The effect of capillary suction potential on the agglomeration of coal in water was investigated at various concentrations of added surface active agent and addition ratios of bridging liquid. Agglomeration was carried out by injecting castor oil as a bridging liquid into the suspension, which consisted of disperse medium and ground coal. An aqueous solution of 10 -2 mol • l -1 -NaCl was used as the disperse medium, and sodium oleate was added to the solution as an additive surface active agent. The main results of this work are as follows:1) The addition of sodium oleate to the disperse medium modified both the contact angle of the bridging liquid on coal particles and the interfacial tension between the bridging liquid and the disperse medium and therefore affected the agglomeration phenomena.2) The equilibrium agglomerate diameter increased as the capillary suction potential increased. Based on a model in which the equilibrium agglomerate diameter is determined by the balance between the cohesive force caused by capillary suction potential and the destructive force caused by agitation, an empirical equation to determine relationship between the equilibrium agglomerate diameter and the cohesive force was obtained.

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