Exploitation of seawater brines for the production of Nesquehonite solids and CO2 utilization

The simultaneous utilization of waste CO2 streams and bivalent rich saline solutions is a crucial opportunity to face climate change challenges. Several authors have investigated desalination seawater brines as promising sources of bivalent solutions for CO2 utilization technologies. However, the Mg2 + and Ca2+ content in brines affects the purity of the synthesized compounds. In this context, the present work thoroughly assesses, for the first time, the direct and indirect mineral carbonation processes of real highly concentrated Mg2+-rich saline solutions (bitterns), the latter being the by-products of the evaporation process of seawater or desalination brines in saltworks or evaporative ponds. For comparison, the indirect carbonation process of real desalination brines was also explored. The bittern had Mg2+ and Ca2+ concentrations of ∼2.00 mol/L and ∼0.004 mol/L, while ∼0.13 mol/L and ∼0.025 mol/L were those in the desalination brine, respectively. Carbonation tests were conducted at room temperature and atmospheric pressure in a (semi-)batch reactor. The high concentration of Mg2+ and the almost absence of Ca2+ in the bittern allowed (i) the production of highly pure Nesquehonite solids (purity ∼99 %) and (ii) almost doubling the CO2 yield (from 23 % to 37 %) through the direct carbonation approach against the indirect one.