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Viscosity and structure evolution of the SiO2-MgO-FeO-CaO-Al2O3 slag in ferronickel smelting process from laterite

X.M. Lv, X.W. Lv, L.W. Wang, J. Qiu, M. Liu
2017 Journal of Mining and Metallurgy. Section B: Metallurgy  
There is a high iron content in the nickel slag that mainly exists in fayalite phase. Basic 10 Oxide can destroy the stable structure of fayalite which is beneficial to the treatment and 11 comprehensive utilization of nickel slag. The reseach was based on the composition of the raw nickel 12 slag, taking CaO-SiO2-FeO-MgO system as the object and CaO as a modifier. The effect of basicity on 13 the melting characteristics, viscosity and structure of CaO-SiO2-FeO-MgO system was studied. The 14
more » ... studied. The 14 relationship between the viscosity and structure of CaO-SiO2-FeO-MgO system was also explored. 15 The results show as follows. (1) When the basicity is lower than 0.90, the primary phase of the slag 16 system is olivine phase. When the basicity is greater than 0.90, the primary phase of the slag system 17 transform into monoxide. When the basicity is 0.90, olivine and monoxide precipitate together as 18 the temperature continues to decrease. At the same time, the liquidus temperature, softening 19 temperature, hemispherical temperature, and flow temperature all reach the lowest value. (2) With 20 the increase of basicity, critical viscosity temperature of CaO-SiO2-FeO-MgO system decreases first 21 and then increases. Critical viscosity temperature is the lowest at the basicity of 0.90, which is 1295 22 ℃. (3) When the slag system is heterogeneous, the viscosity of the molten slag increase rapidity 23 because of the quantity of solid phase precipitated from CaO-SiO2-FeO-MgO system. (4) When the 24 slag system is in a homogeneous liquid phase, the molar fraction of O 0 decreases with the increase of 25 basicity and the mole fraction of Oand O 2-increases continuously at the basicity of 0.38~1.50. The 26 silicate network structure is gradually depolymerized into simple monomers, resulting in the degree 27 of polymerization is reduced and the viscosity is reduced, too. The mole fraction of different kinds of 28 oxygen atom is converged to a constant value when basicity is above 1.20. 29 Keywords: nickel slag; basicity; CaO-SiO2-FeO-MgO system; viscosity; structure 30 31 1. Introduction 32 Iron-rich nickel slag (Nickel slag) is the industrial waste discharged from the process of nickel 33 metallurgy in flash furnace. The production of 1t nickel can produce about 6~16 t slag, and the 34 emissions from Jinchuan Group Co. of Gansu Province in China is more than 1.6 million tons per 35 year, with a cumulative stock of up to 40 million tons [1] . The content of TFe (total iron) in nickel slag 36 is up to 40% and the valuable metal elements such as Ni, Co, and Cu also exist. Fayalite (2FeO·SiO2) 37 that as the main phase in the slag is a co-melt composed by complex silicates [2] . The structure of 38 fayalite is stable, because it is a complex network crystal in which Si-O atom connected with each 39 other, resulting in the low recovery of valuable metal from nickel slag [3] . Adding basic oxides can 40 destroy the network structure of fayalite [4] . If an appropriate amount of CaO is added to the molten 41 nickel slag, the decomposition of the fayalite can be promoted, which is beneficial to the further 42 Preprints ( | NOT PEER-REVIEWED | 108 the temperature at which the fused mass had spread out in a nearly flat layer with a maximum 109 height of 25% of the of original sample. Figure 2 was shown the height changes of slag melting 110 process. These three temperatures characterize the melting trajectory of flux in industrial 111 applications. The hemispherical temperature is referred to as the melting temperature of the mold 112 flux [13, 15] .
doi:10.2298/jmmb150911002l fatcat:xamekx5iurgfrm3lzrcfwsl2tm