No abstract

Abstract:The effect of calcium oxide on the crushing strength, reduction, and smelting performance of high-chromium vanadium-titanium magnetite pellets (HCVTMP) was studied in this work. The main characterization methods of an electronic universal testing machine (EUTM), X-ray fluorescent (XRF), inductively-coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), and scanning electron microscope-energy disperse spectroscopy (SEM-EDS) were employed. The crushing strength was affected by the mineral phases generated during oxidative baking and the subsequently-formed pellet microstructures owing to CaO addition. The reduction and smelting properties of HCVTMP with different CaO additives were measured and characterized with different softening-melting-dripping indices. Although HCVTMP showed the highest crushing strength with CaO addition of ca. 2 wt %, more CaO addition may be needed to achieve high permeability of the furnace burdens and a good separation condition of the slag and melted iron. In the formation process of the slag and melted iron, it can be determined that CaO could have a relationship with the transformation behavior of Cr, V, and Ti to some extent, with respect to the predominant chemical composition analysis of ICP-AES and XRF. With the microscopic examination, the restraining formation of Ti(C,N) and the promoting formation of CaTiO 3 are in accordance with the improved melting-dripping indices, including the decrease of the maximum external static load and gas permeability, and the increase of the melting-dripping zone and dripping difficulty.

Abstract:Coal-based reduction and magnetic separation behavior of low-grade vanadium-titanium magnetite pellets were studied in this paper. It is found that the metallization degree increased obviously with an increase in the temperature from 1100 • C to 1400 • C. The phase composition transformation was specifically analyzed with X-ray diffraction (XRD). The microscopic examination was carried out with scanning electron microscopy (SEM), and the element composition and distribution were detected with energy dispersive spectroscopy (EDS). It is observed that the amounts of metallic iron particles obviously increased and the accumulation and growing tendency were gradually facilitated with the increase in the temperature from 1100 • C to 1400 • C. It is also found that the titanium oxides were gradually reduced and separated from ferrum-titanium oxides during reduction. In addition, with increasing the temperature from 1200 • C to 1350 • C, silicate phases, especially calcium silicate phases that were transformed from calcium ferrite at 1100 • C, were observed and gradually aggregated. However, at 1400 • C some silicate phases infiltrated into metallic iron, as it appears that the carbides, especially TiC, could probably contribute to the sintering phenomenon becoming serious. The transformation behavior of valuable elements was as follows:

Properties of low-grade vanadium-titanium magnetite pellets (LGVTMP) with different MgO contents are investigated. Since MgO can ameliorate the properties of acid pellets, pure MgO reagent is added to LGVTMP as a MgO additive in this paper. The experimental results show that the compressive strength (CS) of different MgO-bearing LGVTMP has a decreasing trend with the increase of MgO content, but all of the pellets are above 2000 N/pellet and meet the requirement of the blast furnace production when the roasting temperature is 1250 C. And the mechanism of MgO on reduction swelling (RS) is different from hematite and magnetite. At 900 C, the RS of LGVTMP mainly occurs in the reduction process of Fe 2 O 3 ! Fe 3 O 4 ! FeO and Fe 2 TiO 5 ! Fe 2 TiO 4 under the atmosphere of 70% N 2 and 30% CO. Moreover, reduction swelling index (RSI) of LGVTMP increases first and then decreases with the increase of MgO content, and 1.25% MgO pellets have worse RSI of 17.9%. In addition, adding MgO can improve the reducibility of LGVTMP due to the decrease of Fe 2 TiO 5 content.

No abstract