No abstract

Treatment and disposal of Basic Oxygen Furnace (BOF) slag, a residue of the steel production process characterized by high basicity and propensity for heavy metal leaching, is a costly burden on metallurgical plants; a sustainable valorization route is desired. The stabilization of BOF slag utilizing hot-stage carbonation treatment was investigated; this approach envisions carbonation during the hot-to-cold pathway followed by the material after the molten slag is poured and solidified. Three experimental 2 methodologies were employed: (i) in-situ thermogravimetric analyzer (TGA) carbonation was used to assess carbonation reaction kinetics and thermodynamic equilibrium at high temperatures; (ii) pressurized basket reaction carbonation was used to assess the effects of pressurization, steam addition and slag particle size; and (iii) atmospheric furnace carbonation was used to assess the effect of carbonation on the mineralogy, basicity and heavy metal leaching properties of the slag. Free lime was found to be the primary mineral participating in direct carbonation of BOF slag. Initial carbonation kinetics were comparable at temperatures ranging from 500 to 800 o C, but higher temperatures aided in solid state diffusion of CO 2 into the unreacted particle core, thus increasing overall CO 2 uptake. The optimum carbonation temperature of both BOF slag and pure lime lies just below the transition temperature between carbonation stability and carbonate decomposition: 830-850 o C and 750-770 o C at 1 atm and 0.2 atm CO 2 partial pressures, respectively. Pressurization and steam addition contribute marginally to CO 2 uptake. CO 2 uptake progressively decreases with increasing particle size, but basicity reduction is similar independent of particle size. The solubility of some heavy metals reduced after carbonation (barium, cobalt and nickel), but vanadium and chromium leaching increased.

The dissolution of alumina spheres in a synthetic CaO–Al2O3–SiO2 (CAS) slag was investigated in situ with a confocal scanning laser microscope (CSLM) in the temperature range between 1470° and 1630°C. Through image analysis, the evolution of the apparent particle radius is obtained as a function of time, exhibiting a clear temperature dependence. The rate‐limiting step of the dissolution process is first evaluated with respect to the classical shrinking core model. Neither the boundary layer diffusion nor the chemical reaction in this model can fully explain the dissolution phenomena. By comparing the experimental results with numerical simulation, the rate‐limiting step was shown to be diffusion in the majority of the tests. Effective binary diffusion coefficients were calculated.

Ferroalloys are added during secondary steelmaking to impart special properties to the steel. Depending upon the ferroalloy quality this may lead to the formation of inclusions. The present knowledge lacks in the exact content of the individual elements and the nature of inclusions dispersed in the ferroalloys. In order to broaden the knowledge concerning ferroalloy quality, eight different ferroalloys (i.e. FeMo, FeNb, HCFeMn, LCFeMn, FeTi70, FeTi35, FeSi75 and FeP) were characterised for their impurity content. The samples were investigated for chemical analysis (inductively coupled plasma atomic emission spectroscopy and Leco combustion technique) and microstructural analysis (SEM energy dispersive spectroscopy). These impurities are linked to the ferroalloy manufacturing route. The inclusions observed in the microstructure are in good agreement with the inclusions extracted by the dissolution technique. In the present manuscript, the possible influence of ferroalloy quality over steel cleanliness is evaluated in the context of the impurities extracted and observed in the ferroalloys.

No abstract