Kinetic and structural constraints during glauconite dissolution: implications for mineral disposal of CO2

The kinetics of glauconite dissolution have been determined in the pH range 2–10 (T = 25°C) using flow-batch reactor experiments. Besides the kinetic characteristics, the structural and textural aspects which could influence its long-term reactivity have also been characterized by means of X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and BET surface area measurements. The results from these analyses showed that glauconite follows a dual dissolution pathway which is pH-dependent, being more stable at neutral or slightly alkaline pH values. Under acidic conditions, glauconite is slightly more soluble than other ubiquitous silicates present in the marine sediments. The dissolution mechanism is incongruent at very acid pH values and tends to be congruent for intermediate and neutral ones. In addition, the results from the structural analyses suggest that the dissolution is a two-step process: the first one involves the disorder of the octahedral and tetrahedral layers, probably following a turbostratic mechanism which is evident in the XRD spectra as selective broadening of several reflections. In the second step, the dissolution of the cations from interlayer positions takes place and leads to the formation of an amorphous residue which acts as a passivating layer and reduces the reactive surface considerably. The influence of these aspects on CO2 capture via carbonation reactions is discussed