Abstract: The leaching behavior of boron mud for preparation of magnesium hydroxide in the sulphuric acid was investigated. The effect of factors，such as reaction temperature，reaction time，amount of sulfuric acid，and sulfuric acid initial concentration，on the leaching rate of Mg were investigated through orthogonal experiments and factorial experiments.Results showed that the most important factor among them was reaction temperature with enough sulphuric acid.The optimal leaching conditions were obtained through experiments：reaction temperature was 95 ℃，reaction time was 3 h，sulfuric acid mass fraction was 40%，and amount of sulfuric acid was 1.2 times more than that of theoretical value.Under the above conditions the leaching rate of magnesium was 95.62%.After completion of the reaction，the primary magnesium sulfate solution was prepared.A purity of 99.35% of the plate-shape magnesium hydroxide was obtained by further gradient alkaline separation and hydrothermal reaction.SEM and XRD results showed that the plate-shape magnesium hydroxide had characteristics of uniform morphology，excellent particle dispersion，and high crystallinity.

Key words: sulphuric acid, boron mud, leaching, magnesium hydroxide