Mechanism of hetero-aggregation of montmorillonite and coal

The mechanism of hetero-aggregation of montmorillonite and coal was investigated through sedimentation tests,Zeta potential measurements,optical microscope photos and some theoretical calculations of DLVO. The results showed that montmorillonite aggregated with coal in the experimental pH range. When pH was above 3,both montmo- rillonite and coal were negative charged,and the electrostatic interaction among particles was repulsive force,which was detrimental to the hetero-aggregation of montmorillonite and coal. Ca2+ and Mg2+ could promote the hetero-aggrega- tion. Dissociative irons could compress the electric double layer weakening the negative charge of minerals. Some disso- ciative irons could broke the electric double layer by adsorbing in the Stern layer. Hydroxyl (MOH+ ) and hydroxide (M(OH)2 ) formed by ion hydrolysis could adsorb on minerals surface and form “ion electrostatic bridge”. DLVO the- ory proved that Ca2+ and Mg2+ could weaken or eliminate the energy barrier between montmorillonite and coal. Adding inhibitors or eliminating Ca2+ and Mg2+ in pulp could weaken the bad effects of montmorillonite on coal slime flotation.