174.6 mg/g. The equilibrium almost reached after 90 min. An endothermic nature of the CV adsorption process has been noticed where 178 mg/g CV content obtained at 80 °C. The CV content decreased from 240 mg/g to 46 mg/g with the SPGMA adsorbent dose increment from 5 to 40 mg. The pH of adsorption exhibited the most pronounced impact, with the highest CV content achieved at a pH of 10.0 corresponding to 190.4 mg/g. The reusability of the produced CV-SPGMA adsorbent was examined for consecutive adsorption–desorption cycles, revealing a loss of just 13% in its initial adsorption efficiency after 10 cycles. In addition, the alterations in the chemical structure and morphology caused by the development of CV-SPGMA composite were observed through the utilization of characterization techniques including Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDAX). Finally, the developed CV-SPGMA composite adsorbent, for the first time, tested for the removal of Cr (VI) and Mn (VII) metal ions from dichromate and permanganate contaminated waters under mild adsorption conditions where shows seven folds affinity towards removal of the Cr (VI), 84.6 mg/g, than Mn (VII), 11.66 mg/g. [ABSTRACT FROM AUTHOR]

Abstract Ettringite is a hydrous calcium aluminum sulfate mineral present in cement. In this study, ettringite was synthesized via co-precipitation to remove methyl blue, dichromate, and copper ions from solutions with various pH values. The synthesized ettringite was characterized using scanning electron microscopy, X-ray photoelectron spectrometry, Fourier transform infrared spectroscopy, zeta potential analysis, and the Brunauer–Emmett–Teller method. Equilibrium adsorption experiments were performed using methyl blue and dichromate at pH values ranging from 5 to 11. To avoid precipitation, equilibrium adsorption experiments were performed on copper ions in solutions with pH values of 3, 4, and 5. The adsorption kinetics experiments for each contaminant were performed at pH 5. The results showed that ettringite was successfully synthesized, and calcite might have precipitated during the synthesis process. The point of zero charge was at pH 8.6. The maximum adsorption capacities for methyl blue, dichromate, and copper ions at pH 5 were 406, 321, and 365 mg/g, respectively. The adsorption kinetics fitted the pseudo-second-order model well. The properties of the contaminants affect their equilibrium and rate constants. Ion exchange is regarded as the primary adsorption mechanism, whereas the other mechanisms include complexation, hydrogen bonding, surface precipitation, π-interaction, and van der Waals forces. This study revealed a new adsorbent, ettringite, for the removal of contaminants from wastewater, which is a promising alternative adsorbent that can be used under specific conditions.

Ettringite is a hydrous calcium aluminum sulfate mineral present in cement. In this study, ettringite was synthesized via co-precipitation to remove methyl blue, dichromate, and copper ions from solutions with various pH values. The synthesized ettringite was characterized using scanning electron microscopy, X-ray photoelectron spectrometry, Fourier transform infrared spectroscopy, zeta potential analysis, and the Brunauer–Emmett–Teller method. Equilibrium adsorption experiments were performed using methyl blue and dichromate at pH values ranging from 5 to 11. To avoid precipitation, equilibrium adsorption experiments were performed on copper ions in solutions with pH values of 3, 4, and 5. The adsorption kinetics experiments for each contaminant were performed at pH 5. The results showed that ettringite was successfully synthesized, and calcite might have precipitated during the synthesis process. The point of zero charge was at pH 8.6. The maximum adsorption capacities for methyl blue, dichromate, and copper ions at pH 5 were 406, 321, and 365 mg/g, respectively. The adsorption kinetics fitted the pseudo-second-order model well. The properties of the contaminants affect their equilibrium and rate constants. Ion exchange is regarded as the primary adsorption mechanism, whereas the other mechanisms include complexation, hydrogen bonding, surface precipitation, π-interaction, and van der Waals forces. This study revealed a new adsorbent, ettringite, for the removal of contaminants from wastewater, which is a promising alternative adsorbent that can be used under specific conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Poly(melamine- co -formaldehyde) (PMF) was templated with SiO 2 nanospheres in H 2 O. • SiO 2 acted as both Pickering-surfactant and template in the synthesis. • PMF prepolymer concentration is decisive for inclusion of SiO 2 into the resin. • This is the first reported aqueous synthesis of porous, column-suitable particles. • The column material was an efficient adsorbent exemplarily shown for dichromate. High nitrogen containing resins such as poly(melamine- co -formaldehyde) (PMF) are known for their very good adsorption properties. Until now, using an ecofriendly hard-templating approach with SiO 2 nanospheres in water for synthesis, only yielded either highly porous particles with diameters up to 1 µm or non-porous particles with diameters above 1 µm. Small particles cannot be used as fixed bed adsorbents in columns because of the very high pressure occurring. To yield particles with high porosity and larger diameters for the use as fixed bed adsorbent, we investigated the influence of several synthesis parameters on porosity and particle morphology. From all variations, we proposed a mechanism for the complex interplay between the PMF prepolymer and resin species with SiO 2 nanoparticles acting both as Pickering-like surfactant and template particle. With this knowledge we were able to produce a suitable column material with high specific surface area up to 260 m2/g. We then proved the application of this material for aqueous dichromate adsorption in batch, yielding a maximum capacity of 138 mg/g with recyclability. In column experiments, the contamination of 5 mg/L dichromate in water was reduced to drinking water safe levels for an influent volume equal to over 160 bed volumes. [ABSTRACT FROM AUTHOR]

Potassium dichromate is widely used in various laboratory and industrial applications. Vitamin C and melatonin are well-known antioxidants. Study the microscopic and morphometric alterations in the thyroid gland in adult male albino rats after the administration of potassium dichromate for successive 2 months and also to assess the possible protective effect of vitamin C versus melatonin on these changes. Sixty adult male albino rats were randomly divided into four main groups. Group I (The control group). Group II received potassium dichromate (25 mg/kg/day) dissolved in distilled water by intraperitoneal (i.p) injection for 2 months. Group III received the same dose of potassium dichromate with vitamin C (120 mg/kg/day) orally through an intragastric intubation. Group IV received the same dose of potassium dichromate and melatonin (10 mg/kg/day) as an i.p injection. Thyroid gland samples were prepared for light and electron microscopic studies. Potassium dichromate group demonstrated congested blood vessels, follicular hyperplasia, follicular enlargement with degenerated lining cells that were exfoliated in the lumen. The parafollicular cells appeared with darkly stained nuclei. PAS reaction showed weak reaction in the colloid with an abnormal pattern of vacuolization. A highly significant increase in the percentage area of fibrosis was detected in Mallory trichrome sections. Ultrastructurally, follicular cells and parafollicular cells appeared irregular in shape with dark, small heterochromatic nuclei. Small, electron-dense granules in the parafollicular cells were found. Potassium dichromate and vitamin C-treated group III showed partial improvement of the thyroid gland. The PAS reaction showed that nearly all the follicles were more or less similar to those of the control group. A significant decrease in the percentage area of fibrosis in group III was found as compared to those in group II. Potassium dichromate and melatonin-treated group showed that the thyroid gland was nearly similar to that of the control group. Vitamin C and melatonin could partially protect against potassium dichromate induced changes in the thyroid gland and the protective effect of melatonin was better than that of vitamin C. [ABSTRACT FROM AUTHOR]

Recent studies have shown that Cr uses other element transporters such as phosphate transporters to enter cells. The aim of this work is to explore the interaction between dichromate and inorganic phosphate (Pi) in the plant of Vicia faba L. To study this interaction, we used three concentrations of Dipotassium hydrogen phosphate (K 2 HPO 4) 10 mM (Pi10), 50 mM (Pi50) and 100 mM (Pi100) added alone or in combination with potassium dichromate (K 2 Cr 2 O 7) Cr + Pi10, Cr + Pi50 and Cr + Pi100. In order to investigate the impact of this interaction on morpho-physiological parameters, the biomass, chlorophyll content, proline level, H 2 O 2 level, Catalase and Ascorbate peroxidase activity and Cr-bioaccumulation has been determined. For the molecular scale, the theoretical chemistry was used via molecular docking to explore the various interactions between dichromate Cr 2 O 7 2−/HPO 4 2−/H 2 O 4 P− and the phosphate-transporter. We have selected the eukaryotic phosphate transporter (PDB: 7SP5) as the module. The results showed that K 2 Cr 2 O 7 negatively affects morpho-physiological parameters and generates oxidative damage (+84% H 2 O 2 than the control), which involved the production of antioxidant enzymes (+147% Catalase and +176% Ascorbate-peroxidase) and Proline (+108%). The addition of Pi improved the growth of Vicia faba L. and induces the partial restoration of the parameters affected by Cr (VI) to the normal levels. Also, it decreased oxidative damage and reduce Cr (VI) bioaccumulation in shoots and roots. Molecular docking has shown that the dichromate structure is more compatible and establishes more bonds with the Pi-transporter which generates a very stable complex compared to HPO 4 2−/H 2 O 4 P−. Overall, these results confirmed that there is a strong relationship between dichromate uptake and the Pi-transporter. • Competition between dichromate and Pi for the use of Pi carrier. • Dichromate is more compatible with the Pi transporter than Pi. • Dichromate crosses the Pi transporter with high selectivity. • Dichromate can inhibit the Pi transporter even at very low concentrations. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel ionic polymer is developed for removal of dichromate and perfluorooctane sulfonate with high efficiency in water. • The ionic polymer exhibits high adsorption capacity, selective adsorption and recycling stability toward PFOS and dichromate. • The adsorption mechanism for synchronous removal of dichromate and perfluorooctane sulfonate has been proposed. The development of porous adsorbents for removal of concomitant perfluorooctane sulfonate (PFOS) and dichromate pollutants is pivotal and challenging in wastewater remediation. Herein, we presented a leaf-inspired artificial cleaning system based on an ionic polymer (ImIP-6) with high local density of imidazolium moieties and charge-balanced chloride for efficiently simultaneous removal of PFOS and dichromate. ImIP-6 exhibits fast kinetics and ultrahigh uptake capacities with maximum adsorption values of 2606 mg g−1 for PFOS and 247 mg g−1 for Cr(VI), which are far superior to many porous sorbents. The mechanism studies have evidenced that ImIP-6 possesses two types of domains for PFOS and dichromate adsorption, in which the imidazolium-based cationic surface induces PFOS enrichment and subsequent formation of micelles on the outer surfaces without significantly interfering the adsorption of dichromate in the interior pores. This work provides one new approach based on biomimetic systems with hierarchical adsorption domains for wastewater remediation. [ABSTRACT FROM AUTHOR]

A comparative study of interaction between chicken egg white lysozyme (Lyz) with two hexavalent chromate ions; chromate and dichromate; which are prevalently known for their toxicity, was investigated using different spectroscopic techniques along with a molecular docking study. Both steady‐state and time‐resolved studies revealed that the addition of chromate/dichromate is responsible for strong quenching of intrinsic fluorescence in Lyz and the quenching is caused by both static and dynamic quenching mechanisms. Different binding and thermodynamic parameters were also calculated at different temperatures from the intrinsic fluorescence of Lyz. The conformational change in Lyz and thermodynamic parameters obtained during the course of interaction with chromate/dichromate were well‐supported by the molecular docking results. [ABSTRACT FROM AUTHOR]

Two novel receptors 5,11,17,23-tetra-tert-butyl-25,27-bis[(ethoxycarbonyl)methoxy]-26,28-bis-[1-methyl-(imidazole)meth-oxy]-2,8,14,20-tetra-thiacalix[4]arene (L1) and 5,11,17,23-tetra-tert-butyl-25,27-bis-[(benzyl)methoxy]-26,28-bis-[1-methyl-(imidazole)-methoxy]-2,8,14,20-tetrathiacalix[4]arene (L2) possessing imidazole moieties based on thiacalix[4]arene in the 1,3-alternate conformation have been synthesized and characterized. The crystal structures of L1 and L2 have been determined. The binding behaviour towards Li+, Na+, K+ and Ag+ ions has been examined by 1H NMR titration experiments in (CDCl3/CD3CN; 10:1, v/v) solution. The exclusive formation of mononuclear complexes of L1 with metal cations is of particular interest revealing a negative allosteric effect in the thiacalix[4]arene family. Liquid-liquid extraction experiments indicate that synthesized L2 can be utilized as an efficient reusable extractant for dichromate anion by controlling the pH of the aqueous solution.

A new probe (Z)-3-((naphthalen-1-ylmethylene)amino)phenol has been synthesized by condensation reaction between 1-naphthaldehyde and 3-aminophenol for the fluorescent sensing of Ce3+ by "on" mode and dichromate (Cr2O72−) by "off" mode. Metal ions—Ag+, Al3+, As3+, Ba2+, Ca2+, Cd2+, Ce4+, Co2+, Cr3+, Cr6+, Cu2+, Fe2+, Fe3+, Hg2+, K+, La+, Li+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Zn2+and anions Br−, C2O42−, CH3COO−, Cl−, CO32−, F−, H2PO4−, HCO3−, HF2−, HPO42−, I−, MnO4−, NO3−, OH−, S2−, S2O32−, SCN−, SO42− do not interfere. The limit of detection (LOD) for sensing Ce3+ and Cr2O72− ions are 1.286 × 10–7 M and 6.425 × 10–6 M, respectively. [ABSTRACT FROM AUTHOR]

Methanesulfonic acid was proven to be an alternative lixiviant for copper leaching from chalcopyrite with hydrogen peroxide as an oxidant. Two alternative oxidants, dichromate and nitrate, were studied for the copper dissolution from chalcopyrite, a refractory copper sulfide mineral. During chalcopyrite leaching tests, both oxidants achieved the copper extraction above 90% in 30 g/L methanesulfonic acid at 75oC. The activation energies in dichromate and nitrate leaching systems were 23 and 43 kJ/mol, classified as mass transfer and chemical reaction-controlled mechanism, respectively. The XRD analysis of a leached residue showed a formation of K-Cr-jarosite from methanesulfonic acid-dichromate system. Methanesulfonic acid with nitrate leaching system could be the most effective and sustainable for chalcopyrite leaching based on the comparative investigation. [ABSTRACT FROM AUTHOR]

A new probe (Z)-3-((naphthalen-1-ylmethylene)amino)phenol has been synthesized by condensation reaction between 1-naphthaldehyde and 3-aminophenol for the fluorescent sensing of Ce3+ by "on" mode and dichromate (Cr2O72−) by "off" mode. Metal ions—Ag+, Al3+, As3+, Ba2+, Ca2+, Cd2+, Ce4+, Co2+, Cr3+, Cr6+, Cu2+, Fe2+, Fe3+, Hg2+, K+, La+, Li+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Zn2+and anions Br−, C2O42−, CH3COO−, Cl−, CO32−, F−, H2PO4−, HCO3−, HF2−, HPO42−, I−, MnO4−, NO3−, OH−, S2−, S2O32−, SCN−, SO42− do not interfere. The limit of detection (LOD) for sensing Ce3+ and Cr2O72− ions are 1.286 × 10–7 M and 6.425 × 10–6 M, respectively. [ABSTRACT FROM AUTHOR]

A new 1,3-distal diphenyl(4-piperidin)methanol-appended calix[4]arene derivative 3 has been successfully synthesized and characterized using FTIR, NMR and elemental analysis techniques. Synthesized 1,3-distal diphenyl(4-piperidin)methanol-appended calix[4]arene derivative 3 has been then grafted onto [3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane-modified Fe3O4 magnetic nanoparticles to produce 1,3-distal diphenyl(4-piperidin)methanol-substituted calix[4]arene derivative-grafted EPPTMS-MN (4). The structure and surface morphology of 1,3-distal diphenyl(4-piperidin)methanol-substituted calix[4]arene derivative-grafted EPPTMS-MN have been determined by a combination of FTIR, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) techniques. Moreover, anion binding capabilities of 1,3-distal diphenyl(4-piperidin)methanol-substituted calix[4]arene derivative-grafted EPPTMS-MN toward HCr2O7-, and H2AsO4- ions have been evaluated. The results indicate that 1,3-distal diphenyl(4-piperidin)methanol-substituted calix[4]arene derivative-grafted EPPTMS-MN exhibited 80% sorption efficacy toward Cr(VI), whereas ∼8% sorption efficacy for As(V) was obtained. [ABSTRACT FROM AUTHOR]

Studies on the oxidation of four unsaturated acids by pyridiniumdichromate (PDC) in dimethylsulphoxide (DMSO) lead to form the product epoxide. The reaction is found to be of first-order w. r. t. PDC and an M-M type (fractional order) kinetics are observed w.r.t. acids. Reactions are performed in a non-aqueous medium, the acid effect is studied by adding para toluene sulfonic acid. The reaction shows catalysis on the addition of an acid. The acid effect is shown through the reaction kobs = a + b [H+]. Oxidation is studied in 19 organic solvent mediums, the effect of solvents experiments with the model of Kamlet's and Swain's multi-parametric equation. Cation solvating effects show the importance of finding out the suitable mechanism with three centered transition state is the taking part in the reaction process. [ABSTRACT FROM AUTHOR]

We have studied three thioacids(TA) namely; thio-glycollic(TGA), thio-lactic(TLA) and thio-malic(TMA) acid by imidazoliumdichromate (IDC) in dimethyl-sulphoxide (DMSO). Oxidation of these thio-acids leads to the formation of di-sulphide di-mmers. The reaction is having a unit order with the IDC. A fractional-order reaction was found w.r.t. TA. Test for free radical was not observed in this reaction. The influence of acidity was observed, which indicated the increase in the rate by the addition of acid. The study of oxidation of TLA was done in various nonaqueous media, and the influence of solvent media was examined by using some multi-parametric equation models. We postulate a mechanism in which a thio-eater is formed, which is decomposing in the rate-determining slow step. [ABSTRACT FROM AUTHOR]

A novel flat supplying membrane equipment (FSME) with a sodium hydroxide solution and a mixture of N235/7301 and petroleum has been studied for dislodging dichromate (which can be expressed as Cr (VI) or Cr2O72−) from simulated mine slops. The FSME contained three parts: as a feeding cell, a reacting cell, and a supplying cell. The flat Kynoar membrane was inlaid in the middle of the reacting cell, using the mixed solutions of petroleum and sodium hydroxide, with Tri (octyl decyl) alkyl tertiary amine (N235/7301) as the carrier in the supplying cell and the mine slops with Cr (VI) as the feeding section. The impact parameters of pH and the other ion density in the feeding solutions, the voluminal ratio of petroleum to sodium hydroxide solution and N235/7301 concentration in the supplying solutions were investigated for the obtaining of the optimal technique parameters. It was found that the dislodging rate of Cr (VI) could reach 93.3% in 215 min when the concentration of carrier (N235/7301) was 0.20 mol/L, the voluminal ratio of petroleum and sodium hydroxide in the supplying cell was 1:1, the pH of the feeding section was 4.00, and the Cr (VI) cinit was 3.00 × 10−4 mol/L. The practicability and steadiness of FSME were gained through the exploration of Cr (VI) adsorption on the membrane surface.

Heavy metals, including a hexavalent form of chromium (Cr(VI)) increasing accumulation in agricultural soil, cause a significant reduction in quality, yield, and growth of rice varieties worldwide. Screening for the selection of tolerant varieties is essential for conventional and molecular breeding. Shaheen basmati (SB) and basmati-385 (B-385) rice varieties, a subspecies of indica, show different sensitivity to Cr(VI), but the underlying mechanisms of this different sensitivity remain elusive. In the current study, we examine the sensitivity of SB and B-385 based on the root, which is the primary organ that encounters water and soil containing Cr(VI), elongation assay, and ethylene's possible role (a stress-responsive phytohormone) in the process. Our results show that SB's seedlings exhibit hypersensitivity as a higher root elongation inhibition than B-385 under different Cr(VI) concentrations. Hypersensitive SB consistently expresses a higher level of ethylene biosynthesis and signaling-related genes than B-385. Moreover, ethylene signaling antagonist (silver, Ag) and biosynthesis inhibitor (aminoethoxy vinyl glycine, AVG) alleviate the difference in Cr(VI)-induced root growth inhibition between SB and B-385, respectively. Taken together, we conclude that ethylene mediates difference in sensitivity based on the difference in root growth inhibition in different rice varieties. [ABSTRACT FROM AUTHOR]

Crystals of cobalt(III) salts dinitro(triethylenetetramine)cobalt(III) dichromate [Co(trien)(NO2)2]2Cr2O7 (1) and dinitro(triethylenetetramine)cobalt(III) thiocyanate [Co(trien)(NO2)2]SCN (2) have been synthesized to investigate [Co(trien)(NO2)2]+ cation as a promising host to capture dichromate and thiocyanate anions. The characterization of the newly synthesized compounds was accomplished by elemental analysis and spectroscopic techniques (IR, UV/visible and 1H-NMR) and solubility product measurement. The asymmetric unit of complex 1 has a half dichromate anion and one [Co(trien)(NO2)2]+ cation while that of complex 2 has one thiocyanate anion and one [Co(trien)(NO2)2]+ cation as divulged by X-ray structure determination. The structural investigation exhibited that the crystal lattice was stabilized by second sphere hydrogen bonding interactions such as N–Htrien···O (dichromate), C–Htrien···O (dichromate), N–Htrien···N (thiocyanate) and C–Htrien···N (thiocyanate) interactions resulting in the formation of supramolecular assemblies. The complexes 1 and 2 were further examined for antibacterial activity and the findings unveiled moderate activity against gram-negative bacteria such as Escherichia coli and Pseudomonas aeruginosa species. These complexes were also scrutinized for anti-proliferative activity against malignant PANC-1 cells using MTT cell survival analysis. Complex 1 exhibited remarkable anticancer activity whereas complex 2 has comparatively lesser anticancer potential. Crystals of cobalt(III) ion [Co(trien)(NO2)2].X (X= ½.Cr2O7 (1)/ SCN (2)) have been synthesized and characterized by various spectroscopic and analytical techniques. Structural study of 1 and 2 were established and divulge formation of supramolecular assemblies through H-bonding. Complex 1 and 2 were further examined for antibacterial and antiproliferative activity. Complex 1 exhibited remarkable anticancer activity whereas complex 2 has comparatively lesser anticancer potential [ABSTRACT FROM AUTHOR]

The liquid-phase extraction performance of phthalonitrile (3 and 4) and isoindoline (5 and 6) substituted calix[4]aren derivatives was studied towards (i) some selected divalent heavy metal cations (i.e Co2+, Ni2+, Cu2+, Cd2+, Hg2+, and Pb2+), (ii) dichromate (Cr2O7 2-/HCr2O7 -), and (iii) arsenate (H2AsO4-/HAsO4 2-). In general, extraction yield was observed to be higher in the case of compounds 3 and 5 (cone conformation) when compared to 4 and 6 (1,3-alternate conformation). This indicated a somehow positive effect of cone conformation on the extraction performance rather than 1,3-alternate conformation. The stoichiometric ratio between the compound 3 and 4 with mercury picrate was estimated through job's plot analysis method. [ABSTRACT FROM AUTHOR]

In this work a 1,2,4‐triazole derivative 1‐(4‐aminobenzyl)‐1,2,4‐triazole (abtz) was utilized, one new cadmium(II) coordination polymer, namely [Cd(abtz)I2]n (1) was prepared through the powerful solvo‐thermal synthetic strategy. In compound 1, the abtz building blocks are interlinked through the central CdII ions forming the two‐dimensional (2D) layer coordination framework. Powder X‐ray diffraction (PXRD) characterization also reveals that we have prepared the pure phases of coordination polymer 1. Optical properties have been determined, which can behave the excellent photo‐luminescent emission of coordination polymer 1. Photo‐luminescent experiment also reveals that coordination polymer 1 can behave the highly sensitive detection for acetone molecules with high Ksv value (Ksv = 4.12 ×104 L·mol–1) in the recyclable detection fashion. Additionally, coordination polymer 1 also can behave the highly sensitive detection for pollutant dichromate with excellent quenching efficiency Ksv (Ksv = 2.12 × 104 L·mol–1) and low detection limit [38 × 10–3 mM (S/N = 3)]. UV/Vis, photo‐luminescent lifetime, and PXRD patterns also have been determined to analyze the detection mechanism. [ABSTRACT FROM AUTHOR]

• Following an IV injection, this in-vivo study confirms rat urinary excretion peak at 6.3 h and a nearly constant amount of intra-erythrocyte chromium for 2 days. • A linear relationship exists between IV Cr(VI) dose and the Cr amount in erythrocytes up to 2 days. • Unlike urinary chromium, Cr in erythrocytes may be a good biomarker of recent exposure to Cr(VI). Hexavalent chromium (Cr(VI)) compounds are classified as carcinogenic to humans. Whereas chromium measurements in urine and plasma attest to the last few hours of total chromium exposure (all oxidation states of chromium), chromium in red blood cells (RBC) is attributable specifically to Cr(VI) exposure over the last few days. Before recommending Cr in RBC (CrIE) as a biological indicator of Cr(VI) exposure, in vivo studies must be undertaken to assess its reliability. The present study examines the kinetics of Cr(VI) in rat after a single intravenous dose of ammonium dichromate. Chromium levels were measured in plasma, red blood cells and urine. The decay of the chromium concentration in plasma is one-phase-like (with half-life time of 0.55 day) but still measurable two days post injection. The excretion of urinary chromium peaks between five and six hours after injection and shows large variations. Intra-erythrocyte chromium (CrIE) was very constant up to a minimum of 2 days and half-life time was estimated to 13.3 days. Finally, Cr(III) does not interfere with Cr(VI) incorporation in RBC. On the basis of our results, we conclude that, unlike urinary chromium, chromium levels in RBC are indicative of the amount of dichromate (Cr(VI)) in blood. [ABSTRACT FROM AUTHOR]

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Highlights • Dichromate induces ROS accumulation by altering the antioxidant system that causes cell/tissue damages. • Ethylene signaling and biosynthesis are induced under high Cr(VI) levels in the aerial parts of Arabidopsis thaliana. • Ethylene mediates Cr(VI) induced ROS accumulation by altering the antioxidant system. • A functioning model for the Cr(VI)-induced crosstalk between ethylene and ROS mediated morph-physiological changes. Abstract Dichromate [Cr(VI)] induces phytotoxicity either directly by interfering in a plant's physiological, biochemical, and/or molecular process or indirectly by stimulating reactive oxygen species accumulation (ROS). The underlying mechanism in Cr(VI)-induced ROS mediated phytotoxicity is elusive. In the current study, we investigate the possibility that Cr(VI)-induced alteration in the total biomass production, cell/tissue viability, and cell cycle-related transcriptome is mediated by the accumulation of high ROS level and that ethylene participates in this process. We showed that high Cr(VI) level reduces total biomass, chlorophyll contents, cell/tissue viability, and expression of cell cycle-related genes. Consistently, the oxidative damage and ROS accumulations were significantly increased in the seedlings exposed to higher Cr(VI) concentrations. Furthermore, Cr(VI)-induced EBS::GUS activity and expression level of ethylene signaling and biosynthesis related genes were also reported in the current study. Moreover, Cr(VI)-induced ROS accumulation by down-regulating enzymatic antioxidant system-related genes was slightly increased by the application of exogenous ethylene precursor (ACC), while significantly reduced by ethylene perception and biosynthesis antagonists silver (Ag) and cobalt (Co) respectively. Taken together, our results showed that ethylene mediates dichromate induced ROS accumulation by suppressing the expression level of enzymatic antioxidant enzymes-related genes. [ABSTRACT FROM AUTHOR]

The system H2SO4-K2Cr2O7 is examined for leaching copper, zinc and iron from the copper smelter slag. The presence of dichromate has a positive effect on the copper recovery, which reaches 68% under the following conditions: 0.5 M K2Cr2O7 + 1 M H2SO4, solid-to-liquid ratio = 15 g: 1 L, 120 min, 298 K. The calculated values of Ea of Cu recovery amounts to 34.60 kJ/mol, that of Zn - to 43.96 kJ/mol, while that of Fe - to 44.33 kJ/mol. The recovery of zinc and iron decreases significantly with the presence of K2Cr2O7 and is only 4% - 5% under the conditions specified. This fact can be associated with the selective adsorption of dichromate ions on the surface of the minerals containing zinc and iron. It prevents the recovery of these metals into the solution. This circumstance can be used to separate copper from zinc and iron during the leaching process. About 68% - 70% of the copper present can be recovered during the first stage; the leaching residue can be used for further extraction of zinc. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new Th-MOF based on (E)-4,4′-(1,2-diphenylethene-1,2-diyl)dibenzoic acid was construted. • The response time of Th-BCTPE @PVDF membrane towards both of the chromates and dichromate is less than 5 s. • Th-BCTPE exhibited highly sensitive and selective detection towards chromates and dichromates via fluorescence quenching. The rapid detection of the aqueous chromates and dichromates is necessary because of their chemical toxicity and the potential threat to the environment. Luminescent metal–organic frameworks have been developed to detect a variety of ions, but the chemical stability of most MOFs is not enough to remain intact in aqueous solution. Herein, a solvothermal reaction based on thorium salt and tetraphenylethene-functionalized ligand (E)-4,4′-(1,2-diphenylethene-1,2-diyl)dibenzoic acid (H 2 BCTPE) produces a new porous metal–organic framework with the formula [Th 6 (μ 3 -OH) 4 (μ 3 -O) 4 (BCTPE) 6 (H 2 O) 6 ]·(DMF) 15 (H 2 O) 29 (Th-BCTPE). It was characterized by SC-XRD, PXRD, TGA, nitrogen adsorption, and fluorescence spectrum. Bearing with high chemical stability as well as high photoluminescence quantum yields, Th-BCTPE exhibited sensitive and selective detection towards Cr(VI) oxyanions via fluorescence quenching. The K SV towards chromate and dichromate are 9.6(3) × 104 M−1 and 1.67(4) × 105 M−1, while the limits of detection are low to 131.8 nM (linear range: 0 to 20 μM) and 75.7 nM (linear range: 0 to 27 μM), respectively. Particularly, the response time of Th-BCTPE @PVDF membrane towards both of the Cr(VI) oxyanions is less than 5 s. Our findings demonstrate that Th-MOFs is a promising luminescent sensor on account of its chemical stability, excellent detection efficiency and quick response. [ABSTRACT FROM AUTHOR]

ABSTRAK Kromium (VI) merupakan polutan logam berat berbahaya bagi kesehatan dan lingkungan oleh karena itu pengambilan ion Cr(VI) dalam air penting dilakukan untuk mengatasi pencemaran lingkungan. Proses adsorpsi merupakan salah satu teknik sederhana yang dapat digunakan untuk pengambilan ion logam. Pada penelitian ini telah dilakukan kajian adsorpsi ion dikromat sebagai model limbah Cr(VI) dalam air menggunakan adsorben zeolit alam termodifikasi amina. Penelitian diawali dengan preparasi adsorben zeolit alam termodifikasi amina. Preparasi dimulai dengan pencucian zeolit alam menggunakan akuades, kemudian refluks zeolit alam menggunakan HCl 3M. Zeolit hasil refluks selanjutnya dimodifikasi menggunakan garam ammonium kuarterner, N-cethyl-N,N,N-trimethylammonium bromide (CTAB) dan amina primer, propilamin (PA). Zeolit alam (Z), zeolit teraktivasi asam (ZA) dan zeolit hasil modifikasi amina selanjutnya digunakan sebagai adsorben untuk adsorpsi anion dikromat. Karakterisasi adsorben dilakukan dengan mengunakan metode spektroskopi infaramerah dan difraksi sinar-X, sedangkan jumlah anion dikromat yang teradsorpsi dianalisis dengan spektroskopi serapan atom. Hasil penelitian menunjukkan bahwa sampel zeolit mengandung mineral klinoptilolit, mordernit dan kuarsa. Struktur zeolit tidak mengalami kerusakan oleh perlakuan termal dan perlakuan kimia. Modifikasi zeolit meningkatkan efisiensi adsorpsi zeolit alam. Ion dikromat dapat teradsorpsi dengan lebih baik oleh zeolit termodifikasi amina daripada zeolit teraktivasi asam dan zeolit tanpa modifikasi, dengan kemampuan adsorpsi zeolit termodifikasi CTAB (CTAB-Z) lebih besar daripada zeolit termodifikasi propilamin (PA-Z). Adsorpsi ion dikromat pada adsorben zeolit berlangsung baik dengan urutan CTAB-Z > PA-Z > ZA > Z, dengan kemampuan adsorpsi masing-masing sebesar 1,96; 1,74; 0,90 dan 0,48 mg/g. Adsorpsi anion dikromat oleh zeolit termodifikasi CTAB merupakan adsorpsi kimia (kemisorpsi) dengan energi adsorpsi sebesar 24,66 kJ/mol. ABSTRACT Chromium (VI) is a heavy metal pollutant that is harmful to health and the environment, therefore Cr(VI) ions in aqueous solution removal is important to overcome the environmental pollution. Adsorption process is one of simple techniques that can be used to take metal ions. Adsorption study of dichromate ions as a wastewater model of Cr(VI) has been conducted in this research by using ammine modified natural zeolite as adsorbents. The research was initiated by preparation of adsorbent of ammine-modified natural zeolites. The preparation was started by washing the natural zeolite (Z) using distilled water and refluxing by 3M hydrochloric acid. Refluxed zeolites (ZA) were modified by a quaternary ammonium salt, N-cethyl-N,N,N-trimethylammonium bromide (CTAB), and a primary amine, propylamine (PA). The natural zeolite (Z), acid activated zeolite (ZA) and amine-modified zeolites were then applied for adsorption of dichromate ions. Characterization of zeolite samples was performed by infrared spectroscopy and X-ray diffraction methods to confirm the crystal structure, and atomic absorption spectroscopy method to analyze the adsorbed dichromate ions. Results showed that all zeolite samples contain clinoptilolite, mordernite and quartz minerals. The zeolite structure was not changed by heat and chemical treatments. Modification of zeolites enhanced the adsorption efficiency of natural zeolites. The dichromate ions were better adsorbed on ammine modified-zeolites compared to that of unmodified-zeolite with adsorption ability of CTAB modified zeolite (CTAB-Z) was greater than that of propylammine modified zeolite (PA-Z). The adsorption of dichromate on zeolite samples was achieved in the order of CTAB-Z > PA-Z > ZA > Z, with the adsorption efficiency was about 1.96; 1.74; 0.90 and 0.48 mg/g, respectively. The dichromate ions adsorption by CTAB modified zeolite is chemical adsorption (chemisorption) with the adsorption energy of 24.66 kJ/mol.

The mechanism of adsorption of dichromate by imidazole ionic liquid-bonded silica gel was studied. Two different adsorbents for adsorption of dichromate ions were synthesized and characterized. By static adsorption experiments, when the pH was 5.6 and the initial concentration of Cr was 200 μg/mL, the adsorption capacity of 1-methylimidazole ionic liquid-bonded silica gel (SilprMmimCl) and 1-ethylimidazole ionic liquid-bonded silica gel (SilprEmimCl) for Cr (VI) was 24.03 mg/g and 16.52 mg/g, respectively. To investigate the mechanism of adsorption on molecular scale, an simplified model of SilprMmimCl and SilprEmimCl have been modeled with [Mmim]Cl, [Emim]Cl, [Mmim][Cr 2 O 7 ] and [Emim][Cr 2 O 7 ]. The structures of related models were optimized at the B3LYP/6-311+G(d, p) level. The weak interaction between cations and anions of models was analyzed by vibration analysis and bond length analysis; the features of bonds at bond critical points and the variations of bond types was studied by Atoms In Molecules (AIM) theory. Simultaneously, noncovalent interactions were characterized and visualized by analysis of Reduced Density Gradient (RDG). Finally, The sequence of intra-molecular interaction energy is [Mmim][Cr 2 O 7 ], [Emim][Cr 2 O 7 ], [Mmim]Cl, [Emim]Cl from big to small, which demonstrates why SilprMmimCl and SilprEmimCl have a good adsorption capacity for dichromate and the adsorption capacity of SilprMmimCl is slightly more than that of SilprEmimCl. [ABSTRACT FROM AUTHOR]

The particle surface properties are essential for understanding froth flotation, particularly for the evaluation of various chemical or reagent effects. Dynamic Vapor Sorption (DVS) is used in the pharmaceutical industry for the evaluation of surface properties and has to the knowledge of the authors not been used for applications in mineral processing. This paper describes an evaluation of industrial ore samples using DVS. Four samples (feed, CuPb concentrate, Cu concentrate and Pb concentrate) from each of the Cu – Pb flotation processes in the Boliden and Garpenberg concentrators, Sweden, were analyzed by DVS in order to investigate if this technique could be used to estimate differences in their hydrophilicity. The DVS measures the water uptake as a function of the relative humidity (%RH) at constant temperature. For both series of four samples, it was found that the DVS-data are in precise agreement with the flotation theory on hydrophobicity (indicated by differences in water uptake). The feed material, without any collectors, adsorbed more water compared to the CuPb bulk concentrate, which in turn adsorbed more water than the Cu concentrate. The lead concentrate on the other hand, which had been depressed by dichromate and should be more hydrophilic, showed a higher adsorbance of water than that of the CuPb concentrate. The repeated measurements of three sub samples from one of the ore samples gave a mean value and an estimated standard deviation of 0.13 ± 0.01%. This shows that the method gives highly reproducible results and that the differences between the samples had high significance. This also shows that the DVS method can serve as a useful complement to traditionally used contact angle or capillary absorption-based measurement methods, especially when screening for new flotation reagents on industrial ore samples. [ABSTRACT FROM AUTHOR]

Summary: Background: Historically, allergic contact dermatitis caused by hexavalent chromium [Cr(VI)] in cement was the most common cause of invalidity attributable to skin disease in Sweden. Since the legislation to reduce Cr(VI) in cement was introduced in 1989, we rarely see allergic contact dermatitis caused by cement. Objectives: To examine the frequency of contact allergy to Cr(VI) in southern Sweden in 2005–2014. Methods: We investigated the occurrence of positive reactions to potassium dichromate 0.5% pet. in consecutively tested dermatitis patients, and compared the occurrence of atopic dermatitis, localization of dermatitis and simultaneous positive reactions to cobalt chloride and nickel sulfate in the Cr(VI)‐positive patients with those in a group of patients with a similar age and sex distribution. Results: In total, 6482 patients were tested, and 233 Cr(VI)‐allergic individuals were found (3.6%). A significantly higher proportion of atopic dermatitis was found among Cr(VI)‐allergic patients, and a significantly higher share of foot dermatitis was found among Cr(VI)‐allergic women, than among controls. Cr(VI) allergy was less likely when both nickel allergy and cobalt allergy were present. Conclusion: A relatively high frequency of contact allergy to Cr(VI) was found. The cause has shifted from cement exposure to other exposures, probably mainly leather. [ABSTRACT FROM AUTHOR]

Geopolymer (GP) consists of polymeric Al and Si tetrahedral network, with alkali metal cation (Na + or K + ) balancing the negative charge of Al tetrahedra. Although immobilization of heavy metal cations, that could balance the negatively charged Al tetrahedra in GP, was extensively studied, this is the first study that deals with immobilization of metal anions (dichromate, permanganate and hexacyanoferrate). GP samples were prepared from metakaolin (MK) as an aluminosilicate material and sodium silicate activator (Si/Al molar ratio 2) in the presence of the three anions. The efficiency of immobilization was studied in terms of % leaching of metal anions using atomic absorption spectrophotometry and in terms of leaching of total metal anions by conductivity measurements. The % leaching was less than 10% when 0.2% (w/w) of metal anion salts were incorporated in the GP. However, the % leaching increased from 10% to 20% with increasing loading of dichromate salt from 0.2% to 1.5% (w/w) which indicates that GP has limited capacity (limited number of pores) for immobilization of metal anions. When silica gel and alumina were employed as additives to MK (changing Si/Al ratio), the leaching of dichromate and total ions increased substantially and the surface of GP becomes more crystalline as indicated by SEM and EDS studies. The present work suggests that the mechanism of heavy metals immobilization by balancing the negatively charged Al tetrahedra of GP is not true. [ABSTRACT FROM AUTHOR]

[Display omitted] • A dual-functional UiO type metal-organic framework (Zr-Sti) was synthesized. • TNP and Cr 2 O 7 2− could be simultaneously detected by the probe. • The probe could be used for TNP and Cr 2 O 7 2− removal with high efficiency. 2,4,6-trinitrophenyl phenol (TNP) and dichromate (Cr 2 O 7 2−) have serious toxicological effects on environment. Therefore, it is very important to detect and remove TNP and Cr 2 O 7 2− in environmental matrix. In this work, a dual-functional UiO type metal-organic framework (Zr-Sti) was synthesized for simultaneous detection and removal of those pollutants in aqueous solution. As for detection, Zr-Sti exhibited sensitive and selective fluorescence response to TNP and Cr 2 O 7 2− with detection limit below μM level, and possible mechanism behind was proposed and partially supported by experiment data. In addition, adsorption capacity of the prepared Zr-Sti for TNP and Cr 2 O 7 2− was further investigated to evaluate its performance in pollutant removal from aqueous solution, and the mechanism behinds the obtained high removal efficiency was proposed. These results together with the satisfied recovery for simultaneous detection of TNP and Cr 2 O 7 2− in real sample, indicate the potential of the prepared Zr-Sti material in the field of environment monitoring and remediation. [ABSTRACT FROM AUTHOR]

Asgat ore sample with estimated content of 431g/t silver was concentrated by using floatation method and obtained freibergite-tetrahedrite concentrate with 9050g/t Ag, 35.75% Cu, 28.5% Sb and 10.6% Fe, respectively. The dissolution of concentrate in acidic potassium dichromate solution has been investigated with respect to the sulfuric acid and potassium dichromate concentrations and by changing leaching temperature and time. Leaching freibergitetetrahedrite concentrate in dichromate acidic solution (K2Cr2O7-0.1M, H2SO4-0.4M leaching time 4h, leaching temperature 95°С) resulted total amount of leaching of 95.65 % silver, 93.85% copper, 99.86 % antimony and 30.18% iron. DOI: http://dx.doi.org/10.5564/mjc.v14i0.196 Mongolian Journal of Chemistry 14 (40), 2013, p36-40

Hexavalent chromium [Cr (VI)]-mediated oxidative stress causes severe hepatic toxicity. This study aims to investigate the protective role of oral vitamin E administration against potassium dichromate (K2Cr2O7)-induced hepatotoxicity. Adult male rats (Rattus norvegicus, n = 24) weighing 150–180 g were used and divided into 4 groups (n = 6 per group): the control group received distilled water; control + vitamin E group received vitamin E (100 mg/kg b.w.); Cr group received K2Cr2O7 (8 mg/kg b.w.), and Cr + vitamin E group received K2Cr2O7 + vitamin E. All treatments were administered orally on a daily basis for 6 weeks. There was a significant accumulation of Cr in the livers of the Cr group compared with the control group. In addition, exposure to K2Cr2O7 induced significant increases in the level of thiobarbituric-reactive substances (TBARS) and significant decreases in glutathione (GSH) content and superoxide dismutase (SOD) activity in the Cr group compared with the control group. Moreover, livers of the Cr group showed major histological alterations, such as severe necrosis, increased lymphocytic infiltration, and a significant decrease in the DNA content. Oral vitamin E administration concomitant with K2Cr2O7 ameliorated all these changes and resulted in normal hepatic histological and cellular contents. In conclusion, oral vitamin E administration has a hepatoprotective role against K2Cr2O7-induced hepatotoxicity in rats.

Abstract: A cationic metal–organic framework (MOF), [Cu2L(H2O)2]⋅(NO3)2⋅5.5 H2O (1) has been successfully synthesized from a zwitterionic ligand 1,1′‐bis(3,5‐dicarboxyphenyl)‐4,4′‐bipyridinium chlorine ([H4L]Cl2). The framework of compound 1 contains classical {Cu2(O2C)4} paddlewheels, and possesses typical nbo‐type topology and two types of channels with sizes of 5.0 and 15.54 Å. Benefitting from the 3D cationic framework and high pore volume, compound 1 shows interesting selective adsorption ability for anionic dyes. Such material can be successfully employed in a chromatographic column to efficiently separate mixed dyes of Fluorescein Sodium and Methylene Blue. In addition, compound 1 exhibits excellent Cr2O72− removal capacity with maximum adsorption amount of 222.5 mg g−1, which ranks among the higher Cr2O72− adsorption amounts of MOF materials ever reported, based on ion‐exchange. The strategy to construct cationic MOFs based on zwitterionic ligands will promote the development of functional porous materials for the capture and removal of anionic pollutant species from contaminated liquid. [ABSTRACT FROM AUTHOR]

A new quinoline-amide calix[4]arene 3 -receptor for detection of hazardous anions and cations have been synthesized. The 3 -receptor was examined for its sensing properties towards several different anions (Cr 2 O 7 2 − , SCN − , F − , Cl − , NO 3 − ) and metal ions (Hg 2+ , Cd 2+ , Ag + ) by UV–vis and fluorescence spectroscopies. It was detected that the 3 -receptor has only sensing ability for Cr 2 O 7 2 − and Hg 2+ ions, resulting in the association constants higher for Cr 2 O 7 2 − than to the Hg 2+ ions. High selectivity towards Cr 2 O 7 2 − were also observed by fluorescence measurement among other ions (F − , Cl − , SCN − , Hg 2+ , Cd 2+ , Ag + ) with a low limit of detection (7.36 × 10 −6 mol dm −3 ). Proton NMR anion-binding investigations revealed a strong interaction of Cr 2 O 7 2 − anion with NH and C H groups of the receptor, showing that the combination with hydrogen-bonds donor groups strengthened the anion receptor association. Furthermore, remarkable association constants for dichromate anion obtained by all techniques strongly suggest the 3 -receptor as a selective Cr(VI) sensor. [ABSTRACT FROM AUTHOR]

Immobilized coupling product (CP) of chitosan with humic acid was prepared to overcome the solubility limitations in using chitosan and HA as adsorbents for heavy metals ions. Two CPs were prepared; FCP from Fluka humic acid and JCP from Ajloun(Jordan) humic acid. The prepared CPs were found to be insoluble in the pH range from 2 to 12. The CPs were studied by elemental analysis, Ba(OH)2 titration, potentiometric titration, FTIR, solid 13C-NMR, SEM and XRD. The results indicated the formation of covalent amide/ester bonds and electrostatic bonds (~~~NH3 + ….– OOC~~~) between chitosan and humic acid. The uptake of Pb(II) and Cd(II) by CPs was found to increase with increasing pH and ionic strength, while, the reverse was observed in the case of Cr2 O7 2– which indicated a unique behavior of CPs compared with free humic acid and chitosan. The adsorption capacities of Pb(II), Cd(II), and Cr(VI) were 33.0, 24.7, and 56.5 mg/g, respectively, in the case of FCP, and 54.9, 20.1, and 54.1 mg/g, respectively, in the case of JCP. The effect of time and temperature on adsorption showed that it is fast, endothermic and entropy driven. The SEM indicated tight surface of CPs due to the strong bonding between chitosan and humic acid. To overcome this problem, CPs were modified by spread over silica gel to produce a high capacity adsorbent (486 mg Pb/g FCP) which has superior removal of low concentrations of Pb < 30 ppm with about 100% efficiency [ABSTRACT FROM AUTHOR]

In this work we have designed a simple, eco-friendly, one-pot method for the synthesis of palladium nanoparticles of quantum dot dimension (PdQDs) using a non-toxic, biocompatible block co polymer which functions as a reducing and stabilizing agent during the synthesis. The entire synthesis is free from any especial experimental set up and reaction conditions. These QDs were characterized by several well know characterization techniques such as UV–vis spectroscopy (UV–vis), transmission electron microscopy (TEM), Fourier transform infra-red spectroscopy (FTIR), dynamic light scattering (DLS), and ξ potential measurements. The transformation of a yellow solution into dark brown solution was indicative of the formation of the PdQDs. The kinetics of this reaction was monitored using a time scan absorption measurement which reveals a sigmoidal curve, a signature of noble metal nanoparticles. The rate of nucleation and growth were calculated using Finke and Watzky model. The synthesized colloidal PdQDs were employed for the reduction of environmentally toxic Cr(VI) to safer Cr(III). The reaction was catalyzed by the PdQDs in presence of acetic acid and was dependent on the concentration of both. The order and rate constant of the reduction reaction was calculated. A comparatively faster and complete reduction of Cr(VI) to Cr(III) using this catalysis was achieved at room temperature in presence γ irradiation, thus making the method more effective in its approach for bulk remediation of Cr(VI). [ABSTRACT FROM AUTHOR]

Electrolyte used in the manufacturing process of sodium chlorate contains chromate primarily to inhibit cathodic loss reactions. Chromate also accelerates the chlorate formation reaction which reduces the concentration of hypochlorite species in the chlorate cell leading to enhanced anodic current yield, reduced risk of oxygen explosions and reduced cost for the purification of the cell gas. Laboratory scale trials show that the rate of chlorate formation can be described as an ‘uncatalyzed’ third order reaction with respect to hypochlorite species and a parallel chromate catalyzed reaction of apparent reaction order 2.2. Validation is presented based on data from electrolysis trials in pilot plant and bench scale at technically relevant conditions. If the dichromate concentration is increased from 0 to 5 g/L, more than 50% of the chlorate may be formed via the chromate catalyzed path and the apparent reaction order changes from 3 to about 2.4. The kinetic effect of the chromate species also lowers the optimum reaction pH below that of the uncatalyzed reaction. Furthermore, anionic hypochlorite does not seem to be necessary to generate chlorate via the chromate catalyzed path. Other hypochlorite consuming reactions such as anodic and homogeneous oxygen formation as well as cathodic reduction and desorption of chlorine species in the cell gas only have a marginal effect on the hypochlorite concentration in the chlorate cell. [ABSTRACT FROM AUTHOR]