ARAGONITE PRECIPITATION UNDER SIMULATED OCEANIC PRESSURES

The intent of this work is to model the natural formation of inorganic calcium carbonate (e.g. aragonite) in a simulated oceanic environment via the replication of pressures, temperatures, and concentration of dissolved ions in an artificial seawater solution. The goals of this study are to better understand the effects of pressure, at predetermined temperatures, on fluid pH, crystal morphology, and crystal size of aragonite. In order to achieve these goals, several laboratory experiments were conducted by one time addition of Na₂CO₃ or NaHCO₃ to artificial sea water. Once ready, the experimental solutions were immediately placed in stainless-steel pressure vessels connected to a high-purity N₂ tank. We tested pressures from 25 to 345 bars. We also conducted experiments at low pressure (1 atm). In this case, the experiments were placed in either a refrigerated water-bath to control the temperature or allowed to equilibrate at room temperature. All experiments were carried out at either room temperature or 7.8 °C. Throughout the duration of the experiments, fluid sub-samples were collected at regular intervals to monitor pH. At the end of each experiment, we collected the crystals precipitated under our experimental conditions. Raman spectroscopy confirms that the precipitated carbonate phase is aragonite. Optical microscopy analysis of the experimental crystals suggests that the addition of Na₂CO₃ leads to the nucleation of spherulites (hemispherical bundles of aragonite needles), whereas the addition of NaHCO₃ causes the nucleation of loose needle-like crystals. Currently, chemical analyses of the experimental crystals are underway in order to determine the effects of pressure on the final chemical composition of the experimental products.