Chemical profiling of metallurgical-grade silicon by ICP-OES after fabrication by aluminothermic reduction

Title : Chemical profiling of metallurgical-grade silicon by ICP-OES after fabrication by aluminothermic reduction

Abstract:

Silicon (Si) plays a very important role in modern technologies across various industries. Therefore, large-scale production of Si is imperative to support the industries and economies. The process of carbothermic reduction of quartz (SiO₂) in a submerged arc furnace has been the primary method for production of metallurgical-grade silicon (MG-Si) for ages. This process infamously produces large amounts of environmentally detrimental gases (CO₂) and consumes large amounts energy in addition to producing products with many impurities. Cleaner and less energy-intensive processes are being developed, with aluminothermic reduction emerging as a leading alternative which uses secondary aluminium and silicon sources.

Critical chemical assays are required to accurately determine the product’s contents. X-ray fluorescence (XRF) spectroscopy is the conventional technique for the analysis of MG-Si. The metallic nature of the Si product (>70% Si) poses challenges for XRF analyses in that Si reacts with and damage platinum (Pt) crucibles, which are generally used for XRF fusions. Moreover, the level of impurities in the Si product determines the grade of the silicon. XRF suffers from relatively high limits of detection compared to techniques such as inductively coupled plasma optical emission spectroscopy (ICP-OES), which might limit its ability to determine the levels of some impurities in the Si product.

This current study explores the full chemical profiling of Si produced by the aluminothermic reduction process using ICP-OES. A quick, safe and simple sample preparation route was involving indirect quantification of Si metal was developed. Critical analytical figures of merit evaluated, viz. accuracy, precision, selectivity, and limits of detection and quantitation, were found to be within acceptable range and suitable for purpose. Recoveries of 100.0±2.0% Si were achieved, demonstrating that with a suitable sample preparation method, ICP-OES is capable of producing high quality chemical analysis of Si metal and its impurities. Full validation of the method has demonstrated that ICP-OES is a competent and reliable alternative to XRF for MG-Si profiling.

Biography:

Odwa Mapazi studied Chemistry at the University of Fort Hare, where graduated with Honours degree in 2012. He then pursued a Master’s, followed by a PhD in Chemistry at the University of Johannesburg, from which he graduated in 2018. He then joined Mintek, gaining experience in mineral characterisation using atomic spectroscopy in the Analytical Chemistry Division. He believes that every different matter is unique and, as such, he participates in applied chemical analysis research to respond to changes in raw and processed mining materials and find analytical solutions.