20 research outputs found
Electrochemical characterization of leached steel-making sludge
In this work, the electrochemical properties of the leached sludge, magnetite and zinc ferrite were studied. Acetic acid was used as a leaching reagent because, in recent years, there has been a surge of interest in using zinc-containing materials as photocatalysts, with acetic acid finding application in their preparation. Various methodological approaches were used, but the best results were achieved with a combination of 1-3 h leaching in 0.01 M acetic acid with a solid/liquid ratio of 500. In this arrangement, zincite was almost completely removed from the sludge, while zinc ferrite and magnetite remained in the solid residue. Ex situ analyses of the main leaching products were performed by X-ray diffraction, infrared spectroscopy, and thermogravimetry. The electrochemical behaviour of solid residue and model systems, that are micromagnetite and zinc ferrite, was studied in alkaline media by means of modified carbon paste electrodes, cyclic voltammetry, and chronocoulometry, with a suitable potential window ranging from 0 to 1.5 V. In summary, a linear dependence of the anodic and cathodic peak height on the square root of the scan rate was found. The position of the anodic and cathodic peaks shifted slightly with scan rate, only at low rates, up to 25 mV/s, the individual peaks coincided. The electrochemical response suggested a quasireversible process.Web of Science121art. no. 1669
Sorpce fosfátů na oxidových systémech soustavy CaO - MgO - Al2O3 - SiO2
Import 10/12/2008PrezenčníNeuvedenoNeuveden
Heterogenní acidobazické rovnováhy fosforu v oxidových systémech
Import 20/04/2006Prezenční výpůjčkaVŠB - Technická univerzita Ostrava. Fakulta metalurgie a materiálového inženýrstv
Mechanisms of phosphate sorption from aqueous solutions by calcined Mg-Al-CO(3) hydrotalcite
Web of Science1051187887
Oxyhumolite as a sorbent of Cu-II from phosphate-containing solutions
This study explores the use of oxyhumolite (OX) for sorption removal of CuII from sewage containing phosphates. It was discovered that the adsorption of CuII markedly depends on pH and linearly increases with increasing pH values. Adsorption efficiency of OX for phosphates is approximately constant (E≈13%) and does not depend on the pH value. The optimum pH range for the selective sorption was determined to be between 3.3–3.7 (ECu≈90%). The good sorption efficiency for CuII results from the high content of humic acids and the presence of inorganic components.Web of Science77111050104
Blast furnace slags as sorbents of phosphate from water solutions
The paper is focused on the sorption of phosphorus from aqueous solutions by crystalline and amorphous blast furnace slags. Slag sorption kinetics were measured, adsorption tests were carried out and the effect of acidification on the sorption properties of slags was studied. The kinetic measurements confirmed that the sorption of phosphorus on crystalline as well as amorphous slags can be described by a model involving pseudo-second-order reactions. For all slag types, phosphorus sorption follows the Langmuir adsorption isotherm. The acid neutralizing capacities of crystalline and amorphous slags were determined. In the case of the crystalline slags, buffering intervals were found to exist during which the slag minerals dissolve in the sequence bredigite–gehlenite–diaspor. There is a high correlation (R2=0.9989) between ANC3.8 and the saturation capacities of crystalline and amorphous slags
Rehydration of calcined Mg-Al hydrotalcite in acidified chloride-containing aqueous solution
The rehydration of periclase-like Mg-Al mixed oxide obtained by calcination of hydrotalcite- like precursor with a Mg/Al molar ratio of 2 was carried out in KCl-HCl solutions at various pH and constant concentration of Cl-. A buffer equilibrium accompanied by leaching out of Mg2+ cations from the solid was observed during rehydration, when reconstruction of the layered hydrotalcite structure takes place. With increasing HCl concentration in the rehydration solution, the Mg/Al molar ratio in the obtained solid gradually decreased from about 1.5 to 0.3. An anomaly was found, when the increasing concentration of acid resulted in increasing pH of final solution. The XRD measurements showed that the initially formed hydroxide form of hydrotalcite is transformed into randomly interstratified forms of the Mg-Al hydroxide hydrate/Mg-Al chloride hydroxide hydrate, which are accompanied by the release of OH- anions into solution. The crystalline structure of rehydrated product decreased as Mg2+ cations were released into solution, which was accompanied by incorporation of Cl- into the solid
Oxyhumolite influence on adsorption and desorption of phosphate on blast furnace slag in the process of two-stage selective adsorption of Cu(II) and phosphate
Two-stage adsorption was used for selective removal of Cu(II) and phosphate from aqueous solutions. In the first stage, adsorption of Cu(II) and phosphate on oxyhumolite (OX) was examined. The pseudo second-order equation was found to be the best fit for the kinetic adsorption data. The adsorption capacity of OX for Cu(II) and phosphate depends on the adsorption time, the equilibrium pH influences only the adsorption of Cu(II). The high adsorption efficiency (E = 95 %, pH 3.5, 0.5 g of the solid sorbent and 50 cm3 of the solution, c = 4 mmol dm−3) of OX for Cu(II) is caused by the presence of humic acids (HA). In the second stage, blast furnace slag (BFS) and activated blast furnace slag (BFS-A) were used to remove phosphates. The presence of OX in the first stage positively influences the adsorption efficiency of sorbents in the second stage due to the soluble humic compounds and residues of humic acids (HA) which support the precipitation of Ca-phosphates on BFS and the ions exchange reactions on BFS-A. Adsorption equilibrium of phosphate on both slags at 298 K can be well described by the Langmuir isotherm equation. Desorption of Cu(II) from OX was around 70 %. The presence of OX in the first stage also influences the desorption of phosphate bound in the second stage. Desorption efficiency of both slags for phosphate was about 60 %.Web of Science68677376
Electrochemical characterization of fine-grained blast furnace sludge after acid leaching using carbon paste electrode
The paper deals with the study of electrochemical properties of blast furnace sludge after acid leaching (BFSL) using modified carbon paste electrodes (CPEs) in acidic (1M HCl) and alkaline (1M NaOH) electrolyte. A polyamide holder with exchangeable tips was developed. The effect of their geometric parameters on the electrochemical response was monitored. The electrochemical characterization was performed by cyclic voltammetry (CV) at different scan rates. The hematite and magnetite served as comparative model modifiers. The identification of reaction products was performed using the RTG diffraction and SEM/EDX analyses. It was found that reduction reactions are suppressed at acidic pH. On the contrary, in an alkaline media, a significant peak corresponding to the electrode reduction of iron oxides based on the scheme (Fe3+Fe2+Fe0) was identified in the BFSL reduction region. XRD and SEM analyses of the active surface of modified CPE showed the formation of nanostructured Fe. The results provide direction for the further use of BFSL.Web of Science22113466345
Interaction des phosphates en solution aqueuse avec une forme calcinée de l'hydrotalcite Mg-Al-CO3
In this study the sorption removal of phosphates from aqueous solutions was investigated. The sorbent used was Mg-Al-CO3 hydrotalcite with a molar ratio of 2:1 calcined at 450 oC. The retention capacity of cLDH was 2.88 mmol P/g. The sorption can be characterized by a kinetic model of the pseudo-second order. Laboratory tests proved the existence of two steps – fast and slow. The fast step is associated with regeneration of the layered structure accompanied by surface adsorption of phosphates and is applied within the first 1.5 to 2 hours. Its rate is controlled by diffusion mechanisms. If abundance of phosphates is present in the solution, the slow step follows, i.e., phosphate intercalation into the interlayer, and eventually precipitation of aluminium phosphate occur. Different sorption mechanisms significantly influence desorption of phosphates.Dans ce travail on a examiné l´élimination des phosphates des solutions aqueuses par sorption. Comme sorbant on a utilisé l´hydrotalcite Mg-Al-CO3 avec un rapport molaire de 2:1, calciné à la température de 450° C. La capacité de rétention cLDH est de 2,88 mmol P/g. On peut caractériser la sorption par le modèle cinétique de pseudo-deuxième ordre. Les tests de laboratoire ont prouvé l´existence de deux étapes - une rapide et une lente. L´étape rapide est reliée à la régénération de la structure disposée en couches qui est accompagnée de l´adsorption de surface des phosphates et cette étape est réalisée pendant les premières 1,5 – 2 heures. Sa vitesse est contrôlée par des mécanismes de diffusion. Si les phosphates sont présents dans la solution en abondance, c´est l´étape lente qui suit, donc l´intercalation des phosphates entre des couches et, le cas échéant, la précipitation des phosphates d´aluminium. Les différents mécanismes de sorption influencent considérablement la désorption des phosphates.Web of Science371201