Study of Acid Leaching in the Preparation of Silicon from Lapindo Mud

Silicon was prepared by metallothermal reduction of high purity silica obtained from Lapindo mud. Silica was extracted as sodium silicate from Lapindo mud using NaOH solution and followed by titration with HCl to produce silica alcogel. Then it was washed and dried to obtain silica xerogels. The silica was characterized using X-ray diffraction and X-ray fluorescence. Silicon was prepared from metallothermal reduction of the silica at 650 °C for 3 hours using magnesium (99% purity) as a reducing agent. The product was then subjected to two stages of acid leaching sequence, first leached with HCl:HF solutions followed with HF:CH3COOH solutions. The product of each leaching step was characterized using X-ray diffraction. The structure of the silica was amorphous and its purity was found to be at 98.1%. The results showed that the reduced xerogels contained silicon, Mg2SiO4, MgO and Mg2Si. First leaching step were proved capable to remove Mg2SiO4 and MgO phases but both of leaching step unable remove Mg2Si in reduction product. The final product showed silicon was the major phase whereas Mg2Si was the minor phase.