J. Shibata et H. Tamakoshi, FLOCCULATION OF FINE HEMATITE IN AQUEOUS- SOLUTION CONTAINING SURFACE-ACTIVE AGENTS, Kagaku kogaku ronbunshu, 20(5), 1994, pp. 701-707
Fine solid particles in aqueous solution are flocculated in some cases
or dispersed in other cases, when surface properties such as hydropho
bicity and surface charge of the solid are changed by adding surface-a
ctive agents. In the present study, flocculation phenomena of fine hem
atite suspension are investigated in the presence of surface active ag
ents such as sodium oleate and sodium salt of 1-dodecane sulphonic aci
d. Amounts of the surfactant adsorbed on hematite and the zeta potenti
al of hematite are measured in order to explain the flocculation pheno
mena. 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 nega
tive charge due to its low solubility. These droplets are adsorbed or
adhere to hematite. On the other hand, 1-dodecane sulphonic acid is ph
ysically adsorbed on hematite, especially below the pH of the point of
zero charge of hematite. The flocculation domain of hematite as a fun
ction 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 ad
sorption more than a mono-layer occurs, hematite particles are dispers
ed.