Inhibition of calcium carbonate nucleation with aminophosphonates at high temperature, pH and ionic strength

Results of a study on the ability of aminophosphonates to inhibit CaCO ₃ nucleation are reviewed. Species discussed include ethylene-, butylene-, pentylene-, and hexamethylene-diaminetetramethylenephosphonate. These species form a homologous series differing only in the number of methylene linkages separating amine functional groups in the backbone structures of the molecules. Performance was gauged by the temperature increases required to induce rapid nucleation in solutions of pH and ion composition similar to those used in the isolation of cellulose fiber for papermaking. Aminophosphonates were found to increase nucleation temperatures sharply at concentrations lower than those typically required with other types of antiscalants. The inhibition ability of the aminophosphonate homologous series decreases with increasing number of methylene linkages. Comparison of performances for the analogues ethylenediamine-tetramethylenephosphonate (EDTMP) and ethylenediaminetetraacetate (EDTA) indicates that distinctly different interactions are responsible for the observed inhibition. A semiempirical equation developed from classical nucleation theory demonstrates that interfacial interactions are primarily responsible for the observed inhibition for EDTMP, whereas solution-phase complexation of calcium ions was previously shown to account for the influence of EDTA. Also studied were binary mixtures involving EDTMP, EDTA, and poly(maleic acid) (PMA). It is shown that the ability of EDTA to raise nucleation temperatures is significantly enhanced by the presence of either EDTMP or PMA. Mixtures of EDTMP and PMA, both of which are believed to function through interfacial interactions, provide inhibition performances between those observed for the individual species when applied at the same concentration.