Recycling of Fine Silicon Particles for Solar Grade Silicon Production
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The production of solar grade silicon wafers results in 50% wasted silicon. Due to the high volume of waste, recycling the fines into a useable material allows for use of all this valuable silicon. Currently there is no reuse/recycle technology used in the solar silicon process. The purpose of the research is to create a reuse/recycle technology. The experimental procedures used consisted of: characterizing the silicon fines used, producing two kinds of silicon agglomerates, green agglomeration strength was tested, and indurated agglomeration strength was tested. Four characterizing tests were completed on the silicon fines; X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), particle size analysis, and Inductively coupled plasma mass spectrometry (ICP-MS). The results of this testing indicated the fines were crystalline silicon. In order to make the two kinds silicon agglomerates in the lab, compressed briquettes were made along with pellets. Briquettes were formed by uniaxial pressing. A variety of briquettes were made using different amounts of water. The size of briquettes that were pressed were 10mm×10mm. Once the briquettes were produced, a drop test was performed to determine the strength. This property is important because the pellet must be able to survive all of its post producing handling without breaking. From the results of the initial testing it can be seen that the optimal water content is in the upper range of 8-10%. Next, briquettes were pressed with three different binders in three different amounts. These briquettes with a binder were tested from their green strength by using the same drop test. Here we see that increased binder amount does not equal increased green strength. After the green briquettes were tested, they were next indurated in the oven, and their strength was looked at. The indurated briquettes that were looked at are briquettes pressed with water and briquettes pressed with a binder. The drop test was used to check the strength. It can be seen that increased drying time, will increase the strength of the briquette. Lastly, a small batch of pellets was created with a pelletizing drum. Two sizes of pellets were created with a binder, and their strength was measured using the drop test. It shows that these pellets, both green and indurated have a lesser strength compared to the briquettes that were created.