Mechanisms of Mineral Scale Inhibition

Abstract

Summary An extensive study of adsorption and desorption isotherms of four phosphonates on barite or calcite are tested for a wide range of solution conditions (0 to 1 M NaCl, 0 to 0.1 M Ca, 0 to 0.33 M sulfate, and 4.6 to 6.4 pH). From these adsorption/desorption observations, it is proposed that the primary driving force for adsorption is related to simple hydrophobic repulsion from solution of a macroneutral molecule and not, as is generally presumed, some specific inhibitor-surface interaction. From the nucleation study, it is observed that the inhibitor needed to completely inhibit barite formation is approximately equal to 16% surface coverage. An equation to predict minimum inhibitor need is proposed based on this model and is compared with field observations. The range of predicted inhibitor concentrations is quite similar to what is observed in the field as a minimum effective dose even though it was derived by a completely independent calculation method.