Development of ore-thermal melting technology for agglomerated charge containing technogenic raw material in silicon production

Abstract

Production of silicon in ore-thermal furnaces (OTF) by carbothermic reduction of quartzites is accompanied by large dust emission, containing significant amount of valuable silica (an average of 86 %). In this regard, works devoted to raw material base expansion due to return of technogenic wastes into technological process are of great significance. To be used in process of silicon smelting in OTF, the dust collected by gas treatment units, consisting of 120 microns particles with predominant fraction of +20 – 50 μm, has to pass through preliminary agglomeration (to prevent its possible fly from reaction zone with process gases). Since charge including agglomerated part must have sufficient strength during transportation and loading to OTF, liquid glass is suggested to be used as a binder with addition of aluminum-containing electrostatic precipitators containing resinous substances (polyaromatic hydro-carbons) as a hardening reagent for dust. Based on the results of tests for strength of the agglomerated charge samples, the following charge components ratio is recommended: 24 – 27 % of silicon production dust; 51 – 53 % of carbonaceous reductant (1:1 mixture of petroleum coke and charcoal); 4 – 5 % oversize of fine-grained silicon; 14 – 15 % of binder (liquid glass and dust of electrostatic precipitators of aluminum-magnesium production in 4:1 ratio) (by weight). With such a composition of charge, the drop resistance coefficient averaged 82.5 %. As a result of physical-chemical study of agglomerated compositions obtained by the proposed method, it was found that they have porous structure (45.5 %) which forms a well-developed active surface of material with an apparent density (1100 kg/cm3), which provides operation of OTF in a stable mode when using agglomerated charge of this composition. Experimental melting carried out in a HTF 17/10 type high-temperature furnace has resulted in a product containing more than 44 % (by weight) of silicon carbide as an obligatory intermediate in carbothermic process, that allows to recommend charge agglomerated by proposed procedure with selected component ratio for use as additives to the main (cobbed) charge in production of silicon by carbothermic method.