Sander Arnout

Dissolution and diffusion behavior of Al2O3 in a CaO-Al2O3-SiO2 liquid : An experimental-numerical approach

A technique to study the dissolution and diffusion behavior of Al2O3 in CaO–Al2O3–SiO2 liquids is presented. The dissolution of spherical Al2O3 particles at elevated temperatures is observed using confocal scanning laser microscopy and interpreted by means of numerical simulations with a lattice Boltzmann dissolution model. The dissolution mechanism is identified as diffusion-controlled and an estimate of the effective binary diffusion coefficient and its activation energy is obtained. The technique is readily applicable to other systems.

Antimony Recovery from End-of-Life Products and Industrial Process Residues: A Critical Review

Antimony has become an increasingly critical element in recent years, due to a surge in industrial demand and the Chinese domination of primary production. Antimony is produced from stibnite ore (Sb2O3) which is processed into antimony metal and antimony oxide (Sb2O3). The industrial importance of antimony is mainly derived from its use as flame retardant in plastics, coatings, and electronics, but also as decolourizing agent in glass, alloys in lead-acid batteries, and catalysts for the production of PET polymers. In 2014, the European Commission highlighted antimony in its critical raw materials report, as the element with the largest expected supply–demand gap over the period 2015–2020. This has sparked efforts to find secondary sources of antimony either through the recycling of end-of-life products or by recovering antimony from industrial process residues. Valuable residues are obtained by processing of gold, copper, and lead ores with high contents of antimony. Most of these residues are currently discarded or stockpiled, causing environmental concerns. There is a clear need to move to a more circular economy, where waste is considered as a resource and zero-waste valorization schemes become the norm, especially for rare elements such as antimony. This paper gives a critical overview of the existing attempts to recover antimony from secondary sources. The paper also discusses the possibility of waste valorization schemes to guarantee a more sustainable life cycle for antimony.

Understanding stainless steelmaking through computational thermodynamics: Part 3 - AOD converting

Abstract The major issue in stainless steelmaking is the difficulty of oxidising carbon from molten steel without also oxidising large proportions of expensive chromium. This can, however, be achieved by reducing the partial pressure of the gaseous product of carbon oxidation, carbon monoxide, by dilution with argon. Modern stainless steelmaking is dominated by duplex processes which prepare a high carbon melt in an electric arc furnace, and then decarburise it in an argon–oxygen decarburisation (AOD) converter. In this work, the thermodynamic basis of preferential carbon oxidation by dilution of oxygen with argon is discussed, together with a review of AOD practice. The AOD process was simulated using computational thermodynamics software to illustrate the way in which it can achieve very low carbon levels in the molten steel bath without excessive co-oxidation of chromium. The slag reduction stage using ferrosilicon additions was also modelled and shown to be able to recover almost all oxidised chromium from the slag, limited only by the accompanying increase in the silicon content of the steel. The models, although simple and easy to develop, correctly predicted all trends in output variables as input parameters were changed and often matched plant data very well. The models provide a valuable learning tool for those interested in pyrometallurgical processing in general, and stainless steelmaking in particular.

Understanding stainless steelmaking through computational thermodynamics Part 1: electric arc furnace melting

Abstract Stainless steel alloys are widely used in many important applications but their production presents difficulties because they contain expensive chromium, which can be extensively oxidised during decarburisation to the very low carbon levels required. Modern stainless steelmaking largely avoids this problem by having two distinct stages and is therefore described as duplex practice. Molten high carbon stainless steel is produced in an electric arc furnace and then the melt is decarburised in an argon–oxygen converter or a vacuum oxygen decarburising converter. In this work, computational thermodynamics has been used to examine the major reactions occurring in the electric arc furnace and to show the effect of various process variables on chromium recovery. It was shown that significant oxidation of the scrap must occur during melting, and that subsequent carbon/oxygen injection initially oxidises some chromium, but then mostly oxidises the added carbon. Chromium was predicted to exist in the slag as CrO and CrO1·5 in almost equal proportions. Increasing the temperature should improve chromium recovery but results in less benefit than expected due to the decreasing activity coefficients of CrO and CrO1·5 and the increasing oxygen partial pressure. Ferrosilicon additions reduce chromium oxides from the slag, but much of the silicon simply dissolves into the steel. Computational thermodynamics is seen to be a very effective educational tool for gaining an understanding of smelting processes.

Chapter 8 – Lead Recycling

Lead is a soft, malleable, ductile, bluish-white, dense metallic element, extracted chiefly from galena (PbS) and found in ores together with zinc, silver and copper (ILA, 2013a).

Determination of the dissolution mechanism of Al2O3 in CaO-Al2O3-SiO2 liquids using a combined experimental-numerical approach

Experimental results obtained from the in situ observation of the dissolution of spherical Al2O3 particles in CaO-Al2O3-SiO2-containing melts at elevated temperatures are analyzed using a lattice Boltzmann dissolution model. Through a comparison of the experimental dissolution curve with analytical predictions and numerical simulations, the rate-limiting step is identified as diffusion control. Estimations of the effective binary diffusion coefficient are obtained, together with an estimate of the activation energy for the diffusion process.

Lattice Boltzmann model for diffusion-controlled indirect dissolution

Indirect dissolution is modelled using a two-component lattice Boltzmann model. A boundary condition is developed to impose equilibrium concentrations on the interfaces. The interfaces are captured using a volume-tracking scheme. The model is applied to a one-dimensional diffusion couple and the expected behaviour is observed. A two-dimensional situation with and without convection is also simulated, and the behaviour under grid refinement is studied.

Lattice Boltzmann modelling of refractory-slag interaction

A model to simulate the dissolution of multi-phase solid structures of arbitrary shape in multi-component fluids is developed. The dissolution reaction is supposed to be congruent and diffusion-controlled. The model uses a multi-component Lattice Boltzmann scheme in combination with a volume-tracking scheme for the moving interfaces. Equilibrium concentrations are imposed on the interfaces using an off-grid boundary condition. The resulting diffusion flux determines the dissolution rate. The model is applied to the dissolution of a laminar multi-phase solid in a diffusion boundary layer, and to a simplified three-component refractory-slag system.