Precipitation and solubility of calcium soaps in basic aqueous media

Measurements of the surface tension of aqueous media containing calcium sal ts of different fatty acids, whose structure only varied by the number of C =C unsaturations along their aliphatic chains, showed that their solubility increased as a function of this parameter going from near zero for calcium stearate to 4 x 10(-4) mol l(-1) for the linolenate homologue. The solubil ity product of the calcium soap corresponding to each tested fatty acid was estimated by using the anionic fatty acids adsorption isotherms in order t o obtain the amount of dissolved ionic fatty acid at increasing concentrati on of calcium ions. These findings are discussed in terms of their serious repercussions on the operations related to flotation deinking in waste pape r recycling. (C) 2001 Academic Press.