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Chemical forms of chromium (Cr) in rice seedlings ( Oryza sativa L. cv. BX139) exposed to either potassium chromate Cr(VI) or chromium nitrate Cr(III) were clarified using a hydroponic study. Seven chemical fractions of Cr in different rice tissues were extracted using a sequential extraction method. Results indicated that exposures to both Cr valents resulted in significant accumulation of Cr in rice tissues and Cr(III) was more bioavailable for rice seedlings than Cr(VI). However, Cr chemical forms were inconsistent in both plant materials (root/shoots) as well as in two different Cr variants. Although both Cr variants caused dose-dependent inhibition on relative growth rates of rice seedlings, different inhibition mechanisms most likely exited using a partial correlation analysis. Both fractions of Cr in cell wall and in intracellular location in roots significantly inhibited the relative growth rates of rice seedlings exposed to Cr(VI), while inhibition of the relative growth rate of rice seedlings exposed to Cr(III) was largely stemmed from Cr partition in intracellular fraction in shoots.

In this research, the chromium (VI) adsorption in potassium chromate (K2CrO4) and potassium dichromate (K2Cr2O7) was studied with the low-cost adsorbent derived from sweet tamarind seeds obtained from the food processing industry in Thailand. The tamarind-seed testa was prepared by decoloring the tamarind-seed husks in boiling water and 1% NaOH solution followed by bleaching in H2O2 solution. The major components found in the tamarind-seed testa were alkali hydrolysable, low molecular-weight carbohydrates. The study found that the adsorbent material derived from tamarind–seed testa could well adsorb chromium ions in both chromium compound solutions at pH 2. The adsorption took place rapidly within the first 4 hours and then gradually declined until reaching adsorption equilibrium in 12 hours. Adsorption of chromium (VI) from potassium chromate solution was superior to that from potassium dichromate. Chromium adsorption at pH 2 fitted well with Langmuir and Freundlich isotherms. The adsorption mechanism in both solutions was a monolayer chemical adsorption rather than multilayer physical adsorption. The adsorbent could almost completely remove chromium in potassium chromate (90% removal) while it could remove 57% chromium from potassium dichromate solution when the initial chromium concentration of 100 mg/l was employed.

Hydroponic experiments were conducted to investigate the influence of chromium (Cr) exposure on assimilation of 15N-labeled nitrate in rice (Oryza sativa L. cv. XZX 45) seedlings. Results showed that exposure of young seedlings to both Cr compounds led to a linear decrease in relative growth rate, nitrate reductase (NR) activity and tissue 15N accumulation though responses differed between the two Cr variants, in which potassium chromate [Cr(VI)] caused more severe effects than chromium chloride [Cr(III)]. Analysis of subcellular distribution of Cr showed that Cr deposition in cell wall was the highest in tissues of rice seedlings exposed to Cr(III), whereas the largest deposition of Cr in the roots was associated with cytosol in the Cr(VI) treatments. Analysis of a partial correlation between tissue fractions of Cr, NR activity and 15N content revealed that depression of NR activity in plant materials of rice seedlings exposed to Cr(III) was mainly associated with a decrease in 15N accumulation, whereas inhibition of NR activity from exposure of plants to Cr(VI) was most likely due to the presence of Cr in cytosol. Information collected here indicated that mechanisms of transport, subcellular distribution and phytotoxicity of the two Cr compounds were different in rice seedlings.

Different Cr–TiO2 nanocomposite photoelectrodes were fabricated by in situ anodisation of titanium in a single step process using potassium chromate as the chromium source. The morphology and structure were characterised by field emission scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. Optical properties were investigated by UV–Vis diffuse reflectance spectra. The visible light photocatalytic activity of the Cr–TiO2 nanocomposite photoelectrodes was evaluated by measuring the degradation of rhodamine B dye under visible light irradiation. The results showed that Cr–TiO2 nanocomposite electrodes have excellent photocatalytic performance. Cr–TiO2 nanocomposite produced using 5 mM K2CrO4 exhibited better photocatalytic activity than did the pure TiO2 and Cr–TiO2 nanocomposite fabricated using other chromium concentrations. The anodisation process developed in this study is facile, reproducible and inexpensive and can be easily scaled up, thereby pioneering the fabric...

The effect of chromium doping on the photovoltaic efficiency of dye-sensitized solar cells (DSSCs) with anodized TiO2 nanotubes followed by an annealing process was investigated. Cr-doped TiO2 nanotubes (CrTNs) with different amounts of chromium were obtained by anodizing of titanium foils in a single-step process using potassium chromate as the chromium source. Film features were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and ultraviolet–visible (UV–Vis) spectroscopy. It is clearly seen that highly ordered TiO2 nanotubes are formed in an anodizing solution free of potassium chromate, and with a gradual increase in the potassium chromate concentration, these nanotube structures change to nanoporous and compact films without porosity. The photovoltaic efficiencies of fabricated DSSCs were characterized by a solar cell measurement system via the photocurrent–voltage (I–V) curves. It is found that the photovoltaic efficiency of DSSCs with CrTNs1 sample is improved by more than three times compared to that of DSSCs with undoped TNs. The energy conversion efficiency increases from 1.05 % to 3.89 % by doping of chromium.

This study examined the microbial precipitations of Cr(III)-hydroxide and Se(0) nanoparticles during anoxic bioreductions of Cr(VI) and Se(VI) using metal-reducing bacteria enriched from groundwater. Metal-reducing bacteria enriched from groundwater at the Korea Atomic Energy Research Institute (KAERI) Underground Research Tunnel (KURT), Daejeon, S. Korea were used. Metal reduction and precipitation experiments with the metal-reducing bacteria were conducted using Cr(VI)- and Se(VI)-contaminated water and glucose as a carbon source under an anaerobic environment at room temperature. XRD, SEM-EDX, and TEM-EDX analyses were used to characterize the mineralogy, crystal structure, chemistry, shape, and size distribution of the precipitates. The metal-reducing bacteria reduced Cr(VI) of potassium chromate (K₂CrO₄) to Cr(III) of chromium hydroxide [Cr(OH)3], and Se(VI) of sodium selenate (Na₂SeO₄) to selenium Se(0), with changes of color and turbidity. XRD, SEM-EDX, and TEM-EDX analyses revealed that the chromium hydroxide [Cr(OH)₃] was formed extracellularly with nanoparticles of 20–30 nm in size, and elemental selenium Se(0) nanoparticles had a sphere shape of 50–250 nm in size. These results show that metal-reducing bacteria in groundwater can aid or accelerate precipitation of heavy metals such as Cr(VI) and Se(VI) via bioreduction processes under anoxic environments. These results may also be useful for the recovery of Cr and Se nanoparticles in natural environments.

Corrosion is one of the degradation materials in Industrial problem. One of the processing to choose material is to determine how to have resistance to all the environment. This research is carried out to determine characterize the effect of various temperatures (150, 200, 250 °C) and time (4,6 and 8 hours) of exposure of Low Carbon Steel in corrosion rate and mechanical properties by using Mass Balance method and Potassium Chromate vapor as medium corrosion. The results have been shown that the increasing temperature ids increasing corrosion rate which is the maximum value is 5,1215 x 10−4 miles/years. The difference in corrosion rate increasing by 6,3 % based on increasing temperature. The microstructure has shown is intergranular corrosion mode.

In order to investigate the toxicological properties of river pollutants, potassium chromate (K2CrO4) and cadmium nitrate tetrahydrate (Cd (NO3)2·4H2O) were selected as they are commonly discharged from industry to nearby rivers. This paper studied the Median Lethal Concentration (LC50) of the pollutants to the adult red zebrafish by acute toxicity experiments within 96 hours. 120mg/L, 130mg/L, 140mg/L, 150mg/L, 160mg/L, 170mg/L potassium chromate solutions and 16mg/L, 20mg/L, 24mg/L, 28mg/L 32mg/L, 36mg/L cadmium nitrate tetrahydrate solutions were prepared with triplicates to determine the LC50. The results of the preliminary experiments and the calibration curves suggested that the LC50 of potassium chromate and cadmium nitrate tetrahydrate were 165 mg/L and 28 mg/L respectively. The toxicity of thresholds and LC100 were also evaluated. Through the observations of the tested subjects in morphological, ethological and anatomical manners, behavioural alterations, oxidative stress, and immunotoxicity were probably their major causes of death.

The common ice plant (Mesembryanthemum crystallinum L.) is a widely studied model due to its tolerance to numerous biotic and abiotic stresses. In this study, carried out in model pots, the plants were treated with variant doses of Cd(II) and Cr(VI) and proved resistant to extreme levels of these heavy metals. Initial toxicity symptoms were observed upon final concentrations of 818 mg Cd kg&minus, 1 soil d.w., and 1699 mg Cr kg&minus, 1 applied as potassium chromate. Biometric analyses revealed that none of the Cr(VI) doses affected dry weight of the plant organs thus maintaining the shoot-to-root ratio. The Cd and Cr hypertolerance strategies were divergent and resulted in different accumulation patterns. For the case of Cd(II), an excluder-like mechanism was developed to prevent the plant from toxicity. For chromate, high accumulation potential together with Cr(VI) root-to-shoot translocation at sublethal concentrations was revealed (up to 6152 mg Cr kg&minus, 1 shoot at 4248 mg Cr kg&minus, 1 soil). It is concluded that M. crystallinum reveals considerable phytoremediation capabilities due to unique growth potential in contaminated substrates and is suitable for bioreclamation of degraded soils. The plant is especially applicable for efficient phytoextraction of chromate-contamination, whereas for Cd-affected areas it may have a phytostabilizing effect.

The effect of inhibitor concentration and immersion time on the corrosion rate and inhibition efficiency of AISI 1019 steel in seawater environment were investigated by means of weight loss measurement (WLM) at an interval of 6days for a period of 60 days. AISI 1019 steel were immersed in seawater solution in the absence and presence of varying inhibitor concentrations of potassium chromate (PC), Sodium Nitrite (SN), Methyl Orange (MO), Methyl Red (MR), Terminalia Catappa Leaves (TCL) Extract, Carica papaya Leaves (CPL) Extract. The results showed that there is an increase in inhibition efficiency with increase in inhibitor concentration and decrease in inhibition efficiency with increase in immersion time. The inorganic inhibitor (potassium chromate), inorganic inhibitor (Sodium Nitrite), the organic Inhibitor (Methyl Orange), the organic inhibitor (Methyl Red), the green inhibitor (Terminalia Catappa Leaves) and green inhibitor (Carica Papaya Leaves) produced their best inhibition efficiency of 71.94%, 634%, 68.94%, 68.32%, 62.7%, 59.79% respectively at a concentration of 10g/L. From the result obtained, the potassium chromate inhibitor has better inhibitory property than other inhibitors, which revealed that it is best suited for inhibition of corrosion of mild steel in seawater environment.

Herein, we successfully prepared ternary ZnO/AgBr/Ag 2 CrO 4 nanocomposites with tandem n–n heterojunctions as novel visible-light-driven photocatalysts having excellent activity. The preparation method is a facile and low temperature and employs zinc nitrate, silver nitrate, sodium hydroxide, and potassium chromate as starting materials without using any post-preparation treatments. The resultant samples were characterized using XRD, EDX, SEM, TEM, UV–vis DRS, FT-IR, and PL techniques. The results revealed that weight percent of Ag 2 CrO 4 has substantial influence on degradation of rhodamine B under visible-light irradiation and the best activity was observed for the ZnO/AgBr/Ag 2 CrO 4 (20%) nanocomposite. Photocatalytic activity of this nanocomposite is about 16 and 7-fold higher than those of the ZnO and ZnO/AgBr samples. Increase of the photocatalytic activity was attributed to more harvesting of the visible-light irradiation and efficiently separation of the photogenerated charge carriers due to formation of tandem n–n heterojunctions between counterparts of the nanocomposite. Moreover, the preparation time and calcination temperature significantly affect the photocatalytic activity. Based on the trapping experiments, it was shown that superoxide ions and holes have major influence on the degradation reaction.

This study investigated the performance of Amberlite IRC 748 resin in removing calcium ions from highly concentrated potassium chromate solution in a fixed bed column. The exchange capacity increased with initial calcium ion concentration and bed height but decreased as flow rate increased. Four different kinetic models, specifically the bed depth service time (BDST), mass transfer, Thomas, and Yoon-Nelson models, were applied to the experimental data to predict the breakthrough curves and determine the column parameters. The BDST model was extended to the prediction of service times of columns operated at different flow rates and influent concentrations; while the experimental and theoretical data points followed a similar trend, they deviated slightly from each other. The Thomas and Yoon-Nelson model predictions were in very good agreement with the experimental results for all the process parameters studied, indicating that they are suitable for use with these kinds of columns. (C) 2015 Elsevier B.V. All rights reserved.

In this study, Bismuth-based glasses were prepared and doped with various concentration of potassium chromate. They were melted in an electrical furnace at 1250°C for 4 hours then pressed with fire frame to plate shape and annealed at 500°C for 10 min. Optical spectra were used to analyze color shade of glasses. Homogeneity of glasses was analyzed by birefringence technique. Glasses color was changed from colorless to slightly and opaque green with an increasing amount of potassium dichromate and birefringence result showed that the glasses are non-homogenous.

Polyvinyl alcohol/potassium chromate (K2CrO4) composite films were prepared by solution casting technique using distilled water as a solvent, and were further investigated using Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, X-ray diffraction, thermogravimetric analysis, optical microscopy, scanning electron microscopy, and dielectric measurements. Microscopic studies reveal that K2CrO4 was homogenously mixed with polyvinyl alcohol matrix due to interfacial interaction between polyvinyl alcohol and K2CrO4. The composite films showed very high dielectric constant and relatively low dielectric loss. Hence, such composite materials with improved dielectric properties could be useful for fabrication of electrical charge storage device.

Cr-doped TiO 2 nanotubes (Cr–TiO 2 NTs) with different amounts of chromium were obtained directly by the electrochemical anodic oxidation of titanium foils in a single-step process using potassium chromate as the chromium source. The effects of chromium amount in anodizing solution on the morphologies, structure, photoabsorption and photoelectrochemical water splitting of the TiO 2 nanotube array film were investigated. Diffuse reflectance spectra showed an increase in the visible absorption relative to undoped TiO 2 NTs. The photoelectrochemical performance was examined under visible irradiation in 1 M NaOH electrolyte. Photo-electrochemical characterization shows that chromium doping efficiently enhances the photo-catalytic water splitting performance of Cr-doped TiO 2 nanotube samples. The sample (Cr–TiO 2 NTs-1) exhibited better photo-catalytic activity than the undoped TiO 2 NTs and Cr–TiO 2 NTs fabricated using other chromium concentrations. This can be attributed to the effective separation of photogenerated electron–hole upon the substitutional introduction of appropriate Cr amount in to the TiO 2 nanotube structure.

The degradation efficiency and kinetic degradation reaction of Ponceau 6R dye using potassium chromate have been investigated under various experimental conditions: different concentrations of H 2 SO 4 and temperatures. The immediate change of the red coloration ( λ max = 518 nm) to colorless was observed after addition of inorganic oxidizing agent (K 2 CrO 4 ) into the protonated form of Ponceau 6R dye after 48 h. This observation could be attributed to the highest oxidized form of this dye obtained (the quinoid one), which undergoes a hydrolysis reaction to produce p -hydroquinone (H 2 Q) by a mechanism similar to Schiff-base hydrolysis. The cationic form of this matrix is a crucial feature for the hydrolysis process. A kinetic model for oxidation of Ponceau 6R by the combination of chromate was developed based on experimental results. The observed kinetic reaction coefficient was determined and correlated as a function of UV spectral intensity of Ponceau 6R at 518 nm. The degradation rate follows pseudo-first order kinetics with respect to dye concentration.

Effect of chromium (both CrIII and CrVI) were studied on the oxidative damages and the induction of antioxidant defence in turnip. For this purpose turnip (Brassica rapa L.) plants were grown in refined sand under three different sources of chromium, i.e., chromium sulphate (CrIII), potassium chromate (CrVI) and potassium dichromate (CrVI) supplied at 250 µM concentrations for 4, 24 and 168 h (7 days) after 50 days of growth in normal nutrition. The extent of oxidative damage was most in dichromate as it caused a maximum increase in lipid peroxidation and H2O2 concentration in leaves of turnip plants. The growth and biomass of plants decreased, while the levels of chloroplastic pigment and iron increased in plants supplied CrVI (both potassium chromate and potassium dichromate). Exposure of plants to Cr led to increase in Cr concentration, more in the roots than in shoots. Excess supply of Cr (chromium sulphate, potassium chromate and potassium dichromate), though inhibited peroxidase activity (at 4 and 168 h exposure), stimulated catalase, ascorbate peroxidase and superoxide dismutase activities. Localization of different isoforms of APX and SOD on native gels revealed activation of certain isoform in the Cr-treated plants.

Dissolution characteristics of copper in hydrochloric acid medium and the effect of potassium chromate and sodium molybdate on the corrosion process have been studied using potentiodynamic technique, and Electro impedance spectroscopy (EIS). corrosion current density ( I corr) were obtained by Tafel extrapolation technique. Charge transfer resistance (R ct) was obtained from the electrochemical impedance spectroscopy (EIS). The corrosion rate was retarded in presence of sodium molybdate mainly because of the adsorption of the inhibitor on the electrode surface and it was found that the optimum concentration of this inhibitor in 1 M HCl was 0.008 M with an protection efficiency 79.17%, while the corrosion rate was accelerated in presence of potassium chromate.

The oxidizing roasting of carbon ferrochrome in the presence of potassium carbonate and air was investigated. The effects of reaction temperature, reaction time, ratio of alkali-to-ore were studied, together with a discussion of the thermodynamics and macro kinetics. It is observed that the reaction temperature and reaction time have significant influence on the roasting reaction. The reaction mechanism changes greatly as the temperature varies. A two-stage roasting process is favorable for the roasting reaction, and a recovery ratio of 96.51% is obtained through this two-stage roasting method. The chromium residue yielded from this method is quite little, only one third of the product. Moreover, the component of Fe in the residue is as high as 54.28%. Therefore, it can be easily recovered to produce sponge iron, realizing zero-emission of chromium residue.

The corrosion behaviour of a FeCrAl alloy was investigated at 600 °C in O2 + H2O with solid KCl applied. A kinetics and microstructural investigation showed that KCl accelerates corrosion and that potassium chromate formation depletes the protective scale in Cr, thus triggering the formation of a fast-growing iron-rich scale. Iron oxide was found to grow both inward and outward, on either side of the initial oxide. A chromia layer is formed with time underneath the iron oxide. It was found that although the alloy does not form a continuous pure alumina scale at the investigated temperature, aluminium is, however, always enriched at the oxide/alloy interface.

The oxidizing roasting process of carbon ferrochrome to prepare potassium chromate in the presence of potassium carbonate and air was investigated. The effects of reaction temperature, reaction time, mole ratio of potassium carbonate to carbon ferrochrome were studied, and thermodynamics and kinetics were also discussed. It was observed that the reaction temperature and reaction time had a significant influence on the roasting reaction of carbon ferrochrome. The reaction mechanism changed greatly as the temperature varied. A two-stage roasting process was favorable for the roasting reaction, and a chromium recovery rate of 97.06% was obtained through this two-stage roasting method. The chromium residue yielded from this method was only 1/3 of the product. Moreover, the component of Fe in the residue was as high as 55.04%. Therefore, it can be easily recovered to produce sponge iron, realizing complete detoxication and zero-emission of chromium residue.

Al-Mg alloys can precipitate β phase, Mg2Al3, along grain boundaries during long-term exposure to moderate temperatures, resulting in susceptibility to intergranular corrosion. It is of interest to investigate the corrosion inhibition of this alloy in this sensitized condition. Furthermore, recent work has shown that the presence of an altered surface layer (ASL) affects the corrosion behavior of polished AA5083, making it difficult to determine the effectiveness of corrosion inhibitors. The combined effects of the presence of the ASL and inhibitors are not well understood. In this work, the effects of adding potassium chromate (K2CrO4), sodium silicate (Na2SiO3), and sodium vanadate (NaVO3) to NaCl solution were examined using electrochemical methods on sensitized and solutionized AA5083 with and without the ASL present on the surface. The ASL alone may protect the alloy depending on whether or not the alloy was sensitized. All of the tested inhibitors exhibited a suppression of the cathodic reaction, with chromate causing mixed inhibition on sensitized AA5083 without the ASL present. The composition and surface morphology of samples exposed to inhibitors were also investigated. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0501509jes] All rights reserved.

The very early stages of KCl-induced corrosion of a FeCrAl and a FeNiCrAl alloy in an 0211420 environment were studied using in-situ Environmental Scanning Electron Microscopy (ESEM). The samples were KCl contaminated and then exposed to lab air at a total pressure of 4.8 Ton at 450 degrees C. After exposure, the samples were analyzed using SEM-EDX, FIB and STEM-EDX. For both alloys, fast oxide growth occurred at the KCl particles. Far away from the KCl particles, a thin base oxide formed with potassium chromate nodules on top. The base oxide was layered, consisting of iron-chromium oxide on top and alumina in the bottom part. The FeCrAl alloy suffered internal oxidation while the FeNiCrAl did not. Both alloys formed sub-scale chlorides. A mechanism is proposed for the reaction of KCl on the surface and for the formation of different surface features at the KCl particles.

We systematically compared the impacts of four Cr salts (chromic chloride, chromic nitrate, potassium chromate and potassium bichromate) on physiological parameters and chlorophyll fluorescence in indigenous moss Taxiphyllum taxirameum. Among the four Cr salts, K2Cr2O7 treatment resulted in the most significant decrease in photosynthetic efficiency and antioxidant enzymes, increase in reactive oxygen species (ROS), and obvious cell death. Different form the higher plants, although hexavalent Cr(VI) salt treatments resulted in higher accumulation levels of Cr and were more toxic than Cr(III) salts, Cr(III) also induced significant changes in moss physiological parameters and chlorophyll fluorescence. Our results showed that Cr(III) and Cr(VI) could be monitored distinguishably according to the non-photochemical quenching (NPQ) fluorescence of sporadic purple and sporadic lavender images respectively. Then, the valence states and concentrations of Cr contaminations could be evaluated according to the image of maximum efficiency of PSII photochemistry (Fv/Fm) and the quantum yield of PSII electron transport (ΦPSII). Therefore, this study provides new ideas of moss's sensibility to Cr(III) and a new method to monitor Chromium contaminations rapidly and non-invasively in water.

Sodium content of foods can be determined by various methods, including an ion-selective electrode (ISE), the Mohr or Volhard titration procedure, or indicator test strips. Some of these methods are official methods of analysis for specific products, and all these methods are faster and less expensive procedures than analysis by atomic absorption spectroscopy or inductively coupled plasma-optical emission spectroscopy. This laboratory exercise allows one to compare sodium analysis of several food products by ISE, Mohr titration, and Quantab® Chloride Titrators.

The main industrial application s of heavy metals in leather and textile manufacturing, electro painting, corrosion inhibitio n, plating, glassware - cleaning solutions and the production of pigments has increase d concentration of hexavalent chromium in the environment that lead to a serious problem to the ecosystem. Since, h exavalent chromium is found to be toxic in human beings. The present study has been designed to determine hexavalent chromium induced bio molecular changes in Spirulina platensis . Spirulina platensis, a filamentous cyanobacterium known as blue green algae of aquatic ecosystem has high economic importance due to i ts therapeutic potential. Blue green algae , Spirulina platensis was exposed to different concentration (0.01, 0.1, 1, 5, and 10 mg/l) of hexavalent chromium as potassium chromate and observed for different growth parameters for 9 days of incubation period. The concentration variation of carbohydrate, protein and chlorophyll - a pigment in Spirulina platensis was observed in the presence of chromium. T he growth of Spirulina platensis was inhibited upon exposure of different concentrations of chromium. Maximum growth inhibition was observed in 10 mg/l of chromium treated cells as compared to control. The extent of toxicity increased wi th increasing concentration of c hromium along with exposure time.

The effect of several important parameters on the removal of hexavalent chromium by humic acid was evaluated using an optimal experimental design based on Box-Behnken Response Surface method. The factors included temperature、pH、initial potassium chromate concentration and adsorbent dosage. A quadratic model for predicting the optimum removal conditions was derived, and the obtained optimal parameters were temperature 51°C, pH=2.34, initial potassium chromate concentration 14.30mg/L and adsorbent 0.58g. At the optimal conditions, the maximal removal rate of hexavalent chromium reached 73.17 %( forecast value was 73.26%).

Phase equilibria of the system KOH–K2CrO4–K2CO3–Al2O3–H2O and its subsystems were investigated at 150 °C in the high alkali concentrated region. In the concentrated alkali region of the system and its subsystems KOH–K2CrO4–Al2O3–H2O and KOH–K2CO3–H2O, the equilibrium solid-phase K2CO3·1.5H2O was found. In the concentrated alkali region of the complex system, potassium aluminate and K2CO3 play an evident salting-out role to potassium chromate, respectively, and their combined operation lowers the solubility of K2CrO4. The solubilizing effect of K2CrO4 on Al2O3 in the system KOH–K2CrO4–Al2O3–H2O is similar to that of Na2CrO4 on Al2O3 in the system NaOH–Na2CrO4–Al2O3–H2O. These findings can provide a significant and precious database for the production of K2CrO4 and K2CO3 and the recovery of alumina from a concentrated alkali solution.

In this paper, effect of potassium-chromate (K 2 CrO 4 ) and sodium-nitrite (NaNO 2 ) on concrete steel-rebar degradation in sulphuric-acid and in sodium-chloride media were studied. Electrochemical monitoring of open circuit potential and compressive strength effect of the different concentrations of these admixtures in steel-reinforced concretes immersed in the acidic/marine-simulating environments were analysed for detailing admixture performance. Results subjected to ASTM C876 interpretations showed that concrete admixed with 0.145 M potassium-chromate exhibited optimum inhibition effectiveness with good compressive strength improvement in the acidic medium. In the saline medium, the concrete admixed with 0.679 M sodium-nitrite exhibited optimal inhibition performance, but with reduction in concrete compressive strength.

A series of CuFe2O4 nanoparticles was synthesized with the assistance of organic amines or inorganic bases via a hydrothermal method. The prepared samples were confirmed as a spinel-type structure by x-ray diffraction. The shapes of the samples were detected by transmission electron microscope (TEM), which confirmed that all the synthesized samples were nanoparticles. The electrocatalytic properties of the samples modified on a glassy carbon electrode were investigated for the reduction of p-nitrophenol, potassium chromate (K2CrO4), and sodium nitrite (NaNO2) in basic solution using the cyclic voltammetry method. The results showed that all the samples showed enhanced catalytic activity for the reduction of p-nitrophenol, K2CrO4, and NaNO2. Among the samples, CuFe2O4 prepared with cyclohexylamine (S-2) showed the highest catalytic activity for p-nitrophenol reduction, whereas CuFe2O4 prepared with NaOH and PVP (S-4) showed the highest activity for both K2CrO4 and NaNO2 reduction in basic solution.

Three chromium-resistant bacteria Bacillus pumilus-S4, Pseudomonas doudoroffii-S5 and Exiguobacterium-S8 were isolated from chromium-contaminated wastewater/soil and could resist very high concentrations of potassium chromate in Luria agar (up to 25 mg ml−1) and acetate minimal medium (2 mg ml−1). The strains showed growth at diverse pH and temperatures and could resist multiple heavy metals. Pseudomonas doudoroffii-S5 reduced (8.27 mg hexavalent chromium 24 h−1) at a lower initial potassium chromate concentration (100 μg ml−1), but overall more chromate (28.4 mg hexavalent chromium 24 h−1) was reduced at a higher initial concentration (1,000 μg ml−1). The addition of various heavy metals (zinc sulphate, copper sulphate, and manganese sulphate at 50 μg ml−1) in the chromium reduction media did not significantly affect the hexavalent chromium reduction potential of these isolates. The chromium removal/detoxification potential of these strains increased when used in conjunction with hydrophytes Eichornia crassipes and Pistia stratiotes. Interestingly, the whole process runs automatically with less energy input, that is, the bacterial strains support the growth of plant while in turn the plant releases exudates that help bacterial growth.

Flotation researchers have long hypothesised that particles have inherently different flotation rates under the same operating conditions because they have different induction times in the flotation cell. The relationship between flotation rate constant and induction time, however, has yet to be explored. Here we analysed the relationship between micro-flotation rate and back-calculated induction time for galena and sphalerite particles. The floatability of the particles was controlled by depression with potassium chromate (galena) and activation with copper sulphate (sphalerite). The bubble rise velocity vs. size in the micro-flotation experiments was determined by high speed video microscopy and followed the prediction for bubbles with the fully mobile air-water interface. Therefore, the theoretical analysis of the micro-flotation results was carried out, based on the potential flow model for water flow around a mobile bubble surface. The relationship between micro-flotation rate constant and back-calculated induction time was found to rapidly decay exponentially. In this model, flotation rate constant is highly sensitive to induction time. For example, a doubling or tripling of induction time results in an order-of-magnitude decrease in flotation rate constant.

The influence of both solid KCl as well as K 2 CO 3 on the oxidation of the 304 L steel has been investigated in the laboratory. Three temperatures were used; 500 °C, 550 °C, and 600 °C. The steel samples were covered either with KCl or K 2 CO 3 and held in two different atmospheres; dried air and air with a water content of 30%. Exposures with no salt were carried out as well. The exposure time in every test was 168 h. The extent of corrosion, the elemental distribution as well as the identification of corrosion products was determined using a scanning electron microscope equipped with an energy dispersive x-ray analyzer (SEM/EDXA). Both salts were found to be corrosive. The structure of the formed oxide layer was similar with both salts, i.e., the outermost iron oxide layer was followed by an oxide layer containing chromium, iron and nickel, followed by a nickel-rich region before the bulk metal. With both salt indications of a potassium–chromium compound, most likely potassium chromate (K 2 CrO 4 ) was found to be formed as an intermediate. The oxide layer thickness distributions showed some differences between the salts as well as differences within a salt under different conditions.

Our ultimate objective is to form nanoparticles by merging oppositely charged nanodroplets containing different constituents of the nanoparticle and construct a desktop apparatus to do this. These nanodroplets will be in oppositely charged aerosols originating from oppositely charged solutions containing the different component of the nanoparticle. In this paper, as the first stage in establishing the feasibility of this concept, we demonstrate that droplets formed from uncharged solutions will merge and the product of such reactions is the same as when their bulk solutions are mixed. We demonstrate that this is the case for three classes of reactions: the chemiluminescent reaction between Luminol and Potassium Ferricyanide, the pH sensitive fluorescence of Umbelliferone and the precipitation of Silver Chromate by reaction of Silver Nitrate with Potassium Chromate. We present arguments that our future goal using oppositely charged droplets is more efficient synthetically and will produce a narrow distribution of nanoparticle sizes.