This paper proposes a new approach on the processing of silicon production waste (microsilica) as a raw material for metallurgical processing. It is known from practice that the granulometric composition of microsilica does not allow its use in metallurgical processing. The authors of this work propose its use together with a reductant as part of a briquetted charge. In this work, the optimal composition of the charge mixture for briquetting is determined. The main focus is on assessing the strength characteristics of the briquettes and analyzing their efficiency in the silicon smelting process. The strength of the briquettes was studied by the dropping method. As a result, in terms of strength and other characteristics, it is highly advisable to use briquettes consisting of 65% of microsilica and 35% special coke screenings. The obtained batches of high-strength briquettes were tested for the smelting of metallurgical grade silicon in a large-scale laboratory ore-thermal furnace to replace the traditional charge mixtures (high-quality quartzites, petroleum coke, wood chips, etc.) with briquettes. It was established that the briquetted monocharge ensures more intensive reduction processes and improves melting conditions compared to the traditional charge. This leads to higher silicon recovery rates, which was confirmed by tests, during which the maximum recovery rate reached 83.1% with a 30% replacement of the charge with briquettes. The batch of metallurgical silicon with 95-96% of Si content was obtained.

Complex ferroalloys which include alkaline earth metals (such as calcium, magnesium, barium and other metals) have particular importance for high-quality metallurgy. In addition, development of the theory and practice of modification of cast iron, cast and deformed steel stipulated necessity in creation of the new type of product — modifiers with participation of rare earth and alkaline earth elements. Alkaline earth metals (AEM), having a high chemical affinity to oxygen and most other harmful impurities, as well as low solubility in liquid iron, are one of the most effective deoxidizers, desulfurizers, dephosphorizers and steel modifiers. The widespread use of AEM in the industry opens up real possibilities for quality improvment of steel and cast iron, reduction of the mass of metal products, rise of their operation reliability and durability and, as a result, significant metal savings. Previously the authors have developed the experimental batch of complex ferroalloy containing calcium, barium and magnesium with the following chemical composition, %: Ca — 11–15, Si — 50–55, Al — 12–20, P — 0,06, S — 0,02, Mg — 1,2, Ba — 1,3 and Fe is the rest. This ferroalloy was obtained as a result of large-scale laboratory tests simulating industrial conditions at the experimental site of Chemical and Metallurgical Institute named after Zh. Abishev. Efficiency of application of each new ferroalloy for deoxidation, microalloying and steel modification is determined primarily by its various characteristics (chemical and phase composition, mineralogy, thermal properties, etc.). Correspondingly, the current research is based on different studies that were carried out for the obtained calcium-containing ferroalloy, including the following ones: investigation of the phase composition by X-ray phase analysis, study of phase transformations during heating by the differential thermal analysis, determination of mineralogical composition and density by metallographic studies and by the pycnometer method. Presented results were obtained during execution of the scientific and technical program No. BR05236708 “Scientific and technological substantiation of widening of raw material base of the ferroalloy industry owing to involvement of slightly coking power generating coals and man-caused wastes in order to receive the new materials of multi-purpose destination”, within the framework of the contract for the programmed and aimed investment for 2018–2020 with the Scientific Committee of the Ministry of Education and Science of Kazakhstan Republic and grant investment of the scientific researches for 2018–2020 with the Scientific Committee of the Ministry of Education and Science of Kazakhstan Republic on the theme АР05130225.

This paper presents the results of optimizing the physicochemical properties of microsilica-based composite briquettes for metallurgical-grade silicon production. Microsilica, a waste product of silicon production, contains a sufficiently high amount of silicon dioxide (96–97%). This fact makes microsilica a promising composite material for metallurgical processing. However, its granulometric composition limits its direct use. The method of briquetting on an industrial briquetting press was used. The influence of the granulometric composition of the composite mixture on the heat tolerance and reactivity of the finished briquettes was studied. The methods of obtaining and testing the briquettes, their composition, and the briquetting and drying process were described. The obtained briquettes were tested for the smelting of metallurgical silicon. The silicon recovery rate in the metal with the standard charge was 71%, while the recovery rate with the briquetted monocharge was 85%. The results of silicon smelting from the briquettes demonstrated the high quality of the obtained metal, corresponding to the standards of metallurgical-grade silicon. The implementation of these technologies improves the quality of the finished product and addresses environmental issues related to the disposal of microsilica, reducing its accumulation and minimizing its impact on the environment.

Currently, enterprises producing crystalline silicon are facing the formation and accumulation of large volumes of microsilica, a technogenic dusty waste formed during the melting of silicon alloys. Due to its chemical composition, this waste can be a significant raw material for metallurgical production. Therefore, this study is aimed to solve the problem of recycling microsilica. For these studies, a technology for the combined briquetting of microsilica and a carbonaceous reducing agent was developed for the production of a pilot batch of briquettes. This paper presents the results obtained from the process of testing the melting of crystalline (technical) silicon from briquetted monocharge obtained from microsilica. The tests were conducted under large-scale laboratory conditions on a 200 kVA ore-thermal furnace, where 30, 50, and 100% replacements of the traditional charge mixture with briquettes were tested. The results of this study showed that briquettes in the melting process of technical silicon can be successfully used in the range of 0 to 50%. The use of briquettes can significantly improve the technological indicators. The maximum extraction of silicon (approximately 83%) was achieved at 30% replacement. The technical and economic indicators of the process also improved. In particular, an increase in productivity was observed in comparison with tests on a traditional charge.

This work presents the results of optimizing the physicochemical properties of composite briquettes based on microsilica for metallurgical-grade silicon production. Microsilica, a waste product of silicon production, contains a sufficiently high amount of silicon dioxide (96-97%). This fact makes microsilica a promising composite material for metallurgical processing. However, its granulometric composition limits its direct use. The method of briquetting on an industrial briquetting press was used. The influence of the granulometric composition of the composite mixture on the heat tolerance and strength of the finished briquettes was studied. The methods of obtaining and testing the briquettes, their composition, and the briquetting and drying process are described. The obtained briquettes were tested for the smelting of metallurgical silicon. The silicon recovery rate in the metal with the standard charge was 71%, while the recovery rate with the briquetted monocharge was 85%. The results of silicon smelting from the briquettes demonstrated the high quality of the obtained metal, corresponding to the standards of metallurgical-grade silicon. The implementation of these technologies not only improves the quality of the final product but also addresses environmental issues related to the disposal of microsilica, reducing its accumulation and minimizing its impact on the environment.

A major problem of the technological production process of the metallurgical-grade silicon is formation of a large amount of microsilica. However, this material can be a significant source of raw materials for its own production. Hence, this study is aimed to solve the problem of micro-silica utilization, i.e. the technogenic dust-like waste generated during the melting of the technical-grade silicon. Within this study, the technology of the joint briquetting of microsilica was investigated with the carbonaceous reducing agents, i.e. by obtaining of mono-charge and by melting of the technical-grade silicon from the obtained mono-charge in the 200kVA ore-thermal furnace. Results of the study show that the briquettes in the melting process of the technical-grade silicon can be used in the range from 0 to 50%. The using of briquettes may significantly improve the technological parameters. When briquetted charge is applied only, the technological parameters will deteriorate significantly. The material balance of silicon melting showed the recovery rates of the main elements (Si, Al, Ca and Fe). It recorded a decrease in content of aluminum from 1.9-2.1% to 0.5-0.7%, calcium from 0.2-0.3% to 0.07-0.1% and titanium from 0.2-0.23% to 0.11-0.13% during the transition to briquetted monocharge. Phosphorus content increased from 0.004-0.005 to 0.011-0.013%.