Relation of contact angle data to Hallimond tube flotation of coal with coagulants and flocculants

Hallimond tube flotation experiments were carried out on two coals (bituminous and sub-bituminous) using coagulants and flocculants. The reagent concentration and pH were studied as variables. Contact angle measurements were conducted by the captive bubble technique. The results show that starch flocculant gives the largest contact angles on the coal surface for the system investigated. The contact angles of the coals and Hallimond tube flotation tests were found to decrease with increasing concentration of coagulant but increase with the flocculant concentration, an effect similar to that produced by surfactants. Electrokinetic data indicate reagent adsorption on the coals.