Presentation of the challenges related to the recycling of Silicon Kerf by LuxChemtech
Presentation of LuxChemtech and its role in ICARUS
Based in the Ore Mountains in Saxony, LuxChemtech, the young German company, which was only founded in December 2019, is dedicated, among other things, to the recycling of semiconductor waste, critical materials and the production of high-tech products. Silicon plays the biggest role in this project. Waste containing silicon is widespread in a wide variety of compositions.
The task of the ICARUS project is to develop and demonstrate sensible and sustainable recycling technologies for this waste. LuxChemtech approaches these potential secondary raw materials with a completely new perspective. The focus is on one hand on the usable energy content of the waste and on the other hand on converting the waste into alternative products.
Figure 1: Dr. Ingo Röver, Dr. Wolfram Palitzsch (Credit: Daniel Müller/LuxChemtech)
Figure 2: LuxChemtech site in Freiberg (Credit: Daniel Müller/LuxChemtech)
Challenges surrounding the recycling of Silicon Kerf
The silicon kerf material, which is often cited in the ICARUS project, plays an important role for LuxChemtech GmbH in its own work package. Waste containing silicon is omnipresent in the PV industry. That´s why some research projects addressed the issue of Si-kerf recycling for the PV industry: SiKeLor, Cabriss, SeLiSi, and Eco-Solar, but none of these projects dealt with the use of energy. Alone the comparison of the standard formation enthalpies for CO2 with -393.6 kJ/mol and SiO2 with -911 kJ/mol shows the energetic potential that is in pure silicon – more than double that for carbon. Different types of Si fines derived from internal and external sources are studied to understand the impact of waste properties on the quality of the final product. The patented process is based on the reaction of free silicon contained in the waste with an alkaline hydroxide solution under controlled temperature and pressure conditions, producing hydrogen, silicates and heat. Silicates are basic products that are used as aqueous solutions or solids in the construction industry. By further treating the silicate solutions with mineral acids, precipitated silica is obtained, which is a sought-after industrial raw material. The use of the reaction heat is also a benefit.
All silicon-containing waste can be understood as chemical energy storage that, through our treatment, can pass on part of the energy as hydrogen, but at the same time release its energy in the form of heat through the exothermic reaction and ultimately even lead to a salable product.
Figure 3: Illustration of the process (Credit: LuxChemtech)
Figure 4: Picture of silicon waste (Credit: LuxChemtech)
ICARUS’s first results
Over the past few months, several interesting silicon-containing wastes have been found, all of which are suitable for the production of hydrogen. The alkali metal silicates produced so far are of equal quality to commercially available water glass products. Interestingly, by filtering the liquid reaction product, we harvest the respective impurities in the silicon, which can be metals or graphite.
Next steps
After all the positive results, we now move on to the crucial phase of a demonstrator to determine the feasibility from an economic and ecological perspective. The data for the involved project partners, such as BIFA, should now be generated here and of course products should be produced for sampling on the market.
