d: operation time of 8 h, NH4+/Al3+ of 1.40, SO42?/Al3+ of 2.90, temperature of 5～15℃ and stirring speed of 35～55 r/min. The synthesis reaction ics experiments were performed. The results show that Al3+ diffusion in the boundary layer is the rate controlling step in the crystallization process. The relationship between Al3+ concentration (C) and time (t) is expressed by C=(C0?Ci)e?kt+Ci. The effect of stirring speed on the particle size distribution of ammonium alum crystals was investigated. When the stirring speed is lower, ammonium alum average particle size is larger and size distribution wider. With increasing of stirring speed, the particle size and distribution range are decreased. Key words: ammonium alum; lipoic acid; wastewater containing aluminum; reactive crystallization; ics
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