Silicon preparation derived from geothermal silica by reduction using magnesium

Abstract

Geothermal silica denotes as a potential source of silica due to high content of silica. Silica can be converted to be silicon through magnesiothermal reduction. The objectives of paper are to obtain the optimum ratio of Mg to SiO2, and to obtain acetic acid concentration in the second leaching of the silicon. At beginning, purification of geothermal silica was carried out through acid leaching by 20% of hydrosulfuric acid (H2SO4) with silica content of 96.3 wt%. Silicon conversion had been performed used magnesiothermic reduction at 650 oC for 7 hours. The mole ratio of Mg to SiO2 used 1.6:1, 2:1, and 2.5:1. The acid leaching process used HCl (3 N) at 60oC for 1 hour and utilized HFof (5 N) with varied acetic acid concentration for 1 hour at 70oC (25, 35, 45, 50, and 60 % ww). Afterward, the results were confirmed by characterization of the silicon with XRF analsys. Silicon yield was achieved at 77.1 wt% with 91.4 wt% of purity at first acid leaching. This results have been generated by use of Mg to SiO2 ratio at 2:1 and leached out by HCl 3 N. However, at second acid leaching with HF-acetic acid mixture released the purity of silicon at 93.9 wt%. Silicon from geothermal silica can replace the use of graphite as anodes of lithium ion batteries.