Performance and mechanism of 1-hydroxy ethylidene-1,1-diphosphonic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid in the inhibition of calcium carbonate scale

The performance and mechanism of typical scaling inhibitors, i.e., 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), in inhibiting calcium carbonate scaling were investigated. Results of the static experiment at 30 °C and 80 °C revealed that at the optimal concentration, the scaling inhibition efficiency of PBTCA was superior to that of HEDP. Additionally, X-ray powder diffraction evaluation demonstrated that in comparison with HEDP, PBTCA inhibited the growth of the (1 0 4) crystal plane of calcite more evidently. Scanning electron microscopy analysis indicated that the addition of scaling inhibitors induced the crystal transformation of CaCO3 from calcite to aragonite. Molecular dynamics simulation also confirmed that the interaction of PBTCA with the (1 0 4) crystal surface of calcite is more apparent than that of HEDP. This observation was a consequence of the PBTCA being more negatively charged, as determined via a quantum chemical calculation. The calculation further indicated that the spatial distance of PBTCA to the (1 0 4) face of calcite was less due to stronger chelating ability and better suitability of the structure. As a result, in the tested temperature range, PBTCA exhibited the more effective inhibitory effect against calcium carbonate scaling.