Preparation method of high-purity ultra-fine aluminum hydroxide powder

The invention discloses a preparation method of high-purity ultra-fine aluminum hydroxide powder. The preparation method comprises the following steps: by taking a sodium aluminate solution prepared from an industrial sodium aluminate solution or an aluminum hydroxide alkali dissolution as a raw material; based on an ion valence state regulation and precipitating adsorption principle, carrying out two-section purification on the solution, and filtering twice, thus obtaining a pure sodium aluminate solution; adding a seed crystal initiator and a sodium precipitation inhibitor so as to prepare a seed crystal slurry; and adding a sodium precipitation inhibitor and other impurity precipitation inhibitors in a pure sodium aluminate solution, adding the seed crystal slurry, carrying out seed precipitation at a high temperature under an approximate homogeneous phase condition, thus obtaining ultra-fine pure aluminum hydroxide; then carrying out residue purification on the solution, carrying out seed precipitation on mother liquor, and feeding washing liquor into a Bayer process system. According to the invention, high-purity ultra-fine aluminum hydroxide powder can be prepared in a low-cost, high-efficiency and environment-friendly mode.