Elsevier

Calphad

Volume 58, September 2017, Pages 229-238
Calphad

Thermochemical analysis for the reduction behavior of FeO in EAF slag via Aluminothermic Smelting Reduction (ASR) process: Part II. Effect of aluminum dross and lime fluxing on Fe and Mn recovery

https://doi.org/10.1016/j.calphad.2017.02.004Get rights and content

Abstract

We investigated Fe recovery from EAF slag by means of aluminothermic smelting reduction (ASR) at 1773 K with Al dross as the reductant, especially the effect of the added amount of the fluxing agent CaO on the Fe recovery. The maximum reaction temperature calculated using FactSage™ 7.0 decreased with increasing CaO addition, but the experimentally measured maximum temperatures increased with increasing CaO addition. We calculated the amounts of various phases before and after Al dross addition under different conditions of added CaO. FeO and Al2O3 contents in molten slag sharply varied within the first 5 min of the reaction, stabilizing soon thereafter. The aluminothermic reduction of FeO appeared to proceed rapidly and in good stoichiometric balance, based upon the mass balance between the consumption of FeO and MnO (ΔFeO and ΔMnO) and the production of Al2O3 (∆Al2O3). Iron recovery from EAF slag was maximized at about 90% when 40 g of CaO was added to 100 g slag. Furthermore, Mn could also be reduced from the EAF slags by the metallic Al in the Al dross reductant. The solid compounds of spinel (MgO∙Al2O3) and MgO were precipitated from the slag during the FeO reduction reaction, as confirmed by means of XRD analysis and thermochemical computations. To maximize Fe recovery from EAF slag, it is crucial to control the slag composition, namely to ensure high fluidity by suppressing the formation of solid compounds.

Introduction

Following Part I of the present series, which included experimental investigations of the reaction between FeO in EAF slags and Al at 1773 K and which emphasized the quantitative determination of iron recovery and reduction behavior, the present study describes the behavior of oxides in EAF slag and the effects of the slag's thermophysical properties on Fe (and Mn) recovery. Al dross is a by-product of Al smelting; it is a heterogeneous mixture of metallic Al and non-metallic compounds. The non-metallic portion is comprised mainly of Al2O3 and also includes small amounts of SiO2 and MgO as well as nitrides, carbides, and salts [1], [2], [3], [4], [5].

Actually, millions of tonnes of Al dross have been discarded in landfills or disposed without treatment, contaminating the environment [3], [4], [6], [7], [8], [9], [10], [11]. Furthermore, it contains small amounts of hazardous metals such as lead [4]. Two of the major aims of environmental policies concerning Al production are to decrease the quantity of Al dross produced and to recycle it in order to provide useful products. Thus, several authors have investigated various potential applications of Al dross [4], [12], [13], [14], [15].

One application of Al dross is as a raw material for Al2O3-containing refractory bric [4], [15]; this use achieves good performance in terms of corrosion resistance, thermal shock resistance, thermal stability, and refractoriness. Al dross can also be used as a source of Al2O3 for cements based on calcium aluminate in various applications [13], [14], including industrial flooring products, chemically resistant mortars, concrete, sewer applications, floor screeds, tile adhesives, protective coatings, and in producing chemistry products. Al dross has been characterized physicochemically, including properties such as density [2], [9], porosity [9], and toxicity [7], and mineralogical and structural interpretations have also been attempted [3], [8], [13], [15].

Some studies have included attempts to recover metallic Al from Al dross [1], [5], [6], [7], [9], [16], [17], [18]. Possible recovery methods include eddy current separation [6], [7], [18], electrostatic separation [5], [9], plasma treatment [1], and froth flotation.[16]. However, the traditional method to recover metallic Al from Al dross is not an efficient or economical approach because recovering only the metallic Al requires high energy input and produces pollutants such as fumes and dust.

Therefore, we propose a new use of Al dross as a reductant to recover iron from slags. In this way, both Al dross and slag can be used to make highly value-added materials, thereby creating an economic benefit while also creating an environmental benefit by reducing the quantity of waste products. However, Al dross does have limitations as a reductant in the aluminothermic reduction process. Adding large amounts of Al2O3 significantly affects several physicochemical properties of slag, such as the melting temperature, crystallization behavior, and viscosity [19]. This can lead to unstable operation, worsening the iron recovery [20], [21]. Thus, slag composition should be controlled to maximize iron recovery, for example by adding CaO as a fluxing agent.

In the present work, based on the quantitative work reported in Part I of this series, we quantitatively investigated the reduction of iron oxide in EAF slags by Al dross in the presence of various amounts of added CaO, with emphasis on quantitative determination of iron recovery. Herein, reduction pathways and temperature variations are illustrated in detail in three-dimensional phase diagrams, and the remarkable influence of the thermophysical properties of slags upon iron recovery are discussed.

Section snippets

Raw materials and experimental procedure

The experimental procedures used were nearly the same as reported in Part I of this series, except that Al dross was used as a reductant and that the industrial EAF slags used here were mixed with CaO, which was calcined from CaCO3 at 1273 K in a muffle furnace for 10 h. Table 1 lists the experimental conditions used in this study.

To confirm the morphology of Al dross, it was observed by means of back scattered electron SEM combined with EDS (Fig. 1). Features in the SEM image of Al dross were

Computational prediction of Aluminothermic Smelting Reduction (ASR) of FeO in molten EAF slag with various amounts of lime fluxing

Computational predictions based on thermodynamic equilibrium of the aluminothermic reduction reaction were carried out using the FactSage™ 7.0 software with the same databases used in Part I of this series. The computation results included fundamental information on maximum temperature within an adiabatic condition, and variations in slag compositions and amounts of precipitated solid compounds at equilibrium conditions. The reduction of iron oxide in molten slag by Al, also known as the

Conclusions

We quantitatively investigated the effect of CaO fluxing upon the reduction of FeO (and MnO) and the subsequent recovery of Fe (and Mn) from EAF slag at 1773 K by considering thermophysical properties such as apparent viscosity. Our major findings can be summarized as follows.

  • 1.

    The contents of FeO and Al2O3 in molten slag rapidly changed within 5 min of reaction initiation, and stabilized soon thereafter. The maximum temperature increased with increasing added CaO content, up to about 1977 K. After

References (22)

  • H.N. Yoshimura et al.

    Ceram. Int.

    (2008)
  • K. Mah et al.

    Conserv. Recycl.

    (1986)
  • B.R. Das et al.

    Min. Eng.

    (2007)
  • E. David et al.

    J. Hazard. Mater.

    (2013)
  • V.M. Kevorkijan

    Compos. Sci. Technol.

    (1999)
  • M.C. Shinzato et al.

    Waste Manag.

    (2005)
  • E.M.M. Ewais et al.

    Ceram. Int.

    (2009)
  • A. Li et al.

    Ceram. Int.

    (2014)
  • H. Soto et al.

    Conserv. Recycl.

    (1986)
  • G. Lazzaro et al.

    Resour. Conserv. Recycl.

    (1994)
  • G.H. Nijhof

    Resour. Conserv. Recycl.

    (1994)
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