Method and system for preparing lithium hydroxide

A method for preparing lithium hydroxide is characterized by including: preparing the mixed lepidolite ore pulp of lepidolite ore, water and slaked lime; placing the mixed ore pulp into a high-pressure hydrothermal reactor to perform hydrothermal reaction so as to obtain lithium hydroxide slurry; filtering and separating the slurry to obtain calcium silicate filter cakes and lithium hydroxide solution; performing evaporation concentration on the lithium hydroxide solution, cooling and crystalizing, centrifugal separating, and washing with warm water to obtain lithium hydroxide wet products and crystalized mother liquid; drying the lithium hydroxide wet products in a drying furnace at low temperature to obtain lithium hydroxide products. The method has the advantages that the method is short in process flow and mild in condition, complex equipment is not needed, lithium hydroxide products are high in purity, and lepidolite decomposition rate is increased effectively.