Room Temperature Magnesite Precipitation

Magnesite (MgCO3) is one of the most stable sinks for carbon dioxide (CO2) and is therefore of great interest for long-term carbon storage. Although magnesite is the thermodynamically stable form of magnesium carbonate, the kinetic inhibition of low-temperature precipitation has hindered the development of carbon sequestration strategies that can be economically conducted under ambient temperature. Here, we document the precipitation of magnesite from waters (magnesite saturation index = 1.45) in batch reactors at room temperature with the aid of carboxylated polystyrene microspheres over the course of 70 days. Microspheres provide surfaces with a high density of carboxyl groups that act to bind and dehydrate Mg2+ ions in solution, thereby minimizing the kinetic barrier and facilitating magnesite formation. Magnesite crystals are observed on sphere surfaces and their organic matrixes. Mineral identification was confirmed by X-ray diffraction and selected area electron diffraction of a thin section obtained by focused ion beam milling. We demonstrate that kinetic barriers to magnesite formation can be overcome at ambient conditions. Incorporating surfaces with high carboxyl site densities into ex situ mineral carbonation processes and the use of such ligands for deep geologic CO2 storage may offer novel and economically viable strategies for permanent carbon storage.