Scale inhibition mechanism of calcium sulfate by gum Arabic: Experimental testing, quantum chemical calculations, and molecular dynamics simulations

In this paper, the scale inhibition mechanism of gum arabic (GA) on calcium sulfate fouling is theoretically and experimentally investigated. A combination of experiments, quantum chemical calculations, and molecular dynamics simulations are carried out. The results demonstrated that GA has the potential to inhibit the precipitation process of calcium sulfate fouling significantly. As the concentration of GA increases, the scale inhibition efficiency also increases. Moreover, with a concentration of 6.8 g/L of calcium sulfate in the solution, it is shown that the scale inhibition efficiency of 1 g/L GA is 97.5 %. Additionally, it is noted that the variation in the solution pH does not significantly affect the GA scale inhibition effect. It was highlighted that carboxyl groups, hydroxyl groups, and ether bond oxygens in the GA molecule are the functional groups that exhibit scale inhibition. These groups serve as the low electronegativity regions with strong interactions with calcium ions. In addition, GA can be adsorbed on the active growth sites on the gypsum surfaces to form a dense, self-assembled barrier film. This film aids in inhibiting the calcium sulfate precipitation process. The findings of this study rank the scale inhibition of GA at different crystal surfaces as follows: gypsum (010) > gypsum (-111) > gypsum (120).