Cr Reduction Rate Research Articles

Photocatalytic reduction of Cr(VI) on WO3 doped long TiO2 nanotube arrays in the presence of citric acid

Photoreduction of Cr(VI) was successfully achieved on WO3 doped TiO2 nanotube (NT) arrays in the presence of citric acid. WO3 doped TiO2 NT arrays were fabricated by annealing anodic titania NTs that were preloaded with peroxotungstic acid. Driven by electrostatic force, the negatively charged peroxotungstic acid sol uniformly clung to the positively charged titania NT arrays, causing a solid solution of WO3 and TiO2 after annealing. The citric acid plays an important role in the photoreduction of Cr(VI): (i) it works as a sacrificial electron donor to deplete the photogenerated holes from the excited TiO2; and (ii) it takes part in the redox with Cr(VI) under UV illumination because of its electron rich property. The photochemical-reduction rate of Cr(VI) in citric acid under simulated solar light was 6.9μg/Lmincm2. Subtracting the part mentioned above, the reduction rate of Cr(VI) due to photogenerated electrons from excited photocatalysts increased from 8.3μg/Lmincm2 on TiO2 NTs to 31.6μg/Lmincm2 on WO3/TiO2 NTs containing 1at% of W. The net Cr(VI) reduction rate on WO3/TiO2 NT arrays is 3.76 times that on the unmodified TiO2 NTs. Since both WO3 and TiO2 can be excited by UV light, the enhanced photoactivity of WO3/TiO2 is attributed to the increased probability of charge–carrier separation and the extended photo-response spectrum in visible light region due to the doping of WO3 (band gap: 2.6eV).

Influence of clay minerals on the reduction of Cr 6+ by citric acid

The influence of clay minerals on the reduction of Cr 6+ by citric acid was investigated at pH values 4.0, 4.5 and 5.0 at 25 °C. The results indicate that montmorillonite and illite greatly accelerate the reduction reactions at pH 4.0 and 4.5, but their effects are dramatically reduced at pH 5.0. The role of clay minerals in accelerating the reactions is in the order: illite > montmorillonite ≫ kaolinite, which has a positive correlation with the amount of Mn 2+ adsorbed on the surfaces of these minerals. With light, Fe 3+ also significantly increases reaction rates. Ethylenediaminetetraacetic acid (EDTA) greatly suppresses the acceleration of the reduction reactions by these minerals, indicating that EDTA competes with citric acid for Mn 2+. Thus, the formation of complexes between Mn 2+ and citric acid could be a prerequisite for the acceleration of the reductions of Cr 6+ by clay minerals. In addition, there is no relationship between the specific surface area of clay minerals and the reduction rate of Cr 6+ by citric acid.

Kinetics of the reduction of hexavalent chromium with the brown seaweed Ecklonia biomass

The dead biomass of the brown seaweed, Ecklonia sp., is capable of reducing toxic Cr(VI) into less toxic or nontoxic Cr(III). However, little is known about the mechanism of Cr(VI) reduction by the biomass. The objective of this work was to develop a kinetic model for Cr(VI) biosorption, for supporting our mechanism. The reduction rate of Cr(VI) increased with increasing total chromate concentration, [Cr(VI)], and equivalent concentration of organic compounds, [OCs], and decreasing solution pH. It was found that the reduction rate of Cr(VI) was proportional to [Cr(VI)] and [OCs], suggesting the simple kinetic equation −d[Cr(VI)]/d t = k[Cr(VI)][OCs]. When considering the consumption of organic compounds due to the oxidation by Cr(VI), an average rate coefficient of 9.33 (±0.65) μM −1 h −1 was determined, at pH 2. Although the function of the pH could not be expressed in a mechanistic manner, an empirical model able to describe the pH dependence was obtained. It is expected that the developed rate equation could likely be used for design and performance predictions of biosorption processes for treating chromate wastewaters.

Predictive value of [18F]FDG PET for pathological response of breast cancer to neo-adjuvant chemotherapy

The aim of this prospective study was to evaluate the predictive value of [18F]fluorodeoxyglucose positron emission tomography (FDG PET) for the pathological response of breast cancer after completion of neo-adjuvant chemotherapy. Fifty patients with newly diagnosed, non-inflammatory, large or locally advanced breast cancer undergoing neo-adjuvant chemotherapy were eligible for this study. Clinical assessment was accomplished by comparing initial tumor size with preoperative tumor size. Pathological responses were classified into three groups: pathological non-response (pNR), pathological partial response (pPR) and pathological complete response (pCR). To determine the effect of reduction rate (RR) of peak standardized uptake values for tumor responses, logistic regression analyses were performed. To identify an optimal threshold value of RR for the prediction of pathological response, receiver operating characteristic analysis was performed. Eight per cent (four of 50) of the patients had pCR and 46% had pPR. Ten per cent of patients had clinical CR and 52% had clinical PR. In clinical response, the RRs (+/- SD) of CR (-83.4 +/- 12), PR (-81.8 +/- 22.7) and NR (-79.7 +/- 31.9) showed no statistical differences (P > 0.05). However, for pathological responses, the RR of CR (-96.5 +/- 3.4) had a lower value than those of PR (-87.9 +/- 15.1) and NR (-56.2 +/- 29.6) (P = 0.0006; CR versus PR, P < 0.05; CR versus NR, P < 0.05; PR versus NR, P < 0.01). When -88% of RR was used as threshold value for differentiation between pCR and pPR, the area under the curve (AUC) was 0.788 [standard error (SE) 0.106; 95% confidence interval (CI) 0.589-0.920]. The sensitivity and specificity were 100% and 56.5%, respectively. When -79% of RR was used as threshold value for differentiation between pathological responders and non-responders, the AUC was 0.838 (SE 0.059; 95% CI 0.707-0.927). The sensitivity and specificity were 85.2% and 82.6%, respectively. Despite some limitations, this study suggests a possible predictive value of FDG PET for the assessment of the pathological response of primary breast cancer after neo-adjuvant chemotherapy. However, these findings deserve further investigation on a larger number of patients, and more frequent and earlier PET scans in each patient need to be performed to allow a better validation of the differentiation between the responder and non-responder groups.

Recovery Rate of Chromium from Stainless Slag by Iron Melts

The kinetic behavior of Cr 2 O 3 reduction by iron melts containing carbon, aluminum and silicon were investigated at various conditions in order to understand effective slag treatment for recovery of chromium from stainless slag. It was found that the recovery rate of chromium was fairly slow, but it was considerably accelerated by the addition of some fluxes, such as Al 2 O 3 and SiO 2 to the slag, which promoted the formation of liquid slag at the early stage of the reaction, and the recovery ratio of chromium was also improved. In addition, SiO 2 addition was more effective for increasing the chromium recovery than Al 2 O 3 addition due to the effect of CaO/SiO 2 ratio of slag on the reduction rate of Cr 2 O 3 in slag. The experimental results were well simulated by the previous kinetic reaction model based on two-film theory. The modeling study showed that the transfer rate of chromium from slag to metal was controlled by the mass transport in the slag phase.

Reduction of Cr(VI) Using Polyaniline–Polystirene-Divinyl Benzene Gels

Wastewaters generated by electroplating, Industry of Pigments, Tannins, etc. contain Cr(VI).The removal of Cr(VI)from wastewaters is necessary due to its toxicity; the admissible concentration being 10 ppm.This work studies quantitatively and qualitatively the possibility of treating waste waters that have a concentration of 0.1 g/l Cr(VI), by using DVB gels coated with Pani films.The Pani films were applied on the DVB's surface both by polymerization of aniline in acid medium, using ammonium peroxodisulphate as the oxidizing agent and by treating the DVB gels with Pani solutions in N,N-dimethylformamide.During reaction, the reduction rate of Cr(VI)decreases because the Pani films are degrading. This degradation is generated by over-oxidation, phenomenon that leads to a series of secondary hydrolysable products.

Reduction Rate of Cr2O3 in a Solid Powder State and in CaO-SiO2-Al2O3-CaF2 Slags by Fe-C-Si Melts.

In order to understand effective conditions to recover chromium from stainless steel-making slags, the kinetic behavior of Cr 2 O 3 reduction by iron-carbon melts were investigated at various conditions by using solid Cr 2 O 3 powder and Cr 2 O 3 -CaO-SiO 2 -Al 2 O 3 -CaF 2 slags. The effect of temperature on the reduction rate of solid Cr 2 O 3 was fairly large and the apparent activation energy was about 180 kJ mol -1 . The overall reduction of solid Cr 2 O 3 was considered to be controlled by a chemical reaction step. For reduction of Cr 2 O 3 in slag, the addition of CaF 2 to slag and of silicon to iron melt promoted the reduction rate, but the reduction of Cr 2 O 3 powder was retarded by the silicon addition. The kinetic behavior of reduction of Cr 2 O 3 in slag could be well simulated by the kinetic reaction model proposed previously. As a result, it was found that the overall reduction rate of Cr 2 O 3 in slag was controlled by the mass transport in the slag phase.

Lelaching Test on Toxic Elements from Steelwork Fume Powders, Stabilised with two Different Procedures.

In this work, experimental results about two stabilisation processes of steelworks powders, obtained, the first, through an hydraulic binder (Portland cement) and ferrous sulphate solution, and the second one by natural clay soil, are reported. The stabilised wastes obtained have been tested by means of two leaching test: IRSA-CNR with 0.5 M CH 3 COOH and UNI 10802 test in distilled water. The first one is the test actually used in Italy for the management of industrial solid waste landfills. The relative results, obtained testing steelworks powder stabilised by means of the first procedure, point out the necessity of operating in a optimal range of pH that is a balance between the optimal thermodynamic conditions, in which Cd ++ and Pb ++ show the minimum solubility, and the kinetic conditions, in which the reduction rate of Cr(IV) is sufficiently fast.

Creatol, an oxidative product of creatinine in hemodialysis patients

Creatol (CTL) is a product resulting from the reaction of creatinine (Cr) with the hydroxyl radical and is identified as a precursor of methylguanidine (MG), a uremic toxin. In this study, we investigated serum CTL levels together with those of Cr and MG in 66 patients who were on maintenance hemodialysis (HD). Prior to dialysis, the mean serum levels of Cr, CTL and MG were 967 (=11.1 mg/dl) ±267 μM, 11.1 ± 4.8μM and 5.8±2.9 μM, respectively. The mean CTL level was about 1.1% that of Cr, and the CTL plus MG level was about 1.4% that of the Cr level. The reduction rates of Cr, CTL and MG by a single HD were 62.6±6.1%, 71.0±10.3% and 51.9±11.6%, respectively. The CTL level at 0.5, 1 and 6h after HD increased rapidly by 20.7±8.7%, 31.7±14.7% and 80.1±27.3%, respectively. There was a significant correlation between CTL or CTL/Cr and parathyroid hormone in patients who had just undergone parathyroidectomy. No significant correlation was found between CTL or CTL/Cr and those factors which seems to be related to the predialysis levels of reactive oxygen. Therefore, because of the good clearance of CTL and its rapid conversion to MG, its usefulness for the estimation of hydroxyl radical generation in HD patients is limited.

天然水中におけるクロムの酸化と還元 ＩＩＩ 中性溶液中における有機物によるクロム（ＶＩ）の還元速度

The reduction rates of Cr(V) by some organic compounds were investigated in order to obtain an information on the reactivity of Cr(VI) and organic matter in natural water. Glycine, serine, tyrosine and aspartic acid reduced hardly any Cr(VI) in the solution of pH 2, while cysteine, tannic acid and lignin rapidly reduced it even at pH 4. The reduction rates of Cr(VI) by cysteine and tannic acid were precisely determined as a function of concentration of reactants, pH and temperature. The emprical rate equations are -d[Cr(VI)]/dt=kcySH·103.3×1011[H +]2[CySH][Cr(VI)] for cysteine and =kTan[H +] [Tannic acid (mg/l)]1/2[Cr(VI)] for tannic acid. The apparent rate constants, kcySH, and kTan were found to be 4.8 and 1.4 x103min-1 at 20°C, respectively. Cr(VI) in fresh water may be reduced at a considerable rate b rganic matter such as tannic acid and some of the humic substances.

活性炭による六価クロム水溶液の還元

Cr (VI) in sulfuric acid solutions was reduced with activated carbons (initial solution; 2.5×10-3 mol/500ml as K2Cr2O7). Reduction rate of Cr (VI) and chemisorption of Cr (total) varied considerably with the various types of activated carbons. The results obtained in these experiments can be summarized as follows;1) Remaining Cr (VI) and Cr (total) decreased rapidly in the initial reaction period (several minutes). The reduction rate of Cr (VI) with the activated carbons decreased gradually in the course of the reaction, while the remaining Cr (total) stayed constant.2) Remaining Cr (VI) decreased with an increase in reaction temperature, and with an increase in the amount of activated carbons, and was propotional to the amount of fine sized particles. However, there was no detectable variation with increasing of Cr (III)/Cr (VI) mole ratio in the initial solution.3) Remaining Cr (total) reached a minimum value at pH 3-4 in the reaction solutions (initial pH; about 2.5). From calculation of all the chemical species in the initial chromate-dichromate solution, it was considered that the predominant species on activated carbons were HCrO4-and Cr2O72-.4) The following eouation can be suonosed for the reduction of aqueous dichromate solutions with activated carbons. 2Cr2O72-+3C+16H+→4Cr3++8H2O+3CO2