Mechanisms and Kinetics of Liquid Silicon Oxidation During Industrial Refining

Abstract

During oxidative ladle refining (OLR) of silicon, the metal surface is partly oxidized, resulting in the formation of a condensed silica fume (SiO 2 ). This fugitive emission of silica represents a potential health hazard to the workers in the silicon and ferrosilicon industry. In the current work, industrial measurement campaigns aimed at recording the fume generation during OLR were performed at the Elkem Salten plant in Norway. The measured amounts of silica produced were 2.5-5.1 kg/h, depending on the gas flow rate in the refining process. The rate of silica production correlates with the total flow rate and amount of air in the purge gas, and increases as the flow rate increases. The results of this work suggest that fume generation during OLR primarily results from oxidation of the exposed metal surface, with oxygen transport from the surrounding atmosphere to the metal surface being the limiting factor. Other identified mechanisms of SiO 2 formation were splashing of the metal and/or oxidation of SiO gas carried with the refining purge gas.

Comparison of Three Real-Time Measurement Methods for Airborne Ultrafine Particles in the Silicon Alloy Industry

“…When liquid silicon is exposed to air, it oxidizes by a two-step mechanism where the silicon first reacts to form SiO gas, which then oxidizes further into SiO 2 particles. Naess et al [3,22,23] provide detailed descriptions of the PM generation mechanisms for silicon alloys. The metallurgical fume generated in the silicon production industry has been characterized by several authors [2,3,24,25].…”

“…Naess et al [3,22,23] provide detailed descriptions of the PM generation mechanisms for silicon alloys. The metallurgical fume generated in the silicon production industry has been characterized by several authors [2,3,24,25]. The CSF protoparticles are typically amorphous silica spheres which may occur independently but more often as agglomerates.…”

“…Primary agglomerates are held together by strong material bridges, whereas secondary agglomerates are held together by weak forces. Næss et al [3] studied CSF from the tapping and refining processes of metallurgical grade silicon and reported an average protoparticle size of approximately 0.06 µm. Kero et al [2] used an ELPI to characterize the PM in a tapping area of a ferrosilicon furnace and found an average primary agglomerate size of 0.17 µm.…”

“…Still, it is difficult to collect all the dust and staff exposure can, at times, be high. Lately, studies have indicated the possible presence of ultrafine dust in ferroalloy (including silicon alloys) production [1,2,3]. …”

Active Oxidation of Liquid Silicon: Experimental Investigation of Kinetics

“…In an earlier study [3], this fume was characterized, and its generation quantified. The fuming mechanism was concluded to be active oxidation of the liquid silicon surface, as described below.…”