Pidgeon process

Abstract: China is the largest producer of magnesium in the world, and supplies currently 40–50% of the world demand for magnesium. The current growth in the demand for magnesium is primarily driven by automotive industry for light weighting automobiles to reduce emissions. Magnesium production in China is based on a thermal process, known as the Pidgeon process that was originally invented in Canada in the 1940s. The raw material used is dolomite, which is initially calcined, and the calcined dolomite is reduced using the Pidgeon process by supplying ferrosilicon and thermal energy to produce pure magnesium crowns. The magnesium crowns are then melted and cast as pure magnesium ingots, which are then exported from China to meet the growing world demand. With a focus on the global warming impact, a cradle-to-gate life cycle study is conducted using averaged data for magnesium production in China. Calculations show that the cradle-to-gate global warming impact of Chinese magnesium ingots is 42 kg CO2 eq/kg Mg ingot, within an uncertain range of 37–47 kg CO2 eq/kg Mg ingot. The value of impact for the magnesium produced in China is ∼60% higher than the global warming impact of aluminium, a competing material that is also produced in China in abundance. The calculated impact for magnesium is discussed in the context of the future magnesium products value chain that may have a strong dependence on the magnesium produced in China. © 2004 Elsevier B.V. All rights reserved.

Abstract: Metallic magnesium is mostly used in lightweight alloys, one of the main purposes of which being to decrease fuel consumption in automotive applications. Several different production processes are currently used worldwide, and the magnesium production scenario is changing rapidly, with Chinese production increasingly dominating the world market. For the purpose of this paper, a novel approach to Life Cycle Assessment (LCA) was applied, in which Material Flow Accounting (MFA) and energy-based methods (Embodied Energy, Exergy Analysis and Emergy Synthesis) are integrated and complemented by a detailed description of the environmental hazards associated with emissions from all the different processes. Furthermore, the findings of the assessment are applied to estimate the Global Warming Potential (GWP) and the Acidification Potential (AP) related to the world primary magnesium production in 2007, with an allocation to the producer countries. Results highlight the relevance in terms of environmental impact of the country where the Mg production process takes place, and clearly identify the dominating Chinese Pidgeon process as the least sustainable Mg production chain, despite its growing diffusion: it has the highest environmental burdens as well as material and energy consumption, and the lowest exergy efficiency.

Abstract: Thermochemical equilibrium calculations indicate the possibility of considerable fuel savings and CO2 emission avoidance in the three steps of the Pidgeon process: (a) calcination of dolomite; (b) production of ferrosilicon from quartz sand, coal, and iron oxide; (c) silicothermic reduction of calcined dolomite by ferrosilicon to magnesium. All three steps should benefit from application of concentrated solar energy as the source of high-temperature process heat, while the first two steps may be adapted to the coproduction of syngas. For the production of ferrosilicon, an experimental study was carried out by thermogravimetry as a model for a solar-driven process. The net reaction at 1823 K was shown to be represented by Fe2O3 + 4SiO2 + 11C → 2FeSi(s) + 10CO(g) + SiC(s) + SiO(g), confirmed by gas chromatographic analysis of the evolved CO and by XRD identification of the solid products FeSi and SiC. This product mixture agrees with that predicted for the thermochemical equilibrium, but differs from that ...