Abstract: Silicon dioxide in the non-quenched high magnesium slag was recycled in order to produce white carbon black by acid leaching method.FT-IR was used for qualitative analysis to product，and XRF was used for quantitatively analysis to product.All effect factors，such as concentration of hydrochloric acid，reaction time，reaction temperature，and washing times， on preparing white carbon black from high magnesium slag were discussed.The optimum conditions on preparing white carbon black were as follows：concentration of hydrochloric acid was 4.0 mol/L，reaction time was 2.5 h，reaction temperature was 55 ℃，and washing times were 6.Under the optimum conditions the yield of white carbon black was 10.90 g from 20 g high magnesium slag，and its purity reached 90.2%.

Key words: high magnesium slag, acid leaching, white carbon black