Abstract
The effect of magnesium addition into a commercial silicon and its leaching refining behavior is studied for producing solar grade silicon feedstock. Two different levels of Mg is added into a commercial silicon and the leaching of the produced alloys by 10% HCl solution at 60 ℃ for different durations is performed. It is shown that the microstructure of the alloy and in particular the distribution of eutectic phases is dependent on the amount of the added Mg. Moreover, the metallic impurities in silicon such as Fe, Al, Ca and Ti are mainly forming silicide particles with different compositions. These silicides are physically more detached from the primary silicon grains and their removal through chemical and physical separation in leaching is better for higher Mg additions. It is observed that the leaching is more effective for the purification of smaller silicon particles produced from each Mg-doped silicon alloy. It is shown that acid leaching by the applied method is effective to reach more than 70% of phosphorous removal. It is also shown that the purity of silicon is dependent on the total Mg removal and effectiveness of leaching on removing the Mg2Si phase.
Highlights
The demand for solar energy has risen quickly in the recent decades, and it will continue to rise due to the global warming and energy demand
The microstructure and phase composition of the metallurgical grade silicon (MG-Si) and the two alloys were studied in similar conditions by FE-Scanning Electron Microscopy (SEM)
In the present work we studied the effect of particle size and leaching time on purification of silicon
Summary
The demand for solar energy has risen quickly in the recent decades, and it will continue to rise due to the global warming and energy demand. EG-Si is of ultra-high purity, usually above 9N (+99,9999999%), which is much higher purity than solar grade silicon (SoG-Si) of 6N purity, required in PV-devices. In the Siemens process, silicon is transformed to trichlorosilane (HSiCl3) or silane (SiH4), which is further purified and silicon is deposited from this gas on silicon rods in bell jars. This is a very slow batch process, and it is very energy consuming to keep the bell jar hot. Regarding the production of toxic chlorine gases in the process in combination with high-energy consumption and rather low yield, this process is not environmentally friendly nor energy efficient for producing SoG-Si [1,2]. It would be more convenient to produce SoG-Si through metallurgical refining route
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