FLOCCULATION OF FINE HEMATITE IN AQUEOUS-SOLUTION CONTAINING SURFACE-ACTIVE AGENTS

Fine solid particles in aqueous solution are flocculated in some cases or dispersed in other cases, when surface properties such as hydrophobicity and surface charge of the solid are changed by adding surface-active agents. In the present study, flocculation phenomena of fine hematite suspension are investigated in the presence of surface active agents such as sodium oleate and sodium salt of 1-dodecane sulphonic acid. Amounts of the surfactant adsorbed on hematite and the zeta potential of hematite are measured in order to explain the flocculation phenomena. Oleic acid can be physically and chemically adsorbed on hematite in the pH region below 10 to give a large negative charge to hematite. At pH less than 3, oleic acid exists as small oil droplets with negative charge due to its low solubility. These droplets are adsorbed or adhere to hematite. On the other hand, 1-dodecane sulphonic acid is physically adsorbed on hematite, especially below the pH of the point of zero charge of hematite. The flocculation domain of hematite as a function of pH and the concentration of surfactants is illustrated in the presence of two surfactants. When adsorption of surfactants less than a mono-layer takes place, hematite particles are flocculated. When adsorption more than a mono-layer occurs, hematite particles are dispersed.