Jadranka Malina

Characterization of Ladle Furnace Slag from Carbon Steel Production as a Potential Adsorbent

A promising type of steel slag for applications is the ladle furnace (LF) slag, which is also known as the basic slag, the reducing slag, the white slag, and the secondary refining slag. The LF slag is a byproduct from further refining molten steel after coming out of a basic oxygen furnace (BOF) or an electric arc furnace (EAF). The use of the LF slag in further applications requires knowledge of its characteristics. The LF slag characterization in this paper has been performed using the following analytical methods: chemical analysis by energy dispersive spectrometry (EDS), mineralogical composition by X-ray diffraction (XRD), surface area properties by the Brunauer-Emmett-Teller (BET) and the Barrett-Joyner-Halenda (BJH) methods, surface chemistry by infrared absorption (FTIR) spectroscopy, and morphological analysis by scanning electron microscopy (SEM). The results showed that the main compounds are calcium, silicon, magnesium, and aluminium oxides, and calcium silicates under their various allotropic forms are the major compounds in the LF slag. Surface area properties have shown that the LF slag is a mesoporous material with relatively great BET surface area. The ladle furnace slag is a nonhazardous industrial waste because the ecotoxicity evaluation by its eluate has shown that the LF slag does not contain constituents which might in any way affect the environment harmfully.

Kinetic Aspects of Methylene Blue Adsorption on Blast Furnace Sludge

For analysis of experimental data, three kinetic models were applied: pseudo first-order, pseudo second-order and Weber-Morris intra-particle diffusion model. Results demonstrate that kinetics of dye adsorption on BFS is best described by the pseudo second-order equation (R 2 ≥ 0.99, F-value=0.86) while fitting to Weber-Morris model has shown that the pore diffusion is not the only rate limiting process in MeB-uptake. Such kinetics can be related to surface characteristics of BFS used: particle diameter d p ≤ 56 mm, specific area 31.46 m 2 g –1 , pore volume 157·10 –3 cm 3 g –1 , and average pore diameter 17.88 nm, mark this industrial by-product as a mesoporous material. Its surface morphology change after MeB adsorption was confirmed by SEM/EDS analyses. The results obtained allow concluding that untreated BFS has the capacity for MeB uptake within the range of concentrations employed and could be considered as potential low cost adsorbent for treating of dye-polluted waste waters.

THERMODYNAMIC AND KINETIC STUDY OF ADSORPTION OF Ni(II) IONS ON CARBON ANODE DUST

In this study the use of carbon anode dust (CAD), which is the solid residue from aluminum production, as a low-cost adsorbent for the removal of Ni(II) ions from wastewater was investigated. A mechanism of adsorption kinetics and thermodynamics was proposed. In order to investigate the adsorption process of nickel ions on CAD three kinetic models were used: Lagergrens pseudo-first-order model, pseudo-second-order model, and the intra-particle diffusion model. Various thermodynamic parameters, such as the energy of activation (Ea), activation enthalpy (ΔH*), activation entropy (ΔS*), and free energy of activation (ΔG*), were evaluated. Observation of the value of the energy of activation suggests that the process uptake of Ni(II) ions can be described as activated chemisorption. The positive values of enthalpy of activation and free energy of activation, as well as negative values of entropy of activation, mean that the process of removal of Ni(II) ions is endothermic, non-spontaneous, and without structural changes in the solid carbon anode dust particles.

Morphology of Co–Cr–Mo dental alloy surfaces polished by three different mechanical procedures

The present study aims at characterizing the three‐dimensional (3‐D) morphology of a Co–Cr–Mo dental alloy surface as a result of three different procedures used for polishing it. The sample surface morphology of the sampled surface was examined employing atomic force microscopy (AFM), statistical surface roughness parameters, and fractal analysis. An extra‐hard dental alloy of cobalt–chromium–molybdenum (Co–Cr–Mo) (Wironit®, from BEGO, Bremen, Germany) was prepared and moulded. Different polishing treatments were carried out on three groups of six samples each—a total of 18 samples. The first group contained six electropolished (EP) samples. The second group containing six samples went through a mechanical polishing process employing green rubber discs and a high shine polishing paste applied by a rotating black brush (BB). The third group comprising six samples as well went through a mechanical polishing process by means of green rubber discs, high shine polishing paste, and a rotating deer leather brush (DL). Fractal analysis on the basis of a computational algorithm applied to the AFM data was employed for the 3‐D quantitative characterization of the morphology of the sampled surfaces. The fractal dimension D (average ± standard deviation) of 3‐D surfaces for BB samples (2.19 ± 0.07) is lower than that of the DL samples (2.24 ± 0.08), which is still lower than that of the EP samples (2.27 ± 0.09). The results indicated the BB samples as presenting the lowest values of statistical surface roughness parameters, thus the best surface finish, while the EP samples yielded the highest values. Microsc. Res. Tech. 78:831–839, 2015.

Passivity of Co-Cr-Mo alloys in lactic acid solutions

The method of potentiodynamic polarization was used to obtain the electrochemical measurements of ten experimental Co-Cr-Mo alloys with different chemical composition in two solutions of 0.1 % lactic acid (LA): medium A containing Cl--ions (0.1 % LA in artificial saliva, pH 6.52) and medium B without Cl--ions (0.1 % LA in distilled water, pH 2.99). These solutions as representative of oral cavity conditions were chosen in order to see if the alloys could be used in dental practice. Wironit® was used as reference material. In vitro experiments have shown that susceptibility to local corrosion was more pronounced in solution A. In contrast, the tendency to general corrosion was greater in solution B. Referring to pitting potential of Wironit®, samples 3 (Co55Cr40Mo5), 6 (Co60Cr30Mo10) and 9 (Co55Cr20Mo25) have shown the best performances with the highest Epitt value in both media. The same is valid for these three alloys if general corrosion was considered.