Effect of cooling conditions on the mineralogical composition of vanadium-bearing converter slags

Abstract

In the hydrometallurgical processing of vanadium slags and the recovery of vanadium pentoxide from the slag, the main phase of the slags -the spinellide -is the phase of the greatest interest from a commercial standpoint.Experience shows that the amount of spinellide which is present varies widely from one heat to the next -from 43 to 78%. This index affects not only the composition of the pig iron being made, but also the specifications of the chosen oxidant, the composition of the additions, the temperature of the pig, and other characteristics.To establish the relationship between the chemical composition of the converter slag and the concentration of spinellide, we statistically analyzed the results from a chemical analysis of a large number of slags. We analyzed about 30 railcars of converter slag that arrived at the shop over a period of 2-2.5 months. Chemical composition was determined by sampling the slag in accordance with the method adopted at the plant: crushing, followed by separation of metallic iron in the form of inclusions, scrap, and dispersed iron. To perform a petrographic analysis, five small samples of slag up to 80 mm in size were taken from each railcar load during the crushing operation. The results of the analysis were then averaged.The slags were divided into three groups based on the concentration of spinellide: nominally, 50%, 60%, and 70%; the actual concentrations were 51.3, 59.99, and 69.7%. The ranges of spinellide concentration in the different groups were 43.4-56.1, 57.2--62.0, and 65.1-78.8%, respectively. The chemical composition of the slags in each group was averaged over 10, 12, and 8 tests (Table 1).It can be seen from the table that metallic inclusions have the greatest effect on the concentration of spinellide. The mechanism of this effect is still unclear, but it can be stated that converter slag which contains no more than 19% metallic inclusions will have a spinellide content in the range 65-75%. A relationship was found to exist between spinellide content and the content of vanadium oxides, but it was not as explicit as had been expected. No relationship was found between spinellide content and the other components of the slag.The presence of spinellide in the slag is not by itself sufficient to be able to fully extract the vanadium in the slag during hydrochemical treatment. An equally important factor is the size of the spinellide grains that are formed. According to process specifications, the optimum grain size is within the range 10-15 Bm. Under production conditions, up to 60-70% of the total mass of spinellides consists of grains of 2.5-5.0 Bin. We assumed that spinellide grains were formed not only during the formation of the slag in the converter, but also during its cooling in air after tapping. To confirm this, we conducted an experiment to establish the effect of cooling time on the granulometric composition of the spinellides in converter slag; vanadium slag from recent commercial heats was used in the experiment. After being discharged from the furnace, ...

Assessment of Super-gravity Concentrating V-containing Spinel Phase from Vanadium Slag

“…Vanadium extraction yield is determined by vanadium oxidation rate in the salt roasting step [3]. However, the small crystal size of V-containing spinel phase and large amount of silicate phases in vanadium slag result in low oxidation rate of vanadium [4][5][6]. Fortunately, according to the experimental result of Zhang et al [7], spinel crystal size is mainly determined by cooling rate of vanadium slag and the optimum experimental parameter that benefits the early precipitation of Vcontaining spinel phase with large size is holding in the interval of 1200-1250 °C more than 45 min.…”

Laboratory assessment of isothermal separation of V containing spinel phase from vanadium slag by centrifugal casting

“…The small crystal size of V containing spinel phase and the large amount of silicate phases in vanadium slag result in a low oxidation rate of vanadium, 1,2 which leads to low P 2 O 5 and vanadium extraction yield. 3 Fortunately, several studies 4 indicate that the optimum experimental parameters that benefit the early precipitation of large size V containing spinel phase is holding at a temperature of 1507–1557 K for >45 min.…”