Abstract:
The purpose of the work was to initiate a systematic investigation within the country on the
possibility of producing solar grade (SoG) silicon from local silica deposits and to achieve
that the objective was to identify a suitable deposit of silica within the country and to develop
techniques for the purification of silica of this deposit so as to make it suitable for the
production of SoG-Si. The characterization and upgradation processes were employed on five
sand samples, collected from Dalia (district Nilphamari), Patgram (district Lalmonirhat),
Bipinganj (district Netrokona), Kuakata (district Patuakhali) and Sharighat (district Sylhet).
The minimum required percentage of silica for the production of SoG-Si is >98%. The
received sand samples contained SiO2 ranging from around 65% to 97%. The characterization
was performed on the basis of material composition, particle size, density, sphericity,
moisture content, material composition and crystallinity on the samples. All five sand samples
contain minimum amount of moisture and negligible organic matter. In case of bulk density
deviation was observed from standard value of 2.65g/cc. Variation was observed in particle
size distribution for Patgram, Dalia and Bipinganj sand. Most of Kuakata sand is sized ~
75μm and for Sylhet it is 0.2mm. The sample containing minimum impurity and perfect
quartz crystal form, collected from Bipinganj was found to have high potential. The sample
from Sylhet containing ~ 86% SiO2 was also considered as a strong contender for further
processing. Traditional beneficiation methods like attrition, acid washing and alkali washing
were performed on the samples. Based on stereomicroscopic observation and XRF result the
optimum level was identified for each beneficiation step e.g. for attrition optimum stirring
speed and time was found to be 800 rpm and 30 minutes respectively. Finally a methodology
was developed for the purification of the samples which lead to the upgraded point of 99.45%
and 95.31% SiO2 for Bipinganj and Sylhet sand sample respectively. The result concludes
Bipinganj sand can be used as raw material for the production solar grade silicon.
