Spinel crystals in tuyere coke

Abstract

A number of dodecahedral and octahedral spinel crystals were found in tuyere coke. The possibility of spinel formation from a gas phase in the tuyere coke can be considered for dodecahedral crystals. The octahedral spinels may have been formed by annealing of precursor mineral aggregates followed by crystallization of new phases. Investigations into spinel crystals can be important for further interpretations of the conditions of origin and subsequent behavior of mineral matter during coke degradation.The amount and nature of the mineral phases in metallurgical coke can be regarded as important factors affecting its properties and behavior in the blast furnace (BF). [1,2] Data on the mineral phases in BF coke are still scarce, however, [2][3][4][5] and their behavior during coke degradation is still poorly understood. Under natural conditions, the composition, morphology, and textures preserve a record of the means by which the minerals were formed, and these data can be used to estimate the conditions of formation of their synthetic analogues, [6] including those originating in coking processes and during the evolution of coke in the BF.The changes that take place in the mineral phases of BF coke can be regarded as either structural or chemical. [2] The structural changes in particular include [2] expansion of metaclays and the swelling and balling-up of aluminosilicates, while the chemical changes are more complex and include (but are not limited to) mineral phase decomposition, alkalization, and the formation of new crystalline and glass phases. Various gases circulating in the BF change the composition of the existing mineral phases and cause the formation of new phases acting as agents for the transport of components through pores.The synthetic equivalents of minerals that have so far been found in tuyere coke but are not observed in primary coke are gupeiite, Fe 3 Si; xifengite, Fe 5 Si 3 ; schreibersite, Fe 3 P; barringerite, Fe 2 P; oldhamite (Ca, Mg, Fe, Mn)S; Al 2 O 3 (corundum crystals); spinel, MgAl 2 O 4 ; and fersilicite, FeSi.We describe here a case study of spinel crystals, which represents the first report on the occurrence and crystalline features of this mineral in tuyere coke.A number of coke samples were selected from drill core 130,303,203, obtained using a mobile tuyere rig from the tuyere zone of the BF at Rautaruukki Steel Works (Raahe, Finland). The samples were cut into pieces about 20-mm long, 20-mm wide, and 5-mm thick, preserving one original surface. The cut pieces were fixed to 28 ϫ 48 ϫ 1-mm glass plates and studied with a JEOL* JSM-6400 scanning *JEOL is a trademark of Japan

Origin and provenance of spherules and magnetic grains at the Younger Dryas boundary

“…The temperature during coal burning in power plants could reach 1,500°C and fly ash containing glass spherules with magnetite has been reported (47). The coke charged in blast furnaces along with iron ore and flux takes part in complex solid-to-solid, solid-to-melt, and solidto-gas reactions (48). The temperature at the tuyere level where hot air is blown into the blast furnace exceeds 2,000°C and samples of tuyere coke taken from operating blast furnaces show a number of high-temperature minerals, including iron silicides, iron phosphides, sulphide, corundum, and even pure spinel (48).…”

“…The coke charged in blast furnaces along with iron ore and flux takes part in complex solid-to-solid, solid-to-melt, and solidto-gas reactions (48). The temperature at the tuyere level where hot air is blown into the blast furnace exceeds 2,000°C and samples of tuyere coke taken from operating blast furnaces show a number of high-temperature minerals, including iron silicides, iron phosphides, sulphide, corundum, and even pure spinel (48). So blast furnaces could produce silicate glass spherules bearing iron silicides and phosphides.…”

Mineral Related CO2and H2O Emissions during the Production of Metallurgical Coke

“…The most common minerals containing H 2 O in coking coals belong to a phyllosilicates group consisting mostly of: [17,18] [24] biotite -K(Mg,Fe 2þ ) 3 S , melting with the formation of an alkali-Si-rich liquid and transformation to another phase (spinel, mullite). [1] The content of major oxides (CaO, MgO, FeO, and MnO) and H 2 O in the minerals as well as their density vary substantially ( Table 2).…”

“…Amongst those are summaries on various minerals and their behavior in general [1][2][3][6][7][8] and, also, detailed descriptions of transformations of particular mineral species in coking and blast furnace (BF) processes as, for example, quartz, [4] and pyrite. [5] During coking processes, the minerals undergo various physical and chemical changes, which include desulfurization, decarbonation, dehydration, dehydroxylation, polymorph transformations, melting with the formation of an alkali and silica-rich liquid, and transformation to another crystalline phase.…”

SiC and Ferro-silicides Formation in Tuyere Cokes

“…9,10) In a blast furnace, silicon also occurs with a number of iron bearing phases and often observed on coke surface. 6) These phases are grouped as iron silicides such as fersilicite (FeSi), xifengite (Fe5Si3), guepiite (Fe3Si) 11) in the order of decreasing silicon concentration.…”