Better understanding on the kinetics and mechanisms of calcite growth, which can help to predict and control calcite mineralization in reservoirs and calcite scale formation on membranes and facilities, is of essential importance considering the abundance of calcite in many natural and engineered systems. Most research has focused on studying the effects of solution conditions on calcite growth, such pH, supersaturation index (SI), calcium-to-carbonate ratio. Less was studied on the effects of the intrinsic factors, such as the reactive site density. In this study, calcite crystals were grown onto gold sensors, having their {10-14} surfaces bonded to the self-assembled monolayers (SAMs) on gold sensors. To generate different reactive site densities on calcite surfaces, solutions having varied saturation indices (SI, 0.1-0.4) were flow through the calcite surfaces, and calcite growth rates (per unite time per unit geometric surface area) were measured using quartz crystal microbalance with dissipation (QCM-D). During pretreatment, decreases in growth rates were observed for all samples until steady-state growth rates were reached. The decrease in growth rate indicated the decrease in reactive site densities on calcite surface during its growth, i.e., fast calcite growth occurred initially at the most reactive sites, and the most reactive sites were changed into less reactive sites during calcite growth. After the pretreatment, the calcite surfaces were exposed to SI = 0.5 solution, and calcite growth rates were quantified. Calcite surfaces, pretreated with solutions having lower supersaturation, were observed to have faster growth rates at SI = 0.5 solution, i.e., fastest growth occurred for calcite pretreated with SI = 0.1 solution. Our observations suggested that the pretreatment generated different reactive site densities on calcite surfaces: the reactive site density will be larger on calcite crystals pretreated with solutions having lower supersaturation.  Step densities, which can be used as an indicative of reactive site densities, were measured by atomic force microscopy (AFM). This study provides unique quantitative data and mechanistic insights on macroscopic calcite growth rate at close to equilibrium conditions.<br/>

Investigating calcium carbonate growth at close to equilibrium conditions

251st National Meeting (2016)

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