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

Abstract

A B S T R A C TApplication 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.

Recovery of ammonia nitrogen and magnesium as struvite from wastewaters in coal‐fired power plant

“…Zeta potential on the Mg (OH) 2 surface declined due to the charge neutralization of PAM, particularly aPAM. The repulsive forces between colloids were weakened, and the enhanced agglomeration trend increased the aggregation size of colloids . Moreover, several colloids were connected by adsorption bridge owing to the combination of amide group (─CONH 2 ) in aPAM and hydroxyl group (─OH) on the surface of Mg (OH) 2, which further faded repulsive forces and advanced the agglomeration ability.…”

“…The repulsive forces between colloids were weakened, and the enhanced agglomeration trend increased the aggregation size of colloids . Moreover, several colloids were connected by adsorption bridge owing to the combination of amide group (─CONH 2 ) in aPAM and hydroxyl group (─OH) on the surface of Mg (OH) 2, which further faded repulsive forces and advanced the agglomeration ability. As shown in Figure a, particle size and zone settling velocity were the greatest and zeta potential and SV 120 were the lowest by adding aPAM and crystal seed (S2) simultaneously, which was advantageous for obtaining Mg (OH) 2 solids.…”

Optimization of atmospheric carbonation in the integrated treatment immediate one-step lime precipitation and atmospheric carbonation. The case study of slaughterhouse effluents

“…These precipitates have a high adsorption capacity for some organic compounds [29][30][31] and phosphorus [32]. According to Zhao et al [33], the Mg(OH) 2 precipitate can neutralize charge, cause enmeshment of colloidal particles, beyond to its adsorptive capacity. In fact, the magnesium concentration was reduced in the entire reaction pH range and for all effluents (Fig.…”