Purification of Refined Metallurgical-grade Silicon up to Solar-grade Silicon by Extraction
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1170-R05-19
Purification of Refined Metallurgical-grade Silicon up to Solar-grade Silicon by Extraction Sergey М. Karabanov1,2, Dmitriy V. Suvorov
1,2
, Boris N. Sazhin1
1
Ryazan Metal Ceramics Instrumentation Plant JSC, 51В Novaya Str., Ryazan 390027, Russia
2
Ryazan State Radio Engineering University, 59/1 Gagarina Str., Ryazan 390005, Russia
ABSTRACT The paper studies the theoretical analysis of silicon purification process using the method of extraction from solid phase in fine-dyspersated condition. Axial profile impurity concentration in silicon particles, time dynamics of average impurity concentration at various purification conditions (temperature, particle size, impurity concentration in extractant) are obtained by numerical simulation. The requirements to a particle size and temperature condition when practically important purification efficiency is reached, are determined. The design of an industrial-scale plant is shown schematically. INTRODUCTION Nowadays due to intensive development of photovoltaics it is important to find new methods of industrial silicon purification to obtain solar-grade silicon for solar cell production [3,4]. These new methods are to be not only economically efficient but also ecologically safe. The ecologically safe methods are based on liquid and gas extraction of impurities from silicon melt, recrystallization, oriented crystallization, vacuum refining, etc. The present paper analyzes theoretically silicon purification by extraction from fine-dyspersated solid phase. Impurity solid phase extraction method The essence of the method is in extractive processing of metallurgical-grade silicon by a substance-extractant at high (more than 1200 °С) temperature. Before the extractive processing the metallurgical-grade silicon was powdered up to 10-80 micron and pretreated by chemical methods. If the impurity concentration in the substance-extractant is less than in silicon particles (the necessary purification condition), the diffusion of silicon impurities, to the particle surface and their further solution in substance-extractant takes place. Mainly, the purification efficiency is limited by the particle size and the impurity diffusion coefficient which strongly depends on temperature. In comparison with traditional purification methods, the method under study has a few advantages: chemically active and ecologically dangerous substances are not used during purification; there is no phase transition of purified silicon and its chemical compounds are not formed. Besides, one of the method advantages is its relatively simple hardware. The plant for silicon purification by extraction method is shown in Figure 1. It consists of a tower filled with the substance-extractant, heaters, and a silicon collector. Silicon powder coming in the tower upper part sinks slowly under gravitation force, and is purified in the
substance-extractant due to the impurity diffusion. In order to decrease the tower height the pumping of the extractant from the bottom to upwards is foreseen, that prov
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