Role of Crystal Seed in Aluminum Hydroxide Crystallization from Ammonia System with Added NH₄Al(SO₄)₂·12H₂O

A method to promote aluminum hydroxide crystal growth through pickling Al(OH)₃ as seed in the ammonia system was proposed to overcome these defects. The experimental results show that, under the conditions of pickling time of 15 min, the acid concentration of 10%, the addition of 70 g/L pickling-Al(OH)₃ seed, and the coarse granular Al(OH)₃ products (d_0.5=85.667) can be obtained. The characterization results show that the phase of the product is gibbsite, consistent with the seed. Moreover, the steps and ledges can be formed on pickling Al(OH)₃ seed surface under the ammonia system, effectively promoting crystal growth. During crystal growth, the roughness of the crystal surface was first increased and then decreased, and the lamellar structure was deposited on the crystal seed surface. The final particles are approximately round, the surface is compact and dense. The growth of the product is surface reaction controlled. In addition, the content of the AlO₆ unit is increased and contributed to Al(OH)₃ crystal growth.