Time filter

Source Type

Luleå, Sweden

Hryha E.,Chalmers University of Technology | Rutqvist E.,LKAB | Nyborg L.,Chalmers University of Technology
Surface and Interface Analysis

Recovery of vanadium oxide from steelmaking slag is of great interest for Swedish steel producers and the technique for assessing the oxidation state of vanadium is crucial in the optimization of vanadium recovery. There is a large spread in the reported values of published V2p 3/2 binding energy values for various oxidation states of vanadium. Therefore, an extensive analysis of vanadium oxide standards was performed aimed at obtaining reliable data and improved methods for the preparation of representative oxide standards. Powdered oxide standards of V 2O 5, VO 2, V 2O 3, and VO, with purity better than 99%, were chosen. In their as-received state, all of the standards are covered by a thin layer of vanadium pentoxide that does not allow accurate evaluation of X-ray photoelectron spectroscopy spectra for vanadium oxides at lower oxidation states. Therefore, different methods for obtaining a representative surface for vanadium oxide standards were tested. The experimental results show high sensitivity of vanadium oxide standards to argon ion etching. Hence, a method to obtain a representative surface of standards by special heat treatment is proposed. Such approach was developed using a preparation chamber (furnace) attached to an X-ray photoelectron spectroscopy instrument. The annealing was performed in a vacuum at defined temperatures from 400 to 900 °C for 4-24 h; the annealing parameters were selected based on thermodynamic equilibrium data for vanadium oxides. Experimental fitting parameters (peak position E and full width of half maximum of the peak) for vanadium V2p 3/2 and oxygen O1s peaks are thus obtained for stoichiometric vanadium oxides. Copyright © 2011 John Wiley & Sons, Ltd. Source

Semberg P.,Lulea University of Technology | Andersson C.,LKAB | Bjorkman B.,Lulea University of Technology
ISIJ International

The addition of MgO to iron ore pellets is known to beneficially influences many high temperature reduction properties such as reducibility and swelling. When the pellet is metallized, MgO dissolved in the wustite concentrates in the unmetallized part, which is why MgO-levels much higher than the average concentration could be expected locally. In this work the impact of the elevated MgO-content on the reduction at 1 000-1300°C was studied by SEM-EDS. The MgO content in the pellet was also varied by additions of a), highly reactive olivine b) unreactive olivine c) combined addition of reactive olivine and fine quartzite and d) combined addition of unreactive olivine and fine quartzite. Two cases of metallization were observed 1) a gradual reduction front with only moderate magnesium levels and 2) a sharp reduction front with strongly elevated magnesium levels before the metal front. The samples with added quartzite reduced a little better at 1 100°C, compared to those with only olivine, but apart from that, reduction was not affected much by the additives in the range 1 000-1 200°C. The greatest difference in reduction degree appeared at 1 300°C where a metal skin formed in most samples, hindering further reduction. At this temperature, the sample with addition of only reactive olivine had superior reducibility due to a porous morphology of the iron being mantained throughout the experiment. © 2013 ISIJ. Source

Semberg P.,Lulea University of Technology | Andersson C.,LKAB | Bjorkman B.,Lulea University of Technology
ISIJ International

In this study the magnesium diffusion behaviour was studied in pellets with fine and course olivine, with and without additional fine quartzite (<20 μm) after isothermal reduction at 1 000-1 300°C. It was found that, by using a fine olivine (<38 μ m) the whole magnesium content of the olivine was dissolved evenly in the wustite and in the slag, already at 1 000°C, in agreement with the equilibrium tie-lines of the FeO-MgO-SiO2 phase diagram. This lead the liquid slag to precipitate into fayalitic olivine and the Al, Na, K, Ca, P-content to enrich in remaining inclusions in the olivine. This crystallization did not occur in the sample with only bentonite addition, or in the sample with unreactive olivine at these temperatures. However, with further addition of fine quartzite, the slag of the sample with coarse olivine also crystallized. In the samples reduced at 1 000-1 100°C, magnesium gradients could be detected in the slag phase around coarse olivine particles until entering the interaction volume of an interfering particle at around ∼600 μ m, or occasionally at distances of more than 1 mm. For the coarse olivine the main rise in magnesium occurs at 1 200°C when the olivine particle cores begin to dissolve. The dissolution of all magnesium of the 2.5% olivine addition during oxidation lead to 6.5% Mg in the crystallized slag phase. The increase in melting point resulting from this compared to fayalite with no magnesium is ∼50°C, according to thermodynamic calculations. © 2013 ISIJ. Source

Zhang Z.X.,LKAB
Rock Fragmentation by Blasting, FRAGBLAST 10 - Proceedings of the 10th International Symposium on Rock Fragmentation by Blasting

Ground vibrations at the Malmberget town had reached 18-19 mm/s from year 2000 to 2002. From 2004 to 2010 the maximum vibrations had been reduced to 9 mm/s and most vibrations reduced to about 5 mm/s, indicating that the technical measures used in the mine are effective in vibration control. These measures include (1) Stress Wave Superposition, (2) Changing Initiation Sequence (CIS in short), and (3) Dividing Ring Blasting (DRB in short). All three methods were proved to be successful in vibration reduction, but the last two are more effective and they do not need additional costs according to the tests in the mine. Because of the two methods, both maximum vibrations and average ones have been reduced by around 50% since 2004. © 2013 Taylor & Francis Group. Source

Herbert R.B.,Uppsala University | Winbjork H.,LKAB | Hellman M.,Swedish University of Agricultural Sciences | Hallin S.,Swedish University of Agricultural Sciences
Water Research

Mine drainage water may contain high levels of nitrate (NO3 -) due to undetonated nitrogen-based explosives. The removal of NO3 - and nitrite (NO2 -) in cold climates through the microbial process of denitrification was evaluated using a pilot-scale fixed-bed bioreactor (27m3). Surface water was diverted into the above-ground bioreactor filled with sawdust, crushed rock, and sewage sludge. At hydraulic residence times of ca.15h and with the addition of acetate, NO3 - and NO2 - were removed to below detection levels at a NO3 - removal rate of 5-10gNm-3 (bioreactor material)d-1. The functional groups contributing to nitrogen removal in the bioreactor were studied by quantifying nirS and nirK present in denitrifying bacteria, nosZI and nosZII genes from the nitrous oxide - reducing community, and a taxa-specific part of the16S rRNA gene for the anammox community. The abundances of nirS and nirK were almost 2 orders of magnitude greater than the anammox specific 16S rRNA gene, indicating that denitrification was the main process involved in nitrogen removal. The spatial distribution of the quantified genes was heterogeneous in the bioreactor, with trends observed in gene abundance as a function of depth, distance from the bioreactor inlet, and along specific flowpaths. There was a significant relationship between the abundance of nirS, nirK, and nosZI genes and depth in the bioreactor, such that the abundance of organisms containing these genes may be controlled by oxygen diffusion and substrate supply in the partially or completely water-saturated material. Among the investigated microbial functional groups, nirS and anammox bacterial 16S rRNA genes exhibited a systematic trend of decreasing and increasing abundance, respectively, with distance from the inlet, which suggested that the functional groups respond differently to changing environmental conditions. The greater abundance of nirK along central flowpaths may indicate that the bioreactor design favored preferential flow along these flowpaths, away from the sides of the bioreactor. An improved bioreactor design should consider the role of preferential flowpaths and the heterogeneous distribution of the genetic potential for denitrification, nitrous oxide reduction and anammox on bioreactor function. © 2014 Elsevier Ltd. Source

Discover hidden collaborations