H2020 SisAl Pilot Project: Innovative pilot for the production of silicon with low environmental impact using secondary raw materials of aluminum and silicon.
- Type Project
- Status Signed
- Execution 2020 -2024
- Assigned Budget 11.942.623,43 €
- Scope Europeo
- Main source of financing Horizon 2020
- Project website Proyecto SisAl Pilot
Carbothermal reduction in submerged arc furnaces (SAF) is currently used for the production of silicones, which play a key role in numerous industries, from electronics and transportation to chemicals, cosmetics, and construction. The EU-funded SisAl pilot project is developing a cost-effective and environmentally friendly process alternative.
The SisAl process involves the aluminothermic reduction of quartz into slag using secondary raw materials, such as aluminum scrap and slag, as substitutes for currently used carbon reducers. With improved valorization of waste and byproduct streams, lower energy consumption, and reduced CO2 and harmful pollutant emissions, it is described as an innovative approach. Furthermore, it significantly contributes to circularity, with the aluminum industry acting as both a raw material supplier and end user.
Detailed mapping of feedstock resources and initial characterization of potential raw materials for use in the SisAl pilot process have been completed. The results of the feedstock mapping, along with the results of the detailed business case evaluation, show that greater emphasis should be placed on potential aluminum sources going forward. The focus for small-scale laboratory work in the pyrometallurgical portion of the project has been on understanding the impact of different feedstocks and process parameters on the SisAl process and preparing for pilot testing at Elkem, RWTH, FRey, and Mintek.
Based on the results obtained at NTNU, Elkem has conducted 22 pilot tests, using different types of raw materials and process parameters. These results confirmed that the small-scale experiments at NTNU are representative of large-scale experiments in terms of raw material and product composition, as well as their interaction with graphite crucible materials.
The experimental work was complemented by modeling work conducted by SIMTEC and ITMATI. Elkem slags were sent to Mytilineos and NTUA Greece for use in small-scale and pilot-scale hydrometallurgical tests, and the silicon produced (>98% Si) was sent to Silicor for further purification to Si-SoG. NTUA performed laboratory-scale modeling and screening of the optimal conditions for extracting alumina from the slags. Research conducted included optimization of crystallization of leachable alkaline phases in produced slags, modeling and testing of alkaline leaching of slags, modeling of alumina precipitation from alkaline leach solutions, modeling and testing of acid leaching of slags, modeling and testing of aluminum chlorohydrate (ACH) precipitation from acid leach solutions, and refining of ACH solutions to achieve high purity levels.
The results during the first 18 months show that the slags produced are/can be made suitable for both alkaline and acid leaching.
Aluminum leaching yields of 100% and 65% have been achieved in acid and alkaline leaching, respectively. Alumina precipitation from the produced and refined acid solution has yielded 99.9% pure alumina to date. BNW updated its short-term European feasibility analyses during the first reporting period with more detailed information on process yields and material prices, yielding overall positive estimates of economic returns.
However, the business outlook for the production of metallurgical grade alumina (MGA) from CaO-AlO slags made with SisAl appears less promising at this time than initial estimates. Other commercial markets requiring these slags in large volumes, such as secondary steelmaking and cement clinker, will be investigated in more detail in the next project period. Flowsheet models using HSC Sim/FACTSage, an environmental assessment of the SisAl process, and the development of a data exchange infrastructure have been established.
The HSC Sim models, developed by HZDR, include:
- Individual flow diagrams for the pyrometallurgical and hydrometallurgical unit operations of the SisAl process for the production of silicon and alumina.
- The conventional submerged arc furnace (SAF) process for silicon production. Flowsheet models have generated mass and energy balances for the SisAl and SAF processes.
NTNU subsequently compared the environmental impacts of conventional SAF and SisAl processes using a Life Cycle Assessment (LCA). The data required for the environmental impact assessment were obtained from the developed flowsheet models. This assessment demonstrated that the SisAl process performs better than the SAF process in almost all impact categories considered. Finally, a detailed dissemination and communication strategy, as well as a dissemination kit, were developed.
Specifically, a website, social media accounts, a file-sharing system (innovation space), and a promotional video for the SisAl concept have been created. Recently, a series of videos and a longer video on Elkem's pilot experiments have been completed and will be published on the SisAl Pilots social media channels in early 2022. Furthermore, SisAl Pilot was presented at the RMIS workshop, a cluster event organized by the European Aluminum Association (EAA) during the fall of 2021, and at various conferences such as Infacon XVI, RawMat, Silicon for the Chemical and Solar Industry XVI, CRU Silicon Conference, and Life Cycle Management Conference.
The SisAl pilot project aims to demonstrate a novel industrial process at TRL 6-7 to produce silicon (Si), a critical raw material (CRM), in different qualities: metallurgical grade (MG-Si, >98%), high purity silicon (HP-Si, >99.9%), solar grade (SoG-Si, >6N), and Al-Si alloys, together with metallurgical grade alumina (MGA) and/or high purity alumina (HPA). SisAl represents an environmentally and economically sustainable alternative to the current carbothermal reduction process in submerged arc furnaces (SAF), enabling silicon production in an increasingly carbon-depleted Europe. For silicon production, the short-term solution of using biocarbon sources as quartz reductants is challenging due to the high competition and prices of this resource for use in chemicals, fuels, etc. Therefore, and given the growing attention paid to the circular economy, the use of secondary sources of aluminum as reducers is more relevant than ever.
Underlying silicon supply issues to the EU from China have also worsened, leaving European industries vulnerable in both the short and long term. The energy situation in China has led to a drop in silicon production and a rise in prices of more than 300% in less than two months during the autumn of 2021. The overall objective of the SisAl pilot project is to scale up and demonstrate a new European clean carbon technology for producing silicon and silicon alloys, along with metallurgical grade alumina (MGA) and high purity alumina (HPA), at TRLs 6-7, validating raw material and product quality, environmental impact, and economic parameters to lay the groundwork for commercialization.
SisAl Pilot aims to demonstrate a novel, patented industrial process for producing silicon (Si, a critical raw material), enabling a shift from the current carbothermic submerged arc furnace (SAF) process to a much more environmentally and economically viable alternative: an aluminothermic reduction of quartz to slag using secondary raw materials such as aluminum (Al) scrap and slag, as substitutes for the carbon reductants currently in use. SisAl Pilot represents an innovative approach and a strong contribution to “circularity” through an industrial symbiosis in which the Al industry will act as both raw material supplier and end-user to the Si industry.
Across all sectors, SisAl Pilot will deliver substantial reductions in material yield losses, increased valorization of waste and by-product streams, with 3x lower energy consumption and radically lower emissions of CO2 and harmful pollutants, at considerably lower cost. The SisAl Pilot project brings together raw material suppliers (Erimsa), key silicon and aluminum players (Wacker, Elkem, DOW, Silicor, SiQAl, Hydro, FRey, Befesa, MYTIL), SMEs/consultants/equipment manufacturers (BNW, SIMTEC, WS and SBC) and research organizations (NTNU, RWTH, NTUA, ITMATI, SINTEF, HZDR, MINTEK) to demonstrate the SisAl process with different raw materials and product outputs in 4 different countries. These pilots will be accompanied by environmental, economic, and technological benchmarking, and industrial business cases will be evaluated in locations in Norway, Iceland, Germany, Spain, and Greece.
The SisAl Pilot's timeline is impeccable: the transformation toward a circular economy, the strong emphasis on climate and future CO2 allocations planned under the EU ETS with the associated risk of carbon leakage from Europe, the increasing difficulty of exporting aluminum scrap from Europe to China, and modern society's ever-increasing need for metallic silicon. With SisAl, all these challenges become new European opportunities.
During the first stage of the project, special attention was paid to operational design, including the agitation method, the charging method, and the mixing of raw materials. It was demonstrated for the first time, at a 300 kg scale, that aluminum slag (a mixture of metal and oxide) is a suitable reducer for slags containing SiO2. Slag is a byproduct of the aluminum industry that contains a considerable amount of valuable aluminum (typically 70–80%).
Currently, additional industrial processes, at considerable cost and with negative environmental impact, are used to recover parts of this aluminum. It has also been demonstrated on a pilot scale that sculls can be used to refine the Si alloy produced by the SisAl process to MG silicon (purity greater than 99%). Short-term European feasibility studies have been updated with more detailed information on process yields and material prices, yielding overall positive estimates of economic returns. These updated studies have laid the groundwork for initial discussions with potential partners who could commercialize the SisAl pilot process.
- NORGES TEKNISK-NATURVITENSKAPELIGE UNIVERSITET NTNU (NTNU)
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