Fig. 1 Schematic diagram of the experimental equipment (a1, 2, 6, 10, and 12: components of the resistance furnace, 3 aluminum melt, 4 slag, 5 lid of crucible, 7 K-type thermocouple, 8 molybdenum wire, 9 alumina sheath), positions of the samples for ICP b

Fig. 2 Samples range in the orthogonal experiments a, effects of reaction time b, electrical voltage c, percentage of LiCl d, Na2B4O7 content e on silicon concentration

Fig. 3 Castings produced by different compositions slag, without Na2B4O7a, with 30 wt% Na2B4O7b

Fig. 4 Variation of the silicon concentration over the reaction time in the single-factor experiments: a mass of 25 g samples at 700 °C, b mass of 25 g samples at 760 °C, c variation in the silicon content at 820 °C

Fig. 5 Micrographs of samples before purification a, after 10 min of purification at 700 °C b

Fig. 6 Integrated rate plot of 25 g 0.22 wt% Si at a 700 °C, b 760 °C, c 820 °C in the single-factor experiments, d a plot between lnk and 1000/T from the experimental data

Fig. 7 Diagram of interfacial reaction, V represents the external potential at interface; red arrows represent the direction of mass transfer

Fig. 8 Temporal variation of silicon concentration in 0.44 wt% Si samples at 720 °C a, 760 °C b, 820 °C c in single-factor experiments

Fig. 9 Changes of silicon concentration with a slag amount, b voltage in single-factor experiments

Fig. 10 Reaction probability with increase in voltage