A molecular dynamics study of the interaction of oleate and dodecylammonium chloride surfactants with complex aluminosilicate minerals.

Surface characteristics of complex aluminosilicate minerals like spodumene [LiAl(SiO(3))(2)], jadeite [NaAl(SiO(3))(2)], feldspar [KAlSi(3)O(8)], and muscovite [K(2)Al(4)(Al(2)Si(6)O(20))(OH)(4)]) are modeled. Surface energies are computed for the cleavage planes of these minerals. Adsorption mechanisms of anionic chemisorbing type oleate and cationic physisorbing type dodecylammonium chloride molecules on two different crystal planes, that is (110) and (001), of spodumene and jadeite are studied in terms of the surface-surfactant interaction energies computed using molecular dynamics (MD) simulations. The conclusions drawn from purely theoretical computations match remarkably well with our experimental results.

Zeta potentials in the flotation of oxide and silicate minerals.

Adsorption of collectors and modifying reagents in the flotation of oxide and silicate minerals is controlled by the electrical double layer at the mineral-water interface. In systems where the collector is physically adsorbed, flotation with anionic or cationic collectors depends on the mineral surface being charged oppositely. Adjusting the pH of the system can enhance or prevent the flotation of a mineral. Thus, the point of zero charge (PZC) of the mineral is the most important property of a mineral in such systems. The length of the hydrocarbon chain of the collector is important because of chain-chain association enhances the adsorption once the surfactant ions aggregate to form hemimicelles at the surface. Strongly chemisorbing collectors are able to induce flotation even when collector and the mineral surface are charged similarly, but raising the pH sufficiently above the PZC can repel chemisorbing collectors from the mineral surface. Zeta potentials can be used to delineate interfacial phenomena in these various systems.

Transformation of calcium fluoride for caries prevention.

Oral application of fluoride for caries prevention may tend to form calcium fluoride (CaF 2) instead of the desired fluorapatite. In view of this, the transformability of CaF2 to fluorapatite has been studied. This investigation shows that CaF2 can be converted to fluorapatite in phosphate solutions ar various temperatures ranging between 25 and 75 degrees C in the pH range of 6.5 to 8.5. In the initial stage, phosphate ions, believed to be HPO4= adsorb on the particle surface. A dissolution/precipitation mechanism is proposed for the growth of fluorapatite.