Magnesium hydroxide coagulation performance and floc properties in treating kaolin suspension under high pH

摘要

Application of magnesium hydroxide as a coagulant for treating kaolin suspension under high pH was studied. The coagulation performance and magnesium hydroxide-kaolin floc properties were investigated under different dosages and pH values. Flocculation index and turbidity removal were then discussed with controlled experiments using intelligent particle dispersion analyzer. Floc size distributions were derived from microscopy and image analysis. The results showed that floc size decreased with increasing coagulant dose. The optimum magnesium ion dose tended to decrease with the increase of initial turbidity and pH value. Higher pH and higher magnesium dose led to rapid floc formation and relatively small flocs. The experiments showed that magnesium hydroxide coagulation process had two stages including fast floc formation and growth of flocs and then the larger flocs break into relative small particles. All of the flocs under investigation showed a limited capacity to regrowth when they had been previously broken. Based on the changes of zeta potential and floc properties, charge neutralization and precipitate enmeshment were proposed to be the main coagulation mechanisms.