Effect of poly(aspartic acid) on the removal rates of brushite deposits from stainless steel tubing in turbulent flow

This research investigates the effect of poly(aspartic acid) (PASP) and its sodium salt on the removal of brushite (dicalcium phosphate dihydrate, DCPD) deposits from stainless steel tubing in turbulent flows. In the absence of PASP, DCPD removal is dominated by the abrasion of solid particles from the deposit by fluid shear and is influenced by the kinetics of the interfacial dissolution process. The presence of PASP promotes DCPD removal for pHs between 4 and 10, with an optimum enhancement at pH 5. A decrease in the sensitivity of the removal rate to shear forces indicates that PASP inhibits solids detachment from the deposit for pH < 5. At higher pHs, PASP appears to reduce the shear stress required to remove particles from the deposit. A model for the interfacial dissolution process that includes mass transfer, adsorption equilibria, and the kinetics of acid dissolution and surface complexation is used to explain the trends of the experimental data on removal rates.