The invention provides a method for preparing solar grade
silicon from silica serving as a
raw material. In the method, the silica serves as the
raw material, and CaCl2 is taken as a
molten salt electrolyte; and the method comprises the following steps of: reducing the silica at the temperature of between 600 and 1,000 DEG C by using the
molten salt electrolyte to directly electrolytically reduce
silicon in the silica into elementary
silicon; adding a compound into the elementary silicon according to a
mass ratio of 1:3-9, and introducing protective gas at the temperature of between 600 and 1,200 DEG C for
crystallization; putting the crystalized silicon into
hydrochloric acid liquid with the concentration of between 1 and 5 mol / L according to a
solid-liquid
mass ratio of 1:1-8, and performing acid leaching for 2 to 48 hours; washing by using water for 2 to 5 times, and
drying at the temperature of between 40 and 150 DEG C; melting the dried silicon at the temperature of between 1,450 and 1,650 DEG C, and performing
vacuum evaporation under the vacuum condition at the temperature of between 1,600 and 1,650 DEG C and under the pressure of between 1*10<-2> and 1*10<10> Pa; and condensing the evaporated melt silicon at a condensation speed of between 0.1 and 5 mm / h to prepare the solar grade silicon. By reducing to remove impurities such as
oxygen,
phosphorus, aluminum,
calcium,
titanium and the like, and through high temperature
crystallization and acid leaching for removing
boron, the product has the purity of over 99.99991 percent, and the method has the advantages of short production flow, low cost and light environment
pollution.