Interactions between calcite, NaDBS, Pb(II) and Cd(II) ions in seawater

It was demonstrated by a Coulter counter method in combination with photomicrographs that the commercially used anionic surfactant sodium dodecylbenzene sulfonate (NaDBS) forms solid crystals with major seawater cations as Na+, Mg2+, Ca2+ and Sr2+ and thus can be removed from seawater to sediments. In the presence of calcite particles suspended in seawater with variable concentrations of NaDBS, complicated mutual interactions occur resulting in partial calcite dissolution, and consequently in surface area diminuation. Namely, from Coulter counter kinetic measurements simultaneous decrease of the total number and total volume of particles was observed. Partial dissolution of calcite was also confirmed by the weight loss in the presence of ct(NDBS) = 1.6 × 10−3 mol l−1. Remobilization of lead and cadmium ions from calcite particles occurs up to ct(NaDBS) = 1 × 10−3 mol l−1. At concentrations above that value, an increased removal of these ions can be explained with their adsorption on a reprecipitated calcium salt (either with DBS− or with SO2−4 from SW).