Metallurgical silicon refining using electron-beam plasma

The possibilities of plasma-chemical refining of metallurgical silicon have been demonstrated. It is shown that by electron-beam refining it is possible to reduce the concentration of phosphorus and boron, as well as the main metallic impurities by evaporation of both these impurities and their volatile compounds.

Effects of Slag Treatment Conditions on Boron Removal from Metallurgical Silicon by United Gas-slag Refining Technology

Impurities in industrial silicon strongly affect the performance and use value of silicon products, so that raw industrial silicon must be refined to reduce the impurity content and improve its quality. In this work, the effect of the conditions of the refining process on the removal of impurities was studied. The slag agent and industrial silicon powder are uniformly mixed, and a mixed gas of Ar-H 2 O-O 2 is blown into the melt for refining experiments when the set refining temperature is reached. 3% mass fraction high-purity boron powder is pre-melted into industrial silicon raw materials to prepare Si-3%B alloy raw materials, and then the Si-3%B alloy raw materials are refined and pickled with CaO-SiO 2 -CaCl 2 . The composition of the slag agent, the slag-agent-to-silicon mass ratio, the refining time, and the refining temperature conditions were explored, and the best efficiency of boron removal was found to be 96.77%, with the boron content in silicon decreased from 22 ppmw to the lowest value of 0.6 ppmw. The boron content in refined silicon shows a clear decrease, demonstrating that slag-making gas blowing refining is effective for the removal of impurities in industrial silicon.

A digital control system designed for ore thermal furnaces producing metallurgical silicon

This paper considers the key control issues related to non-adjustable parameters in the production of metallurgical silicon in ore thermal furnaces. A series of experiments has been conducted to confirm the possibility of introducing the electrode off-position control. Thus, additional control parameters were introduced in the process control system. The electrode positioning algorithm was tested and adjusted to minimize electrode bending and reduce the risk of breakage and to minimize end cracking and spalling during restarting in the current production environment. An integrated 3D model of the thermal field distribution has been developed and built that accounts for the charcoal moisture content, the position of the electrodes and the power emitted as the charge gets hot. Substantiation is given to the application of this adaptive adjustment algorithm to control the changing parameters as determined by the process conditions, such as the moisture content of the charge, the position of the electrode, the power mode of the furnace. The authors propose to expand the existing control system by adding a digital module, i.e. due to the integration of electrode off-position signals and the use of the adaptive adjustment algorithm and avoiding using any additional corrective signals. This research was carried out as part of the Governmental Assignment No. 075-03-2020-127/1 for the year of 2020, Project No. FSRW-2020-0014. Subject: A crossdisciplinary approach to the comprehensive exploitation of natural resources and conservation. Area (a 2020 topic): “Comprehensive processing of minerals and man-made materials and gasification of solid hydrocarbons: A review and concept elaboration”. As greenhouse gases and carbon are produced as a result of electrode destruction, it is proposed to use the method of gasification and dispose of the heat produced.

HIGH PURITY REFINED METALLURGICAL SILICON AS A BASIS FOR PRODUCING SILICON FOR SOLAR ENERGY

The paper analyzes the growth in the global production of solar modules over the past 10 years. Problems of obtaining refined metallurgical silicon of high grades and silicon for solar energy are considered. The prospects of using high-purity quartzites of the Eastern Sayan are shown. The technology of direct silicon production for solar energy developed at the Institute is described.

STATE OF SILICON PRODUCTION IN RUSSIA AND THE WORLD, ITS REFINING TO HIGH GRADES AND "SOLAR" QUALITY

The paper presents the state of silicon production in the world and Russia over the past few years and the prospects for its development until 2024. Technologies for refining metallurgical silicon to high grades and “solar” quality are evaluated.

Mathematical Modeling оf the Silicon Production Process from Pelletized Charge

The paper considers the problem of recycling the dust waste resulting from metallurgical silicon production; such dust contains considerable amounts of valuable silica. The problem is solved by redirecting this byproduct to the silicon smelting process. We herein propose using the dust left in silicon and aluminum production as a component of pelletized charge, used for silicon smelting in ore-thermal furnaces (OTF). Mathematical (physico-chemical) modeling was applied to study the behavior of pelletized-charge components, in order to predict the chemical composition of smelting-produced silicon. We generated a model that simulated the four temperature zones of a furnace, as well as the crystalline-silicon phase (25°С). The model contained 17 elements entering the furnace, due to being contained in raw materials, electrodes, and the air. Modeling produced molten silicon, 91.73 wt% of which was the target product. Modeling showed that, when using the proposed combined charge, silicon extraction factor would amount to 69.25%, which agrees well with practical data. Results of modeling the chemical composition of crystalline silicon agreed well with the chemical analysis of actually produced silicon.