Adsorption and contact angle of single and binary mixtures of surfactants on apatite

Adsorption and contact angle of single and binary mixtures of sodium oleate and ethoxylated nonylphenol type nonionic surfactants on apatite minerals were studied. The effect of Ca2+ ions was investigated in the absence and presence of nonionic surfactants. The results showed that multilayers of oleate adsorbed on apatite surface and the presence of Ca2+ ions increased the adsorption by causing surface precipitation of oleate salt as calcium oleate. However, the presence of nonionic surfactant decreased oleate adsorption due to competition between the surfactants and prevention of oleate ions from precipitation as calcium oleate. Ethoxylated surfactants adsorbed on apatite as multilayers and the amount of adsorption decreased with increasing EO segments per molecule. When tested separately, the contact angle in oleate solutions was significantly larger than in nonionic surfactant solutions. The presence of a nonionic surfactant, NP-4, increased the contact angle of oleate solutions at relatively low concentrations of both the reagents.