Decoupling Inhibitor Mechanisms in Surface and Bulk Processes: Studies of BaSO₄

Chemical inhibitors are used to prevent crystallization fouling, but they can be environmentally hazardous. While reducing inhibitor concentrations could minimize their environmental impact, they could, below a certain threshold, promote surface deposition. In this study, we investigated the effect of a commercial polymeric scale inhibitor on BaSO₄ formation on surfaces and in the bulk phase. Surface deposition studies were performed in a one-direction flow-through experimental setup. We investigated the deposition behavior of BaSO₄ at inhibitor concentrations ranging from 0 to 100 ppm, and BaSO₄ saturation ratios (SRs) ranging from 6.6 to 457.1. Crystal deposition was visualized using high-resolution X-ray micro-computed tomography and characterized through advanced image analysis and scanning electron microscopy (SEM). Bulk phase studies were conducted at SRs spanning from 6.6 to 1000, and samples were analyzed through inductively coupled plasma analysis. We show that observations made in bulk phase studies do not directly apply to surface deposition. Our findings show that while high inhibitor concentrations can prevent surface deposition, intermediate concentrations could accelerate deposition. The enhanced deposition likely occurs because the inhibitor predominantly inhibits nucleation over crystal growth. We previously showed that BaSO₄ deposition at high SRs occurs primarily through nucleation. This results in the formation of fragile structures that are more susceptible to detachment processes. Therefore, as nucleation processes are inhibited, stable surface structures form, subsequently enhancing the net deposition rate. SEM revealed a change in the crystal habit of surface deposits and bulk precipitates as a function of SR and inhibitor concentration. Our findings can be used to optimize the usage of chemical inhibitors and understand how crystal resilience is essential for surface deposition processes.