NOVELTY - A raw material silicon melt solution containing aluminum in casting mold is cooled in the state which provides temperature gradient (T) in one direction. The silicon directional solidification material contains purified silicon portion having aluminum concentration (C) less than the target maximum aluminum concentration (C10max (ppm)), and crude silicon portion having aluminum concentration more than the target maximum aluminum concentration. A crude silicon portion is removed from the obtained silicon directional solidification material, to obtain purified silicon.    USE - Manufacture of purified silicon for solar cell.    ADVANTAGE - The method efficiently provides purified silicon in high yield.    DETAILED DESCRIPTION - A raw material silicon melt solution containing aluminum in casting mold is cooled in the state which provides temperature gradient (T) in one direction. The silicon directional solidification material contains purified silicon portion having aluminum concentration (C) less than the target maximum aluminum concentration (C10max (ppm)), and crude silicon portion having aluminum concentration more than the target maximum aluminum concentration. A crude silicon portion is removed from the obtained silicon directional solidification material, to obtain purified silicon. The target value (Y0) of the yield percentage is a ratio between the mass of the purified silicon and mass of the raw material silicon melt solution. The temperature gradient (T) is in the state of reference temperature gradient (T0 ( degrees C/mm)) and the raw material silicon melt solution is cooled such that it is solidified at solidification rate (R) with respect to the reference solidification rate (R0 (mm/minute)). The target maximum aluminum concentration (C10max (ppm)) satisfies a formula: k'x C2x (1-Y0)k'-1, where k' is aluminum effective distribution coefficient and C2 is aluminum concentration of raw material silicon melt solution. The reference temperature gradient and reference solidification rate satisfies a relation: k=(K1x Ln(R0)+K2)x (K3x exp(K4x R0x (K5x C2+K6)))x (K7x T0+K8)-K9 (I), where Kl is constant of 1.1x 10-3 plus minus 0.1x 10-3, K2 is constant of 4.2x 10-3 plus minus 0.1x 10-3, K3 is constant of 1.2 plus minus 0.1, K4 is constant of 2.2 plus minus 0.1, K5 is constant of -1asterisk10-3 plus minus -0.1x 10-3, K6 is constant of 1 plus minus 0.1, K7 is constant of -0.4 plus minus 0.1, K8 is constant of 1.36 plus minus 0.01 and K9 is constant of 2x 10-4 plus minus -1x 10-4.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of the manufacture of silicon directional solidification material. (Drawing includes non-English language text)    Mold (3)    Heater (6)    Furnace (7)    Low temperature side of temperature gradient (21)    Solid phase (24)