Enrichment Characteristics of Cr in Chromium Slag after Pre-Reduction and Melting/Magnetic Separation Treatment

Concentrating the chromium in chromium slag and improving the chromium–iron ratio is beneficial for the further utilization of chromium slag. In this paper, chromium slag obtained from a chromite lime-free roasting plant was used as the raw material. Pellets made of the chromium slag and pulverized coal were reduced at different pre-reduction temperatures and then separated by a melting separation process or magnetic separation process, respectively. The mass and composition of the metallized pellets before separation, along with the alloy and tail slag after separation, were comprehensively analyzed. The experimental results showed that the output yield of alloy, iron recovery rate, and chromium content in the alloy were all higher when using melting separation than when using magnetic separation, because of the further reduction during the melting stage. More importantly, a relatively low pre-reduction temperature and selection of magnetic separation process were found to be more beneficial for chromium enrichment in slag; the highest chromium–iron ratio in tail slag can reach 2.88.

Design and Construction of a Laboratory-Scale Direct-Current Electric Arc Furnace for Metallurgical and High-Titanium Slag Smelting Studies

A novel direct-current electric arc furnace (DC-EAF) was designed and constructed in this study for experimentally investigating high-titanium slag smelting, with an emphasis on addressing the issues of incomplete separation of metal and slag as well as poor insulation effects. The mechanical components (crucible, electrode, furnace lining, etc.) were designed and developed, and an embedded crucible design was adopted to promote metal-slag separation. The lining and bottom thicknesses of the furnace were determined via calculation using the heat balance equations, which improved the thermal insulation. To monitor the DC-EAF electrical parameters, suitable software was developed. For evaluating the performance of the furnace, a series of tests were run to determine the optimal coke addition under the conditions of constant temperature (1607 °C) and melting time (90 min). The results demonstrated that for 12 kg of titanium-containing metallized pellets, 4% coke was the most effective for enrichment of TiO2 in the high-titanium slag, with the TiO2 content reaching 93.34%. Moreover, the DC-EAF met the design requirements pertaining to lining thickness and facilitated metal-slag separation, showing satisfactory performance during experiments.

Physical-Chemical and Pyrometallurgical Estimation of Processing of Complex Ores with Extraction of Iron, Vanadium, Titanium

The metallurgical characteristics of pellets (reducibility, strength after reaction, softening start and end temperatures), phase composition (X-ray phase analysis), and porosity were studied. Blast furnace smelting parameters were calculated using laboratory pellets with different basicities and degrees of metallization. Pellets were obtained from complex titanium-magnetite ores. The vanadium extraction of this ore into metal did not exceed 10 % during smelting of metallized pellets in an arc steelmaking furnace, but special techniques could raise this to 85 %. According to calculations from the Institute of Metallurgy of the Ural Branch of the Russian Academy of Sciences (IMET UB RAS), vanadium extraction up to 80–90 % can be achieved by using high-base and partially metallized pellets. The influence of changes in the composition and metallurgical characteristics of titanomagnetite pellets with increasing basicity (especially relative to strength after reduction) should be taken into account.

Study of hot briquetted iron secondary oxidation speed aimed at forecasting of its metallurgical value retention duration

Hot briquetted iron (HBI), as also metallized pellets, undergo oxidation during transportation and storing. To forecast acceptable duration of HBI storing with metallurgical value retention it is important to have scientifically based data on the briquettes secondary oxidation speed. Methods of determining metallized pellets secondary oxidation speed are presented in domestic and foreign practice, but the matter of HBI secondary oxidation in scientific and technicalliterature practically is not covered. To determine HBI secondary oxidation speed two methods elaborated and tested at the Department of metallurgy and metal science of Stary Oskol Technological Institute after A.A. Ugarov (branch of National Research Technological University “MISiS”). The first– weighting method – based on determining of metal iron content change in HBI during a long term storing. During the experiment the mass of each briquette was weighted every 12 h within a month. The result of metal iron content determining by the experiment and by a chemical analysis had a difference of less than 1%. The weighting method enables to obtain the HBI reaction ability values without particular expenses, but requires carrying out long term enough experiments untilcomplete moisture removal out of the studied samples. The other method – determination of oxygen absorption speed bybriquettes in a closed vessel. It enables determining the reaction ability of the reduced iron within a comparatively short period, enables sufficient reliability duringthe briquettes testing. Based on it a methodology elaborated for determining of HBI secondary oxidation speed, meeting the requirements of real production. During loading-unloading operations, briquettes can partially go to ruin. The forming fragments of different sizes undergo a higher degree of oxidation that decreases the HBI metallurgical value. In view of this, studies of HBI oxidation speed continue depending on different sizes content and finalization of the methodology of determination of HBI secondary oxidation speed.